Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
2000-01-14
2004-09-28
Jung, Min (Department: 2663)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S395310
Reexamination Certificate
active
06798776
ABSTRACT:
CROSS-REFERENCE TO THE APPENDIX CONTAINING SOFTWARE
Appendix A, which is a part of the present disclosure, lists the computer programs and related data in one embodiment of this invention. This listing of computer programs contains material which is subject to copyright protection The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the present disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to the field of computer networks. More particularly, the present invention relates to the field of computer networks which are based on datagram packet switching.
2. Background of the Invention
Computer Networks are used to interconnect computers and peripherals to allow them to exchange and share data such as files, electronic mail, databases, multimedia/video, and other data.
Packet Switching
Nearly all computer networks use packet switching, which divides longer units of data transfer into smaller packets which are sent separately over the network. This allows each packet to be processed independently from another packet without having to wait for the entire data transfer to be completed. It also enables communications between a plurality of computer systems to be intermixed on one network. Host interfaces connect the computer systems to a network allowing each, computer system to act as the source and destination of packets on the network.
A first key issue in packet switched networks is addressing. The addressing in packet switched networks is conventionally performed by one of two approaches, known as virtual circuit packet switching or datagram packet switching.
Virtual Circuit Packet Switching
In the virtual circuit approach, before any data can be transmitted, a virtual circuit must be first established along the path from the source to the destination in advance of any communication. After the virtual circuit is setup, the source can then send packets to the destination. Each packet in the virtual circuit approach has a virtual circuit identifier, which is used to switch the packet along the path from source to the destination.
The virtual circuit approach reduces the size of the identification required in each packet header. It also allows additional information about the packet handling to be established as part of the virtual circuit setup operation. Another claimed benefit is that forwarding and switching of virtual circuit packets can be made more efficient because of the virtual setup process. However, the virtual circuit approach incurs the cost of delay to setup the virtual circuit before sending any data, and it incurs the cost of maintaining the virtual circuit state in each network device along the virtual circuit path, even if a virtual circuit is idle. Also, in practice the memory space for virtual circuit state in network devices has limited the number of circuits that are available, which complicates the behavior of network nodes that need to create virtual circuits to communicate.
Datagram Packet Switching
In the datagram approach, each datagram packet is a self-contained unit of data delivery. A typical datagram packet includes a globally unique source address, a globally unique destination address, a protocol type field, a data field, and a cyclic redundancy checksum (“CRC”) to insure data integrity.
Datagrams can be sent without prior arrangement with the network, i.e. without setting up a virtual circuit or connection. Each network device receiving a datagram packet examines the destination address included in the datagram packet and makes a local decision whether to accept, ignore, or forward this packet.
Various conventional network devices learn information from observing datagram packet traffic in data networks. For example, a conventional network switch device that interconnects multiple network segments can “learn” the location of network stations connected to its ports by monitoring the source address of packets received on its ports. After it has associated a station address with a certain port, the network switch can then forward datagram packets addressed to that station to that port. In this type of device, the datagram source address is used to learn the location of a station on the network, whereas the forwarding decision is made on basis of the datagram destination address alone.
Datagram packet switching has the advantage that it avoids the overhead and cost of setting up virtual circuit connection in network devices. However, it incurs the expense of transmitting a larger packet header than required for virtual circuit switching, and it incurs the cost for processing this larger packet header in every network device to which it is delivered. Also, there is no virtual circuit setup process to establish additional information for datagram packet processing. Another disadvantage of datagram packet switching is that it is difficult to control packet flow to the same degree as with virtual circuits because there is, in the conventional case, no state in the network devices associated with the traffic flow.
The datagram packet switching approach has been extensively used in shared media local area networks. Shared media networks provide for a multiplicity of stations directly connected to the network, with the shared media providing direct access from any transmitter to any receiver. Since the receivers need to be able to distinguish packets addressed specifically to them, each receiver needs to have a unique address. In addition, since the unit of access to the shared medium is one packet, each packet needs to contain the unique address capable to identify the receiver. As a result, all commonly used local area networks are based on datagram packet switching and have no provisions for virtual circuit setup.
Media Access Control Protocol
The network access mechanism in shared media local area network will now be further described. This function, commonly known as the media access control or MAC protocol, defines how to arbitrate access among multiple stations that desire to use the network. Individual stations connected to the network have to adhere to the MAC protocol in order to allow proper network operation.
A number of different media access control protocols exist. The MAC protocol, in conjunction with the exact packet format, is the essence of what defines a local area network standard. The following is a brief overview of local area network standards that are in wide use today.
The most widely used local area network is commonly known as Ethernet and employs an access protocol referred to as Carrier Sense Multiple Access with Collision Detection (CSMA/CD). [see U.S. Pat. No. 4,063,220, issued Dec. 13, 1977, for a Multipoint Data Communication System with Collision Detection, Inventors Metcalfe, Boggs, Thacker, and Lampson]. The current definition of the Ethernet CSMA/CD protocol is defined in IEEE Standard 802.3, published by the Institute of Electrical and Electronics Engineers, 345 East 45th Street, New York, N.Y. 10017. The Ethernet standard specifies a data transmission rate of 10 or 100 Megabits/second.
Another widely used local area network standard is Tokenring, also known as IEEE Std 802.5, transmitting at a speed of 4 or 16 Mbits/sec and FDDI or Fiber-Distributed-Data-Interface which sends data at a speed of 100 Mbits/sec. Both Tokenring and FDDI are based on a circulating token granting access to the network, although their respective datagram packet formats and other operating aspects are unique to each standard.
What is common to all these media access control mechanisms is that they do not include provisions for virtual circuit setup and have no provisions to specify attributes that relate to virtual circuits, such as traffic management or flow control for specific connections. This limits the ability of conventional local area networks to accommodate higher level network functions or to support vi
Bechtolsheim Andreas V.
Cheriton David R.
Baker & Botts L.L.P.
Cisco Technology Inc.
Jung Min
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