Method and apparatus for efficient signaling in an ATM...

Details Method and apparatus for efficient signaling in an ATM... Method and apparatus for efficient signaling in an ATM...

1998-11-30

2003-12-09

Pham, Chi (Department: 2667)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S397000, C370S522000, C370S535000

Reexamination Certificate

active

06661795

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to asynchronous transfer mode (ATM) networks. More particularly, the present invention relates to signaling techniques employed by ATM networks. Specifically, the present invention relates to signaling techniques that facilitate the efficient handling of concurrent ATM signaling cells over a single connecting link associated with an ATM switch.
BACKGROUND OF THE INVENTION
ATM is a virtual connection oriented technique that may be employed as a low level operating protocol in conjunction with a higher level operating protocol or physical layer such as the internet protocol (IP), an asymmetric digital subscriber line (ADSL) system, or the like. Unlike the conventional public switched telephone network (PSTN), an end-to-end ATM connection is not uniquely associated with a devoted connection circuit. Rather, an end-to-end ATM transmission is associated with a virtual connection that may share one or more switched communication links with any number of other virtual connections.
FIG. 1
depicts a portion of a typical ATM virtual connection that links a first ATM end device, e.g., a first personal computer (PC)
100
, to a second ATM end device, e.g., a second PC
102
.
A typical ATM network
104
may include a first ATM switch
106
and a second ATM switch
108
. In a practical network, any number of additional ATM switches may be present to facilitate the establishment of virtual connections between a plurality of ATM end devices. For example, a practical network may include one or more additional ATM switches operatively coupled between ATM switch
106
and ATM switch
108
. In accordance with conventional techniques, a virtual circuit connection (VCC) between first PC
100
and second PC
102
is established during a signaling procedure. Signaling between first PC
100
and first ATM switch
106
(and between second PC
102
and second ATM switch
108
) is typically performed in accordance with the UNI 3.1 Specification or the UNI 4.0 Specification (both published by the ATM Forum). The entire content of both of these UNI Specifications is hereby incorporated by reference. Signaling between ATM switches is typically performed in accordance with various NNI (network to network interface) protocols. The UNI 3.1, UNI 4.0, and NNI protocols are known to those skilled in the art and, accordingly, will not be described in detail herein.
According to current conventions, ATM cells contain 53 bytes (one byte includes eight bits) of information; five of the bytes are employed as a header while the remaining bytes contain the payload or data. The header information conveys a connection identifier that includes a virtual path identifier (VPI) and a virtual circuit identifier (VCI). In conventional ATM networks, the VPI at the user to network interface (the interface between an ATM end device and an ATM network) is eight bits long (occupying one byte) and the VCI is 16 bits long (occupying two bytes). During the normal data transmission mode, the VPI and VCI values are utilized to identify where the given ATM cell is to be routed throughout the ATM network. Different VPI and VCI values may be utilized between ATM switches and between ATM switches and ATM end devices. If an ATM cell is a signaling cell, then a predetermined VCI value (and possibly a predetermined VPI value) is used to identify that the cell contains signaling information rather than data. For example, in accordance with the UNI 3.1 Specification, signaling cells include VPI=0 and VCI=5; the UNI 4.0 Specification only requires that signaling cells include VCI=5. These aspects of ATM signaling are described in more detail below.
ATM signaling messages may include one or more ATM cells. Accordingly, a given control task or other function that is to be carried out by way of signaling may require the transmission of a plurality of cells. For example, ATM Adaption Layer 5 (AAL 5) and the service-specific connection-oriented protocol (SSCOP) provides mechanisms for the reliable transmission of signaling messages.
In the exemplary system shown in
FIG. 1
, first ATM switch
106
is associated with a table
110
of VPI and VCI values (the table is used for the transfer of data rather than for signaling purposes). As shown in table
110
, an ATM cell from first PC
100
may be received by first ATM switch
106
on its port
1
. This cell may be associated with the values VPI=10 and VCI=100. As described in more detail below, the particular VPI and VCI values assigned to a given connection are established by the respective ATM switch during signaling. These values of VPI and VCI are utilized by first ATM switch
106
to determine where to route the current ATM cell. In other words, for a specific combination of VPI, VCI, and an input port number, table
110
indicates where the cell is to be routed. Thus, first ATM switch
106
may modify the virtual connection values such that VPI=10 and VCI=150 before outputting the cell onto port
2
(by way of a prior signaling procedure, first ATM switch
106
knows that the given cell is to be routed to second ATM switch
108
via the virtual connection shown in FIG.
1
).
Assuming that no intervening ATM switches are present between first ATM switch
106
and second ATM switch
108
, the cell will eventually be received on input port
4
of second ATM switch
108
. As shown in a table
112
associated with second ATM switch
108
, if second ATM switch
108
receives a cell with VPI=10 and VCI=150 on input port
4
, then it determines that the cell is to be routed to second PC
102
via output port
3
. Accordingly, second ATM switch
108
changes the virtual connection values to VPI=20 and VCI=50, and makes the cell available on output port
3
.
Eventually, second PC
102
obtains the cell from second ATM switch
108
and, by processing the VPI and VCI values, determines that the cell payload contains information associated with a specific application. A similar technique may be utilized to transmit information from second PC
102
to first PC
100
.
In a practical ATM network, any given ATM switch may be coupled to a plurality of ATM end devices and/or to a plurality of other ATM switches. Furthermore, one ATM end device, e.g., first PC
100
, may be virtually connected to a number of different ATM entities via a single physical link (between first PC
100
and a single input port associated with first ATM switch
106
). Consequently, the ATM switches may be configured as complex fabrics capable of receiving, processing, managing, and routing a large number of ATM cells associated with many different ATM end devices. To this end, tables
110
and
112
in
FIG. 1
may include any number of vertical entries that uniquely associate specific input ports, output ports, and virtual connection values (the particular layout of tables
110
and
112
may vary according to the specific application).
As mentioned above, the tables employed by the ATM switches may be constructed “on-demand” during a signaling procedure associated with the establishment of each virtual connection. (The “manual” construction of tables associated with permanent virtual connections are not described herein). Since ATM connections are established before data cells are transmitted, signaling channels are initialized prior to the transmission of messages. As stated above, the details of ATM signaling are known to those familiar with ATM networks. For example, Onvural and Cherukuri, SIGNALING IN ATM NETWORKS (Artech House, 1997) contains a detailed explanation of ATM signaling procedures and specific signaling message formats. The entire content of this book is incorporated herein by reference.
Briefly, the UNI 3.1 signaling protocol dictates that ATM signaling cells must be identified by the following virtual connection identifier: VPI=0 and VCI=5. Thus, whenever an ATM switch or an ATM end device receives a cell with VPI=0 and VCI=5, it will recognize the cell

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