Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Reexamination Certificate
1999-08-20
2003-09-02
Yao, Kwang Bin (Department: 2664)
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
C370S395410
Reexamination Certificate
active
06614756
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to data communications networks and more particularly relates to a method for detecting and recovering from signaling congestion in a connection oriented network such as an Asynchronous Transfer Mode (ATM) network.
BACKGROUND OF THE INVENTION
Asynchronous Transfer Mode
Currently, there is a growing trend to make Asynchronous Transfer Mode (ATM) networking technology the base of future global communications. ATM has already been adopted as a standard for broadband communications by the International Telecommunications Union (ITU) and by the ATM Forum, a networking industry consortium.
ATM originated as a telecommunication concept defined by the Comite Consulatif International Telegraphique et Telephonique (CCITT), now known as the ITU, and the American National Standards Institute (ANSI) for carrying user traffic on any User to Network Interface (UNI) and to facilitate multimedia networking between high speed devices at multi-megabit data rates. ATM is a method for transferring network traffic, including voice, video and data, at high speed. Using this connection oriented switched networking technology centered around a switch, a great number of virtual connections can be supported by multiple applications through the same physical connection. The switching technology enables bandwidth to be dedicated for each application, overcoming the problems that exist in a shared media networking technology, like Ethernet, Token Ring and Fiber Distributed Data Interface (FDDI). ATM allows different types of physical layer technology to share the same higher layer—the ATM layer.
ATM uses very short, fixed length packets called cells. The first five bytes, called the header, of each cell contain the information necessary to deliver the cell to its destination. The cell header also provides the network with the ability to implement congestion control and traffic management mechanisms. The fixed length cells offer smaller and more predictable switching delays as cell switching is less complex than variable length packet switching and can be accomplished in hardware for many cells in parallel. The cell format also allows for multi-protocol transmissions. Since ATM is protocol transparent, the various protocols can be transported at the same time. With ATM, phone, fax, video, data and other information can be transported simultaneously.
ATM is a connection oriented transport service. To access the ATM network, a station requests a virtual circuit between itself and other end stations, using the signaling protocol to the ATM switch. ATM provides the User Network Interface (UNI) which is typically used to interconnect an ATM user with an ATM switch that is managed as part of the same network.
SVC Connection Establishment
Networks that are connection oriented typically have two stages for connecting network users from point to point. The first stage in the establishment of the connection utilizes some form of signaling mechanism and in the second stage, data is transferred via the connection established in the first stage.
An example of such as connection oriented network is an ATM network. In the first stage, virtual connections are created using a complicated signaling/routing protocol such as Q.SAAL, Q.93, IISP, and/or PNNI between peer network nodes along the connection path to provide network users a service for establishing a connection to another network user. This connection is termed a Switched Virtual Connection (SVC) and, once created, is used as the data path between the users that have been connected.
The connection originator uses the signaling protocol to convey the service details it is requesting the network to provide, e.g., destination address (the called address), class of service (CoS), traffic descriptor, protocol which is to used by the virtual connection, network transit, etc. In addition, the originator provides information about itself, in particular, its own address (the calling address).
Once the network receives the request from the originator user, it attempts to find a route to the destination that has sufficient resources to fulfill the specific characteristic requirements of the request as provided by the originating user. If the network finds a satisfactory route with the necessary resources to establish the connection, and if the called user also has sufficient resources to establish the connection, the connection is then established. Once the route is established, data can flow between source and destination over the connection.
Such a network may carry another type of connection known as a Permnanent Virtual Circuit (PVC) which are typically established under manual management control. The service provided by PVCs and SVCs are the same, with the different being their method of establishment.
The signaling/routing protocol used typically consumes a high percentage of computation resources in a node. This makes the connection establishment process slow. PVCs, as an alternative to SVCs are set via management in a manual fashion on each network node along the path. The PVC connections are typically stored in the system memory within the nodes making up the connection and are recreated in the event one or more portions of the connection go down. The connections are recreated and restored automatically, quickly and without the overhead of the signaling and routing protocol.
In the course of network operations, SVCs may be constantly created and torn down. SVC connections may be created very quickly and last for a relatively short lifetime duration, i.e., on the order of hundreds of milliseconds, seconds, etc., before being removed. In many networks today SVCs serve to connect well known services located in the network to well known clients also connected to the network. These connections are utilized as permanent connections, as they are established and may not be taken down for days, weeks, or months. In many cases, SVCs are established on a permanent basis, whereby they are never taken down and remain up until the occurrence of a network failure.
Call Control
A block diagram illustrating an example ATM network comprising a plurality of switches serving to connect a source and destination end station is shown in FIG.
1
. The example network, generally referenced
10
, comprises an ATM network
24
consisting of end stations
12
labeled end station A and B, edge devices
14
labeled edge device A and B and a plurality of ATM switches
16
labeled ATM switch #1 through #5.
As described previously, in ATM networks, signaling is used as the main method of creating and terminating VCC connections. The connections created are used as the infrastructure to applications located at the higher layers. Examples of higher layer applications include LANE, MPOA, etc.
A block diagram illustrating a call control software/hardware application within an ATM switch and the plurality of signaling entities established and operative under its control is shown in FIG.
2
.
With reference to
FIGS. 1 and 2
, the call control model shown, generally referenced
30
, is used for signaling in ATM switches wherein each switch comprises N ports (input and output). The call control entity
32
is shown communicating with a plurality of signaling entities
34
labeled signaling entity #
1
through signaling entity #N. Each signaling entity
34
functions to establish, terminate and maintain SVCCs using standards based interface signaling specifications such as UNI v3.0 or 4.0, PNNI signaling, etc.
The call control entity
32
functions to provide routing, bandwidth management and hardware programming services to the SVCCs. A key assumption made by the switch, however, is that the signaling is a reliable service. In other words, when a signaling Protocol Data Unit (PDU) is generated by the upper signaling application layer and passed to lower layers for transmission, it is assumed that the PDU was successfully transmitted to the destination via the network. The signaling entity represents a state machine at an upper l
Margulis David
Morgenstern Meir
3Com Corporation
Sutton Paul J.
Yao Kwang Bin
Zaretsky Howard
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