Dynamic trunk protocol

Details Dynamic trunk protocol Dynamic trunk protocol

1998-08-27

2002-09-03

Marcelo, Melvin (Department: 2663)

Multiplex communications

Communication techniques for information carried in plural...

Adaptive

C370S467000

Reexamination Certificate

active

06445715

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to network switches and, more specifically, to a technique for efficiently interconnecting switches in a data communications 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, segments and subnetworks. These entities are typically software programs executing on hardware computer platforms, such as end stations and intermediate stations. An example of an intermediate station may be a switch or router which interconnects the communication links and subnetworks to enable transmission of data between the end stations.
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 allow 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.
Modem 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. 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 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
. The term TCP/IP is commonly used to refer to the Internet architecture.
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 is 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 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 network switch logically separates the segments within a network and generally operates at layer
2
to transfer frames among entities of the network using MAC addresses. Typically, the switch is a computer comprising a plurality of ports that couple the switch to the other network entities over various types of network segments and media, such as Ethernet, fiber (FDDI) or token ring connections. A network entity may consist of any device that “sources” (i.e., transmits) or “sinks” (i.e., receives) frames over such media. A router, on the other hand, is typically a computer that connects different subnetworks and directs network traffic based on destination network layer addresses (layer
3
) of the packets.
Switches and routers generally perform the same operation; namely, switching of data frames/packets. That is, switches use layer
2
switching to forward frames and routers use layer
3
switching to route packets. As noted, a difference between layer
2
and layer
3
switching involves the type of information inside the frame/packet that is used to determine the correct output port. Layer
2
switching generally comprises a “store-and-forward” operation in which a frame arrives on an input port of the switch from an input media and is forwarded to an output port for transmission over an output media. With layer
2
switching, frames are switched between ports based on MAC address information stored and maintained in a forwarding database (table) of the switch. With layer
3
switching, packets are “routed” based on network layer information.
Layer
2
switching generally prevents frames transferred between two ports from being

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