Multiplex communications – Pathfinding or routing – Through a circuit switch
Reexamination Certificate
1999-10-29
2003-09-30
Vanderpuye, Kenneth (Department: 2661)
Multiplex communications
Pathfinding or routing
Through a circuit switch
C370S395100
Reexamination Certificate
active
06628649
ABSTRACT:
BACKGROUND OF THE INVENTION
A typical communications network includes many hosts interconnected by various data communication devices. The data communications devices can be routers, bridges, switches, network access servers, gateways, hubs, concentrators, repeaters and so forth which can exchange data over an interconnection of data links. The data links may be physical connections or may be provided using wireless communication mechanisms. Applications which execute on the hosts can use various protocols to transfer data such as voice, video and computer application data (all collectively referred to herein as “data”) across the network. The hosts may be general purpose computer systems such as personal computers, workstations, minicomputers, mainframes and the like, or the hosts may be dedicated special purpose computer systems or devices such as web-site kiosks, voice/data terminals, telephony, facsimile or email servers, video servers, audio servers, and so forth. Each host (computer system or other networked device) couples either physically or via a wireless data link to one or more of the data communications devices that form the network.
Generally, there are two basic implementations of modern communications network architectures: connection-based network architectures (
FIG. 1
) and connectionless network architectures (FIG.
2
).
Connection-based Networks
FIG. 1
illustrates an example of a prior art connection-based network
100
. Generally, the connection-based network
100
provides a single dedicated data path or “connection”
103
through each data communications device
120
through
127
for all data (not specifically shown) transferred, for example, between hosts
118
and
119
. The dedicated connection path
103
represents the resources (e.g. circuits, buffers, ports, bandwidth, etc.) in each data communications device (
120
,
124
,
125
,
126
and
127
) that are pre-allocated or dedicated to handle data transmission for the duration of the data communication session between the hosts
118
,
119
. Each data communications device
120
through
127
on the dedicated connection path
103
maintains the connection
103
(i.e., keeps resources allocated) for the life of the data communications session, even though data flow may not be constant (e.g. the data flow may be bursty) at all times during the session.
Once a connection is established in each of the data communications devices
120
,
124
,
125
,
126
and
127
(defining the connection path
103
), subsequent data transmissions between the hosts
118
and
119
may be performed with little additional work. This is because there is no need for each data communications device to determine a complex routing decision (i.e., selecting from multiple paths) for each data portion (e.g., packet, frame or cell) that arrives at the device. Rather, as a data portion arrives at one of the devices
120
through
127
, the device simply channels the data along the pre-established connection
103
that is assigned for that data. Data communications devices used in connection-based network architectures are typically referred to as “switching devices” or “switches.”
An example of a well known connection-based network is the Public Switched Telephone Network (PSTN). In a typical telephone network, when a caller picks up a telephone handset and dials a telephone number, one or more switches in the telephone network configure resources (e.g. phone lines and electronic switch circuitry) to provide a dedicated connection between the source (caller) and destination (callee) telephones. The connection exists for the duration of the telephone call and is maintained whether or not people are actually speaking to each other. All voice information takes the same connection path through the telephone network from one telephone to another. The connection is terminated (i.e., torn-down) when either party hangs-up their handset, causing each telephone switch used along the connection path to release any resources used for that connection.
In the context of computer networks, an example of a connection-based network is a network constructed from an interconnection of Asynchronous Transfer Mode (ATM) switches. ATM switches allow connections (typically called circuits or virtual circuit connections) to be established between hosts (which are typically computer systems). ATM switches transmit data in relatively small portions called cells using virtual circuits within each ATM switch that are dedicated to transferring data for the life of a particular session of data communications.
Changing the path of data for an active data communications session in a connection-based network is difficult since, generally, all data communications devices (e.g., ATM switches, telephone switches) on the entire connection path must reconfigure new connection information for the data and furthermore, these changes must be coordinated precisely across all the data communications devices. As such, connection-based network devices such as ATM switches generally provide only a single but very reliable path (e.g., connection
103
in
FIG. 1
) through the network upon which the data travels from one host to another during a session of data communication.
Connectionless Networks
FIG. 2
illustrates an example of a connectionless network
101
. In contrast to connection-based network architectures, connectionless network architectures such as connectionless network
101
generally operate using a hop-by-hop methodology to transfer data within the network. During a single session of data communications, various data portions for that session, such as packets, may each take different paths
104
through the network
101
, hence the name connectionless network. As an example, for data sent from host
105
to host
106
, the data communication device
110
may forward some data to data communications device
111
, while other data may be sent to data communications device
114
, depending upon current conditions in the network
101
. Conditions such as congestion or data link and/or data communications device failures may change during the life of a single data communications session and may affect decisions on where to send or route data with the connectionless network.
As indicated above, the process of determining the route(s) on which data shall be transferred to a network is usually called routing. There are various types of routing operations commonly used in communications networking. Three of such routing operations, referred to as routing protocols, are: unipath routing, equal cost multipath routing, and unipath multipath routing. The routing protocols enable a device to select a particular path of link for data transfers. Once selected, a process of forwarding is used to transfer data from device to device in the network. Both routing and forwarding occur in both connectionless and connection-oriented networks. However, a device in a connectionless network which routes and forwards data is referred to loosely as a “router.”
In general, unipath routing protocols use only one path at a time to a given destination, even if several equally good paths are available. Most routing protocols are unipath, or have a unipath mode of operation. A commonly used routing protocol called Open Shortest Path First (OSPF) typically operates in a unipath mode unless equal-cost multipath routing is enabled or turned on in the protocol.
Equal-cost multipath routing protocols will distribute data traffic such as packets across multiple paths to a given destination, but only if there are multiple paths available, each with the same minimum cost or weight. Costs and weights are simply metrics associated with paths that can be used to determine path selection if multiple paths are available to reach a single destination. In equal cost multipath routing, if there is only one path available with the minimum cost, then the equal-cost multipath routing protocol will choose only that one path.
Unequal-cost multipath routing protocols may distribute traffic across multiple paths
Figaro Rodolphe
Kline Peter
Lawrence Jeremy
Raj Alex E.
Chapin & Huang LLC
Chapin, Esq. Barry W.
Cisco Technology Inc.
Vanderpuye Kenneth
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