Dynamic AAL2 path configuration in ATM system

Details Dynamic AAL2 path configuration in ATM system Dynamic AAL2 path configuration in ATM system

2001-01-09

2004-07-06

Vincent, David (Department: 2661)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S395640

Reexamination Certificate

active

06760335

ABSTRACT:

This invention relates to dynamic AAL2 path allocation/configuration in an ATM system
etwork. More particularly, certain embodiments of this invention relate to determining when to add and/or drop AAL2 mux(es) to/from an AAL2 signaling relation between two or more ATM nodes, and proceeding to add and/or drop AAL2 mux(es) based upon a result of such a determination.
BACKGROUND AND SUMMARY OF THE INVENTION
Asynchronous Transfer Mode (ATM) is becoming increasingly used in communication networks. ATM is a packet-oriented transfer mode which uses asynchronous time division multiplexing techniques. Packets are called cells and have a fixed size. See, for example, U.S. Ser. No. 09/188,347 (hereby incorporated herein by reference) for a description of certain aspects of ATM technology. See also WO 99/33316, which corresponds to Ser. No. 09/188,347 in certain respects.
As shown in
FIG. 1
, an ATM cell typically includes or consists of 53 octets, five of which may form a header and forty eight of which may constitute a “payload” or information portion of the cell. The header of the ATM cell includes two quantities which are used to identify a connection in an ATM network over which the cell is to travel, particularly the VPI (Virtual Path Identifier) and VCI (Virtual Channel Identifier). In general, the virtual path is a principal path defined between two switching nodes of the network; while the virtual channel is one specific connection on a respective principal path. Compressed voice (e.g., cellular telecommunications systems) is an application to which ATM (and AAL2 below) is well adapted and used in.
Between termination points of an ATM network a plurality of nodes are typically situated, such as ATM switching nodes having ports which are connected together by physical transmission paths or links. The switching nodes each typically have several functional parts, a primary of which is an ATM switch core. The switch core essentially functions like a cross-connect between ports of the switch. Paths internal to the switch core are selectively controlled so that particular ports of the switch are connected together to allow a cells ultimately to travel from an ingress side of the switch to an egress side of the switch.
A protocol reference model has been developed for illustrating layering of ATM. The protocol reference model layers include (from lower to higher layers) a physical layer (including both a physical medium sublayer and a transmission convergence sublayer), an ATM layer, an ATM adaptation layer (AAL), and higher layers. The basic purpose of the AAL layer is to isolate the higher layers from specific characteristics of the ATM layer by mapping the higher-layer protocol data units (PDU) into the information field of the ATM cell and vise versa. There are several differing AAL types or categories, including AAL0, AAL1, AAL2, AAL3/4, and AAL5.
AAL2 is a standard defined by ITU recommendation I.363.2 (hereby incorporated herein by reference). An AAL2 packet is shown in
FIG. 2
as comprising a three octet packet header, as well as a packet payload. The AAL2 packet header includes, for example, an eight bit channel identifier (CID), a six bit length indicator (LI), a five bit User-to-User indicator (UUI), and five bits of header error control (HEC). The AAL2 packet payload, which carries user data, can vary from one to forty-five octets. AAL2 uses ATM virtual connections (VCs) in the ATM layer in such a way that several AAL2 connections can be multiplexed on an ATM VC. The ATM VC is often referred to as an AAL2 path, and each AAL2 connection in the AAL2 path is identified with a channel identifier (CID).
FIG. 3
shows how plural AAL2 packets can be inserted into a standard ATM cell (i.e., multiplexing). In particular,
FIG. 3
shows a first ATM cell
20
1
and a second ATM cell
20
2
. Each ATM cell
20
has a header
22
(e.g., cell
20
1
has header
22
1
and cell
20
2
has header
22
2
). The payload of the ATM cells
20
begin with a start field
24
(e.g., cell
20
1
has start field
24
1
and cell
20
2
has start field
24
2
). After each start field
24
, the ATM cell payload contains AAL2 packets. For example, the payload of ATM cell
20
1
contains AAL2 packets
26
1
and
26
2
in their entirety, as well as a portion of AAL2 packet
26
3
. The payload of cell
20
2
contains the rest of AAL2 packet
26
3
, and AAL2 packets
26
4
and
26
5
in their entirety. In addition, the payload of cell
20
2
may include padding
28
.
FIG. 3A
illustrates another example of AAL2 multiplexing. The CID in the AAL2 packets provide for multiplexing up to
248
AAL2 connections in a single ATM VCC (virtual channel connection). Thus, AAL2 packets from several AAL2 connections can be multiplexed inside the payload of ATM cells of the ATM link as illustrated in FIG.
3
A.
FIGS. 3A
is similar to
FIG. 3
in this regard.
The start field
24
, shown in
FIG. 3B
, facilitates one AAL2 packet bridging two ATM cells as shown in
FIGS. 3 and 3A
. Start field
24
may for example include a six bit offset field (OSF), a one bit sequence number (SN), and one parity bit (P). The six bit offset field (OSF) may contain a value, represented by offset displacement
29
in
FIG. 3
, indicative of the octet in the payload whereat the first full AAL2 packet begins. For ATM cell
201
, the value of the offset field (OSF) is one, since AAL2 packet starts just after start field
24
1
. For ATM cell
20
2
, the value of the offset field (OSF) is one (in view of start field
24
) plus the number of octets of AAL2 packet
26
3
protruding into cell
20
2
.
As can be seen, AAL2 advantageously allows multiplexing of data from many users within a single ATM VCC. In such multiplexing scheme, each user's data is typically carried in a separate AAL2 packet, but AAL2 packets of differing users may be carried in the same ATM cells or cells borne on the same ATM VC. Thus, assuming each user has a different channel identifier (CID) value, as many as 248 user channels can be multiplexed onto one ATM VC. AAL2 thus allows more efficient utilization of low speed links than standard ATM while still maintaining low delay properties.
Q.2630.1 (hereby incorporated herein by reference) is an AAL2 signaling standard for setting up and releasing switched AAL2 connections between nodes in an AAL2 network. Signaling between two nodes is handled by a pair of peer AAL2 signaling entities that interwork in an AAL2 signaling relation. The AAL2 capacity of an AAL2 signaling relation includes the group of AAL2 paths and their associated peer AAL2 multiplexor(s)/demultiplexor(s) that are allocated to the relation. Hereinafter, the term “AAL2 mux” is used to denote or mean AAL2 multiplexor and/or AAL2 demultiplexor throughout this patent.
Conventionally, AAL2 paths are established by management operations. Grouping of AAL2 paths to AAL2 signaling relations is also typically handled by management operations. This means that if the AAL2 capacity need for an AAL2 signaling relation changes, an AAL2 path must be setup/released and added/deleted from the AAL2 signaling relation by such management operations.
Unfortunately, needed and/or required AAL2 capacity in an AAL2 signaling relation is often difficult to predict as it can vary significantly over time as a function of many things. This is problematic as management predictions regarding AAL2 capacity are often incorrect or off-mark, which can result is valuable resources being unduly wasted.
In accordance with certain embodiments of this invention, AAL2 paths are dynamically established and/or released in an ATM network/system. For purposes of example, during network operation a determination(s) may be made as to whether AAL2 mux resources are lacking and/or excessive relating to a particular AAL2 signaling relation(s). When AAL2 mux resources are determined as lacking for the AAL2 signaling relation, then at least one AAL2 mux is added to the relation. However, when AAL2 mux resources are determined as excessive for the AAL2 signaling relation, then at least one AAL2 mux is remo

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