AAL2 packet exchange device

Details AAL2 packet exchange device AAL2 packet exchange device

1999-06-01

2003-07-15

Vu, Huy D. (Department: 2665)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S395600, C370S395100

Reexamination Certificate

active

06594267

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to an AAL2 packet exchange device for executing interchanging of CPS packets (AAL2 packets according to ATM adaptation layer
2
) extracted from input ATM cells and thereby remultiplexing the CPS packets in output ATM cells.
DESCRIPTION OF THE PRIOR ART
As an ATM (Asynchronous Transfer Mode) adaptation layer for ATM signal transfer, there has been standardized the AAL2 (ATM Adaptation Layer type
2
(ITU-T I.363.2)). According to the AAL2, the payload (48-byte information field) of an ATM cell is used for carrying a CPS-PDU (Common Part Sublayer-Protocol Data Unit) (48 bytes). The 48-byte CPS-PDU is composed of a CPS-PDU header (1 byte) and a CPS-PDU payload (47 bytes), and CPS (Common Part Sublayer) packets are filled (multiplexed) in the CPS-PDU payload. The CPS packet is a variable length packet whose maximum length is 48 bytes (or 64 bytes (option)), which is composed of a CPS packet header (3 bytes) and a CPS packet payload (45 bytes or less). In the CPS packet header, a CID (Channel IDentifier) (1 byte) which is used for designating the logical channel of each CPS packet is included. At an ATM switch for executing ATM cell transfer according to the AAL2, CPS packets are extracted from two or more CPS-PDUs (i.e. from two or more ATM cells), and the extracted CPS packets are re-multiplexed in one or more CPS-PDUs, and the CPS-PDU is filled in a new ATM cell and transmitted (see Japanese Patent Application Laid-Open No.HEI 10-294743 and International Publication No. WO96/26589, for example).
FIG. 1
is a schematic block diagram showing an example of a conventional AAL2 packet exchange device.
FIG. 2
is a table showing information which is stored in an ATM cell header search table 5 which is shown in FIG.
1
.
FIG. 3
is a schematic diagram showing variable length packet interchange operation which is executed by a variable length packet interchange device
1
(i.e. the AAL2 packet exchange device) which is shown in FIG.
1
.
Referring to
FIG. 1
, a variable length packet interchange device
1
(i.e. the AAL2 packet exchange device) is placed in front of an ATM switch
6
. The variable length packet interchange device
1
includes a variable length packet extraction section
2
and a variable length packet re-multiplexing section
3
. The variable length packet extraction section
2
extracts variable length packets (CPS packets) from inputted ATM cells. The variable length packet re-multiplexing section
3
extracts channel identifiers (CIDs) from headers of the CPS packets. A CPU
4
searches the ATM cell header search table 5 of
FIG. 2
using the CID (packet address) of each CPS packet, and thereby obtains a VPI/VCI and ATM cell header information concerning each of the CPS packets. Thereby, CPS packets corresponding to the same VPI/VCI (in the ATM cell header search table 5) is gathered in each buffer of the variable length packet re-multiplexing section
3
, and the CPS packets corresponding to the same VPI/VCI is multiplexed by the variable length packet re-multiplexing section
3
in an ATM cell having the VPI/VCI. By such operation, the CPS packets A, B, C, D and E shown in
FIG. 1
are re-multiplexed in the ATM cells
7
a
,
7
b
and
7
c
shown in
FIG. 1
respectively to be outputted to the output lines.
However, the conventional AAL2 packet exchange device involves the following drawbacks or problems.
When CPS packets (variable length packets) are extracted from a plurality of ATM cells and the extracted CPS packets are re-multiplexed in ATM cells according to the VPI/VCI (obtained from the ATM cell header search table 5), the CIDs in the re-multiplexed CPS packets are not altered, therefore, CID collision can occur in an ATM cell to be outputted. For example, referring to
FIG. 3
, two ATM cells are supplied to the variable length packet interchange device
1
. The first ATM cell contains 4 CPS packets whose CIDs are “A”, “B”, “C” and “D”, and the second ATM cell contains 4 CPS packets whose CIDs are “E”, “F”, “C” and “G”. The 8 CPS packets are extracted from the two ATM cells, and re-multiplexed in two ATM cells (for example) according to the VPI/VCIs searched from the ATM cell header search table
5
using the CIDs of each CPS packet. As a result, CID collision occurs in the second output ATM cell (i.e. in the second ATM cell to be outputted), that is, two CPS packets having the same CIDs “C” are multiplexed in one ATM cell. Referring to the two input ATM cells on the upper side of
FIG. 3
, it can be judged that the two CPS packets having the same CIDs “C” have supplied from different sources if the VPI/VCI of the first input ATM cell differs from that of the second input ATM cell. However, when the second output ATM cell containing the two CPS packets having CIDs “C” is outputted and supplied to the next ATM switch etc, it can not be judged that the two CPS packets having CIDs “C” have supplied from different sources, since the two CPS packets have the same CIDs “C” and are contained in an ATM cell having a VPI/VCI.
In order to avoid this problem, the two CPS packets having the same CIDs “C” have to be multiplexed in different ATM cells having different VPI/VCIs. As a result, usage efficiency of each VP/VC has to be decreased. Further, the number of ATM cells generated and outputted by the AAL2 packet exchange device is necessitated to be increased in order to avoid the CID collision, and thus the load on the next ATM switches is necessitated to be increased.
SUMMARY OF THE INVENTION
It is therefore the primary object of the present invention to provide an AAL2 packet exchange device by which multiplexing efficiency on each ATM connection can be increased, and thereby increase in the number of ATM cells and increase in the load on ATM switches can be avoided.
In accordance with a first aspect of the present invention, there is provided an AAL2 packet exchange device which is placed in front of an ATM switch for executing CPS packet re-multiplexing into ATM cells. The AAL2 packet exchange device extracts CPS-PDUs (Common Part Sublayer- Protocol Data Units) from ATM cells which are supplied from input ATM lines, extracts CPS packets from the CPS-PDUs, alters CIDs (Channel IDentifiers) of the CPS packets if necessary so that CID collision will not occur between CPS packets supplied from different sources to be outputted to the same output ATM connection, multiplexes the CPS packets to be outputted to the same output ATM connection in ATM cells of the same output ATM connection, and thereby realizes re-multiplexing of CPS packets extracted from ATM cells supplied from different sources into the same ATM connection without the CID collision.
In accordance with a second aspect of the present invention, in the first aspect, the AAL2 packet exchange device comprises a selector means, a path setting table means, a first memory means, a CPS-PDU processing means, a CPS packet processing means, a second memory means, a CPS-PDU generation means, an ATM cell generation means and a multiplexing means. The selector means selects ATM cells containing CPS-PDUs and ATM cells not containing CPS-PDUs from ATM cells supplied from the input ATM lines, outputs the ATM cells not containing CPS-PDUs untouched, and extracts the CPS-PDUs from the ATM cells containing CPS-PDUs. The path setting table means stores a table indicating each correspondence between a first internal address for discriminating between input ATM connections, an input CID, a second internal address for discriminating between output ATM connections, and an output CID. The first memory means stores the CPS-PDUs extracted by the selector means and the first internal addresses concerning the CPS-PDUs. The CPS-PDU processing means extracts CPS packets from the CPS-PDU which has been stored in the first memory means, stores the front part of a CPS packet if the CPS packet has been split across two CPS-PDUs, and regenerates the CPS packet when the rear part of the CPS packet is supplied, by adding the rear part to the front part of the CPS packet which has

Affiliated with

Also associated with

Rating

AAL2 packet exchange device does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with AAL2 packet exchange device, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and AAL2 packet exchange device will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3002909