Centralized queuing for ATM node

Details Centralized queuing for ATM node Centralized queuing for ATM node

1998-11-09

2003-01-07

Yao, Kwang Bin (Department: 2664)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C455S422100

Reexamination Certificate

active

06504845

ABSTRACT:

BACKGROUND
1. Field of the Invention
The present invention pertains to communications systems, and particularly to communications systems which employ ATM technology.
2. Related Art and Other Considerations
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.
As shown in
FIG. 1
, an ATM cell consists of 53 octets, five of which form a header and forty eight of which 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; the virtual channel is one specific connection on the respective principal path.
Between termination points of an ATM network a plurality of nodes are typically situated, such as 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 a 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, and 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. 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 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
FIG. 3
shows how plural AAL2 packets can be inserted into a standard ATM cell. 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
has padding
28
.
The start field
24
, shown in
FIG. 4
, facilitates one AAL2 packet bridging two ATM cells. Start field
24
includes a six bit offset field (OSF), a one bit sequence number (SN), and one parity bit (P). The six bit offset field (OSF) contains 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
22
1
, the value of the offset field (OSF) is one, since AAL2 packet starts just after start field
24
1
. For ATM cell
22
2
, the value of the offset field (OSF) is the sum of one (in view of start field
24
1
) and the number of octets of AAL2 packet
26
3
protruding into cell
22
2
.
In an ATM based telecommunications system where different quality of service classes are supported, some connections are more delay sensitive than others. In order to cater to these differing sensitivities, advanced queue management is required. As used herein, advanced queue management involves handling ATM cells of differing priority. Such advance queue management can include specific traffic management per ATM-VCC with weighted fair queuing, early packet discharge, available bit rate (ABR) accommodation, and shaping of outgoing traffic according to a traffic contract, for example. Handling of ATM traffic management is specified in the ITU I.371 Recommendation or in ATM-FORUM Traffic Management Specification 4.0.
High cost ATM switching nodes normally have advanced queue management, to a certain degree, at every output. In this regard, a typical ATM switching node the ATM switch core has a plurality of switch ports. Each utilized switch port generally has a circuit board connected thereto, with the circuit board having one or more functional units provided thereon. Some such circuit boards function as extension terminals (ETs) for interfacing the switching node with other nodes of the ATM network. Each extension terminal (ET) typically has an ingress side for handling cells received on an incoming link from another node, as well as an egress side for handling cells being sent out on an outgoing link to that other node.
In a high cost ATM switching node, either or both the ingress and egress side of an extension terminal (ET) can have some advanced queuing arrangement for the queuing of cells. For example, in an arrangement known as an input queued switch, the ingress side can have one or more buffers for queuing incoming ATM cells destined for the switch core, with a switch or selector for selecting among the buffers to obtain ATM cells for transmission to the switch core. Similarly, in an output queue switch, plural buffers can be provided on the egress side, along with a switch or selector for obtaining ATM cells from the buffers for transmission on the outgoing link. In addition to advanced queue management provided on boards such as extension terminals (ETs), queuing management can also be provided internally in the switch core in a technique known a shared queue switching. Further, combinations of both input queued switching, output queued switching, and shared queue switching are known.
Advanced queue management seeks, among other things, to control the outputs when congestion occurs in case of a temporary or permanent overload. Simple low cost ATM switches may not have advanced queue management, but instead only simple FIFO structures. Typically a low cost switch cannot, at overload, separate real time high priority traffic from not real time low priority traffic.
From a network perspective, not every switching node necessarily needs to have advanced queue management. In most cases, only a few switch outputs require advance queue handling. For other outputs overloads do not occur (since on those outputs total control of traffic is provided or al traffic has the same priority). To pay the cost for advanced queue management at all outputs of an ATM switch when only a few outputs require such is not cost effective.
Even in situations requiring advanced queue management for each output, the degree of management may vary and therefore need not be rigid. Such is especially the case since ATM quality of service handling has not been definitively defined and is not matured, i.e., new services with differing quality of service requirements may appear in the future. Such may particularly be the case in the fields of cellular telecommunications and certain internet traffic.
What is needed therefore, and an object of this invention, is a flexible and economical advanced queue management technique.
BRIEF SUMMAR

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