Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-12-21
2004-10-19
Ton, Dang (Department: 2666)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S423000, C370S428000, C370S432000, C370S471000, C370S474000
Reexamination Certificate
active
06807172
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to computer networks and, more specifically, to a network switch having a distributed forwarding mechanism architecture for learning and switching frames within a computer network.
BACKGROUND OF THE INVENTION
Data communication in a computer network involves the exchange of data between two or more entities interconnected by communication links and subnetworks. These entities are typically software programs executing on hardware computer platforms, such as end stations and intermediate stations. Examples of an intermediate station may be a router or switch that interconnects the communication links and subnetworks to enable transmission of data between the end stations. A local area network (LAN) is an example of a subnetwork that provides relatively short distance communication among the interconnected stations, whereas a wide area network enables long distance communication over links provided by public or private telecommunications facilities. Accordingly, the switch may be utilized to provide a “switching” function for transferring information between, e.g., LANs.
Communication software executing on the end stations correlate and manage data communication with other end stations. The stations typically communicate by exchanging discrete packets or frames of data according to predefined protocols. In this context, a protocol consists of a set of rules defining how the stations interact with each other. In addition, network routing software executing on the routers allows expansion of communication to other end stations. Collectively, these hardware and software components comprise a communications network and their interconnections are defined by an underlying architecture.
Modern communications network architectures are typically 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. Predetermined services are performed on the data as it passes through each layer and the layers communicate with each other by means of the predefined protocols. The lower layers of these architectures are generally standardized and are typically implemented in hardware and firmware, whereas the higher layers are generally implemented in the form of software running on the stations attached to the network. An example of such a communications architecture is the Internet communications architecture.
The Internet architecture is represented by four layers which are termed, in ascending interfacing order, the network interface, internetwork, transport and application layers. These layers are arranged to form a protocol stack in each communicating station of the network.
FIG. 1
illustrates a schematic block diagram of prior art Internet protocol stacks
125
and
175
used to transmit data between a source station
110
and a destination station
150
, respectively, of a network
100
. As can be seen, the stacks
125
and
175
are physically connected through a communications channel
180
at the network interface layers
120
and
160
. For ease of description, the protocol stack
125
will be described.
In general, the lower layers of the communications stack provide internetworking services and the upper layers, which are the users of these services, collectively provide common network application services. The application layer
112
provides services suitable for the different types of applications using the network, while the lower network interface layer
120
accepts industry standards defining a flexible network architecture oriented to the implementation of LANs.
Specifically, the network interface layer
120
comprises physical and data link sublayers. The physical layer
126
is concerned with the actual transmission of signals across the communication channel and defines the types of cabling, plugs and connectors used in connection with the channel. The data link layer (i.e., “layer 2”) is responsible for transmission of data from one station to another and may be further divided into two sublayers: Logical Link Control (LLC
122
) and Media Access Control (MAC
124
).
The MAC sublayer
124
is primarily concerned with controlling access to the transmission medium in an orderly manner and, to that end, defines procedures by which is the stations must abide in order to share the medium. In order for multiple stations to share the same medium and still uniquely identify each other, the MAC sublayer defines a hardware or data link address called a MAC address. This MAC address is unique for each station interfacing to a LAN. The LLC sublayer
122
manages communications between devices over a single link of the network.
The primary network layer protocol of the Internet architecture is the Internet protocol (IP) contained within the internetwork layer
116
(i.e., “layer 3”). IP is a network protocol that provides internetwork routing and that relies on transport protocols for end-to-end reliability. An example of such a transport protocol is the Transmission Control Protocol (TCP) contained within the transport layer
114
(i.e., “layer 4”). The term TCP/IP is commonly used to refer to the Internet architecture; the TCP/IP architecture is well-known and described in
Computer Networks,
3
rd Edition
, by Andrew S. Tanenbaum, published by Prentice-Hall (1996).
A router is an intelligent intermediate node that implements network services such as route processing, path determination and path switching functions. The route processing function allows a router to determine the type of routing needed for a packet, whereas the path switching function allows a router to accept a packet on one interface and forward it on a second interface. The path determination function enables the router to select the most appropriate interface for forwarding a packet. A switch, on the other hand, provides the basic functions of a bridge including filtering of data traffic by MAC address, “learning” of a MAC address based upon a source MAC address of a frame and forwarding of the frame based upon a destination MAC address. In addition, the switch provides the path switching capability of a router.
FIG. 2
is a highly schematic block diagram of a conventional bus-based network switch
200
comprising a plurality of ports (P) coupled to forwarding engine circuitry (FE) via a bus
210
. The ports may be implemented on various line cards (LC) of the switch, while the forwarding engine may be located on a separate supervisor card (SC). Broadly stated, when a frame is received at a port of the network switch, it is driven over the bus to all of the ports as a forwarding decision is rendered by the forwarding engine. The forwarding engine renders the forwarding decision by, inter alia, accessing a forwarding table (FwdT) to “look-up” a destination MAC address of the frame. If the destination MAC address is in the table, the forwarding decision is passed to all of the ports and only those ports selected by the decision receive the frame, while all of the other ports discard the frame. An example of such a bus-based network switch is disclosed in U.S. Pat. No. 5,796,732 to Mazzola for an Architecture for an Expandable Transaction-Based Switching Bus, which patent is hereby incorporated by reference as though fully set forth herein.
In addition to rendering the forwarding decision, the forwarding engine may then search the forwarding table for a source MAC address of the frame and if that address is not in the table, the forwarding engine “learns” that address. For example, if the source MAC address of the incoming frame is A and that address is not in the forwarding table, the forwarding engine learns the source address of that frame in a conventional manner. When a subsequent frame is received at the switch from another source B which has a destination address of A, the forwarding engine may then be able to properly forward that frame to the destination.
The performance of such a bus-based
Chang Chingwei
Davar Jonathan
Edsall Thomas J.
Levenson Herman
Lue Rong-Lung
Cesari and McKenna LLP
Cisco Technology Inc.
Palmehra Inder
Ton Dang
LandOfFree
Method and apparatus for learning and switching frames in a... 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 learning and switching frames in a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for learning and switching frames in a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3315597