Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-08-04
2003-10-28
Nguyen, Chau (Department: 2663)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S466000
Reexamination Certificate
active
06639917
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to data communications networks and more particularly to a converged service for transporting frames between interconnected local area networks employing the same or different frame protocols.
BACKGROUND OF THE INVENTION
Initially, computer systems conformed to what could be described as a host-centric model. Individual users interacted with a single, central host computer or mainframe through workstations attached to the mainframe either directly or indirectly through devices commonly referred to as cluster or display controllers. Virtually all of the data processing power resided in the mainframe with the individual workstations having relatively little data processing power or “intelligence”. The mainframe controlled all communications among workstations or between workstations and system resources, such as disk drives and printers. Assuming that the exchanges of data between workstations or between workstations and system resources could be characterized as “communications”, the communications were localized in nature.
Data communications networks evolved as a consequence of a need for users attached to different mainframes to communicate with each other. Early data communications networks consisted of a number of isolated host-centric systems which were connected through public or private switched telephone networks. Communication controller devices provided the interfaces between the mainframes and the switched telephone networks. In such data communications networks, the mainframe in each of the connected host-centric systems played a central role in management of the connections between workstation users in the different systems.
Over time and as a result of improvements in computer technology, the processing power originally confined to mainframes began to appear in smaller and smaller computers including devices now commonly referred to as personal computers. Over a relatively short period of time, personal computers were developed that possessed the processing power formerly found only in mainframes.
To take advantage of the distribution of processing power to personal computers and of improvements in data communication technology, new types of networks, generically referred to as local area networks or LANs, were developed. At the most basic level, a local area network or LAN consists of a plurality of workstations or other devices (such as printers or disk drives) which are all connected to a shared communications medium. Any device attached to a shared communications medium may be generically identified as a “station”. Data to be exchanged between stations in the same local area network is written onto the communications medium by the source station and then copied from the medium by the destination station. Even where the area network is connected to a mainframe, the mainframe plays no significant role in the transfer of data between devices in the same local area network.
While several different kinds of local area networks have been proposed, the two most common kinds in current use are Ethernet and Token Ring local area networks. There are significant differences between these two kinds of local area networks.
An Ethernet local area network may also be referred to as a Carrier Sense Multiple Access/Collision Detect or CSMA/CD network. In an Ethernet local area network, all stations have an equal opportunity to transmit information across the shared bus. If a station has information to transmit, it first listens to the shared bus to determine whether any other station is already using the bus. If the bus is found to be idle, the listening station begins to transmit data. If the bus is found to be busy, the listening station waits for a predetermined period of time before trying to access the bus again. Information transmitted onto the bus is received by every station attached to the bus; that is, the information is broadcast. A station for which the information is intended recognizes its own address in the information and accepts the transmitted information. All other stations discard or ignore the information.
Token Ring local area networks use a logical ring to which all stations are connected. Any station who wishes to transfer information onto the ring must first acquire a “token”, which is a special data structure or frame. Once the station has the token, it may transfer information onto the ring. The information flows in one direction around the ring and through each of the connected stations. If a station is not intended to receive the information, it simply passes the information on to the next station on the ring. If a station is intended to receive the information, it copies the information into station memory for its use but still passes the information on to the next station on the ring. The information remains on the ring until it traverses the entire ring and reaches the source station. The source station strips the information from the ring and writes a “free” token back on to the ring The token circulates around the ring until it is acquired by another station having information to transmit.
Both Ethernet and Token Ring technologies have their virtues. Ethernet installations tend to be less expensive than Token Ring installations. On the other hand, Token Ring networks can handle larger frame sizes than Ethernet networks, can accommodate a frame handling technique known as source routing and can accommodate different priority levels of data. These capabilities allow load balancing, automatic route recovery without session loss and use of redundant addresses in Token Ring local area networks.
Both Ethernet and Token Ring local area technologies are defined by specifications issued by the Institute of Electrical and Electronic Engineers (IEEE). Ethernet local area network technology is defined in IEEE 802.3 specifications while Token Ring local area network technology is defined IEEE 802.5 specifications. The IEEE specifications define many aspects of each of these local area network technologies, including the structure of the data frames which are used to transport information within the local area network. For reasons which are not important to an understanding of the present invention, the frame structures used in Ethernet local area networks are different than the frame structures used in Token Ring local area networks.
If individual local area networks were always to remain isolated one from another, the differences in frame structures would pose no problem. However, because users' needs to communicate are not limited to the particular local area network to which they are attached, it is desirable to interconnect different local area networks to permit users on those different networks to communicate as if they were on the same network. One problem in interconnecting local area networks is that such networks may not be directly connected with another but may be separated by intervening networks, including wide area networks following a system architecture unlike any local area network architecture.
Techniques have been developed to interconnect local area networks even where those networks are linked only by an intervening network. One known technique requires that the intervening network encapsulate the local area network data into a frame or packet structure which the intervening network can handle. This may require that the local area network data be segmented at the point of entry into the intervening network and then reassembled at the point of exit from the intervening network. The encapsulation approach has the drawback that end-to-end transmission efficiency is degraded since the frame or packet structure used in the intervening network will add a considerable number of non-data bits to the information flow. Routing techniques have also been use to transport the data between separated local area networks. The routing techniques also degrade the transmission efficiency between the two end stations on the communications path.
Clearly, it is desirable to allow local area networ
Ellington, Jr. William Woollcott
Love Robert Daniel
Wilhelm Kathleen Miriam
George Keith M.
Munoz-Bustamanta Carlos
Nguyen Chau
Sawyer Law Group LLP
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