Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
2000-05-19
2004-09-14
Pham, Chi (Department: 2667)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S469000
Reexamination Certificate
active
06791979
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to computer networks and, more particularly, to the distribution of packet prioritization information among stations of 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 which 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; in contrast, a wide area network (WAN) enables long distance communication over links provided by public or private telecommunications facilities.
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.
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. Specifically, 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. Examples of such communications architectures include the Systems Network Architecture (SNA) developed by International Business Machines Corporation and 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
of the Internet architecture 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, on the other hand, 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 and provides for environments that need connectionless or connection-oriented services at the data link layer.
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 is established between the source and destination stations. This connection, e.g., an IEEE 802.2 LLC Type 2 or “Data Link Control” (DLC) connection as referred hereinafter, is based on the use of service access points (SAPs); a SAP is generally the address of a port or access point to a higher-level layer of a station. Once the connection has been established, data is transferred sequentially over the path and, when the DLC connection is no longer needed, the path is terminated. The details of such connection establishment and termination are well-known and, thus, will not be described herein.
The transport layer
114
and the internetwork layer
116
are substantially involved in providing predefined sets of services to aid in connecting the source station to the destination station when establishing application-to-application communication sessions. The primary network layer protocol of the Internet architecture is the Internet protocol (IP) contained within the internetwork layer
116
. IP is primarily a connectionless network protocol that provides internetwork routing, fragmentation and reassembly of datagrams 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
. Notably, TCP provides connection-oriented services to the upper layer protocols of the Internet architecture. 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 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 field) to the data frame generated by the sending process as the frame descends the stack. At the destination station
150
, the various 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.
SNA is a mainframe-oriented network architecture that also uses a layered approach. The services included within this archi
Berl Steven H.
Tam Ulrica
Cesari and McKenna LLP
Cisco Technology Inc.
Jones Prenell
Pham Chi
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