Note: Descriptions are shown in the official language in which they were submitted.
CA 02505004 2005-04-22
A Sub-rate Transmission Method for User Data Services in
Transmission Devices of a Metropolitan Area Network
Field of the Invention
The present invention relates to data transmission in a Metropolitan Area
Network
(MAN), and more particularly, to a sub-rate transmission method for user data
services
in transmission devices of a MAN.
Background of the Invention
In a MAN, a user normally leases bandwidth based on transmission rate of
Synchronous Digital Hierarchy (SDH), i.e., bandwidth level of the Virtual
Channel-Trunk
(VC-TRUNCK) on the MAN transmission device channel side. For example, at
present
the bandwidth leasable to users is categorized into the levels of VC-12, VC-3
and VC-4,
among which the bandwidth value of VC-12, 2.048Mbps, is the smallest one. If a
user
desires a bandwidth less than 2.048Mbps, he has yet to lease a bandwidth of VC-
12 alone
since this is already the smallest leasable bandwidth for users, resulting in
waste of
system resources. Similarly, if the desired bandwidth level is between VC-12
and VC-4,
the user may either lease a VC-4, resulting in waste of system resources as
well because
the desired bandwidth level is less than VC-4; or lease more than one VC-12,
which will
also lead to waste of system resources because, when the desired bandwidth can
not be
divided exactly by 2.048Mbps, there must be a VC-12 providing more capacity
than the
requirement of the user.
To avoid waste of resources caused in the above situations and make more
effective
use of the bandwidth capacity of a MAN, a sub-rate transmission method for
data services
has so far been proposed. With this method, as shown in Figure 1, Ethernet
data packets
from different input ports can be transmitted through one same VC-TRUNCK, then
separated at the terminal transmission device and transmitted to respective
output ports.
The Ethernet data packets herein are also called data frames. In this way,
data of different
users can be transmitted through the same VC-TRLTNCK, thus effectively
avoiding waste
of resources and improving utilization of bandwidth.
To differentiate the data which are transmitted through the same VC-TRLTNCK
but
CA 02505004 2005-04-22
come from different input ports and to forward them to respective output
ports, each data
frame is identified in the prior sub-rate transmission method. Specifically
speaking, by
taking use of IEEE (International Electric and Electronic Engineering)
standard 802.1 P/Q,
the whole MAN is divided into a plurality of Virtual Local Area Networks
(VLANs)
among which mutual access is disablement, and each user is assigned with one
or more
VLANs. In this way, data frames in the same VC-TRLTNCK can be differentiated
according to the VLAN Identifier (VLAN ID) which is unique in the entire MAN.
And
the terminal transmission device, by referring to the pre-stored corresponding
relationship
between the VLAN IDs and output ports, is able to determine the output port
for each of
the data frames transmitted through the same VC-TRUNCK so that the data frames
can
be transferred correctly to their respective output ports. Obviously, it is
possible to
incorporate the priority defined in the IEEE Standard 802.1 P and assign
different
priorities for VLANs so as to realize Quality of Service (QoS) to a certain
extent.
Figure 2 shows an Ethernet data frame format with VLAN ID conforming to IEEE
802.1 Q. As shown in Figure 2, a data frame is composed of a destination
address field, a
source address field, a 802.1 Q header label field, a length/type field, a
data field and a
check field. Among them, the 802.1 Q header label field includes a Tag
Protocol Identifier
(TPID) and Tag Control Information (TCI), the combination of which is called a
VLAN
Tag, with VLAN ID being a component of TCI. At present, the VLAN ID defined in
IEEE 802.1 Q has only l2bits, so that at most 21z VLANs, i.e., 4096 VLANs, can
be
accommodated in a whole MAN. With the expansion of the MAN, it is obvious that
4096
VLANs can not satisfy the service demand, thus restricting the development of
the MAN.
In addition, since the assignment of VLAN ID for each user must be made by
unified
planning within the whole MAN, the operation is rather complicated, bringing
inconvenience to users.
Summary of the Invention
In view of the above, it is an object of the present invention to provide a
sub-rate
transmission method for user data services in transmission devices of a MAN.
With this
method, the MAN is capable of accommodating more VLANs and assigning VLAN IDs
unrestrictedly, thus facilitating further development of MAN as well as
bringing more
convenience to users.
For the above purpose, a method of sub-rate transmission for user data
services in
z
CA 02505004 2005-04-22
transmission devices of a MAN according to the present invention comprises:
a. pre-configuring each transmission device to form forwarding table items
representing corresponding relationship between self defined tags and
transmission lines;
b. after receiving a user data frame, an original transmission device nesting
a
self defined tag into the user data frame according to said forwarding table
items to form
a self defined data frame, then transmitting the self defined data frame; and
c. after receiving the self defined data frame, a terminal transmission device
determining an output port for transferring the data frame by searching the
forwarding
table items with the nested self defined tag, then deleting the nested self
defined tag and
sending the original user data frame to the said output port.
In this method, the format of the self defined tag may be the same as that of
the
VLAN Tag in the user data frame.
In this method, the self defined tag may be a Virhzal Channel Line (VCLine)
tag
comprising at least a VCLine ID. The VCLine tag may further comprise a field
representing the type of the VCLine. The length of the VCLine ID may be a self
defined
value.
In this method, the self defined tag may be a tag complying with the
definition of
the Multi Protocol Label Swap (MPLS) protocol.
The self defined tag may adopt a local variable, in this case the
configuration of
transmission devices in step a is implemented when it is determined that more
than one
data frame is to be transferred in one same virtual channel. Alternatively,
the self defined
tag adopts a global variable, in this case the configuration of transmission
devices in step
a is implemented when a virtual channel is assigned.
The self defined tag is located either before or after the original VLAN tag
in the
data frame.
It can be seen from the technical schemes of the present invention, a self
defined tag
is nested in a user data frame, adopting either a global variable with more
bits or a local
variable which can be readily changed from node to node, so that more VLANs
than 4096
as in the prior art can be accommodated, promoting greatly the application of
the MAN
and reducing the cost by increasing the user data services it accommodates.
In addition, with a self defined tag nested, the VLAN identifier in the user
data
frame is not necessarily unique, accordingly the safe isolation of user data
is simplified
and convenience brought to the user's operation.
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CA 02505004 2005-04-22
Brief Descri~~tion of the Drawings
Figure 1 is a schematic diagram showing user data transmission between MAN
transmission devices by way of sub-rate transmission.
Figure 2 shows a format of an Ethernet data frame according to the prior art.
Figure 3 is a flow chart showing general processing according to the present
invention.
Figure 4 shows a tag-nesting mode according to a first embodiment of the
present
invention.
Figure 5 shows a tag-nesting mode according to a second embodiment of the
present
invention.
Figure 6 shows a tag-nesting mode according to a third embodiment of the
present
invention.
Detailed Descriution of the Invention
The present invention will be described in detail hereinafter with reference
to the
accompanying drawings.
In the present invention, in order to support more VLANs than 4096 as in the
prior
art, besides the original VLAN ID, a self defined tag is nested into a data
frame, forming
a self defined data frame to differentiate more different VLANs. Figure 3
shows the
general processing flow of the present invention. A detailed description of
this invention
will be given below with reference to Figure 3.
In step 301, each transmission device receives items of a forwarding table and
updates the pre-stored forwarding table according to the received items. 'The
items of the
forwarding table may be configured and issued by a network administrator
either at the
time when multiple user data frames pass through VC-TRLJNCK between
transmission
devices or at the time the user leases a line.
It should be noted that a forwarding table representing the corresponding
relationship between self defined tags and transmission lines is pre-stored in
each
transmission device of the MAN. For the original transmission device of a
whole
transmission line, this forwarding table is used to establish a self defined
tag of a data
frame according to the input port number and the VLAN ID of the data frame,
i.e., to
establish a self defined tag according to transmission line through which the
data frame
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CA 02505004 2005-04-22
will pass. For an intermediate transmission device, this forwarding table is
used to
determine the next channel according to the self defined tag. And for the
terminal
transmission device, this forwarding table is used to determine an output port
according to
the self defined tag. The said original transmission device, intermediate
transmission
device and terminal transmission device are all concerned with the whole
transmission
line through which the data frame passes during the transmission. Operations
like adding
and modifying table items can be performed to this forwarding table.
In step 302, the original transmission device receives a user data frame
through
GE/FE ports.
In step 303, after receiving the user data frame, the original transmission
device sets
a self defined tag mode according to the demand for service, then nests a
corresponding
self defined tag into the user data frame by means of hardware, software, or
combination
of hardware and software, forming a self defined data frame. After that this
self defined
data frame is transmitted to a terminal transmission device through a VC-
TRUNCK. The
specific way of nesting a tag is known to those skilled in the art and will
not be further
described here.
In step 304, the terminal transmission device receives via its GE/FE port the
self defined data frame transmitted in step 303.
In step 305, after receiving the self defined data frame, the terminal
transmission
device extracts the nested tag from the self defined data frame and searches
the items of
the forwarding table with reference to the information in the extracted tag,
then it deletes
the nested tag and transmits the data frame to the output port corresponding
to the user
according to the items of the forwarding table, thus sending the data frame to
the user
correctly.
The self defined tag mode mentioned in step 303 will be described hereinafter
in
detail with reference to three embodiments.
Figure 4 shows a tag-nesting mode according to the first embodiment of the
present
invention. In this embodiment as shown in Figure 4, the nested self defined
tag is a
VLAN tag. 'That is, a self defined tag defined completely the same as the
original VLAN
Tag is added before the VLAN Tag in Figure 2. Therefore, in case of sub-rate
transmission of user data service, the nested self defined tag can be used to
differentiate
data frames with the same ULAN Tag. In this mode, the self defined tag may be
a local
variable, that is, there may be different self defined tags between different
nodes between
s
CA 02505004 2005-04-22
two transmission devices and it is not required that the self defined tag
remains the same
during the whole transmission process. This is because the same problem will
arise that
no enough VLANs can be supported if the self defined tag remains the same
during the
whole transmission process since there are only 12 bits assigned for the
nested
self defined tag as well. For intermediate transmission devices, it is the
only requirement
that different data frames can be differentiated with nested self defined
tags. By flexibly
configuring self defined tags between different nodes, this embodiment is able
to
accommodate more VLANs compared with the prior art so long as data frames
transferred between two same nodes have different self defined tags.
In terms of self defined tags nested in this mode, the specific transmission
process is
as follows. When there are a plurality of data frames being transmitted
through the same
VC-TRUNCK, a nested field of VLAN ID will be configured by the network
administrator in order to differentiate different user data services and the
forwarding table
items are issued to all the transmission devices. MAN transmission devices,
after
receiving user data frames and determining that it is a sub-rate transmission
of user data
service, nest the self defined tags of the same format as that of the original
VLAN tag and
transfer the data according to the forwarding table. The terminal transmission
device,
after receiving the data frame with a nested tag, deletes the nested self
defined tag and
transfers the user data frame to the user according to the corresponding
relationship
between self defined tags and output ports. In this VLAN-nesting mode of the
first
embodiment, the forwarding channel is searched by means of "Port + VLAN +
nested
VLAN". The nested VLAN herein is a local variable, and it constitutes a
designation
address of the user data frame together with "VLAN" and "Port". Therefore, the
VLAN
ID in the user data frame is not necessarily unique throughout the whole
network, it is
only required that a nested VLAN ID is assigned for use in transmission
between two
nodes of the transmission devices.
Figure 5 shows a tag-nesting mode according to the second embodiment of the
present invention. In this embodiment as shown in Figure 5, the nested self
defined tag is
a Virtual Channel Line (VCLine) tag. That is, a self defined VCLine tag
adopting a global
variable is added before the VLAN Tag in Figure 2.
As shown in Figure 5, in the second embodiment, the tag nested before the
802.1 Q
tag comprises a VCLine ID field and a type field. When a user leases a line
from the
service provider, the service provider will assign a VCLine ID to the user
every time a
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CA 02505004 2005-04-22
line is set for him, and the user can define by himself the length of the
VCLine ID. In
addition, the type field is a field not used by IEEE and can be employed by
the equipment
manufacturer, so it may be used here for representing the type of the VCLine.
Since the
user can define by himself the length of VCLine ID as of more than 12 bits in
this mode,
more VLANs can be readily accommodated.
In terms of the tag-nesting mode shown in Figure 5, the transmission process
is as
follows. During the process of configuring the transmission line that the user
has leased
from the service provider, the network administrator issues a VCLine ID
directly to the
items of forwarding tables of all transmission devices. The original
transmission device in
the MAN, after receiving the 802.1 Q ULAN data frames of the user, adds nested
VLAN
Tag into the data frames no matter whether there is a sub-rate transmission of
user data
services. The terminal transmission device, after receiving the data with the
VCLine ID,
deletes the VCLine ID and transfers the 802.1 Q data frames to the user.
Compared with
the mode of searching the forwarding channel by means of "Port + ULAN + nested
VLAN" in the first embodiment, the second embodiment is of high transferring
efficiency
because only VCLine ID is involved for the search. In addition, since VCLine
is a global
variable and the user can define its length by himself, there is no
restriction to the amount
of user data services it accommodates.
Figure 6 shows a tag-nesting mode according to the third embodiment of the
present
invention. In this embodiment as shown in Figure 6, the nested self defined
tag is a Multi
Protocol Label Swap (MPLS) tag, that is, a MPLS tag adopting a local variable
is nested
after the VLAN Tag in Figure 2.
As shown in Figure 6, the MPLS tag complies with the definition of the MPLS
protocol, in which the Label field is equivalent to the VLAN ID in the first
embodiment,
but different from the first embodiment in that the Label field is 20-bit,
thus more VLANa
can be accommodated.
In terms of the tag-nesting mode shown in Figure 6, the transmission process
is as
follows. When there are a plurality of user data frames being transferred
through the same
VC-TRUNCK, the network administrator assigns MPLS Labels to differentiate
different
user data services and issues forwarding table items to each transmission
device. The
transmission devices in the MAN, after receiving the user data frames, add
nested MPLS
tags into the frames. The terminal transmission device, after receiving the
data frames
with nested MPLS tags, deletes the nested MPLS tags and transfers the data
frames to the
CA 02505004 2005-04-22
user. In this mode of nesting MPLS tags according to the third embodiment, the
forwarding table items are searched according to the Label field in the MPLS
tag. 'The
forwarding table items are in static configuration and support user data
service packets of
the MPLS type.
Obviously, the self defined tag in the third embodiment may adopt a global
variable
as well. In this case, the self defined tag can be configured and
corresponding table items
issued to all transmission devices at the time when a user leases a
transmission line from
the service provider.
In addition, the self defined tags can be nested to different positions of the
original
data frames. For instance, in the first embodiment the self defined tag can be
placed after
the original VLAN Tag. And the self defined tags in the second embodiment may
adopt a
local variable as well.
The self defined tag according to the present invention is not limited to the
above-mentioned formats in these three embodiments, instead other formats
complying
with other communication protocols can be adopted also. Thus it should be
understood
that the embodiments described herein are to be regarded as illustrative
rather than
restrictive. Variations and changes may be made by those skilled in the art
and equivalents
employed, without departing from the spirit of the present invention.
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