Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
WO 92/2118? PCT/US91/034~88
1 ~1a9~~s
DYNAMIC CHANNEL ALLOCATION METHOD AND SYSTEM
FOR INTEGRATED SERVICES DIGITAL NETWORK
Technical Field
This invention relates generally to
Integrated Services Digital Network (ISDN), and more
particularly to controlling dynamic channel allocation
in ISDN and to creating a virtual channel out of
underlying network channels.
_Hackcrround Art
A digital telecommunication network can be
characterized by two general features, the existence
of well defined digital interfaces to Customer Premise
Equipment (CPE) which are the end nodes of the
network, and an interconnected switching backbone
network which is capable, upon demand, of creating
point-to-point connections between any two end
nodes. An example of such a network architecture can be
found in the ISDN specifications which have been
developed by the International Telegraph and
Telephone Consultative Committee (CCITT). Although
aspects of the invention may be relevant to other types
of digital telecommunication networks, in the
paragraphs below, the general features of a digital
telecommunication network upon which this invention
depends will be described using examples drawn from
ISDN.
A complete description of the architecture of
ISDN is beyond the scope of this specification. For
details, and for an extensive bibliography of
references of ISDN, see Stallings, ISDN, An
Introduction, MacMillan Publishing Company, 1989. In
WO 92/Z1187 ~ ~ ~, S 2 PCT/US91/03448
general, all ISDN interfaces to customer premises
equipment (CPE) can be characterized by the use of
time division multiplexing at the physical layer to
partition the bandwidth of a single physical link into
multiple independent channels, such as the two B
channels and the D channel found in the Basic Rate
Interface (BRI). The B, or "bearer",' channel is used to
transmit user information. The D channel carries
signalling or control data which provides control over
the use of the two B channels in the BRI as well as
user data which often is in tine form of packets. These
channels can be considered as independent ISDN
resources available to the end user. ISDN also defines
a specific data link layer and network layer
protocol to be used over the D channel between the
CPE and the Local Exchange (LE).
The B channel in an ISDN network is a full duplex,
64000 bit per second, synchronous user channel.
There are many modes of operation for the B channel.
The preferred embodiment of this invention is
described in the environment of the BRI and is based in
part on the capability of the B channel to carry
digital data or PCM-encoded digital voice in a
transparent manner across the circuit switched backbone
network. The same principles could be extended to the
Primary Rate Interface (PRI). Before a circuit switched
B channel can be used by end users, the channel
must be connected through the ISDN. Requests for
channel connection are made by the CPE to the LE
using a protocol over the D channel. The LE routes
the request through the ISDN using other protocols,
until the destination LE is reached. The destination
LE then issues a call connection request to the
destination CPE which can accept the call. Either
WO 92/21187 PCT/US91 /~U3448
3
r
~~~';~~~
party to a call can disconnect the call. This action
also involves relaying a series of messages over
the respective D channels and other network
activity. The ISDN network itself can also disconnect
the call due to error conditions inside the
network. Unlike analog telecommunication networks, the
time to connect or disconnect a channel is
anticipated to be very short, potentially on the order
of a second.
.An important characteristic of B channels in an
ISDN is that the network_ is permitted to create
independent paths inside the network for each circuit
switched B channel. Thus if a CPE connects two B
channels to another CPE, the CPE can not rely on the
network to synchronize the transmissions across the
two channels. A second important characteristic of B
channels in an ISDN is that they can be used for
multiple purposes, such as voice service or data
service, and a BRI can support multiple devices such as
a computer and a telephone.
When one considers using the data services of ISDN
to connect computers, the bandwidth of a single B
channel is a serious limitation. This is particularly
true when one considers that many computer network
applications are geared toward local area networks in
which applications commonly achieve point-to-point
communication speeds on the order of several hundred '
thousand bits per second or greater. Another
disadvantage of the use of circuit switched B channels
34 is the bursty nature of data traffic and the fact that
the tariff structure for circuit switched
channels is independent of the data traffic over the
channel. This can lead to inefficient use of a
channel resulting in excessive channel usage cost.
WO 92/21187 ~ PGT/US91 /03448
~1.6~J~~b
An additional limitation is the desire to share
the TSDN interface with other devices, such as a
telephone, without having to statically allocate a
channel to each user of the interface. Tn the event
of contention far a channel between different users,
high priority channel users should be able to
preempt channels from low priority channel users. The
present invention addresses these limitations and
provides a method to overcome them.
Dynamic channel (bandwidth) allocation per se is
not new to ISDN. U.S. Pat. Na.. 4,763,321 and U.S. Pat.
No. 4,805,167 describe techniques to accomplish channel
synchronization at the physical level (bit level
synchronization) by manipulating the ISDN interface
frame structures (TDM frames) to create a high data
rate virtual channel. However, it is disadvantageous to
carry out operations at the physical level (Level 1 of
OSI) which require manipulation of hardware. The
present invention does not operate at the physical
level and makes no attempt to manipulate the ISDN
physical interface.
Disclosure of Invention
Accordingly, a broad object of the invention is to
improve bandwidth utilization of ISDN.
Another object is to dynamically allocate B
.channels between ISDN communication partners in
response to preassigned priorities and real time
events.
Another object of the invention is to enable
computer networking on ISDN while retaining support of
traditional telephone services.
An additional object is to carry out automatic
ISDN channel allocation in a manner that is transparent
CA 02109836 1999-11-03
to a user.
Still another object of the invention is to carry
5 out improved protocol for implementing dynamic
bandwidth allocation in ISDN.
A further object of the invention is to carry out
the aforementioned objects without manipulation of
data at the physical layer.
Accordingly, the present invention provides in a
computer interface to ISDN, a method of automatically
allocating/de-allocating B-Channels, above a LAP-D
protocol of Layer 2, comprising the steps of:
(a) monitoring events supplied to the ISDN which
indicate requests to use or release a B-Channel;
(b) evaluating channel usage priorities associ-
ated with events monitored in step (a);
(c) based upon said channel usage priorities,
automatically setting up or tearing down circuit
switched B-Channels associated with said ISDN; and
activating a virtual B-Channel between two compatible
computer processes using a circuit switched B-Channel
set up in step (c), and wherein step (c) includes the
steps of logically adding or deleting circuit switched
channels to or from said virtual B-Channel dynamically
based on bandwidth requirements by the processes, and
tearing down said virtual B-Channel based upon a
condition predetermined by said computer processes.
To achieve the above and other objects, the
invention provides a computer program implementation
that enables a CPE device to dynamically manage the
ISDN resources available to it in such a manner as to
overcome the above mentioned limitations of ISDN. The
invention enables ISDN to accommodate a computer
network while retaining the ability to also support
CA 02109836 1999-11-03
5a
traditional telephony services.
The present invention further provides an
apparatus for interfacing a computer to ISDN,
comprising:
a processor;
a virtual B-Channel between said computer and
said ISDN; and
program means executable by said processor and
operating above a LAP-D protocol of Layer 2 for
monitoring events supplied to the ISDN which indicate
requests to use or release said virtual B-Channel,
evaluating channel usage priorities associated with
users generating events, and based upon channel
bandwidth requirements by said events and said channel
usage priorities, logically adding or deleting circuit
switched channels to or from said virtual B-Channel.
One aspect of the invention carries out dynamic
channel allocation in an ISDN line by monitoring
events supplied to the line which indicate requests to
use or release a B-Channel, evaluating channel usage
priorities associated with users generating events
monitored, and, based upon channel usage priorities,
automatically setting up or tearing down B-Channels
associated with the line. Processing takes place
above LAP-D protocol.
In accordance with a preferred embodiment of the
invention, upon a hardware platform are provided first
and second program modules, a Channel Management
Module (CMM) and a Virtual Channel Module (VCM), to
implement dynamic channel allocation. The program
modules cooperate to control bandwidth between
communication partners by selective allocation and de-
CA 02109836 1999-11-03
5b
allocation of virtual B-Channels between them in
response to preassigned priorities and real time
events.
The first program module, CMM, monitors requests
WO 92/21187 , ~ 6 PGT/US91/03448
1.
to connect and disconnect B channels by potential end
users and the second module (VCM). The CMM is capable
of signalling the VCM to farce deallocation of a B '
channel from a virtual channel based on a request for
channel connection by a higher priority end user. The
CMM signals the VCM to indicate the existence of
available B channels when end users disconnect the
channel.
The second module, VCM, provides a block
oriented transport service to various computer
processes which can operate over one or more B
channels. This service operates above the data link
layer and manages the multiplexing of messages across
one or more data link connections which operate on a
B channel so as to ensure properly ordered delivery
of message blocks. Channels are added or deleted on a
dynamic basis, without interrupting the flow of data.
The service supports the allocation and deallocation of
channels based on signals from the CMM. Channel
deallocation also takes place in response to high error
rates in message transmission.
The grogram modules implemented in accordance with
this invention provide control logic for a CPE device
to allocate and deallocate ISDN channels to a plurality
of end users, i.e., the local analog telephone
equipment, the various processes running on the local
computer system, and similar entities located remotely
on the ISDN network. Implementation is based both on
user specified priorities and the real time
requirements of each user. The modules also support the
virtualization of B channel resources so as to overcome
the bandwidth limitations of a single B channel.
Still other objects and advantages of the present
invention will become readily apparent to those skilled
WO 9/21187 ~' '° ' PGT/US91 /03448
..
in this art from the following detailed description,
wherein only the preferred embodiment of the invention
are shown and described, simply by way of illustration
of the best mode contemplated of carrying out the
invention. As will be realized, the invention is
capable .of other and different embodiments, and its
several details are capable of modifications in various
obvious respects, all without departing from the
invention. Accordingly, the drawing and description
are to be regarded as illustrative in nature, and not
as restrictive.
_Hrief Description of the Drawings
FIGURE 1 is a circuit diagram of the hardware
platform upon which programming in accordance with the
invention is implemented.
FIGURE 2 is a' system software module diagram of a
communication coprocessor system known in the prior art
and forming part of the hardware platform shown in
FIGURE l for implementation of the present invention.
FIGURE 3 is a software module diagram
corresponding to FIGURE l including additional software
modules comprising an aspect of the invention.
FIGURE 4 is a message interface diagram for the
additional modules shown in Figure 3.
FIGURES 5(a) and 5(b) are diagrams of B channel
state tables and priority levels maintained by the'Cl~i.
FIGURE 6 is a flow chart of programming carrying
out an aspect of the invention.
FTGURE, 7 is a representative view of a circuit
board carrying the hardware shown schematically in
FIGURE 1.
F~GURE 8 is a flow chart of programming for
removing B-channels from the virtual channel in
IS,,~. ~'.
.t!Y.
!v1,
WO 92/21187 , ~ ~ ~ g PGT/US91/03448
a.'vv
C..,f:...
~.,..ri
cat .
y;~...
~f.-
~~s- response to an excessive error rate in accordance with
>.,~;
another aspect of the invention.
~.': FIGURE 9 is a flow chart of a routine for sending
y.
Yfii
to a remote resource.
FIGURE 10 is a flow chart of a routine for
f'v receiving from a remote resource.
,,;,, ,
r: Detailed Description of the Invention
~ra~; 1 . Overview
~~'~~ 10 The preferred embodiment of the invention provides
,
k
Y~
: a computer-to-ISDN interface residing at customer
; ..
rti.:
:
BLS
~.r,.
,
f.:...:,;.
. premesis equipment (CPE) and operating abave LAP-D
~;
, protocol to perform dynamic channel allocation and
,
a~~.. deallocation in response to processes occurring on the
,.y
15 ISDN and in accordance with user priorities. In the
-'~~ preferred embodiment, the CPE comprises a computer
communication coprocessor board which contains an
yj RJ-45 BRI interface (either at the ISDN T reference
point or at the U reference point), an RJ-11
xi
:' 20 interface,, a shared memory interface to an AT bus, and
a UART interface to an AT bus. The interface is
~ implemented by programming executed by a processor
~:~a that, in the preferred embodiment, is mounted on a
commercially available Telios B101 ISDN communications
-7 25 coprocessor board. The programming alternatively can
'
be executed by other systems having the characteristics
~~
described below.
>:,
,fir
:-,Ff 2 . System Reauirements
;
30 The system includes a real time operating system
''~ kernel capable of supporting multiple processes
which execute as threads in a common address
,k~ space. A message passing and signalling system
permits various processes on the ISDN to communicate
"~:
WO 92/21187 PCT/US91/0.3448
_.
r~
;: with each other. The kernel supports voluntary
r~~ blocking of a process until the occurrence of an
~~ event in the system and process rescheduling based on
,,
,~
5'Syi the occurrence of the event have taken place. (As used
t~:
S an "event" is a hardware interrupt or the
herein
~,. ,
~'~~t. arrival of a message sent by another process in the
Via= system.) This type of system support is common to
r~. many real time operating system kernels such as PSOS,
t:ri
VRTX, or RTU.
~~'w . 10 Furthermore it is assumed that the system has an
I:t.
i~~:~~' initial startup process which supports the loading
of additional processes and their initialization, as
e.;
~~~. well as initialization of various hardware devices in
~'~:v the system. The preferred embodiment of the invention
~t;y.-.;
r 15 is based on the PSOS kernel together with a
,
,a capability for initialization and downloading other
proces ses . .
~'-- The system furthermore includes hardware interrupt
routines Which support plural hardware interfaces in
':~ 20 the system and which use real time kernel message
_:.
passing to cause a process to be executed to further
r service the event. The following hardware interrupt
routines preferably are present in the system:
1. At least one interrupt routine to support HDLC
Hr 25 level 2- operations on the two B channels and the D
channel, such as flag detection and generation, zero
bit insertion and deletion, CRC checking ~ and
generation, and address masking. Such a routine may
operate with a DMA controller.
30 2. An interrupt routine to support a shared
memory interface to a computer system bus, such as
an ISA bus (AT bus). This routine, which may be in the
_ form of a co-routine on the computer processor,
must be able to route messages to all the processes in
WO 92/21187 PGT/US91 /03448
the system.
3. An interrupt routine to support a UART
interface to the ISA bus or other computer system bus.
4. The system furthermore should include a
5 software module which implements the user side of
the TSDN D channel signalling protocol. This includes
the data link layer, that is, LAP-D, as specified in
ISDN specification Q.921, and the network layer as
specified in Q.93I.
10 5. The system must be able to support an analog
telephone, manage the conversion of analog to digital
signals according to the ISDN standard, and interface
to the program interrupt routines to support
connection/disconnection of a voice call.
6. The system additionally must implement a data
link layer protocol which can support a separate data
link connection over each of the B channels. It is
assumed that the partner for this data link connection
is a similar process running on a similar TSDN
communication coprocessor system. The data link
process wily have an implementation which supports
full duplex operation by separate transmit and
receive queues and interrupt driven thread
dispatchingbased on the event of a message arriving
to the system or a message being queued for
transmi sion. In other words, the transmit and
receive threads are non-blocking from a dispatch
point of view.
7. The system of the preferred embodiment further
should include a software module which implements a
translator to map the AT command set into TSDN commands '
to connect and disconnect B channels. This module
will also implement a PAD function to interface a byte
oriented DART to a block oriented HDLG controller.
wo 9zizi is7 ~crius9mo3aas
11
3. Platform Hardware
The hardware platform in the preferred embodiment
is implemented by the commercially available Telios
B101 ISDN Communication Coprocessor System board. The
process identified as 4 in the preceding system
requirements is carried out by Signalling Interface
Process (SIP) software accompanying the Teleos B101.
The capability identified as 5 is implemented by the
VFI processes in Telios B101, and the function
identified as 7 is implemented by its AT/PAD: process.
Further details of the Telios B101 communication
- coprocessor are given in the B101PC Hardware Reference
Manual (REV A), 1990, available through Telios
Communications Incorporated.
The present invention is implemented at customer
premesis equipment, preferably by incorporation on at
least one printed circuit board 700 as shown in FIGURE
7, adapted to be mounted in an available slot of a
personal computer PC. A conventional analog telephbne T
is connected to the board 700 at and RJ-11 plug 702.
The hardware platform upon which the invention is
implemented, and as depicted schematically in FIGURE 1,
includes an internal buss 100 supporting a
microprocessor 102, preferably a 68000 type, such as a
68HCOOCP-12). A direct memory access (DMA) controller
104 , such as an NEC uPD 71071 Controller, on the ~ buss
handles memory to :memory and serial I!0 to memory
transfers. An HDLC controller 106, such as an NEC uPD
72001, connected to the RAM 104, processes the data
link layer (layer 2 of the OSI model). The DMA. and HDLC
controllers 104, 106 together operate at LAP-D
protocol, carrying out conversion of data in parallel
bit format to serial bit format for supply to ACFA 110
CA 02109836 1999-11-03
WO 92/21187 PCT/US91 /03448
12
and IPAT 112. The ALFA 110 and IPAT 112, which are
commercially available ISDN chips, provide physical
interfacing with the ISDN, performing framing,
electrical signal conversion, and D channel
collision detection functions. Using the RJ-11 plug
shown in Figure 7 at the rear of the coprocessor
board, the ACFA 110 is interfaced to an analog
telephone 126 through a CODEC 128.
The HDLG 106 controller has four channels, with
one line incoming and another outgoing for each channel
for full duplex operation. _Logic implemented in the
HDLC controller 106 identifies start and stoD_ bits of
each incoming block.
Upon receipt of a block as determined by the start
and stop bit framing patterns, and following error
detection using a checksum protocol indicating the
block contains no errors, the HDLC controller 106
instructs the DMA controller 104 to pass the block to a
selected location in a random access memory (RAM) 114
on the buss. If there is an error in the block, an
error routine is executed.
Upon transmission of data, start and stop_ flags
are applied to define a block, bit stuffing is carried
out as necessary, and the block is discharged on the
two B-channels comprising the BRI. Another HDLC
controller 118, operating with a DMA controller 120,
carries out similar functions for the D-channel of the
ISDN line. Communication between the DMA controller 120
and the RAM 114 in the preferred embodiment is
implemented using the SIP protocol of the commercially
available Telios B101 ISDN communication coprocessor
board.
Also residing on buss 100 is a UART 122 forming a
COM port that interfaces data bidirectionally,~one
WO 92/21187 PCT/US91 /03448
13 '?IQ~vS~~
block at a time, between buss 100 and a buss 124, that
preferably is an ISA (AT compatible) buss, upon which
resides the user's personal computer.
Another interface to user buss 124 is a memory 128
that is shared by both busses 100 and 124. The shared
memory 128 is controlled by a shared memory controller
126 divided into two blocks, one for control
information and the other for utilities such as
debugging. The shared memory 128 receives data at
separate read/write ports in a known manner to provide
service to both of the busses 1.00 and 124.
Each program module, described below, will support
message passing interfaces to and from other processes
in the system and is an event driven, dispatchable
thread being run under the real time kernel.
4. Platform Software
Figure 2, depicting symbolically the software
architecture for implementing the computing platform,
provided in the preferred embodiment by the Telios
communication coprocessor system, provides the
principal program modules and their interfaces resident
in the system. An off-board PC Comm Package 210
together with UART 212 on the user buss 124 is coupled
to the communication coprocessor circuit shown in the
FIGURE at board resident UART 214. User side ISDN D
channel signalling protocol is carried out at the data
link layer (LAP-D as specified in Q.921) and at the
network layer (Q.931) by software module 218. In the
Telios B101 coprocesesor board, module 218 is
implemented by a protocol termed "SIP", as mentioned
earlier.
AT/PAD 216 multiplexes between the first and
second B-channels forming the BRI by accessing
WO 92/21187 PCT/US91/03448
14
alternatively LAPD 1 and LAPD 2 modules 220 and 222
together with corresponding HDLC modules 224 and 226.
These modules enable a separate data link connection
over each of the B-channels in the system. The data
link process implements full duplex operation using
separate transmit and receive queues and interrupt
driven thread dispatching based on the event of a
message arriving to the system or a message being
queued from transmission. These processes are
implemented in the Telios coprocessor board as the
V.120*/LAPD1 and V.120**/LAPD~ processes.
Shared memory manager module 230 directs flow of
data between the shared memory 232 and the three BRI
channels through interface 218 and HDLC 228 (D-channel)
and LAPD, HDLC modules 220-226 (H1- and B2-channels).
The architecture further supports an analog
telephone, managing conversion of analog to digital
signals according to the ISDN standard including D
channel signalling (SIP) protocol.. This is termed the
VFI processes in the Telios B101.
5. Dvnamic Channel Allocation
Referring to FIGURE 3, the preferred embodiment of
the invention is provided as two new program modules
302 and 304 to provide channel allocation management
and virtual channels of greater bandwidth than a single
B channel. For convenience, the description of these
modules is provided with respect to the Teleos 8101
ISDN Communication Coprocessor System, but the
concept can be applied to any system supporting
these new program modules. Program modules other than
the new modules 302, 204 in Figure 3 correspond to like
modules in FIGURE 2.
Module 302, the Channel management module (Cl~i),
WO 92/21187 PCT/US91/03448
~i~°~~~~
monitors B channel usage and preempts the use of a B
channel by a lower priority user when the channel is
needed by a higher priority user. To accomplish this
function, CMM 302 maintains a state table 502, shown
5 symbolically in FIGURE 5(a), which indicates the state
of each B channel including whether the channel is a
"preemptable channel", that is, whether the channel
is connected or disconnected and if connected,
whether it is being used by a process that could
10 release the channel in the event of preemption by a
higher priority device. This~process is carried out in
the invention by Virtual Channel Process, described ir.
more detail hereinafter, when more than one channel as
part of a virtual channel is requested. The state
15 table also records if a channel is in use as a result
of preemption .
As shown in Figures 3 and 4, information necessary
to maintain the table comes from messages sent by the
signalling interface module 218 (SIP processes in the
Telios communication coprocessor ) to the CI~t; messages
are sent each time module 218 receives a request for
channel connection or disconnection. Local requests
originate from a user process running on the computer
via shared memory interrupt manager 230, the Virtual
Channel Process via internal message passing, AT/PAD
processes via DART 214, or the Telios VFI process via
Analog Phone Support 221. Remote requests arrive over
the D channel. Upon receipt of such a message, the Cl~i
302 updates the state table 502 to record the new state
of a B channel.
The C1~2 502 also includes a table 504, shown
symbolically in FIGURE 5(b), which maintains priority
levels P ( n ) for all the end users n in the system . Tn
the event that the CI~I detects contention for a B
WO 92/21187 . PC'f/US91/03448
16
channel, i.e., there is a request to connect a new
channel but all the channels are in use, the following
additional action takes place. '
Referring to the flowchart of FIGURE 6, and the
S message interface diagram of FTGURE 4, the CMM 302
first determines if a request for channel connection is
received (step 600). When a request arrives, the module
302 determines whether the request is from an end user
with greater priority than the users that are
currently occupying the channels (step 602). If the
request is from a user of equal or lower priority, the
CMrI takes no action and the signalling interface
process 218 will deny the request (step 604). In the
event that the request is from a higher priority
user, the CMM 302 determines if a preemptable channel
exists ( step 606 ) . If such a channel exists, the CMM
will signal the process using the channel to logically
free the channel from use (step 608), and when CMM
302 receives a signal indicating that the channel is no
longer in use, step 610, the CMM will send a message to
the signalling interface Which will cause the channel
to be disconnected (step 612). In this manner a
channel will be made available to the higher priority
end user. An example of this occurs when the Virtual
Channel Process is using both B channels and the end
user requesting a new channel is the analog
telephone.
In the event that the CMM 302 receives a message
indicating that a channel has been disconnected, in
step 614, the Cl~t determines if the channel was a
preempted channel (step 616). In this case the CMM
will signal the process which had the channel preempted
to reconnect the channel (step 618).
The virtual channel module (VCM) 304 provides the
WO 92/21187 PCT/US91 /03448
17
~~~.~9~~~
capability to dynamically combine multiple,
circuit-switched B channels into a single virtual
channel which is capable of carrying a properly
ordered sequence of data blocks. The VCM 394
comprises a block multiplexer/demultiplexer with
buffering support to overcome the lack of
synchronization across B channels inherent in the ISDN
network. As shown in Figure 4, VCM 304 operates in
conjunction with the CMM 302 to allocate and
i0 deallocate B channels based on events monitored by the
CMM 302. The VCM 304 has a black oriented interface to
the computer processes which use block send and block
receive commands via the shared memory interface 126 of
the communication coprocessor circuit shown in FIGURE
1. The computer process views the virtual channel as
an ordered stream of blocks and has no knowledge of on
which B channel the block is actually sent or received.
The only indication to the computer process that the
virtual channel is in use is the speed (bandwidth)
available for transmission; as more channels are added
or deleted,. the bandwidth increases or decreases
correspondingly.
The VCM 304 implements a protocol which operates
as an upper sublayer of the data link layer, similar
in purpose to but different in implementation from the
LSO Multiple Link Procedure. This aspect of the
invention is significant, as no processing at~ the
physical layer, together with disadvantages associated
therewith, takes place.
6. Virtual Channel Protocol
6.1 8-Channel State Transitions
Component channels allocated for a virtual
B-channel have three defined states, viz., activated,
WO 92/21187 PCf/US91 /03448
1S
deactivated, and transient states. In the deactivated
state, data transfer is forbidden although control
protocol exchange is not. Component channels that have '
been allocated but not joined to the virtual channel
are initially in the deactivated state, A channel is '
deactivated for a sender immediately after the
deactive b command, described later, has been
queued for transmission. For a receiver, a channel is
deactivated immediately after the command is received.
Only a bi-directionally deactivated channel is removed
and physically disconnected from the virtual
channel of which it was a member.
In the activated state, both data and control
protocol transfer are permitted. A channel is
activated to a sender only after acknowledgement of the
active b command has been received. For a receiver,
a channel is activated immediately following receipt of
the active b command.
The transient state is defined by guarding
periods before acknowledgements are received from the
far-end. No user data can be sent over a channel in the
transient state.
A vi=tual channel can be in either of two states,
transient and steady. A virtual channel is transient
when any component channels are transient. If no
component channel is in the transient state, the
Virtual Channel is in the steady state.
6.2 Virtual Channel Multi_plexin4
In a virtual channel, data received for
transmission is sequentially distributed, one packet
at a time, in a round- robin fashion over the channels
in active state. The remote virtual channel process
receives and recovers data in the same round-robin
~.~ .;~. ; w. v, ... ,; ;,,: .._... , . ; , .
WO 92/21187 PGT/US91 /03448
29 .~
sequence.
To add and delete channels, protocol messages
are exchanged by the sender and receiver which cause
the virtual channel to enter the transient state. An
active b command is sent to add a channel; a deactive b
command is sent to delete one. When a virtual channel
is in the transient state, the round-robin send and
receive mechanism continues but the additional features
. are added. On the receive side, a trace-back timer is
used to ensure that error conditions on a transient
line will not block the virtual channel for a long
period of time. On the transmit side, if no user data
is available, SYNC vB protocol messages optionally are
sent on active lines to ensure that the receiver will
initiate the trace back timer.
The traceback timer, which is implementation by
programming within the program module VCM, is based
upon an "optimistic algorithm" that assumes that a
transmission sent ultimately will be received by the
transmission partner. It is started at the probable
logical end of transmission for recovery of time-
inverted progogation of physical events. In the
preferred embodiment, the traceback timer is iniated
upon transmission of a block. If the communication
partner does not respond within a predetermined amount
of time, determined by the timer, the transmission is
deemed to be invalid, and the channels are torn 'down
and' reinitiated. The operation of the traceback timer
within the present system, depicted in the flow chart
of Figure l0, is described in detail later.
Rather than global sequence numbers, a packet
generation number preferably is used and has meaning
only in terms of round-robin line scanning. Thus i'
two channels are in use, the first two packets will be
.. .. .._. .. ...._.. ..~....,_,. :. »,:~. ~,.::-.:- . ;. -a.. ...._ .,..~,..
.,~."-.:.. ,.:.. ..~._ ,; : ...;.., :. ~--.;;, , s,~:, ;....,.,..... .....:. ,
. ~~.':;,. ~ , , .. ,;,...,.... . , .
~,~.:i'' :".:'~:' .:''..~'~ , .v ,.... ~ .,.,.~.. ;:..~... .':(.:.,.., n=
.~,.r". . m.~.~. ,..~~,:".. , ;".. ;,,." , ,~..~.,. ;.w;w . ,::....,.
.: ',..;..., ...'.. :~.. . ~:, -".:'...~.~:,. ~...~..,.m_ . ~ .,.... :
...,;~..., :i,.~, ":; '-,.. , .~..;.,.,,.... .,. , ~.,.,.. ., :~~~.:.. ~ ,':.
,..,.,.~.. . , ,.._.... . .,.; .,
.... .. :'~ .:":..,..... ~:;:-.; '.'.~' ;,:~: .'..,' ~a~.. 'S . ,~, ..n -.'.
....'\... ' ' ', w.
WO 92/21187 PCf/US91103448
~!~()~~;~~
sent with a generation number of 1, the second two
packets with a generation number of 2, etc. The
sending and receiving processes both keep track of '
generation numbers and both use the same round-rabin
5 ordering so as to provide correct sequencing of '
packets.
6.3 Protocol Fields and Commands
The protocol commands, together with detailed
10 format and bit definitions used for controlling and
multiplexing over the virtual_channel, are as follows.
* DATA
Ossnnnrm : one byte as header of client's data for
15 transmit.
* RQST Bs
lOlnnnnn: one byte header of one or multiple control
bytes. The first control byte can further specify
20 explicitly whether the data is global. If the~header
does not specify, whether the data is global depends on
the address bytes which follow. No address byte for
in-band operation is required, and multiple address
bytes imply that the in-band line is not explicitly
included. The explicit global commands have the
leftmost bit on, followed by explicitly specified
address bytes. If the left- most two bits are both on,
the data is a broadcast and no address bytes follow.
Multiple bytes are useful for off-band control.
Preferably, only one byte of in- band control is
employed. The leftmost third bit is reserved, and
the fourth bit is for system control point
specification. These are external or internal
indicated by E and I respectively as follows. The last
..... ,. ... . ,.,: ~ . . :~-; -. ,~..: ;; ;: ,... :, _ .. .. .. .,. ..
..,. .. . f. . _ . , . .
WO 92/21187 PGT/US91/03448
21 ~1~~~3~
four bits define the commands of this category. At
present, these are: DEACTIV Bs group: uwxlz, w bit is
reserved and a defines two system points.
DEL Bs - (0X00 0), an external
; delete
command
DEX Bs - (DEL Hs ; 1), an DEL Hs, followed by
external setup
DIL Bs - (DEL Bs ; 0X10), internally initiated
delete command
DIX Bs - (DEX Bs ; 0X10), DIL Bs, followed by
internal setup
ACTIV Bs group: uwxOz, w bit is reserved, a the
same as defined above.
ADD Bs - (0X00 ; 2), an external add command.
AID Bs - (ADD Bs ; 0X10), an internally
initiated ADD Bs
* SYNC vB
110nnnnn: one byte only, used for time-fill and
synchronization.
* RA Bs
lllnnnnn: one byte header, followed by no or
multiple optional bytes. This is an acceptance
acknowledge in reply to a RQST Bs, and in-band is
implied if no other bytes follow. Similar to' the
case in RQST Bs, the first by which follows can further
specify whether it is global. The left- most two bits
have exactly the same meanings, which describe the
scope of the possible additional address bytes.
The leftmost third bit, if on, turns the whole
meaning of the response into a negative
acknowledgement. The last five bits are the same as
WO 92/21187 PCT/US91/03448
22
for RQST Bs.
* MODE vB '
1000000m: for virtual channel operation and format
specification. This has two members, MODE rst with m
- 0 and MODE lbc with m = 1; MODE rst defines the nnnnn
five bit generation number. The mode negotiation can
proceed only when all component channels are in
deactivated states, or UNA will be received. if the
optional attributes are not accepted, UNA will also be
received. A REJ will be received if the remote end
does not support or will not accept this request. In
addition to this role of mode negotiations, MODE vB
resets the generation number or the global
1~ sequence number for transmitter and the corresponding
variable back to 0 to restart and resets the
transmitter and receiver (loop) pointers back to the
first component position.
* RR
10000010: Informs the far-end receiver that this
end is ready.
10000011: Informs the far-end receiver that his end is
not ready.
* ATTRB vB
100000100: The parameters in APPENDIX I follow this
for far-end negotiation.
* UA
w.,. , , , ' ' :,, : , .,;'
WO 92/21187 c
~) ~ ~ ~ $ ~ ~CT/US91/03448
23
10010000: This unnumbered positive response means
acceptance in the mode negotiation. The same MODE vB
packet will be sent back as bi-directior_
initialization, following the UA. The UA is also
used for acknowledgement to flow control commands RR
and RNR. It is used for acceptance acknowledgement to
ATTRB vB as well as unnumbered commands.
* UNA
10010100: a negative response for refusing, used
similarly to UA.
*. REJ
10011100: as explained in the MODE vB description.
All those unnumbered are in-band, although MODE
vB is for global. The "nnnnn" is a module 32
correlation generation number assigned to each round of
transmissions. The "ss" in the DATA command,' which
has four values 11, 10, O1 nd 11, is for framA
segmentation.
6.4 Protocol Processing
Programming described with reference to Figures 9
and 10 is provided for the two key routines in the
Virtual Channel, Send To Remote 'and
Receive_From Remote: Both routines are initiated when
a message is received from another process in the
system, as shown in FIGURE 4.
Process: Send To Remote
Entry Condition:
...,. ..:'..: .: P ..;;._ ... . '' .-~, ~._ ' . , s., t.i,. .,."..., .. ,...
i t . ' ' .
a .t. ~:-. . :.; , ..' ...v .~t. of .,.,:.~::.e. . ._..,. .':~ . ".~.~~a .'v'~
.'.:: .v _ ,':'. ,:: ,.~ ~.. ; '~. . ,..
WO 92/21187 PCT/US91/03448
~'~~~~1~~,~ 24
This task executes when either a message arrives
from another process requesting that a block of data '
be sent on the virtual channel (VC), or when the
process itself must transmit messages due to virtual '
channel protocol processing, shown in FIGURE 4.
Data Structures Assumed:
1. Circular List of Transmission Lines maintained in
the Round- Robin order of transmission.
2. Current Line Ptr.
3. VC Header block with current generation number.
Figure 9 is a flow chart describing the send to
remote routine in accordance with an aspect of this
invention. Assume initially that a message is received
on a channel from a remote source, represented by step
900. A decision is made on whether the virtual channel
currently is in a steady state, i.e., not active (step
902). Assuming that the channel is in steady state,
step.904 queries whether a data block is ready t~ send,
i.e., a full block of data has been assembled. Onlv
when a data block is ready, step 906 adds a virtual
channel header to the data block, sends the block to a
current line LAPD process, and then updates the current
line to the next line in round-robin fashion. When a
complete round of lines has been completed (step 908),
the current generation number of the virtual channel
header is updated in step 910.
If step 902 determines that the virtual channel is
not in a steady state condition, step 912 of the
program determines whether the current line is active.
If the current line is active, step 914 creates an
._;r.~,~, ~_ , . ~:.:~~ -~:.~°. , :°:~~r ~:.~: .a.:.",~.,~;,
w.._....
WO 92/21187 PCT/US91/03448
~'~.'~~~~~
active channel. If the current line is not active,
step 914 determines whether a data block is ready for
sending. When a data block is ready, steps 916, 918
and 920 carry out block assembly by adding a virtual
5 channel header the block to be sent, then sending the
block to the current line LAPD process, updating the
line in round-robin fashion and finally updating the
virtual channel header generation sequence number as in
steps 906-910.
10 When step 914 determines that a data block is not
ready to send, step 922 querj.es whether the transient
line has any data to send. If there is not data to
send, step 924 updates the current line in round-robin
fashion. If data is available for sending, step 926
15 prepares data for transmission by carrying out a
synchronization protocol, i.e., sending fill blocks
with the virtual channel header, and then updates the
header generation sequence number.
Fseudo code corresponding to the above routine is
20 shown in Appendix II.
Process: Receive From Remote
Entry Condition:
25 Thi task executes when either a message arrives from
the data link layer indicating that a new block has
arrived from the Remote VC partner, or when the local
Send To PC indicates that it is ready to receive
another block.
Data Structures Assumed:
1. Circular List of Message Queues kept in the
round-robin order of transmission.
WO 92/21187 PCT/US91 /03448
26
2. Current Queue Ptr.
3. VC Header block with current generation number.
Protocol for receiving channel data from a remote
source, in accordance with an aspect of this invention,
can be better understood with reference to Figure 10.
Assume initially that a message is received from a
. remote source (step 1000). Step 1002 determines
whether the virtual channel is in steady state.
Assuming that the virtual ,.channel currently is in
steady state, the message to be sent is placed in queue
for the appropriate channel (step 1004). In step 1000,
the queue is interrogated in a round-robin sequence to
determine whether it is empty. When the queue.is not
empty, step 1008 processes the queue in round-robin
order and sends the message to the appropriate party.
This sequence of steps is repeated until a complete
round of lines has been finished, determined by step
1010, and then the virtual channel header generation
sequence number is updated (step 1012)..
If the virtual channel is determined in step 1002
not to be in steady state, the traceback timer, noted
previcously, and which preferably is software
implemented, is queried to determine whether it is
triggered (step 1014). Assuming that the timer has not
yeti been triggered, step 1016 detects whether the
current line is empty. Only if the current line is
empty, and assuming also that a non-empty line
currently exists, and the generation number of messages
on this line is current or future, determined by step
1018, the timing by the traceback timer is initiated.
The program exits to step 1000 when either a message on
the transient line arrives, or the traceback timer
,:., ._ ~. : .. ~ ~ ,~. :. . .
~:-,. . ~ . : ~.~
,: . . ..: :,r ~. ., ..:°.. ~..,,_ :,_ . . :, ~ v: . :. ;~ .. .. . ::>
,~ ~::~ ::.. . : :.w, .; . . . , ,
WO 92/21187 PCf/US91/03448
27 r'~.~~~~~~~
expires (step 1020).
If step 1014, determines that the traceback timer
is not triggered, step 1022 places a new message for
the appropriate channel in the queue. If there is a
message on the transient line, and the traceback timer
is set, step 1024, the traceback timer is disabled
(step 1026). If there is no message, the queue is
queried on a round-robin basis to determine whether it
is empty (step 1028). Assuming that the queue is not
empty, the line is processed in round-robin order, steta.
1030, and the generation number of the message is read
at step 1032 to determine whether it is current. If i~
is current, the message is delivered to the appropriate
party (step 1034), if not, the message is discarded in
step 1036.
On the other hand, if the queue on a round-robin
basis is not empty, the virtual channel header
generation sequence number is updated (step 1038).
Pseudo code corresponding to the the above routine is
given in Appendix III.
6.5 Dvnamic Channel Control
The computer program which is using the Virtual
Channel controls the number of 3 channels which car.
participate in the virtual channel by sending commands
to the CMM module 302 to indicate that a channel
should be added to or deleted from the virtual channel.
Channel allocation/deallocation can also occur
based on actions by C1~I 302 as described earlier . In
the event that a channel is deallocated and then
disconnected by the partner who was the calling party
(i.e. the partner who did not originate the call), it
is advantageous to provide a mechanism to indicate that
the origina l party called should reestablish the
WO 92/21187 PGT/US91103448
pl~~~G~~~ 28
channel. The virtual channel protocol supports this by
using control messages to indicate to the communication
partner th~.t the preempted channel is available again. '
Using the routine shown in FIGURE 8, the VCM 304
deletes a B-channel it a high line error rate is
detected. A predefined threshold rate of errors in a
given period of time is provided to the VCM in step
802. If the data link layer for a given B-channel
reports an error rate above this threshold, determined
by step 804, the VCM 304 logically removes the B-
channel from the virtual channel (step 806) and
rectuests the CMM 302 to have the channel disconnected
(step 808).
The invention described herein accordingly
carries out dynamic channel allocation in an ISDN line
by monitoring events supplied to the line which
indicate requests to use or release a B channel,
evaluating channel usage priorities associated with
users generating events monitored, and, based upon
channel usage priorities, automatically setting up or
tearing down B channels associated with the line.
Processing takes place above I,AP-D protocol. Upon a
communication coprocessor platform are provided first
and second program modules, a channel management module
(CMM) and a virtual channel module (VCM), to implement
dynamic channel allocation. The program modules
cooperate to control bandwidth between communication
partners by selective allocation and deallocation of
virtual B channels between them in response to
pseassigned priorities and real time events. The CMM
monitors requests to connect and disconnect B channels
by potential end users and the VCM. The CMM is capable
of signalling the VCM to force deallocation of a B
channel from a virtual channel based on a request for
WO 92/21387 PCT/US91/03448
channel connection by a higher priority end user. The
CMM signals the VCM to indicate the existence of
available B channels when end users disconnect the
channel. The VCM provides a block oriented transport
service to various computer processes which can operate
over one or more B channels. This service operates
above the data link layer and manages the
multiplexing of messages across one ar more data link
connections which operate on a B channel so as
to ensure properly ordered delivery of message blocks.
Channels are added or deleted ~on a dynamic basis,
without interrupting the flow of data. Channel
deallocation also takes place in response to high error
rates in message transmission.
In this disclosure, there is shown and described
only the preferred embodiment of the invention, but, as
aforementioned, it is to be understood that the
invention is capable of use in various other
combinations and environments and is capable of changes
or modifications within the scope of the inventive
concept as expressed herein.
.. .. . . ,_. . : ... . _ .. . _...,. ,, , ,:. ,. . - .. .., .: .. . .: .._.
.. .:. .. ...
:........r , . ~ .~, . , .. ., . .. . ... . , .
WO 92/21187 3 ~ PGT/US91 /03448
st~;:~9
A_pPENDIX
Virtual B Channel Attributes (~ ianauaae)
J
~ypedef struct 1
long err threshold; ! one out of e~ ~"hrashold -tames =
sno er i action tares j act on cont~.g er r actior. ~res
;
=
snow action oerm:t: i* allow deactivation of er=ored cnanne:
er_ ~ -
sncr _ max sand wid t; ~ max- allowed banawidt:~
*
sner: hign_util tares: !* high etfacW ve ~ viand wid=~ _~resnc:c
=
v ~ t W 'arcs :
snc~ hick aus L _ ,. ~ g .- _
' * one hi n a _il oL,: c _ h:ca aus:
sno:: action :n=es: !* act on contig high busy-L=i_ ~zres
aign =
~
sno high;~etion j* allow bandwidth ineremer~ n==ions
oerm~t: =
sno~ min aand_widt::; ~ minimum allowed bandwid=~ _-
a
snc~ low=ut:.l tares : ~ low effective ~ aandwidt:~ t.~.~.resnoi=
snot low_ousy util thres; j~ one low util ou:~ c: low muse a
sno_- low action tn=es; ~* act on contig iow flusy L~::-~nres
~
sno low=action nermi~; ~* allow basrdwidth decremen~ a~mons
~ =
snort set up_retry tares: i max contig retry oefore givlag Lp
snow no action tn=es: ,~*no action threshold time
? YB T~SHOLD:
Table I - Virtual 8 Charu~el Attributes (in ~ language reorasenta=-o~
.." _._..~ ",.. ::~..,., -..:~~-;- mrZ ~ -. ~. ,..'; ...-,..~, ~:.' -,~..'..."
,.;.., :~::-. ~ v' ;' -;;.:.-.. ..;.... , ., .y;,..-...,.,..., , _ ... .; . .
...,...... ".
WO 9Z/21187 P('T/US91/03448
31
~d~.~9~~~
APPENDIX II
SEND TO REMOTE ROUTINE
If (VC is in Steady State)
If (Datablock is ready to send)
{ add VC Header to Datablock;
send block to Current Line LAPD Process;
update Current Line to Next_Line in Round-robin
fashion;
If (finished complete round of lines)
update VC Header Generation Sequence Number;
Else
exit; /* no data to send */
Else /* VC in Transient State_*/ ,
If (Current Line is active)
I
If (Datablock is ready to send)
~ add VC Header to Datablock;
send block to Current_Line LAPD Process;
update Current~Line to Next Line in Round-robin
fashion;
If (finished complete round of lines)
update VC Header Generation Sequence Number;
Else if (Transient Line has nothing to send)
update Current_Line to Next Line in Round-robin
fashion;
Else If (Transient Line has something to send)
send Fill blocks with VC Header;
update VC Header Generation Sequence Number;
}
Else /* Current Line is Transient Line */
send VC protocol message to create active
channel;
WO 92/21187 PCT/US91/03448
32
APPENDIX III
RECEIVE FROM REMOVE ROUTINE
Receive_From Remote IF (VC is in Steady State)
place new message on queue for appropriate
channel;
While (Processing all queues in Round-Robin order
and queue is not empty)
Deliver message to appropriate party,.
If (finished complete round of lines)
update VC Header Generation Sequence Number;
Eise (VC is in Transient State)
If (traceback timer has not triggered)
If (Current Line is empty)
{If (non-empty line exists) and
(generation number of message on this line is
current or future]
Start Traceback timer;
Wait for message on the transient line or
timer to expire;
}
}
Else
place new message on queue for appropriate
channel;
If (message is on transient line and Traceback
timer is set)
disable Traeeback timer;
Else /* traceback timer has triggered)
While (Processing all lines in Round-Robin
order)
~ if (generation number of message in queue is
current)
Deliver message to appropriate party
else if (generation number is past)
discard message;
}
Update VC Header Generation Sequence Number
