Note: Descriptions are shown in the official language in which they were submitted.
CA 02239479 2000-06-13
BROADBAND SWITCHING NETWORKS
The present invention relates to broadband switching
networks using ATM (Asynchronous Transfer Mode) techniques.
This application is divided from application 2,047,948,
filed July 26, 1991.
Efforts for integrating individual service networks
such as telephone networks, data networks, FAX networks,
and so forth which have been developed and constructed over
100 years of history into one network system with ISDN
(Integrated Services Digital Network) have been made
throughout the world.
As the first step for constructing the ISDN system,
narrow band ISDN systems have been operated in advanced
countries including Japan since 1988. In addition, besides
integration with a broadcasting network by using a
broadband ISDN based on the ATM technics, the engineering
developments of the ISDN network have been initiated by
CCITT (International Telegraph and Telephone Consultative
Committee) and promoted in major laboratories in the world.
The broadband ISDN network is provided with an ultra
high speed user-network interface with a transmission speed
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of 155.52 Mbps or 622.08 Mbps. Thus, through the same
interface, the conventional telephones, facsimile machines,
and so forth can be treated as a constant speed service CBR
(Continuous Bit Rate), while computer data with large
capacity and ultra high speed including motion pictures,
such as, high definition TV pictures, CAD (Computer Aided
Design) data, and computer graphics data, and so forth can
be treated as a variable speed service VBR (Variable Bit
Rate). Thus, with the CBR and the VBR services, various
data can be flexibly transmitted through the same interface.
However, thus far before making a communication, the
user had to declare call attribute data such as peak
traffic, mean traffic, burstiness, terminal equipment type,
service quality (for example, cell loss rate, cell
transmission delay), and the like upon the network. In
accordance with the call attribute data that the user has
declared, the network estimates a required communication
resource necessary for making the communication with respect
to the call, checks the use state of the resource in the
network, and determines whether or not to accept the call
request. As the result of the determination, when the call
request is accepted, the information to be transmitted is
divided into packets which have a constant length (53
octets) (the packets are named cells) and then sent to the
network. However, occasionally, cells which do not conform
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with the attribute data being declared may be sent to the
network.
Thus, when unexpectedly excessive cells are sent to the
network and they are concentrated in one path (as the
burstiness is strong, this. tendency becomes remarkable),
they reside in the network. To prevent that, ATM switches,
each of which is a constructional key element of the
broadband ISDN network, are provided with a cell buffer with
a large storage capacity. However, if such a cell
buffer cannot store the cells which stay in the network,
they will be lost. This situation is named a cell discard.
When the network receives cells and then marks those which
exceeds the range of attribute data declared by so-called
polling function as violation cells, they are discarded. In
addition, when a terminal equipment sends cells as non-
priority cells in VBR such as class B (variable bit rate
picture communication) (for example, in hierarchical picture
coding system, a method where cells are divided into
priority cells and non-priority cells depending on their
importance is being considered), they are discarded. If the
buffer does not fully store the cells even after the marked
cells are discarded, cells in class A (circuit emulation
communication) or the like will be also discarded.
Generally, a bit error due to noise or the like over
the transmission path is checked with a CRC code disposed at
the last position of information to be transmitted. When
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necessary, by issuing a retransmission request to the sender
side, the information with respect to a bit error can be
restored. However, when the cell discard is performed,
since the receiver side cannot know the transmission of
cells, it cannot request the retransmission of the cells to
the sender side.
Since the cell discard will become a critical problem
in data communication with respect to class C (connection
oriented) and class D (support of transmission of
connection-less data), a sequence number is provided for the
information field of each cell (48 octets) as an ATM
adaptation layer function. In addition, a mechanism for
detecting the cell discard and for issuing a retransmission
request on the receiver side is additionally provided.
On the other hand, for calls in the classes A and B,
which should be transmitted in real time, CCITT has
recommended a coding system which can withstand the cell
discard.
Major problems with respect to the broadband ISDN
switching networks which have been studied mainly by CCITT
are summarized as follows.
(1) Service quality
(a) Cell discard
As was described earlier, by assigning a sequence
number, it is possible to detect a cell loss on the receiver
side. However, since calls in the classes A and B should be
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transmitted in real time, it is substantially difficult to
restore cells which are lost by the retransmission. By the
coding method, which is a future study subject, it may be
possible to reduce the adverse effect of the discard of non-
priority cells. However, besides the discard of the normal
cells (those which are neither violation cells nor non-
priority cells), the discard of violation cells will result
in critical problems.
In other words, when a honest (innocent) user
unconsciously violates the range of the attribute data being
declared, cells that the user has transmitted will be
discarded regardless of whether they are priority cells or
non-priority cells. In other words, the information
received by the network may be lost. In addition, the
sender side cannot know what and how much information is
lost. To prevent that, a prudent and honest user will
always have to declare the attribute data with an allowance
although he or she knows that the communication fee will
becomes expensive.
On the other hand, a user who wants to save the
communication fee will declare the attribute data which is
rather small while observing the traffic condition of the
network although he or she knows that violation cells may
take place. In other words, each user will haggle with the
network about the negotiation of the attribute data like
playing a game therewith. Whenever the user repeats success
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and failure in the negotiations with the network, his or her
action will escalate.
The increase of such users causes the traffic in the
network to be abnormally increased and thereby loosing
ordinal cells transmitted by prudent and honest users.
Thus, the users have suspicion and apprehension about the
network. It is inevitable that the essential purpose of the
public communication network, which is "correct, fast, and
impartial communication transmission", is discarded.
Moreover, even in the classes C and D, the same
situation will take place. Particularly, in data
communication, as was described above, since the loss of
information is never permitted, the retransmission of cells
which were lost will be performed in a high rank layer.
As the traffic is heavy, probability of occurrence of a
cell discard will become high. When the retransmission of
cells which were lost is repeated, the traffic will become
much higher.Thus, the network will become congested. In
other words, the cell discard will result in deteriorating
the stability of the network.
(b) Variation of cell delay
As was described above, in high traffic conditions,
cells will reside in the network. In other words, the cells
will be transmitted with a delay. As the capacity of the
switch (the scale of ATM switch) becomes large and/or the
number of relays in the network increases, the amount of
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delay increases. In addition, the amount of delay varies
depending on the traffic condition in the network. This
variation of the amount of delay is named the variation of
cell delay. For calls in the classes A and B, which should
be transmitted in real time, it is necessary to provide a
buffer on the receiver terminal equipment side so as to
compensate the variation of cell delay. For example, in a
relatively small scaled broadband switching network
accommodating about 100 lines (interface), the variation of
cell delay is in the range from about several ~ sec to about
several msec. However, in an international communication,
since there are many relaying networks, the variation of
cell delay may be several 100 msec (excluding the absolute
delay time involved in long distance transmission). Thus,
each terminal equipment should be provided with a buffer
with large capacity (several Mbytes for a terminal equipment
with an information speed of 100 Mbps). To prevent that, it
is necessary to decrease the variation of cell delay itself
in the network in a manner to perform priority control in
accordance with required service quality by using an ATM
switch, which will be described later.
(c) Call connection time
The conventional switches including those for narrow
band ISDN systems usually take several seconds, occasionally
more than 10 seconds, or 20 seconds for connecting a call
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(until an originating user of a telephone hears a ring back
tone ) .
When the originating terminal equipment issues a call
set request to a switch node it performs a terminating
process for the call. Thereafter, the switch node obtains a
line connected from the originating terminal equipment to
the terminating terminal equipment and performs an
originating process to the terminating terminal equipment.
However, when a call passes through a plurality of
relay switch nodes, since each relay switch node
individually performs the terminating process, line
obtaining process, and originating process, the connection
time becomes much longer.
On the other hand, the broadband ISDN network employs
the conception of above mentioned logical bus so as to
simplify the processes required in each relaying node.
However, it is necessary bidirectionaly to negotiate with
the network the attribute data which was negotiated upon the
set of the call, to obtain a band in a virtual path in
accordance with the negotiated result, and to perform an
originating process to the terminating terminal equipment
(from the originating terminal equipment to the terminating
terminal equipment through the network; from the terminating
terminal equipment to originating terminal equipment through
the network). There is no denying the fact that the call
which is connected from the originating terminal equipment
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to the terminating terminal equipment takes a time on the
order of seconds.
However, for calls in the classes A and B, where it is
estimated that their communication times are equal to or
longer than those of telephones, the connection time on the
order of seconds does not result in a remarkable
problem.
However, in a computer communication where information
is intermittently transmitted, if a call connection takes a
time on the order of seconds whenever the information is
transmitted, the performance of the computer cannot be
satisfactorily used and thereby the operability of the
system is degraded. To prevent that, in LAN (Local Area
Network), which is a dedicated local area computer
communication system, a system named a connection-less is
used to allow the user not to realize a long connection time.
When the broadband ISDN is practically used, it will be
possible to transmit a file with a storage of 1 Mbytes in
several msec. Thus, in a computer communication, where the
performance is intensively advanced as technologies are
rapidly innovated at the present time,'it can be said that
the utilization of the connection-less system will become
mandatory.
On the other hand, the above mentioned class D for
"support of transmission of connection-less data" supposes
inter-LAN connections. In this class, when a call is
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initially connected, a connection time equivalent to those
in the classes A and B is permitted. After the call is
connected, the path is held for a long time. The routing
control from end to end is handled by the user (upper layer)
rather than the network.
In the LAN system, where the same communication medium
is shared by a large number of users, a traffic always takes
place over the LAN and between LANs. Thus, even if the path
is held in the broadband ISDN network for a long time, it
can be operated in commercial basis. However, when one
computer terminal equipment is connected directly to the
broadband ISDN network, for example in the case where a
remote user accesses a central data base, if a path is held
in the class D for a long time, it cannot be operated in
commercial basis because information is intermittently
transmitted as was described earlier. In addition, for
example by providing the network with a permanent virtual
path, where from the standpoint of the user it seems that a
dedicated line is routed between both the ends and thereby a
call connection is not required, and with a function for
generating the address of a cell header by using the address
of an upper header, which are subjects to be studied in
future, a connection-less service can be accomplished.
However, with the above permanent virtual path and the
function, the network should hold a particular communication
resource always or until the communication is completed so
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that it can handle the accessing of each user anytime.
Thus, an expensive communication fee will be applied to each
user. Most of users who make much account of cost
performance along with performance should select the
connection oriented data communication in the class C with
consideration of connection item on the order of seconds.
In other words, it is suggested that the ordinary users
frequently issue call connection requests in the network and
thereby it tends to be congested and loose the stability
thereof.
It is estimated that half the full families will use
advanced personal computer communication systems with
hypermedia or the like in the year of around 2000. However,
unless the broadband ISDN network effectively operates the
communication resources at inexpensive cost and provides
connection-less services with a light load thereof or
reduces a call connection time to the same level as the
connection-less services, it will not be able to attract the
ordinary computer users which expectedly have huge latent
demands (although LAN connection users are limited only to
major companies and the like). In addition, with respect to
the stability of the network, it is no exaggeration to say
that such problems should be solved as soon as possible
along with the necessity of stability of the network.
(2) Declaration of attribute data
(a) Reliability of user declaration
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As was described above, in the broadband ISDN, before
starting the communication, each user should declare to the
network complicated and difficult parameters such as peak
traffic, mean traffic, burstiness, terminal equipment type,
and service quality (QOS: cell discard rate, transmission
delay time, and the like) as attribute data. The
materialization of the attribute data is still being studied
by CCITT at the present time.
It will be very difficult for the ordinary users to
correctly understand the meaning of the attribute data and
to correctly estimate and declare to the network each
parameter value with respect to the call to be made. To
prevent that, at the sacrifice of the flexibility, which is
the greatest feature of the broadband ISDN, several service
items which are combinations of the above mentioned
attribute data will be provided so that the users can select
them.
Although the network obtains a communication resource
in accordance with declared data, each user can
unidirectionally send cells to the network regardless of the
declared data.
To allow the network, which tries to deliver received
cells with the best effort, to stably and effectively
operate, the correctness of the declared attribute data is
preconditionally required.
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Another problem for materializing the broadband ISDN is
how to establish with flexibility suitable for various
communication needs of the users the declaration method and
operation method of attribute data which do not adversely
affect the stability and the like of the network even if the
declared data contains errors and false data.
(c) Charging method
Another subject to be solved in future is what charging
method is set in the broadband ISDN network. At the present
time, this subject is not being studied. However, depending
on the charging method being set, it will remarkably affect
the stable operation of the network and the design of the
communication equipment such as switches. Thus, this
subject should be solved as soon as possible.
Of course, the charging method to be set should be
reflected with attribute data declared by each user. The
charging method should be user friendly, false resisting,
and inductive of proper use of communication resources in
the network. Besides simplification of attribute data,
establishment of method with general view is required.
(3) Construction/process of broadband switches
(a) Buffer capacity of ATM switch
As was described earlier, for the ATM switches, each of
which is a key element for accomplishing the broadband ISDN,
cell buffers with a large storage capacity are required. In
addition, each switch should achieve a throughput of 155.52
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Mbps or 622.08 Mbps. To break the engineering problems of
the switch including the development of the construction
method for improving the effectiveness thereof, they are
being intensively studied and developed in many laboratories
and the like. For each ATM switch employing the Bather-
Banyan network method, the common buffer method, or the
like, which are considered at the present time, even if it
is small in scale such as 8 x 8, a buffer with large
capacity for storing several hundred cells will be required
as will be described later in more detail. The buffer with
large capacity is mainly used when calls with large
burstiness are gathered in a path in the same direction.
Such a buffer remarkably disturbs the production of large
capacity of the ATM switch LSIs along with the suppression
of variation of cell delay. By reconsidering the method
suitable for the broadband ISDN, if the storage capacity of
the buffer were be remarkably reduced,~the effect will
unexpectedly become large.
(b) Priority control
As was described earlier, the ATM switch determines and
controls which cells are output to a desired path with a
high precedence in accordance with the service quality (such
as cell discard rate and communication delay time) that each
user has declared and or whether they are non-priority cells
or violation cells. Such a control means prevents the ATM
switch LSI from providing large capacity and from decreasing
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the cost thereof along with necessity of high speed cell
buffer with large storage capacity.
(c) Policing function
AS was described earlier, at the present time, each
user can unilaterally send cells to the network even if the
attribute data (or service item) is not what was declared to
the network when he or she has set the call. A function for
supervising the range of the attribute data (or service
item) and for adding it with a violation cell mark if the
cell violates the range of the attribute data (or service
item) may be provided in each subscriber line interface,
which is followed by the ATM switch, so as to further
improve the supervisory function, to discard cells in
accordance with the traffic condition in the network, and to
prevent excessive cells from entering the ATM switch. Thus,
the some improvements such as decrease of the storage
capacity of the buffer may be expected for the ATM switch.
However, only with such improvements, many problems and
subject involved in the broadband ISDN network at the
present time cannot be comprehensively solved unlike the
present invention.
(d) Call acceptance control
A call acceptance control is used to estimate a
communication resource necessary in the network in
accordance with the attribute data declared by the user and
to determine whether or not the resource is accepted. To
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satisfy a particular traffic intensity necessary for the
switch, this control should be accurately and rapidly
processed with a simple algorithm. This control method is
being evaluated in related study associations.
(e) Charging/traffic totalization
As was described earlier, in the broadband ISDN which
has been studied, the cell discard and preference control
are performed in the switch. Thus, a difference takes place
between information that each user transmitted and that
which was transmitted to the receiver side through the
network. In addition, the service quality varies for each
call and depends on the traffic condition in the network.
Thus, when the charging of cells is measured or the traffic
in the network is measured for each destination, it is
necessary to provide a calculating function in the network
(followed by the ATM switch).
However, although a cell which flows in the network has
information named a cell header (5 octets) for performing
routing control, it contains a virtual path identifier
(VPI), a virtual channel identifier (VCI), and the like,
which identify the receiving rather than information for
identifying the sender. Thus, it is difficult practically
to accomplish the above mentioned object. In other words,
in the available method, the number of cells which are sent
at the entrance of the network is measured without a
provision for checking whether the cells are really sent to
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the destinations. Thus, the users will not satisfy the
network system at the present time.
(4) User-network interface ( UNI)
Thus far, CCITT has intensively studied the
fundamental framework of the broadband ISDN. However, the
evaluation of the practical user-network interface is a
subject to be studied in future. In evaluating the
interface, the method where interface is shared by a
plurality of terminal equipments, so-called multi-point
multi-drop connections, accomplished in narrow band ISDN,
will become important, since the interface provides an ultra
high speed transmission. In addition, the interface will
require compatibility with a transmission speed of 64 kbps,
which is the basic speed of the narrow band ISDN so that the
broadband ISDN and the narrow band ISDN are mutually
connected.
Summary of the Invention
Therefore, an object of the present invention is to
provide broadband switching networks for mitigating
problems and subjects involved in the above mentioned ISDN
public networks, in particular, user-network interface,
which is a subject be solved, without deviation from
fundamental framework which has been studied by CCITT thus
far.
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To accomplish the above object, a broadband switching
network according to the present invention has a plurality of
broadband switch nodes and a broadband switch inter-node
transmission line for connecting the plurality of broadband
switch nodes, information being transmitted by cells, each
of which comprises a header and an information field,
wherein the broadband switch node comprises a broadband
input and output port for inputting and outputting the cells
to and from the broadband inter-node transmission line, and
switch means for separating the cells being input through
the broadband input and output port and for multiplexing the
cells so as to output them, wherein data composed of the
plurality of cells is transmitted and received through the
broadband switch node by constant bit rate transmission,
variable bit rate transmission, or a combination of the
constant bit rate transmission and the variable bit rate
transmission.
Thus, in the broadband switching networks according to
the present invention, with flow control performed
cooperatively by the network and terminal equipments,
excessive cells do not enter the network and thereby
prevent cell discard from taking place in the network.
In addition, by randomizing arrival intervals of cells
which enter the network (or an ATM switch), the burstiness
of cells disappears and thereby remarkably reduces the
storage capacity of the buffer of the ATM switch. In
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addition, the variation of cell delay can be remarkably
reduced.
In addition, since no cell discard basically takes
place, it is always not necessary to assign for each cell a
cell sequence number in information field by the ATM
adaptation layer unlike the related art. Thus, the
transmission speed of user information can be increased so
as to effectively use the resources in the network.
Moreover, by providing a transmission service in
constant bit rate transmission, a transmission service in
variable bit rate transmission for effectively using
statistical multiplex effect characterized by the ATM, and a
transmission service which is a combination of both the
services suitable for transmitting pictures and the like,
the user only needs to declare a transmission speed thereof
instead of a combination of complicated attribute parameters
unlike the related art. Thus, since it is not necessary to
cause the network to unilaterally restrict service items,
the flexibility, which is the most important aspect of the
broadband ISDN network, is not lost and the network can be
widely used for various user needs in the future.
Furthermore, the present invention also proposes a
practical system for accomplishing the flow control and the
randomization of cell arrival with respect to a multi-point
connection service, which is a subject to be defined by
CCITT in future. Thus, according to the present invention,
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with the same communication medium, communication with high
efficiency can be provided.
In addition, for calls which have been interrupted or
disconnected, the related communication resources are
registered on management tables so as to quickly handle
repeated call set request. In accordance with the traffic.
condition and other call requests, the communication
resources are erased and released from the management
tables. Thus, according to the present invention, services
with the same quality as connection-less services can be
provided. Besides inter-LAN connections in the class D, -
which are mostly used by large companies, the present
invention provides remarkable benefits to communications
using personal computers and the like. Thus, the
communication resources in the network can be effectively
used.
Moreover, since the present invention provides
practical calculating methods for cell unit fees for
transmission speeds, communication time unit fees, path
holding time unit fees in accordance with service systems,
it promotes the users to use proper communication resources
in the network, while preventing other users from being
adversely affected by false declaration. In addition,
according to the present invention, the network can be
effectively operated.
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Furthermore, according to the present invention,
neither polling function nor priority control is required in
the network unlike the related art. Thus, the call
acceptance control is simplified. Further, switch nodes or
cross-connect nodes constructing the broadband ISDN networks
or broadband industrial information communication networks
will be readily developed.
Brief Description of Drawings
Fig. 1 is a block diagram showing an outlined
construction of a broadband switching network of an
embodiment according to the present invention;
Fig. 2 is a block diagram showing an outlined
construction of B-TE 1 shown in Fig. 1;
Fig. 3 is a block diagram showing an outlined
construction of an ATM switch node 2 focusing on a
subscriber line interface;
Fig. 4 shows diagrams representing examples of
attribute data declared by B-TE upon setting a call;
Fig. 5 is a schematic showing an example of
registration of calls from a plurality of B-TEs in a virtual
path being set between terminating ATM switch nodes;
Fig. 6 is a schematic showing an example of an ATM cell
transmitting sequence in a variable bit rate transmission;
Fig. 7 is a schematic showing an example of cell
transmission sequence in a constant bit rate transmission;
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Fig. 8 shows diagrams representing the relationship
between cell discard rate and buffer capacity with respect
to traffic with strong randomness and with respect to
traffic with strong burstiness for separated buffer type ATM
switch and shared buffer type ATM switch being
prototypically made
Fig. 9 is a schematic showing the state where cells are
input to the ATM switch at random time intervals regardless
of CBR, VBR, or MBR service through five input lines and
then output from three output lines
Fig. 10 is a schematic showing a SDH (Synchronous
Digital Hierarchy);
Fig. 11 shows schematics representing frames in multi-
point connection by cell base interface;
Fig. 12 is a schematic showing SOH cells in a control
window area
Fig. 13 is a block diagram showing an example of
connections in accordance with the present invention;
Fig. 14 is a schematic showing an example of a call
control sequence in the connections shown in Fig. 13;
Fig. 15 is tables representing examples of management
tables in an ATM switch node in the case where an interrupt
message is used
Fig. 16 is a schematic showing a sequence in the case
where a disconnection message and a release message are
used;
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Fig. 17 shows management tables used in the sequence
shown in Fig. 16;
Fig. 18 is a table representing fees by transmission
rates for constant bit rate transmission and variable bit
rate transmission;
Fig. 19 is a table representing practical communication
fees for CBR service, MBR service, and VBR service; and
Fig. 20 is a schematic showing connections of a
plurality of virtual paths routed between B-TEs through
relay switches.
Fig. 21 is a table showing cell discard ratios (upper
row) and 99.9 ~ delay time periods (lower row) for several
load conditions in the cases of random traffic and burst
traffic with average burst length of 10 in 64 x 64 switch
(buffer length . 2560) of shared buffer type;
Fig. 22 is a sequence schematic showing a process in
each phase by signaling of layer 3;
Fig. 23 is a connection information management table;
Fig. 24 is a table for managing bands for use and
number of VCs being set;
Fig. 25 is a table showing virtual band data; and
Fig. 26 to 28 are schematics showing an algorithm for
controlling call acceptance.
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Description of Preferred Embodiments
Now, with reference to the accompanying drawings, an
embodiment according to the present invention will be
described.
Fig. 1 is a block diagram showing an outlined
construction of a broadband switching network of an
embodiment according to the present invention.
A broadband ISDN terminal equipment (hereinafter named
a B-TE) la is connected through a subscriber line interface
3a to two ATM switch nodes 2a and 2b which construct a
broadband ISDN network. In addition, the ATM switch node 2b
is connected to a B-TE lb on the receiver side through a
subscriber line interface 3b. Moreover, between the two ATM
switch nodes 2a and 2b, a virtual path 4 is disposed.
Although in the figure, only the two ATM switch nodes are
shown, a plurality of relay (cross connect) nodes may be
disposed between the nodes 2a and 2b. ~In other words, an
aspect of the broadband ISDN networks is such that a virtual
path is routed between two ATM switch nodes, which terminate
B-TEs. Besides the B-TEs la and lb shown in the figure, the
virtual path may be shared by other B-TEs terminated by the
same switch nodes, as will be described later in more
detail. In the broadband ISDN network, the address of an
ATM cell, which is transmitted from a B-TE, is identified
with a virtual channel identifier (VCI) and a virtual path
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identifier (VPI), which are provided at the beginning of the
ATM cell.
The virtual channel identifier (VCI) is used to
identify a B-TE or a subscriber line interface, which is
directly connected to an ATM switch node. On the other
hand, the virtual path identifier (VPI) is used to identify
a virtual path in the broadband ISDN network.
In the figure, so-called network termination units
(which are termed NT1 and NT2 by CCITT) are not shown so as
to simplify the description.
Fig. 2 is a block diagram showing an outlined
construction of the B-TE 1 shown in Fig. 1. A terminal
equipment such as a computer (hereinafter named a TE) shown
in Fig. 1 is connected to a subscriber line interface 3
through an access unit (hereinafter named an AU) 11. The AU
11 is composed of connection interface circuits 12 and 15
for connecting the TE 10 and the subscriber line interface
3; a buffer memory 13 for transmitting and receiving ATM
cells; and a controller 14 for controlling transmission and
reception of the ATM cells.
The AU 11 can be connected with a plurality of TEs. A
practical subscriber line interface where a plurality of TEs
are connected to the AU 11 will be described later in more
detail with reference to Fig. 11.
CA 02239479 1998-07-27
Fig. 3 is a block diagram showing an outlined
construction of an ATM switch node 2 focusing on the
subscriber line interface circuit.
As shown in the figure, the ATM switch 24 is provided
with a plurality of input and output ports. A plurality of
subscriber line interface circuits 20 and a plurality of
inter-node transmission lines 25 are connected through the
input and output ports.
The subscriber line interface circuit 20 is composed of
a connection interface circuit 21 for transmitting and
receiving ATM cells to and from a B-TE through the
subscriber line interface 3; a controller 22 for controlling
the transmission and reception of the ATM cells; and so
forth. A memory equivalent to the buffer memory disposed in
the above mentioned AU is not always required between the
connection interface circuit 21 and the ATM switch 24. In
addition, a plurality of above mentioned virtual paths 4 may
be disposed over the inter-node transmission path 25.
Moreover, the controller 22 and the ATM switch 24 are
connected to a main control unit 26 for controlling all of
the ATM switch node 2.
In this construction, the conventional polling function
in the subscriber line interface circuit, the ATM cell
priority control in the ATM switch, and so forth, which were
used in the related art are not necessary (as will be
described later in more detail).
26
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Fig. 4 shows diagrams representing examples of
attribute data declared from a B-TE when a call is set.
In a pseudo line communication of class A where the
traffic intensity is constant as shown in Fig. 4 (a), as a
constant bit rate (CBR) service, an information transmission
speed Uc with a constant bit rate of 64 kbps, 10 Mbps, or
the like, which is used for a 48 octet information field in
an ATM cell or a user information transmission area other
than an ATM adaptation layer used for cell discard and so
forth, is declared. This transmission area is named SAR-
PDU: Segmentation And Reassembly - Protocol Data Unit and
has an area of 47 octets in the class A).
Although the length of the SAR-PDU area depends on each
class, as will be described later, according to the present
invention, since the cell discard rate can be decreased in
such that it can be practically ignored, it will be possible
to omit all or part of the ATM adaptation layer. Thus,
unless otherwise noted, an information transmission speed
with respect to the above mentioned information field will
be used in the following description.
In a variable bit rate picture communication of class B
where traffic always takes place and the traffic intensity
always varies as shown in Fig. 4 (b), as an MBR (mixed bit
rate) service which is a combination of a CBR service and a
variable bit rate VBR service, an information transmission
27
CA 02239479 2000-06-13
speed Uc with a constant bit rate and an information
transmission speed Uv with a variable bit rate are declared.
As the information transmission speed with variable bit
rate, it is possible to consider for example a peak speed, a
mean speed, or a mean speed at which cells (information) are
transmitted. However, for simplifying the description, the
peak speed will be used in the following.
In a connection oriented data communication of class C,
where the traffic intermittently takes place as shown in
Fig. 4 (c), as a VBR service, an information transmission
speed Uv with a variable bit rate is declared.
In a support of connection-less data communication of
class D, where LANs are connected as shown in Fig. 4 (d), by
considering the traffic which takes place between the LANs
and a charging system which will be described later, the
user selects one of the VBR service (when the traffic
intensity is small and it intermittently takes place), the
MBR service (when the traffic intensity varies in a large
level and takes place almost anytime), and the CBR service
(when the traffic takes place almost in a constant level).
In accordance with the selection being made, the user
declares one of Uv, Uc + Uv,and Uc.
The relationship between the service categories which
have been studied by CCITT thus far and the MBR service is
as follows. It is possible to understand that the sub
category, which is the connection type service, is composed
28
CA 02239479 2000-06-13
of only the CBR service part of the present embodiment; and
each of the sub categories B, C, X, and connection-less type
service is composed of both or either the CBR service part
or the VBR service part.
With respect to the conventional attribute data, it was
necessary to declare the peak traffic (speed), mean traffic
(speed), burstiness, terminal equipment type, service
quality (such as cell discard rate and communication delay
time), and so forth. On the other hand, according to the
present invention, it is possible to declare only Uc or Uv
and if necessary terminal equipment type.
Even if the attribute data is remarkably simplified in
such a manner, it does not affect the stable operation of
the broadband ISDN network and user communications at all.
Rather, according to the present invention, the attribute
data helps to provide higher quality services than those of
the conventional services.
Next, practical means for providing the high quality
services will be described.
Fig. 5 is a schematic showing an example where calls
from a plurality of B-TEs have been registered in a virtual
path 30 which is disposed between two terminating ATM switch
nodes.
A B-TE 1 registers transmission speeds Ucl and Uvl.
Each of a B-TE 2 and a B-TE 3 registers transmission speeds
Uv2 and Uv3. Each of a B-TE 4 and a B-TE 5 registers
29
CA 02239479 1998-07-27
transmission speeds Uc4 and UcS. Thus, a virtual path 30
has a particular VBR band 31 for accommodating the
transmission speeds Uvl to Uv3 and a CBR band 32 which is
the sum of the transmission speeds Ucl to Uc5. By applying
a statistical multiplex effect, which is one of features of
the ATM system, the VBR band helps to effectively use the
resources of the network. For example, to set a particular
VBR band, the root of the sum of squares of Uvl to Uv3 is
obtained or the maximum transmission speeds of Uvl to Uv3
and the traffic of the virtual path are measured for a
particular time period. Thereafter, the VBR band is set so
that the cell rate of ATM cells whose transmission is
controlled to 5 $ or less.
In the example shown in Fig. 5, the band of the virtual
path 30 is the sum of the VBR band 31 and the CBR band 32.
However, it is possible to set a virtual path with a wider
band than that shown in Fig. 5. In this case, in the range
of the band, new calls can be accepted. When a new call
exceeds the band or when the system is precisely operated so
that the virtual path does not have an excessive band, it is
possible to vary the band of the virtual path in accordance
with the traffic condition.
Moreover, in the example shown in Fig. 5, the VBR band
31 is provided in common with the classes B to D. However,
it is possible to set the band in accordance with the
characteristics of each class, namely, the calculation
CA 02239479 1998-07-27
result of the root of the sum of squares (when the mean
traffic intensity, namely use rate, of transmission with
variable bit rate is high like in the classes B and D), the
measurement result of the maximum transmission speed (when
the mean traffic is low like in the class C), or the
measurement result of the real traffic over the virtual path
(when the traffic intensity cannot be expected).
When the maximum transmission speed is set to the VBR
band, calls declared with transmission speeds slower than
the maximum transmission speed can be unlimitedly accepted.
For example, the number of ATM cells (traffic
intensity), which enter the network, is always measured by
the subscriber line interface circuit. When the mean
traffic intensity in the VBR band becomes a particular level
(for example, the mean use rate is 0.8), the network can
widen the band when necessary or request a B-TE which is
transmitting cells thereto to decrease the transmission
speed. Alternatively, the network can restrict the
acceptance of new calls.
Fig. 6 is a schematic showing an example of an ATM cell
transmission sequence in a variable bit rate transmission.
When the physical speed of the subscriber line
interface is assumed to be 155.52 Mbps, which has been
defined by CCITT, the B-TE requests the ATM switch node to
transmit the number of cells in the next i-th frame, each
frame having for example an interval of 5.875 msec. The ATM
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CA 02239479 1998-07-27
switch node measures the number of cells from calls which
pass through the same virtual path. When the total value of
the number of cells requested is equal to or less than that
which can be transmitted for each frame in the VBR band (for
example, when the VBR band has a transmission speed of 10
Mbps, 10 Mbps / (48 octets x 8 bits) x 5.875 msec = 153
cells), the ATM switch node permits the B-TE to transmit the
number of cells requested. On the other hand, when the
number of cells requested exceeds that which can be
transmitted, the ATM switch node assigns to each B-TE the
number of cells divided in proportion to the transmission
speed registered when the call is set and then notifies each
B-TE of the result as Npi so as to control the number of
cells transmitted. When each B-TE is assigned Npi cells, it
transmits to the network the number of cells so that it does
not exceed Npi. Thereafter, the same sequence is repeated
for each frame until all the call is completed.
In the above description, each B-TE requests the ATM
switch node to permit the number of cells to be transmitted
in the next frame. With tradeoffs of slight decrease of
charging accuracy and resource use efficiency, the network
can assign the number of cells to be transmitted in the next
frame in accordance with the number of cells transmitted in
the preceding frames and then notify each B-TE of the
result. In other words, without the necessity of requesting
the number of cells to each B-TE, the transmission of cells
32
CA 02239479 1998-07-27
can be controlled so as to prevent excessive cells from
entering the network.
Anyway, by processing the transmission of cells from
each user to the network at each frame interval, the above
mentioned cell transmission control can be performed along
with a randomization process of cell transmission timing,
which will be described later. In addition, with the number
of cells in each frame, the parameter data to be declared to
the network can be simplified. Moreover, when the number of
cells permitted by the network is less than that requested
by each terminal equipment, each terminal equipment can
delay the transmission of cells or discard it. Thus,
according to the present invention, the transmission quality
can be improved in comparison with that of the related art.
These features will be described in the following in more
detail.
Fig. 7 is a schematic showing an example of a cell
transmission sequence in the constant bit rate transmission.
As shown in the figure, in the constant bit rate
transmission, the transmission rate is constant. Thus, the
number of cells, Nc, transmitted in each frame is also
constant. However, in this state, as a precondition each
user does not set a transmission speed which exceeds that
being registered. In addition, as will be described later,
some dishonest users may transmit to the network cells which
exceed registered transmission speeds. To prevent that, by
33
CA 02239479 1998-07-27
notifying each user of the number of cells which can be
transmitted in each frame (in the constant bit rate
transmission, it is not always necessary to cause each user
to request the network to permit the number of cells to be
transmitted in each frame), the transmission of cells can be
substantially controlled.
In the above example, the frame interval is set to
5.875 msec, which is 47 times longer than the basic frame
interval of 125 ~ sec in the narrow band ISDN network.
Thus, since the frame interval of SAR-PDU in the class A is
47 octets, when one cell is transmitted at a frame interval
of 5.875 msec, the transmission speed of the user
information becomes 64 kbps. Thus, the compatibility with
the narrow band ISDN network can be obtained and the mutual
connection therewith can be readily accomplished. However,
the frame interval according to the present invention is not
limited to that described in the above mentioned example.
Rather, it should be noted that the present invention can be
applied in other frame intervals.
In addition, when the transmission speed is 64 kbps or
less, the number of cells which can be transmitted in each
frame becomes less than 1 cell. Thus, it is possible for
the ATM switch node to notify each B-TE of the number of
cells to be transmitted in a plurality of frames so as to
control the transmission of cells. Alternatively, it is
possible for the network to do those so that a mean bit rate
34
CA 02239479 2000-06-13
for a long time meets the transmission speed being
registered without setting a particular frame interval.
Moreover, in the above mentioned example, when the
number of cells being requested exceeds that which can be
transmitted, the number of cells divided in proportion to
the transmission speed registered when the call was set can
be assigned to each B-TE. However, it is also possible to
assign the number of cells in proportion to the transmission
speed to each B-TE. In other words, when Uvl is 10 Mbps and
Uv2 is 1 Mbps, respectively, the number of cells can be
divided in the ratio of 10 to 1. In addition, the number of
cells may be divided in accordance with a charging system,
which will be described later. In other words, when the
unit link fees for 10 Mbps and for 1 Mbps ~ 29 per min and ~
6 per min, respectively, the number of cells can be divided
in the ratio of 29 to 6. Moreover, the number of cells can
be divided in accordance with the square root of the
transmission speed. Furthermore, various other methods can
be considered.
If the B-TE requests the ATM switch node to permit the
number of cells which exceeds the transmission speed
registered when the call was set, even if the virtual path
has enough capacity, the number of cells to be transmitted
can be controlled regardless of the CBR service, the VBR
service, or the MBR service so that the transmission speed
becomes a speed equal to or less than the registered speed.
CA 02239479 1998-07-27
Thus, the network can prevent dishonest users from
performing false declarations.
Thereafter, since each B-TE transmits ATM cells in
accordance with a command from the ATM switch node,
excessive cells which exceed the transmission capacity of
the network do not enter the network. When the ATM switch
is provided with a cell buffer having a proper storage
capacity, the network can stably operate without necessity
of the cell discard and that of the polling function which
was required in the related art.
When the number of cells which is not permitted by the
broadband switch node enters the network or when it is
performed in a timing not permitted thereby due to a failure
of a terminal equipment or the like, by additionally
providing over the interface simple hardware such as a gate
which is open and closed in accordance with a bit map of
which the network has informed the terminal equipment, it is
possible to prevent excessive cells from entering the
network.
On the other hand, in the classes B to D, the network
controls the transmission of cells from each B-TE. Thus,
each B-TE cannot always transmit required information. In
the class B, where ATM cells should be transmitted in real
time, the B-TE cannot transmit in the next frames the ATM
cells which cannot be transmitted. Thus, in this class, the
cells which cannot be transmitted are discarded in the B-TE.
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CA 02239479 1998-07-27
However, in the variable bit rate picture communication
using the above mentioned hierarchical picture code system,
each B-TE can identify which ATM cells have higher
precedences. Thus, in the case where Uc is declared for
transmitting ATM cells with high precedence which remarkably
affect the quality of pictures and Uv is declared for
transmitting ATM cells with low precedence, when the
transmission of cells is controlled by the network, namely,
Npi is lower than Nri, each B-TE can discard ATM cells from
those with lower precedence. Thus, the degradation of the
picture quality can be minimized.
On the other hand, in the classes C and D, where data
communication is handled, normally the real time property is
not required. Thus, ATM cells which could not be
transmitted can be transmitted in the next frames. This
operation is equivalent to the flow control which has been
often used in computer communications.
As was described above, the difference between the
constant bit rate transmission CBR and the variable bit rate
transmission VBR is that the cell transmission of the former
may be controlled by the network, while that of the latter
is not controlled by the network. Thus, in the constant bit
rate transmission CBR, the transmission at a constant speed
is always assured. In addition, by applying a randomization
of cell arrival intervals, which will be described later,
the time period of which ATM cells stay in the network can
37
CA 02239479 2000-06-13
be remarkably reduced. Although ATM cells enter the network
and then they are equally processed without being discarded
and priority-controlled regardless of the constant bit rate
transmission CBR or the variable bit rate transmission VBR,
the network can stably and effectively operate. Thus, the
processes of the ATM switch and the like are simplified.
In contrast, when cells in the constant bit rate
transmission which are processed in the network in a
different manner from that in the variable bit rate
transmission are transmitted with a high precedence, the
cell transmission order is inverted in the MBR service
consisting of the constant bit rate transmission and the
variable bit rate transmission. Thus, the processes
conducted on the receiver side will become complicated.
As was described above, in the classes B to D, since
the network controls the transmission of cells, excessive
cells do not enter the network. Thus, the storage capacity
of a buffer can be correspondingly decreased. On the other
hand, when the arrival intervals of ATM cells which enter
the network or the ATM switch are at random, namely, when
the burstiness (a group of ATM cells which are
simultaneously generated) is low, the probability of
concentration of ATM cells over the same out line (virtual
path) becomes low. Thus, the buffer capacity in the ATM
switch can be further reduced. In addition, the network
staying (delay) time of cells due to the buffering is also
38
CA 02239479 1998-07-27
decreased. Thus, the network can equally process cells
regardless of the cell types.
With the network equalization process for cells, the
CLP bit becomes unnecessary. However, for example, by
indicating a VBR cell with this bit, the interwork between
the B-ISDN network and the N-ISDN network will be improved.
Fig. 8 shows diagrams representing the relationship
between cell discard rate and buffer capacity for traffic
with strong random property [Fig. 8 (a)] and for traffic
with strong burstiness [Fig. 8 (b)) with respect to a
separated buffer type ATM switch and a shared buffer type
ATM switch which were prototypically made (reference: Endoh
et al. "ATM Exchange Memory Switch with Shared Buffer",
Journal, The Institute of Electronic, Information, and
Communication Engineers of Japan, B-1, Vol. J72-B-1, No. 11.
pp. 1062-1069, November 1989").
According to the result of the above mentioned
experiment, even if the buffer storage capacity of the
random arrival is decreased into 1/l6th to 1/l8th that in
the burst arrival, the same cell discard rate can be
accomplished. In addition, the cell delay time in the
random arrival is decreased to 1/l6th to 1/l8th that in the
burst arrival. As shown in the figure, since the cell
discard rate is exponentially decreased in accordance with
the storage capacity of the buffer, when the buffer has a
capacity which is slightly larger than what is required
39
CA 02239479 2000-06-13
(which is much smaller than that required in the related
art), the cell discard rate can be decreased so that it is
practically ignored.
The cell discard rates and the delay time periods of an
ATM switch with cell transmission timing being randomized
were simulated. By using such results, the possibility of
the network equalization process will be described in the
following.
Fig. 21 is a table showing cell discard ratios (upper
row) and 99.9 $ delay time periods (lower row) for several
load conditions in the cases of random traffic and burst
traffic with average burst length of 10 in 64 x 64 switch
(buffer length . 2560) of shared buffer type.
In the case of the burst traffic input, even if the
load being applied is 85 ~, the cell discard rate is
approximately 10-2 . which is a very bad value. In addition,
the delay time period becomes close to the buffer length.
Thus, to obtain the reasonable throughput, it is obvious to
use the priority control. On the other hand, in the case of
the random traffic input, even if the high load of 95 $ is
applied, the cell discard rate is equal to or less than
10-1; In addition, the delay time period is 68 cells or less,
namely 185 ~ sec in a transmission of 155.52 Mbps). It
seems that such characteristics do not practically affect
the operations of the network. In particular, with respect
to the variation of delay time period, by using a control
CA 02239479 1998-07-27
window area (equivalent to around 80 cells) provided in UNI,
which will be described later, and by providing a circuit
for compensating the variation of delay time period in a
later stage of the switch, it is possible to usually
accommodate cells in each frame.
Thus, the network equalization process can be
accomplished in the network without necessities of priority
control which does not need to distinguish the CBR cells and
the VBR cells. While the frame intervals are required over
the UNI, they are not always required in the network. Thus,
it is necessary to determine whether or not to use the frame
intervals from the standpoints of the compensation of the
variation of the delay time periods, the compatibility with
the STM system, and so forth.
Fig. 9 is a schematic showing a state where cells are
input to a ATM switch 24 at random intervals regardless of
the CBR, the VBR, or the MBR service through five input
lines and then output to three output lines.
As shown in the figure, ATM cells transmitted from the
B-TE in each frame are input successively to the ATM switch
24 at random time periods. The ATM cells are output to each
output line in the input order without much concentration.
In this example shown in Fig. 9, the frame interval is 5.875
msec, which is the same as that of the above mentioned
example. However, when the physical speed of the subscriber
line interface is 155.52 Mbps, one frame can accommodate
41
CA 02239479 1998-07-27
2075 ATM cells. This number of cells is the size of the
population enough to randomize the arrival intervals of the
ATM cells. The frame interval of 5.875 msec is an enough
time period for performing a process sequence such as
calculating the number of cells required from the B-TE,
assigning the number of cells permitted, and randomizing the
transmission (arrival) intervals of the ATM cells by means
of hardware logic (for example, numeric values of 1 to 2075
assigned at random are stored in ROM and then those being
read in succession are set to the transmission positions of
the cells in frames).
The calculation and the assignment of the number of
cells can be satisfactorily processed by DSP provided for
each VP.
Since the arrival intervals of the ATM cells are
randomized, depending on the attributes of calls (for
example, classes A and B), it is necessary to provide a
buffer memory on the receiver side so as to compensate the
variation of cell delay time periods which takes place due
to the randomization and delay in the network. The amount
of maximum variation is equivalent to approximately a time
period of one frame. Even in an international communication
where a call passes through a plurality of networks, at most
the maximum variation is as small as 20 msec.
With respect to the variation of cell delay time
periods, as was described earlier, by using the control
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CA 02239479 1998-07-27
window area (equivalent to approximately 80 cells) provided
over the UNI and by proving the circuit for compensating the
variation of call delay time period in the lower stage of
the switch, cell can be always accommodated in each frame.
The arrival intervals of the ATM cells can be
randomized in the following manners.
(1) When the subscriber line interface is used only by one
B-TE (in the non-multi-point connection), a particular
transmission timing of a plurality of ATM cells is
randomized in each frame by using the buffer 13 and the
controller 14 in the B-TE shown in Fig. 2.
(2) The subscriber line interface circuit in the broadband
switch node is provided with a buffer memory (not shown in
Fig. 3). When ATM cells are output from the interface
circuit to the ATM switch, the cell intervals are randomized
in the circuit not in the B-TE.
(3) The controller 22 in the subscriber line interface
circuit 20 shown in Fig. 3 calculates the transmission
timing where the cell intervals are randomized. The result
is notified to each B-TE by using SOH (Section Over-Head)
located at O & M (transmission Overhead for Maintenance)
disposed in each subscriber line interface on the SDH
(Synchronous Digital Hierarchy) base shown in Fig. 10, which
is now being studied by CCITT, or on the cell base shown in
Fig. 11. Each B-TE transmits the cells in the timing being
notified.
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CA 02239479 1998-07-27
With respect to the CBR cells, it is necessary to
further study whether to randomize the transmission timings
of the cells in each frame or to constantly assign the
transmission timings upon setting of the call so that the
cells are disposed in equal intervals in each frame. In the
former, the generating mechanism of the random timings can
be simplified. On the other hand, in the latter, the
variation of cell delay time periods which takes place from
end to end can be decreased.
Fig. 10 shows a case where the ATM cells are
transmitted with SDH frames which are being studied by
CCITT. As shown in the figure, each SDH frame is divided
into a section area and a path area. The path area is
composed of POH and an area for transmitting user
information. The frame interval is 125 ~ sec. The SOH and
the POH in the section area is used for an OAM function
(such as performance monitoring and alarming) over the NNI
(Network to Network Interface). By using this area for
notifying a subscriber terminal equipment of the number of
cells which can be transmitted, the present invention can be
applied to the ATM cell transmission on the SDH base. In
this case, with the cell transmission timings which are
randomized on the terminal side rather than those of which
the network notifies the terminal side, not only the cell
transmission control of short frame intervals of 125 ~ sec
can be accomplished, but cell transmission timings with a
44
CA 02239479 1998-07-27
plurality of frames can be readily determined. In addition,
with a plurality of SDH frames, the frame intervals of the
cell transmission control according to the present invention
can be formed. The SDH frame intervals constructing the
frame intervals should be determined from the standpoints of
the cell transmission control method, effective use of the
network resources, and so forth.
Fig. 11 shows an example of an embodiment of the so-
called multi-point connection service where a cell base
subscriber line (or private system) interface is passively
connected with a plurality of AUs (in the case of the
subscriber line interface, the AUs have both functions of
NT1 and NT2) through for example optical star couplers so as
to share the same transmission media, each AU being
connected to a plurality of TEs.
The frame interval of this embodiment is 5.875 msec,
which is the same as that in the above mentioned example.
The frame interval is composed of a control window area for
transmitting SOH cells and an information cell area for
transmitting conventional ATM cells with respect to both
down link (cells are transmitted from the broadband switch
node to the AU) and up link (cells are transmitted from the
AU to the broadband switch node).
For each of the down link and the up link, the
information cell transmission area can accommodate up to
2075 cells. However, on the up link side, a guard with 8
CA 02239479 2000-06-13
bits is provided between two successive ATM cells so as to
prevent ATM cells from colliding with each other due to the
multi-point connection and to establish the bit-
synchronization of the ATM cells on the receiver side. In
addition, on the down link side, a control window area which
has up to 79 SOH cells (part of which are used for
controlling the transmission delay time periods and for
performing the O & M) is provided. On the other hand, on
the up link side, a control window area which has 16 or 32
SOH cells for requesting the number of cells in accordance
with the maximum number of multi-points (the number of AUs),
SOH cells for measuring transmission delay time periods
(which may have the O & M function), a window for measuring
the transmission delay time periods (other than SOH cells
for measuring the transmission delay time periods are not
transmitted), and so forth are provided. The transmission
delay time period measurement is used to measure two-way
transmission time periods of ATM cells over the transmission
path, which are necessary to compensate the delay time
periods thereof. Besides an example of a construction of
the multi-point connection, since details of the access
control are known they are not described in the following.
In such a construction, each AU requests the broadband
switch node to permit.the number of ATM cells to be
transmitted, NRi, in the next frame for each of a plurality
of TEs connected thereto by using the SOH cells for
46
CA 02239479 1998-07-27
requesting particular cells. The broadband switch node
obtains the number of cells to be permitted, Npi, for each
TE in accordance with the above mentioned procedure. In
addition, the broadband switch node randomizes the cell
transmission timings over the entire interface so as to
prevent the cells from colliding each other and then
notifies each AU and each TE of the result in a bit map
format by using the SOH cells for assigning cells on the
down link side. On the up link side, an information field
of the SOH cells for requesting the number of cells is 84
octets, which is the same as that of the conventional cells.
However, when 8 bits are assigned for identifying each TE
and 16 bits for describing the number of cells requested,
the number of cells requested from 16 TEs or more can be
expressed with one SOH cell. On the other hand, as shown in
Fig. 12, when cells are assigned by the broadband switch
node in the bit map format, if 8 bits are assigned for
identifying each TE, an information length of 8 x 2075 bits
is required in total. However, even if a CRC code and the
like are added, when around 48 SOH cells are used, the above
identification can be satisfactorily performed. In
addition, when the number of AUs is 16, the window for
measuring the transmission delay time periods on the up link
side becomes 67.3 ~ sec, which can cover the transmission
path of up to 7 km in length. On the other hand, when the
number of AUs is 32, the window for measuring the
47
CA 02239479 1998-07-27
transmission delay time periods on the up link side becomes
22.8 ~ sec, which can cover the transmission path of up to 2
km in length. The length of the transmission path of 7 km
is the maximum length that the subscriber line interface can
cover in the narrow band ISDN network or the like. On the
other hand, the length of transmission path of 2 km is the
maximum transmission path required in a local area network
such as PBX.
As described above, the number of cells, Npi, which are
transmitted from a TE is assigned by the network in
accordance with the request issued therefrom. Thus, the
network can always, accurately, and readily deal with the
number of cells transmitted from each of TE and thereby
precisely charging fees or measuring the traffic intensity,
which will be described later.
In the above mentioned description, the virtual path is
routed between two nodes which terminate B-TEs. However, as
shown in Fig. 20, when a plurality of virtual paths are
disposed through tandem switches between B-TES (from end to
end), the following process can be performed.
In the figure (which represents only one direction
where cells are transmitted from the left to the right), ATM
switch nodes 51, 52, 55, and 56 function as local switch
(LS) stations for terminating B-TEs, while ATN switch nodes
53 and 54 function as tandem switch (TS) stations for
terminating and relaying virtual paths among the ATM switch
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CA 02239479 2000-06-13
nodes 51, 52, 55, and 56. In particular, the ATM switch
node 53 also functions as a tandem local switch (TLS)
station for terminating B-TE. The TS or TLS station is
installed as a terminating station of a virtual path routed
between long distance trunk line areas, for example, between
Tokyo and Osaka. Thus, the TS and TLS stations differ from
a cross connect node, which does not terminate a virtual
path. Virtual paths VPI1 and VPI2 of the ATM switch node 51
accommodate virtual channels VCI1 to VCI3 and virtual
channels VCI4 to VCIS, respectively. A virtual path VPI3 of
the ATM switch node 52 accommodates virtual channels VCI6
and VCI7. The ATM switch node 53 which terminates and
relays of virtual paths rewrites VCI and VPI in a cell
header so as to convert VCI1 to VI5 accommodated in VPI1
into respective VCI11 to VCI15 and send them to a VPI4.
Likewise, VCI6 and VCI7 accommodated in a VPI3 are converted
into respective VCI16 and VCI17 and then relayed to the
VPI4. In addition, the VPI4 accommodates VCI18 to VCI20
which are terminated by the ATM switch node 53. On the
other hand, the ATM switch node 54 terminates the VPI4,
converts the VCI11 and VCI12 into respective VCI21 and
VCI22, and relays them to a VPI6. In addition, the ATM
switch node 54 converts the VCI18 into a VCI25 and relays it
to a VPI7 so as to transmit each cell to the ATM switch node
55. Moreover, the ATM switch node 54 converts the VCI13
into a VCI26, relays it to a VPI8. In addition, the ATM
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CA 02239479 1998-07-27
switch node 54 converts the VCI16 and VCI17 into respective
VCI29 and VCI30 and relays them to a VPI10 so as to transmit
each cell to the ATM switch node 56.
In the above mentioned construction, the ATM switch
node 51 assigns the number of cells for each frame with
respect to the VCI1 and VCI2 (or B-TE) in the above
mentioned manner (Figs. 6 and 7) so that it does not exceed
that which can be transmitted on the band of the VPI5 which
has been registered in the switch node 51. Likewise, the
number of cells for the VCI3 is assigned in accordance with
the band of the VPI8 by each ATM switch node which
accommodates them. The number of cells for the VCI4 and
VCI5 is allocated in accordance with the band of the VPI6 by
each ATM which accommodates them. After the number of cells
are allocated, the transmission timings are randomized for
each subscriber line interface accommodating each VCI or for
each VPI.
When the number of cells is assigned in accordance with
the above mentioned method, the band of VPI4 should be the
same as or larger than the sum of the bands of VPI5 to
VPI10. Likewise, the band of VPI1 should be the same as or
larger than the sum of the bands of VPI5 and VPI8.
Moreover, the band of VPI2 should be the same as or larger
than the band of VPI10. For example, with respect to the
VPI4 which accommodate a large number of VPIs and is routed
for a long distance, cells are not always transmitted in the
CA 02239479 1998-07-27
full bands of VPIs. Thus, the band of VPI4 is more narrowed
than the sum of the bands of VPI5 to VPI10. In other words,
with the statistical multiplex in the virtual path level,
the resources in the network can be more effectively used.
Several methods for accomplishing the statistical multiplex
in the virtual path level will be described in the following
(it is assumed that only the band of VPI4 routed for a long
distance is narrow so as to simplify the description).
As a first method, the number of cells which can be
transmitted in the VPI4 has been assigned to the VCI1 to
VCIS, VCI6 to VCI7, and VCI18 to VCI20. For example, the
switch node 51 performs the statistical multiplex between
the VPI1 and VPI2 so that the number of cells assigned for
the VPI1 and VPI2 does not exceed that of the sum of the
VCI1 to VCIS.
As a second method, the number of cells to be
transmitted in the next frame requested through the VCI1 to
VCI7 and through the VCI8 to VCI20 is calculated by for
example the switch node 53. When the number of cells which
was calculated exceeds that which can be transmitted in the
band of VPI4, the number of cells which can be transmitted
are proportionally divided for the VPIS to VPI10 as were
described with reference to Figs. 6 and 7. The switch node
53 notifies the ATM switch nodes 51 and 52 of the results.
Thus, each of the switch node 51 and 52 assigns the number
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CA 02239479 1998-07-27
of cells requested from B-TE so that it does not exceed that
being received from the switch node 53.
As a third method, the number of cells transmitted from
for example the VPI4 is calculated by the switch node 54 for
each of the VPI5 to VPI10. The switch node 54 estimates the
state of traffic variation of each VPI in accordance with
the calculated results, assigns the maximum number of cells
which can be transmitted from each VPI on the order of
seconds or minutes, and notifies the ATM switch nodes 51,
52, and 53 of the results. Each of the switch nodes 51, 52,
and 53 assigns the number of cells which can be requested
from B-TE so that it does not exceed that being received
from the switch node 54.
As a fourth method, the number of cells which enter the
network is calculated by the switch nodes 51, 52, and 53,
which are entrances of the network or by the switch nodes 55
and 56, which are exits of the network. Each switch node
notifies a management node (not shown in Fig. 20) of the
calculated results. The management node estimates the state
of traffic variation on the order of several ten minutes or
several minutes, assigns the maximum number of cells which
can be transmitted from each VPI, and then notifies the ATM
switch nodes 51, 52, and 53 of the results. Each switch
node assigns the number of cells requested from B-TE so that
it does not exceed that being received from the management
node.
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In the first method, since a closed process is
available for each switch node which terminates a B-TE, this
method can be most readily accomplished. However, the first
method is inferior to the second method with respect to
effective use of the resources in the network. In the
second method, since the statistical multiplex can be
performed for each frame, the use efficiency of the
resources (VPI4) in the network can be most improved.
However, the number of cells which can be transmitted should
be calculated for each frame and the notice with respect to
the results should be sent to other nodes. Thus, a sequence
of processes and notices should be performed and issued at a
high speed. On the other hand, in the third and fourth
methods, although the required speed is not higher than that
of the second method, the use efficiency of the resources in
the network is decreased. In particular, in the fourth
method, since the management node can assign cells by
considering the entire network, this method is effective
when the construction of the network is complicated. Besides
the above methods, other various methods such as a
combination of the first method and the third method or the
fourth method can be considered. However, as was described
above, other methods are inferior to the second method to
some extent with respect to the effective use of the
resources in the network.
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On the other hand, CCITT defines that even if the sum
of virtual channels instantaneously exceeds the band of a
virtual path due to statistical multiplex, the virtual path
should satisfy the quality of services (QOS) for all the
virtual channels. However, the method for accomplishing the
above requirement is a subject to be studied in the future. In
other words, only cells with low priority or with violation
mark, that the network does not assure to transmit, are
statistically multiplexed between virtual paths. Thus, the
statistical multiplex is not positively used between virtual
paths. In contrast, according to the present invention, all
cells which enter the network can be statistically
multiplexed between virtual paths. Thus, an instantaneous
traffic variation can be absorbed (without necessity of
changing the registration of the bands of virtual paths) and
thereby the resources in the network can be effectively
used.
Next, an embodiment of a call connection method for
shortening a call connection time in computer communication
will be described in focusing on the class C.
Fig. 13 is a block diagram showing an example of
connections according to the present invention.
B-TE la to ld are connected to ATM switch nodes 2a and
2b through virtual channels 33a to 33d. The virtual
channels have bands 31 over a virtual path 4ab routed
between the ATM switch nodes 2a and 2b.
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CA 02239479 2000-06-13
To simplify the description, the virtual channels and
the virtual path only in one direction are described in the
figure. However, actually, the virtual channels and the
virtual path in the reverse direction are also routed. In
addition, due to the same reason, a virtual path for
controlling calls is also omitted in the figure.
Fig. 14 is a schematic showing an example of a call
control sequence in the above mentioned connections.
Reference numerals 34a to 34x represent call control
signals for setting a data link. Reference numerals 35a to
35c represent information transmission processes which are
made between two B-TEs.
Fig. 15 show examples of management tables 36ab and
36ba representing the relationship among a terminal
equipment identifier TEIj of B-TE, a virtual channel
identifier VCIk, transmission speeds Uc and Uv and so forth
when a call number CRi against virtual paths 4ab and 4ba
routed from the ATM switch node 2a to 2b and from 2b to 2a
is used as a key.
When the call set request message 34a for setting a
call from the B-TE la to the B-TE lb is transmitted to the
ATM switch node 2a, the switch node analyzes the call set
request message 34a, which includes the above mentioned
attribute data (the type of service (CBR, VBR, or MBR),
transmission speed, class, and so forth) and then selects
the corresponding virtual path 4ab. In addition, the switch
CA 02239479 1998-07-27
node references the remaining band of the management table
36ab shown in Fig. 15 (a) with respect to the virtual path
4ab and checks whether or not the required transmission
speed can be obtained. When the switch node determines that
the required speed can be obtained, it assigns a call number
CRi and a virtual channel identifier VCIj, registers the
identification of the CBR service and/or the VBR service (in
the case of a call which requests the MBR service, both CBR
and VBR are registered for one call number), the
corresponding transmission speeds Uc and Uv, class, and so
forth on the management table 36ab, and then updates the
remaining band.
Thereafter, the ATM switch node 2a transmits the call
set message 34b to the ATM switch node 2b. Then, the switch
node 2b transmits the call set request message 34c to the B-
TE lb. When the ATM switch node 2b receives the response
message 34d from the B-TE lb, it selects the virtual path
4ba routed from the B-TE lb to the B-TE la in accordance
with the attribute data contained in the response message
(occasionally, the B-TE la may declare to select it).
Thereafter, the ATM switch node 2b references the management
table 36ba and registers required data such as VCIj by using
the same call number CRi.
Thereafter, the response messages 34e and 34f are
transmitted in succession to the B-TE la. Thus, the data
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CA 02239479 1998-07-27
link is established between the B-TE la and the B-TE lb and
thereby a communication ready state takes place.
After the data link is established, information
transmission 35a is performed by the user. After the
information has been transmitted, before next information is
transmitted, the B-TE transmits the interrupt message 34g to
the ATM switch node 2a.
When the interrupt message 34g is a call in the class
C, the ATM switch node 2a writes on the management table
36ab the interrupt start time in the call state column with
the call number and sends the interrupt message 34h to the
ATM switch node 2b. In addition, the ATM switch node 2a
writes the interrupt start time on the management table 36ba
and sends to the B-TE lb the notification message 34i for
notifying it that the user interrupted the call and to the
B-TE la the interrupt acknowledgment message 34j.
When the B-TE la sends the resumption message 34k to
the ATM switch node 2a in such a state, the ATM switch node
2a clears the interrupt start time on the management table
36ab in accordance with the call number CRi. In addition,
the ATM switch node 2a also clears the interrupt start time
on the management table 36ba by means of the resumption
message 341 and sends to the B-TE lb the notification
message 34m for notifying it that the user resumed the call
and to the B-TE la the resumption acknowledgment message
34n. Thus, the information transmission process 35 is
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CA 02239479 1998-07-27
resumed between the users. Thereafter, the interrupt and
the resumption of the call are repeated in the same
procedure. When the ATM switch node 2a receives the
disconnection message from a B-TE, it erases the
registrations with respect to the call on the management
tables 36ab and 36ba and then updates the remaining band
thereof. On the other hand, when the ATM switch node 2a
receives a new call set message 34o from another terminal
equipment B-TE lc, it references the management tables.
After that, when the ATM switch node 2a determines that the
remaining band is insufficient, it erases calls in the class
C which have been interrupted in the order of older ones
from the management tables in the sequence shown by
reference numerals 34p to 34x of Fig. 14. Thus, the ATM
switch node 2a obtains the required band and releases the
erased calls from the tables.
On the other hand, when a B-TE which has interrupted a
call receives another call from another B-TE, the ATM switch
node erases the registrations with respect to the call on
the management tables 36ab and 36ba, and sends the release
message to the related B-TE. Thereafter, the former B-TE
accepts the reception of a new call. When a B-TE which has
interrupted a call sends another call to another B-TE, the
ATM switch node erases the registrations with respect to the
call which has been interrupted from the management tables
and releases the erased call. Thereafter, the former B-TE
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CA 02239479 1998-07-27
originates the call. When a B-TE has interrupted a call for
a long time and the call has been erased and released from
the management tables due to the traffic condition of the
network, if the B-TE repeats a call once again, the sequence
of processes is repeated from the issuance of the call set
request message.
Figs. 16 and 17 show a sequence and management tables
in the case where a disconnection message or release message
is used instead of the interrupt message, respectively.
In Fig. 16, as shown by reference numerals 40a to 40x,
disconnection messages or release messages are used instead
of the interrupt messages. However, the sequence shown in
Fig. 16 is basically the same as that of the conventional
originating and terminating sequence.
An identifier TEIj of the party's terminal equipment
instead of the call number is registered on management
tables 37ab and 37ba shown in Figs. 17 (a) and (b).
When the network receives a repeated call set request
message 40m, it searches the management tables both on a
calling side TEIi and a called side TEIj. When the
registered content accords with the declared attribute data,
the flow of the network immediately enters a call set
process with the called side without a band obtaining
process for the call.
In this embodiment, even if a terminal equipment
transmits a disconnection message to the network, the
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CA 02239479 2000-06-13
network does not erase the registration data of the call.
When another terminal equipment originates a call and the
remaining band in the network becomes insufficient, the
network erases registration data of calls in the same
condition as described in the above mentioned embodiment.
Now, the ISCP (ISDN Signaling Control Part) signal
system where the call control and the connection control are
separated from the layer 3 will be described in the
following.
Fig. 22 is a sequence schematic showing a process in
each phase by signaling of layer 3.
1. Call set request
The network performs a simple call acceptance control
against a call set request and sets a call in accordance
with the call acceptance control. Thereafter, the network
registers the user connection information on a connection
information management table. In the call set phase, the
network routes the call in accordance with the E. 164
address. At that time, a real communication resource (band)
is not held.
2. Connection set request
When a user transmits information, he or she requests
the network to assign a resource (band). In the classes
where information should be transmitted in real time, such
as the class A (pseudo line switch) and the class B
(variable length coded picture signal), the assignment of a
CA 02239479 2000-06-13
resource will be performed in the call set phase. The
network assigns the band in accordance with declared data
such as peak speed and registers the band information on the
connection information management table.
3. Connection interrupt request
When a user or a terminal equipment determines that
information is not transmitted for the time being, he or
(she) or it releases the resource while the call takes place
and then registers the call state on the connection
information management table so as to effectively operate
the communication resource. The released resource may be
used by a band assignment request by another call. In
addition, irrespective of the class for use, the above
mentioned process will be performed for a call which should
be relayed.
When the number of calls to be transmitted exceeds that
which can be relayed, the network releases the VC
connections of calls with lower priorities from those which
have been interrupted on the VC management table and erases
them out of the management table. Thereafter, the network
treats the call state of a call which is newly interrupted
as the interrupt state and then notifies the switch node on
the other user of the interrupt. On the other hand, the
network notifies the user who requested to interrupt the
call that it has accepted the interrupt so as to get ready
for accepting a new call from the user. When the network
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requires a band due to a request from a user, it releases a
VC which has been interrupted (erases it out of the
management table) and then makes a new connection for the
new call.
4. Connection resumption request
When the transmission of information is resumed from
the connection interrupt state, with respect to the user or
the terminal, the flow enters the information transmission
phase. The network assigns a communication resource in
accordance with the connection information management table
and the band management information. When the communication
resource (band) cannot be obtained, the network does not
accept the resumption of the transmission and performs the
standby process or the release process.
5. Release request
The user or the network releases a call when the
communication is completed or when a particular call is
released in the connection interrupt state.
In the present invention, so as to effectively use the
communication resources, a new band management method which
can assign a pool band besides a band with respect to a call
is required.
Thus far, as the call acceptance control, various
methods such as virtual band method and virtual line method
have been known. For simplification, only the virtual band
method will be described in the following.
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A switch node has a connection state management table
for managing the connection state of a call for each VP
which is terminated thereby and a band management table for
managing the band for each VP. Regardless of the call
acceptance control method, as shown in Fig. 23, the
connection management table has a call identification number
such as a global call number, a set VCI number, a call type,
and a time stamp. On the other hand, the band management
table has a table storing a use band for each VP and the
number of set VCs and the number of pool VCs for each call
type as shown in Fig. 24 and virtual band data for each call
type which is set through off-line as shown in Fig. 25.
With reference to Figs. 26, 27, and 28, an algorithm of
the call acceptance control will be described in the
following.
With respect to a conventional connection set, the
network selects a VP and then determines the number of set
VCs, the band for use, and the required band. When the
conditions are satisfied, the network permits the connection
set.
With respect to a band pool, the network holds a
virtual band as a using band as it is and increments the
number of pool VCs.
When the pool band is resumed, the network determines
whether or not to release it in accordance with the number
of pool VCs for each call type.
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When the traffic intensity in the VP becomes high and
the band for use becomes insufficient, the band of the pool
VC is assigned.
As was described above, communication resources are
pooled on a particular table so as to promptly handle a
resumption request. The band being pooled for a resumption
request from a user is held in the next resumption phase so
as to promptly resume the transmission of information.
However, when the traffic intensity in the network
becomes high and the remaining band in the VP becomes
insufficient, the band being pooled is used so as to accept
a new call. Even if the remaining band is sufficient, when
there is a call which is still interrupted for a particular
time period, the network issues an alarm message or a
disconnection message to a user and prompts him or her to
release the call and the band so as to prevent the band from
being improperly pooled.
Once the above processes are performed, information can
be transmitted with a response equivalent to connection-less
(at an inexpensive fee). In addition, from the standpoint
of the network, call loss does not increase in the
communication resources.
To further improve the use efficiency, when the value
determined by the limitation including the internal memory
and the like rather than time exceeds its threshold value,
the network issues an alarm message or a disconnection
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CA 02239479 2000-06-13
message against a call which is newly accepted (connection)
or discarded (connection) by using LRU (Least Recently Used)
algorithm.
In the above mentioned embodiment where the interrupt
message is used when a call has been registered on
management tables, the transmission of information can be
resumed in a very short time such as on the order of several
msec or several ten msec. Thus, each user can use an inter-
computer communication of the broadband ISDN network with a
high response equivalent to connection-less, namely, without
necessity of a waiting time. Moreover, in the broadband
ISDN network, when the resources in the network become
insufficient, since a band which is held for a call which
has been interrupted, namely, a communication resource can
be released to another user, the resources in the network
can be effectively used. In addition, it is not necessary
to charge a call which has been interrupted. Moreover,
after a call is interrupted, even if the user leaves the
terminal equipment and the call is not disconnected and
released, when a predetermined time period elapses and the
traffic intensity becomes high, the call is erased from the
management tables and released from the network. Thus, it
is not necessary to provide the management tables with too
large a space. In other words, the users can inexpensively
use services which are equivalent to connection-less system.
CA 02239479 1998-07-27
In addition, the network can effectively use the resources
thereof.
In the above description, the B-TE transmitted the
interrupt message or the disconnection message to the
network. However, it is also possible to transmit such a
message by the consideration of each user. In addition,
when a timer in the B-TE counts for example 1 minute after
data is transmitted, the network can write the interrupt
start time in the call state column of each management table
so as to rapidly deal with the later call resumption. As
another method, by considering the charging system for use,
which will be described later (even if communication is
completed within 1 minute, the path holding unit fee for 1
minute is charged), when information has not been
transmitted, 1 minute after a call was set, the network can
write the interrupt start time in the call state column of
each management table so as rapidly deal with the later call
resumption. Moreover, when the timer in the network counted
a predetermined time period, the network can write the
interrupt start time in the call state column of each
management table so as rapidly deal with the later call
resumption.
In the above description, the network wrote the
interrupt start time on each management table and erased the
registrations of calls from each table in the order of older
ones. However, it is possible to provide priority order in
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CA 02239479 1998-07-27
accordance with the number of interrupt/resumption times in
the past. In addition, by considering the effective use of
the resources in the network, it is possible to provide
priority order in accordance with transmission speeds or to
affect user requests to the priority order.
Moreover, since the number of parameters for the above
mentioned management tables was relatively large, table
search will take a long time. However, by providing a
plurality of tables with keys of call numbers, priority
order, terminal equipment identifiers, and so forth, the
load of process can be decreased and thereby particular
resumption process can be more rapidly executed.
In the above description, when the remaining band in
the virtual path became insufficient or when another call
was attempted to be terminated to a particular B-TE, the
registration of the call was attempted to be terminated to a
particular B-TE, the registration of the was erased.
However, depending on the traffic condition in the network,
it is also possible to erase calls which have been
registered on each management table and which have been
interrupted or disconnected when the band of another virtual
path becomes insufficient or when a new virtual path is
provided.
In the above description, one virtual path is provided
between the ATM switch nodes 2a and 2b. However, when the
virtual path was relayed with the plurality of nodes, by
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providing each node with the management tables, calls can be
interrupted, resumed, and released in the same procedures as
were described above.
In the above examples, the present invention was
applied only to calls in the class C. However, it is
obvious that the present invention can be applied to calls
in other classes, namely, the class A, class B, and class D.
In addition, the present invention can be also applied to
the broadband ISDN networks, private branch exchanges (PBX),
and the like besides the broadband ISDN networks.
To sum up, the aspect of the above mentioned embodiment
is as follows. Communication resources are registered to
particular management tables so that calls which have been
interrupted or disconnected can be rapidly resumed or
reconnected in accordance with the requests. Registrations
of calls are erased from the management tables in accordance
with the traffic condition or communication requests for
other calls so as to release the resources. There will be
many methods for accomplishing such an aspect. In this
embodiment, the method for accomplishing the aspect is
generically named the immediate connection service. Then,
with reference to Figs. 18 and 19, a charging system which
is an important factor for inducing suitable uses of the
resources in the broadband ISDN network and for stably and
effectively operating the network will be described.
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CA 02239479 1998-07-27
Fig. 18 shows a table representing fees by transmission
rates for constant bit rate transmission and variable bit
rate transmission.
In the constant bit rate transmission, when the number
of cells transmitted per minute at a transmission speed Uc
is represented with (1), it can expressed as follows.
106 x Uc Mbps / (48 octets x 8 bits) x 60 sec.
When the Uc is 64 Kbps, 1 Mbps, 10 Mbps, and 100 Mbps, the
transmission capacity becomes 104 cells/min, 1.56 x 105
cells/min, 1.56 x 106 cells/min, and 1.56 x 10' cells/min,
respectively. When the cell unit fee (2) for a short
distance communication (the communication fee depends on the
distance of communication), namely, the transmission fee per
cell, is for example ~ 4 x 10-4 x Uc-1~3. The communication
time unit fee per minute (3) can be expressed by the product
of the number of cells transmitted and the cell unit fee.
In other words, the communication time unit price (3) per
minute is in proportion to Uc2~3. Thus, the communication
fee is obtained by the unit fee times the communication
time.
On the other hand, in the constant bit rate
transmission, from the standpoint of the user, since the
number of cells transmitted is controlled by the network,
the service quality is low. In contrast, from the
standpoint of the network, the communication resources can
be effectively used. In addition, with computer
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CA 02239479 1998-07-27
communication, excessive call requests to the network and a
long time holding of a virtual path can be suppressed. When
the cell unit fee (5) is set to for example 1/4th that of
the constant bit rate transmission; the path holding time
unit fee (6) is set to for example l/lOth that of the
communication time unit fee (3) in the constant bit rate
transmission; and the path holding time unit fee for one
minute is charged for a call of less than 1 minute, then the
sum of the number of cells transmitted times the cell unit
fee (5) and the path holding time times the path holding
time unit fee (6) becomes the communication fee to be
charged.
Fig. 19 shows a table representing practical
communication fees for the CBR service applicable for the
classes A and D, the MBR service applicable for the classes
B and D (assuming that overall transmission speed = Uc + Uv
and Uc = Uv), and the VBR service applicable for the classes
C and D.
As shown in the figure, in the CBR service, the
communication fees at 64 Kbps, 1 Mbps, 10 Mbps, and 100 Mbps
are ~ 10/min, ~ 62/min, ~ 290/min, and ~ 1345/min,
respectively. With reference to the figure, even if the
transmission speed is increased by 10 times, the
communication fee is increased by around 4.6 times. Thus,
the user can positively use the high speed communication
services with which the broadband ISDN network is provided.
CA 02239479 1998-07-27
In addition, in the above mentioned charging system, the
network can prevent the user from declaring an unnecessarily
high speed of transmission.
On the other hand, in the MBR service, where the
traffic intensity always varies due to long holding time, in
the assumption that the mean use rate in the variable bit
rate transmission is denoted by ~ (the number of cells
transmitted = the maximum number of cells transmitted x
at any transmission speed, when ~ = 0.1, ~ = 0.5, and ~ _
1.0, the communication fees become more inexpensive by
approximately 35 ~, 25 ~, and 15 $ than those in the CBR
service, respectively. Thus, the MBR service will demand
the user to properly declare a combination of the constant
bit rate transmission and the variable bit rate
transmission.
On the other hand, in the classes 3 and 4, where
computer files and the like are mainly transmitted, when the
file capacity is denoted by F Mbytes, the communication
speeds to be declared with the most inexpensive fees at F =
1 Mbytes, F = 10 Mbytes, and F = 100 Mbytes are 133 kbps,
1.3 Mbps, and 13 Mbps, respectively. All the file
capacities of the files take approximately 1 minute to
transmit.
It is possible to decrease the file transmission time
on the order of several seconds by declaring the
transmission speed ten times higher than each of above
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files. At that time, the increases of the communication
fees are only at most 10 to 30 ~. On the other hand, when
the transmission speed 10 times faster than the above is
declared (the files can be transmitted on the order of 1 sec
or less), the communication fees will be increased by 4
times or more. Thus, the cost performance from the
standpoint of the users will be remarkably decreased. In
other words, when the user can withstand a communication
time for approximately 1 minute, he or she can most
inexpensively transmit a file. On the other hand, when the
user wants to transmit a file over a man-machine interface
within several seconds, the communication fee will be
increased only by approximately 10 to 30 $. However, when a
file is transmitted at a very high speed or a very slow
speed, the communication fee will be adversely increased.
Thus, the user is induced to declare a moderate transmission
speed.
In Fig. 18, as was described earlier, while the file
capacity F is divided by 48 octets, which are the
information field length of ATM cells, CCITT is now
considering that the length of the SDU area in the classes C
and D is 44 octets. Thus, from the standpoint of the
transmission capacity of the SDU, no problem will take
place.
Moreover, in the above description, the practical
calculation expressions were exemplified in such that the
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cell unit fee in the constant bit rate transmission was in
proportion to Uc-1~3. However, the present invention is not
limited to such calculating expressions. Rather,
combinations of various coefficients can be considered. In
addition, in the above description, the cell unit fee in the
constant bit rate transmission was the same as that in the
variable bit rate transmission regardless of the classes and
service types. Rather, it is possible to set the cell unit
fees by the classes and by the service types. In other
words, since the present invention is characterized in that
the CBR service, the VBR service, and the MBR service are
provided to the user; the user declares a transmission speed
of the desired service; the cell unit price according to a
transmission speed determined between the user and the
network, the communication time unit fee, and the path
holding time unit fee are defined so that the user can use a
proper resource in the network; and the fee in accordance
with the number of cells actually transmitted, the
communication time, the path holding time, and communication
distance is charged to the user. Thus, many calculating
expressions are satisfied in the above mentioned scope.
As was described above, according to the broadband
switching networks of the present invention, with flow
control performed cooperatively by the network and terminal
equipments, excessive cells do not enter the network and
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thereby prevent cell discard from taking place in the
network.
In addition, by randomizing arrival intervals of cells
which enter the network (or an ATM switch), the burstiness
of cells disappears and thereby remarkably reduces the
storage capacity of the buffer of the ATM switch. In
addition, the variation of cell delay can be remarkably
reduced.
In addition, since no cell discard basically takes
place, it is always not necessary to assign for each cell a
cell sequence number in information field by the ATM
adaptation layer unlike the related art. Thus, the
transmission speed of user information can be increased so
as to effectively use the resources in the network.
Moreover, by providing a transmission service in
constant bit rate transmission, a transmission service in
variable bit rate transmission for effectively using
statistical multiplex effect characterized by the ATM, and a
transmission service which is a combination of both the
services suitable for transmitting pictures and the like,
the user only needs to declare a transmission speed thereof
instead of a combination of complicated attribute parameters
unlike the related art. Thus, since it is not necessary to
cause the network to unilaterally restrict service items,
the flexibility, which is the most important aspect of the
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broadband ISDN network, is not lost and the network can be
widely used for various user needs in the future.
Furthermore, the present invention also proposes a
practical system for accomplishing the flow control and the
randomization of cell arrival with respect to a multi-point
connection service, which is a subject to be defined by
CCITT in future. Thus, according to the present invention,
with the same communication medium, communication with high
efficiency can be provided.
In addition, for calls which have been interrupted or
disconnected, the related communication resources are
registered on management tables so as to quickly handle
repeated call set request. In accordance with the traffic
condition and other call requests, the communication
resources are erased and released from the management
tables. Thus, according to the present invention, services
with the same quality as connection-less services can be
provided. Besides inter-LAN connections in the class D,
which are mostly used by large companies, the present
invention provides remarkable benefits to communications
using personal computers and the like. Thus, the
communication resources in the network can be effectively
used.
Moreover, since the present invention provides
practical calculating methods for cell unit fees for
transmission speeds, communication time unit fees, path
CA 02239479 1998-07-27
holding time unit fees in accordance with service systems,
it promotes the users to use proper communication resources
in the network, while preventing other users from being
adversely affected by false declaration. In addition,
according to the present invention, the network can be
effectively operated.
Furthermore, according to the present invention,
neither polling function nor priority control is required in
the network unlike the related art. Thus, the call
acceptance control is simplified. Further, switch nodes or
cross-connect nodes constructing the broadband ISDN networks
or broadband industrial information communication networks
can be readily developed.
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