Electrical computers and digital processing systems: multicomput – Network-to-computer interfacing
Reexamination Certificate
1998-08-17
2003-02-04
Etienne, Ario (Department: 2153)
Electrical computers and digital processing systems: multicomput
Network-to-computer interfacing
C370S463000
Reexamination Certificate
active
06516352
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of interface hardware for local area networks, and more particularly to a network interface which efficiently switches between different links to a local area network.
DESCRIPTION OF THE RELATED ART
Local area networks (LANs) have forever changed corporate and personal computing. First used for sharing simple information and resources among personal computer users, LANs have dramatically evolved over the last ten years to become the premier strategic computing platform for businesses today. All but the smallest corporations rely on LANs and their dependence and appetite for this technology shows no signs for slowing. Indeed, LANs have matured to the point of peer status with personal computers themselves. As the market and deployment of ever more powerful computers continues to grow, the expectation of providing equally high performance network connectivity grows as well.
One example of a local area network, LAN
10
, is depicted in FIG.
1
. As shown, LAN
10
includes a server computer
14
and a plurality of client computers
16
. Computers
14
and
16
are coupled by LAN hardware
12
, which includes the actual transmission medium (e.g., fiber-optic cable or copper cable such as unshielded twisted pair (UTP)) as well as various network hardware elements such as hubs, switches and routers.
The advantages of LANs are numerous. By providing easy access to shared data (on server computer
14
, for example), computer users are allowed to interpolate more effectively. Users are also able to share expensive peripheral devices such as printers, faxes and CD-ROMs between client computers
16
. These peripheral devices are also coupled to the various client computers via LAN hardware
12
. The cost of client computers may also be decreased by lessening the needs for high-capacity disk drives on individual workstations. By storing data on one or more central servers accessible through the LAN, this also provides an easier solution for backup of vital data.
A LAN includes two or more computer systems which are physically and logically connected to one another. The type of connection between the computer systems is referred to as the topology of the LAN. In a bus topology, computer systems and devices are attached at different points along a bus. Data is then transmitted throughout the network via the cable. The speed of transmission of the network is governed by the type of cable. One disadvantage of this topology is that a break in the cable disables the entire network. Furthermore, provisions have to be made for re-transmission of data in cases in which multiple computers contend for the bus (cable) at the same time, causing data collision (and possible loss of data).
Another type of topology is the ring topology, in which computer systems are daisy-chained together in a circle. In such a configuration, data is transmitted from node to node (computer to computer). The data is passed from computer to computer until the correct destination is reached. While this avoids the problem of data collision, a break in the connection disables the entire network.
A third type of topology is the star topology. In this configuration, all computer systems are routed to a central location called a hub. This allows for easy modification of the network (adding, deleting, moving computers) without having to bring down the entire network. Furthermore, the entire network does not go down if one individual connection is broken.
Hybrid topologies combining one or more of the above network configurations may also be utilized to further increase flexibility.
In order to permit a full range of data communications among disparate data equipment and networks, the International Standards Organization (ISO) developed a reference model known as Open System Interconnection (OSI) in 1974. OSI is a seven-layer model which ideally allows standardized procedures to be defined, enabling the interconnection and subsequent effective exchange of information between users. OSI defines the functions of each layer but does not provide the software and hardware to implement the model. The model's goal is to set a standard for communication product vendors. The seven layers in sequence from top (layer
7
) to bottom (layer
1
) are as follows: application, presentation, session, transport, network, data link, and physical. A given network does not have to implement each layer of OSI to be compatible with this standard.
Layer
7
, the application layer, is responsible for specialized network functions such as file transfer, virtual terminal, and electronic mail. The purpose of this layer is to serve as the window between correspondent application processes which are using the OSI to exchange meaningful data. Examples of application layer protocols include SNMP, RLOGIN, TFTP, FTP, MIME, NFS, and FINGER. Layer
6
, the presentation layer, is responsible for data formatting, character code conversion, and data encryption of data generated in the application layer. This layer is not always implemented in a network protocol. Layer
5
, the session layer, provides for negotiation and establishment of a connection with another node. To do this, the session layer provides services to (a) establish a session connection between two presentation entities and (b) support orderly data exchange interactions. This includes establishing, maintaining, and disconnecting a communication link between two stations on a network, as well as handling name-to-station address translation. (This is similar to placing a call to someone on the telephone network with knowing only his/her name, wherein the name is reduced to a phone number in order to establish the connection).
Layer
4
, the transport layer, handles the reliable end-to-end delivery of data. This layer ensures that data is delivered in the same order that it was sent. It also ensures that data is transmitted or received without error, and in a timely manner. Transmission control protocol (TCP) is a common transport layer protocol. Layer
3
, the network layer, routes packets of information across multiple networks, effectively controlling the forwarding of messages between stations. On the basis of certain information, this layer will allow data to flow sequentially between two stations in the most economical path both logically and physically. This layer allows units of data to be transmitted to other networks though the use of special devices known as routers. Internet Protocol (EP) is an example of a network layer protocol which is part of the TCP/IP protocol suite.
Layer
2
, the data link layer, is responsible for transfer of addressable units of information, frames, and error checking. This layer synchronizes transmission and handles frame-level error control and recovery so that information can be transmitted over the physical layer. Frame formatting and cyclical redundancy checking (CRC), which checks for errors in the whole frame, are accomplished in this layer. It also provides the physical layer addressing for transmitted frame. Serial Line IP (SLIP) and Point-to-Point Protocol (PPP) are examples of data link protocols. Finally, layer
1
, the physical layer, handles the transmission of binary data over a communications network. This layer includes the physical wiring (cabling), the devices that are used to connect a station's network interface controller to the wiring, the signaling involved to transmit/receive data, and the ability to detect signaling errors on the network media. ISO 2110, IEEE 802, and IEEE 802.2 are examples of physical layer standards.
For a bus or star topology, a transmission protocol is needed for devices operating on the bus to deal with the problem of data collision (two devices transmitting data over the bus at the same time). One such technique implemented in the OSI data link layer is called carrier sense multiple access/collision detect (CSMA/CD). Under this technique, hardware residing in a network interface card (NIC) within a given computer system senses the voltage change of t
Booth Bradley J.
Fesas, Jr. Nestor A.
Kass William
Sharp Robert O.
Blakely , Sokoloff, Taylor & Zafman LLP
Edelman Bradley
Etienne Ario
Intel Corporation
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