Derived VLAN mapping technique

Details Derived VLAN mapping technique Derived VLAN mapping technique

1998-03-11

2001-03-27

Nguyen, Chau (Department: 2739)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S401000

Reexamination Certificate

active

06208649

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to computer networks and, more specifically, to a technique that enables control of broadcast domains by a switch capable of supporting different protocols within a computer internetwork.
BACKGROUND OF THE INVENTION
Communication in a computer internetwork involves the exchange of data between two or more entities interconnected by communication media. The entities are typically software programs executing on hardware computer platforms, such as end stations and intermediate stations. In particular, 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. A protocol, in this context, consists of a set of rules defining how the stations interact with each other.
A switch is an example of an intermediate station having a plurality of ports that interconnect the communication media to form a relatively small domain of stations, such as a subnetwork. Subnetworks or subnets provide an organizational overlay to an internetwork that facilitates transmission of data between the end stations, particularly for broadcast transmissions. Broadcasting is a powerful tool used to send a single frame to many stations at the same time. However, improper use of broadcasting can impact the performance of stations by interrupting them unnecessarily. The subnet functions to limit the proliferation of broadcast frames to stations within a broadcast domain. A router is an intermediate station that interconnects domains or subnets and executes network routing software to allow expansion of communication to end stations of other subnets. 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 internetwork. 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 internetwork. Examples of communications architectures include the Internet Packet Exchange (IPX) communications architecture and, as described below, 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 an internetwork
100
. As can be seen, the stacks
125
and
175
are physically connected through a communications medium
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 internetwork, while the lower network interface layer
120
accepts industry standards defining a flexible network architecture oriented to the implementation of local area networks (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 medium and defines the types of cabling, plugs and connectors used in connection with the medium. 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 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 internetwork.
The primary network layer protocol of the Internet architecture is the Internet protocol (IP) contained within the internetwork layer
116
. IP is a network protocol that provides internetwork routing and 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
. The term TCP/IP is commonly used to refer to the Internet architecture. Protocol stacks and the TCP/IP reference model are well-known and are, for example, described in
Computer Networks
by Andrew S. Tanenbaum, printed by Prentice Hall PTR, Upper Saddle River, N.J., 1996.
Data transmission over the internetwork
100
therefore consists of generating data in, e.g., sending process
104
executing on the source station
110
, passing that data to the application layer
112
and down through the layers of the protocol stack
125
, where the data are sequentially formatted as a frame for delivery onto the medium
180
as bits. Those frame bits are then transmitted over an established connection of medium
180
to the protocol stack
175
of the destination station
150
where they are passed up that stack to a receiving process
174
. Data flow is schematically illustrated by solid arrows.
Although actual data transmission occurs vertically through the stacks, each layer is programmed as though such transmission were horizontal. That is, each layer in the source station
110
is programmed to transmit data to its corresponding layer in the destination station
150
, as schematically shown by dotted arrows. To achieve this effect, each layer of the protocol stack
125
in the source station
110
typically adds information (in the form of a header) to the data generated by the sending process as the data descends the stack.
For example, the internetwork layer encapsulates data presented to it by the transport layer within a packet having a network layer header. The network layer header contains, among other information, source and destination (logical) network addresses needed to complete the data transfer. The data link layer, in turn, encapsulates the packet in a frame, such as a conventional Ethernet frame, that includes a data link layer header containing information required to complete the data link functions, such as (physical) MAC addresses. At the destination station
150
, these encapsulated headers are stripped off one-by-one as the frame propagates up the layers of the stack
175
until it arrives at the receiving process.
FIG. 2
is a schematic diagram of a frame format of an Ethernet frame
200
comprising destination and source MAC address fields
210
,
220
and a protocol type field
230
that identifies the protocol (e.g., IP, IPX, AppleTalk, DECNet) of the data carried by the frame. Data field
250
contains information, including the network addresses, provided by the higher internetwork layers of the protocol stack. These network addresses are used by

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