Efficient network multicast switching apparatus and methods

Details Efficient network multicast switching apparatus and methods Efficient network multicast switching apparatus and methods

2002-10-07

2004-10-12

Rao, Seema S. (Department: 2666)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S410000, C370S432000, C370S465000

Reexamination Certificate

active

06804236

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the distribution of multicast messages in a computer network and, more specifically, to efficient network multicast switching apparatus and methods.
2. Brief Description of Related Prior Art
Data communication in a computer network involves data exchange between two or more entities interconnected by communication links and subnetworks. These entities are typically software programs executing on hardware computer platforms, such as endstations and intermediate stations. Examples of an intermediate station may be a router or switch which interconnects the communication links and subnetworks to enable transmission of data between the endstations. 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.
Communication software executing on the endstations correlate and manage data communication with other endstations. 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 allow expansion of communication to other endstations. 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 five layers which are termed, in ascending interfacing order, physical interface, data link, network, 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 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 interface layer
120
accepts industry standards defining a flexible network architecture oriented to the implementation of LANs.
Specifically, the interface layer
120
comprises the physical interface layer
126
, which 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”)
121
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 network.
The primary network layer protocol of the Internet architecture is the Internet protocol (IP) contained within the network layer
116
(i.e., “layer 3”). IP is a network protocol that provides network 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
. The term TCP/IP is commonly used to refer to the Internet architecture. (See, e.g., Tanenbaum,
Computer Networks, Third Ed
., Prentice Hall PTR, Upper Saddle, River, N.J., 1996).
Data transmission over the network
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 channel
180
as bits. Those frame bits are then transmitted over an established connection of channel
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 network 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 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.
A router is an intelligent intermediate station that implements network services such as route processing, path determination and path switching functions. The router also provides interfaces for a wide range of communication links and subnetworks. 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, or forwarding decision, function enables the router to select the most appropriate interface for forwarding a packet.
A switch 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 many cases, the destination of a data message issued by a source (“sender”) may be more than one, but less than all of the entities (“receivers”) on a network; thi

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