Method and apparatus for forming a virtual circuit

Details Method and apparatus for forming a virtual circuit Method and apparatus for forming a virtual circuit

1998-04-17

2002-02-19

Ton, Dang (Department: 2661)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

Reexamination Certificate

active

06349098

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to digital data networks. More particularly, the present invention relates to apparatus and methods for efficiently forming a virtual circuit.
BACKGROUND OF THE INVENTION
Asynchronous Transfer Mode (ATM) is an emerging technology in the fields of telecommunication and computer networking. ATM permits different types of digital information (e.g., computer data, voice, video, and the like) to intermix and transmit over the same physical medium (i.e., copper wires, fiber optics, wireless transmission medium, and the like). ATM works well with data networks wherein digital data from a plurality of communication devices such as video cameras, telephones, television sets, facsimile machines, computers, printers, and the like, may be exchanged. Communication between the above mentioned data networks requires a technique of bi-directionally transporting a stream of related ATM cells (referred to as a “call”) between a variety of sources and receivers. One such arrangement is a single source sending to a single receiver known in the art as a point to point (or unicast) as exemplified by a person to person telephone connection. Another possible arrangement is from one source to multiple receivers known in the art as point to multipoint (or multicast). One such multipoint system is exemplified by a conventional video on demand (referred to as VoD) system where any number of end users (home consumers, for example) may communicate real time with a root server. The root server in turn commands a main server to transmit the requested selection to the requester end user.
To facilitate discussion, prior art
FIG. 1A
illustrates a digital network
100
, including an ATM switch
102
and a plurality of communication devices
210
,
220
,
230
,
310
,
320
, and
330
. ATM switch
102
represents a digital switch suitably arranged to couple two or more of communication devices
210
,
220
,
230
,
310
,
320
, and
330
in either a bi-directional or uni-directional mode. ATM switch
102
may also represent a data network such as a local area network (LAN), a wide area network (WAN), or the global data network popularly known as the Internet. Each of communication devices
210
,
220
,
230
,
310
,
320
, and
330
is coupled to ATM switch
102
via associated ATM ports
210
(
p
),
220
(
p
),
230
(
p
),
310
(
p
),
320
(
p
), and
330
(
p
) Each ATM port may include a Segmentation and Reassembly layer (SAR) and a Service Access Point (SAP). The SAR provides a method of breaking up into cells arbitrarily sized packets associated with any of the plurality of communication devices
210
,
220
,
230
,
310
,
320
, and
330
and reassembling them such that information from different communication devices may be readily intermixed and transmitted regardless of its original format. The SAP function is twofold, first, in an outgoing call to a destination port, a destination SAP specifies the ATM address of the destination port; secondly, when preparing to respond to an incoming call, a local (or receiver) SAP specifies the ATM address of the receiving port.
A switch matrix
260
couples selected ones of the incoming ports to selected ones of the destination ports. In our example, port
210
(
p
) may be couple to any of ports
220
(
p
),
230
(
p
),
310
(
p
),
320
(
p
), and
330
(
p
) by way of switch matrix
260
. An interconnect bus (not shown) couples processors associated with each bi-directional port and switch matrix
260
and is used to transfer all transactions between the processors.
FIG. 1B
is an illustration of an ATM cell
120
representative of a UNI (User-to-Network Interface) system. ATM cell
120
includes
53
octets of 8 bits each. The
53
octets are grouped into two fields, the cell header
122
and the payload or information field
130
. The cell header
122
contains protocol control information including data fields VPI (Virtual Path Identifier) and VCI (Virtual Circuit Identifier) used to define a virtual circuit over which ATM data cells corresponding to a call are transported through ATM switch
102
. Cell header
122
also contains other protocol control information such as Payload Type Indicator (PTI), Header Error Control (HEC), and Generic Flow Control (GFC), and Cell Loss Priority (CLP) each of which corresponds to a desired Quality of Service (QoS) associated with the virtual circuit defined by VPI, VCI. QoS parameters can be either specified explicitly by the user or implicitly associated with specific service requests. The payload
130
is an information field of
48
octets containing the data to be transported from the sender port to the receiver port over the aforementioned virtual circuit.
Referring to
FIG. 1C
, a conventional method of setting up virtual circuit capable of servicing a unicast transmission through microprocessor based ATM switch system
100
will be discussed. For sake of this discussion only, assume a call initiator (not shown) wishes to use a telephone
201
to communicate with a receiver (also not shown) who uses a computer
331
to access an internet provider (IP) telephony service. In order to successfully couple telephone
201
to computer
331
, ATM switch system
102
must set up a connection, referred to as a virtual circuit between incoming port
210
(
p
) and receiving port
330
(
p
). It should be noted that all connections are bi-directional and the distinction between sender and receiver is purely artificial and is for illustrative purposes only.
The call initiator begins the call setup procedure by using telephone
201
to dial the telephone number of the intended receiver. A SETUP signal
301
a
is then forward from an input processor
216
to a network processor
266
by way of a bus
270
. Network processor
266
, in turn, forwards SETUP signal
301
a
hop-by-hop to output processor
316
also by way of bus
270
. SETUP signal
301
a
may include routing, QoS parameters, as well as additional parameters related to traffic control and shaping.
Upon receipt of SETUP signal
301
a
, network processor
266
echoes back a CALLPROCEEDiNG signal
301
b
to Input processor
216
. CALLPROCEEDING signal
301
b
contains the virtual path indicator/virtual circuit indicator (VPI/VCI) associated with an arbitrated virtual circuit capable of transporting the ATM cells associated with the call. Upon receipt of SETUP signal
301
a
, output SAP processor
316
sends CALLPROCEEDING signal
310
b
to network processor
266
. If output processor
316
accepts the call (based on a predetermined conflict resolution algorithm), it responds by sending a CONNECT signal
301
c
to input processor
216
by way of network processor
266
over bus
270
. The last message of the call set up procedure is a CONNECT ACKNOWLEDGE signal
301
d
which is sent by input processor
216
to network processor
266
and output processor
316
over bus
270
. The virtual circuit coupling telephone
201
to computer
331
is now available to transport the ATM data cells associated with the call.
At the conclusion of the call, either party may initiate a RELEASE signal that is forwarded to network processor
266
over bus
270
. Network processor
266
echoes back a RELEASE COMPLETE signal to both input processor
216
and output processor
316
over bus
270
. The RELEASE COMPLETE signal results in the virtual circuit associated with the just completed call to be invalidated.
A point to multipoint, or multicast, call is set up in a similar fashion but includes the additional steps related to adding and ultimately removing the additional receivers (or leafs). By way of example, a root will originate the connection that eventually terminates at two or more leaf nodes. The initial set up procedure is the same as discussed above, except that the original signaling request identifies the call as multicast (i.e., having two or more destination ports). The root, which in our discussion would be input processor
216
, signals network processor
266
over bus
270
the address of the first leaf node. New destinations (r

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