Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-08-10
2004-03-30
Jung, Min (Department: 2663)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S401000
Reexamination Certificate
active
06714541
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to computer networks and, more particularly, to use of a routing information field of a token ring frame to increase the efficiency of intermediate devices of a computer network.
BACKGROUND OF THE INVENTION
Data communications in a computer network involves the exchange of data between two or more entities interconnected by communication links and subnetworks. These networks are typically software programs executing on hardware computer platforms which, depending on their roles within a network, may serve as end stations or intermediate stations. Examples of intermediate stations include routers, bridges and switches that interconnect communication links in subnetworks; an end station may be a computer located on one of the subnetworks. More generally, an end station connotes a source of or target for data that typically does not provide routing or other services to other computers on the network. A local area network (LAN) is an example of a subnetwork that provides relatively short-distance communication among the interconnected stations; in contrast, a wide area network (WAN) facilitates long-distance communication over links provided by public or private telecommunications facilities.
End stations typically communicate by exchanging discrete packets or frames of data according to pre-defined protocols. In this context, a protocol represents a set of rules defining how the stations interact with each other to transfer data. Such interaction is simple within a LAN, since these are typically “multicast” networks: when a source station transmits a frame over the LAN, it reaches all stations on that LAN. If the intended recipient of the frame is connected to another LAN, the frame is passed over a routing device to that other LAN. Collectively, these hardware and software components comprise a communications network and their interconnections are defined by an underlying architecture.
Most computer network architectures are organized as a series of hardware and software levels or “layers” within each station. These layers interact to format data for transfer between, e.g., a source station and a destination station communicating over the network. Specifically, predetermined services are performed on that data as it passes through each layer, and the layers communicate with each other by means of the predefined protocols. This design permits each layer to offer selected services to other layers using a standardized interface that shields the other layers from details of actual implementation of the services. The lower layers of these architectures are generally standardized and implemented in hardware and firmware, whereas the higher layers are usually implemented in the form of software. Examples of such communications architectures include the System Network Architecture (SNA) developed by International Business Machines (IBM) Corporation and the Internet Communications Architecture.
The Internet architecture is represented by four layers termed, in ascending interfacing order, the network interface, internetwork, transport and application layers. The primary internetwork layer protocol of the Internet architecture is the Internet Protocol (IP). IP is primarily a connectionless protocol that provides for internetworking routing, fragmentation and reassembly of exchanged packets—generally referred to as “datagrams” in an Internet environment—and which relies on transport protocols for end-to-end reliability. An example of such a transport protocol is the Transmission Control Protocol (TCP), which is implemented by the transport layer and provides connection-oriented services to the upper layer protocols of the Internet architecture. The term TCP/IP is commonly used to denote this architecture; the TCP/IP architecture is discussed in
Computer Networks
, 3
rd edition
, by Andrew S. Tanenbaum, published by Prentice-Hall, PTR in 1996, all disclosures of which are incorporated herein by reference, particularly at pages 28-44.
SNA is a communications framework widely used to define network functions and establish standards for enabling different models of computers to exchange and process data. SNA is essentially a design philosophy that separates network communications into several layers termed, in ascending order, the physical control, the data link control, the path control, the transmission control, the data flow control, the presentation services and the transaction services layers. Each of these layers represents a graduated level of function moving upward from physical connections to application software.
In the SNA architecture, the data link control layer is responsible for transmission of data from one end station to another. Bridges or devices in the data link control layer are used to connect two or more LANs so that end stations on either LAN are allowed to access resources on the LANs. Connection-oriented services at the data link layer generally involve three distinct phases: connection establishment, data transfer and connection termination. During connection establishment, a single path or connection, e.g., an IEEE 802.2 logical link control type 2 (LLC2) connection, is established between the source and destination stations. Once the connection has been established, data is transferred sequentially over the path and, when the LLC2 connection is no longer needed, the path is terminated. Reliable communication in the data link layer is well known and described by Andrew Tanenbaum in his book
Computer Networks, Second Edition
, published in 1988, all disclosures of which are incorporated herein by reference, especially at pages 253-257.
FIG. 1
is a schematic block diagram of a conventional computer network
100
having a source end station (Host A) coupled to a Token Ring (TR) network TR
1
and a destination end station (Host B) coupled to TR
2
. The TR networks are of a type that support Source Route Bridging (SRB) operations with respect to the contents of a routing information field (RIF) of a frame. A SRB bridge B
1
interconnects TR
1
and TR
2
such that the SRB network
100
effectively functions as a LAN. Host A communicates with Host B by exchanging TR frames over LLC2 connections or sessions through the SRB network
100
. To send a TR frame from Host A to Host B along a particular path of the network, the source may insert information within the RIF of the frame that specifies the particular path to the destination.
FIG. 2
is a schematic diagram of a portion of a conventional TR frame
200
comprising destination address (DA) and source address (SA) medium access control (MAC) fields
202
-
204
and a RIF header
210
. The RIF header
210
, in turn, comprises a type (TYPE) field
212
, a RIF length indicator (LENGTH) field
214
, a direction bit (DIRECTION) field
216
and a ROUTE field
220
that may include a plurality of ring number (RN)/bridge number (BN) pairs or route descriptor (RD) “hops” needed to describe the path. Each RD comprises 2 bytes, wherein the RN is 12 bits and the BN is 4 bits. For example, the ROUTE field
220
of TR frame
200
transmitted by Host A to Host B may contain [0011.0020]. The RIF header
210
terminates with a 4-bit padding (PAD) field
228
of zeros.
The bridged TR network
100
is typically implemented through the use of TR concentrators (or “hubs”) interconnected in a “daisy chain” manner, wherein each concentrator is coupled to end stations via point-to-point wires. Access to each token ring of network
100
is determined in accordance with a token message that propagates among all of the end stations coupled to the ring. A concern with this conventional network arrangement involves the limited bandwidth available to each station over the wires; for example, all end stations coupled to a physical token ring share 16 megabits (Mbps) of bandwidth.
An attempt to increase bandwidth in a token ring environment involves the use of intermediate stations that are compatible with the Dedicated Token Ring (DTR) bridge standard promulgated by the Institute of Elec
Iyer Jayaraman
Patel Kushal A.
Cesari and McKenna LLP
Cisco Technology Inc.
Jung Min
LandOfFree
Method and apparatus for encoding bridging/switching... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for encoding bridging/switching..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for encoding bridging/switching... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3261932