Protocol

Protocols

Protocols represent an agreement among different parts of the network i.e. how data is to be transferred. Though you are not supposed to see them and only a few people understand them, their effect on system performance can be spectacular. A poorly implemented protocol can slower data transfer but software following standard protocols can make communications between dissimilar systems possible. For instanse, the TCP/IP protocol enables you to transfer data between computers that have different architectures and operating systems.

The key elements of protocol are syntax, semantics and timing.

1.          Syntax specifies the signal levels to be used and the format in which the data is to be sent.

2.       Semantics specifies the information structure needed for coordination among machines and for data handling.

3.      Timing includes speed matching so that a computer with a 33.6 kilobit per second port can talk to one with a 56 kilobit per second port and the proper sequencing of data in case it arrives out of order.

IEEE 802.X Standards:- The Institute of Electrical and Electronics Engineers (IEEE) has developed a set of standards describing the cabling, physical topology, electrical topology and access scheme of network products. The committee structure of the IEEE is numbered like the decimal system. The general committee working on these standards is 802. Various subcommittees, designed by decimal numbers, have worked on different versions of the standards.

These standards describe the protocols used in the lower two layers of the OSI model, the Physical & Data-Link layers. They don’t go above those layers.

IEEE 802.3 & 802.5:- IEEE standard 802.5 describes the Token-Ring architecture. The work of this committee received a lot of attention and leadership from IBM. This standard describes a token-passing protocol used on a network of stations connected in a special way, combining an electrical ring topology where every station actively passes information to the next one in the ring.

IBM’s Token-Ring system is important to corporate data processing managers because IBM supports a number of mainframe computers Token-Ring interfaces.

Many vendors make Token-Ring interface cards for popular minicomputers. These allow easy interaction without the use of complex and expensive micro-to-mainframe links and gateways.

IEEE 802.3, on the other hand, describes a standard that owes a lot to the earlier Ethernet system. It uses Carrier Sense Multiple Access (CSMA) signaling on an electrical bus topology. The standard leaves room for several wiring options. One extension to the 802.3 standards introduced signaling at 100 megabits per second under what is commonly called Fast Ethernet or the 100 Base-T standard. You can buy 802.3 interface cards for the PC from dozens of manufacturers. Similar cards designed for popular minicomputers are also widely available.

IEEE 802.6:- Metropolitan-Area Networks or MANs make up the 802.6 sub-category of the IEEE 802 standards project. Metropolitan networks can take many forms but the term usually describes a backbone network of fiber-optic cables that could span hundreds of square miles. The telephone companies provide a great deal of MAN connections, as do a growing number of cable television companies. While some organizations install their own microwave systems for MAN circuits, the majority lease circuits from local telephone companies or cable television companies.

TCP/IP:-  The earliest large network systems were fielded by the Department of Defense (DoD). The DoD financed the development of interactive network communications software for many different mainframes and minicomputers. The standard core of the DoD specified software consists of programs that implement two protocols, that is. Transmission Control Protocol (TCP) and Internet Protocol (IP). The availability of TCP/IP software and the power of the biggest TCP/IP application, the Internet make them attractive to face the challenge of integrating dissimilar computer systems. TCP/IP software is popular on large networks because it works and is available for practically in all computers.

TCP and IP perform primarily what the OSI model terms layer-3 (Network) and layer-4 (Transport) functions. Particularly important is the capability to communicate and to order data among two or more different computer systems.

Companies like Net Manage and Walker Richer and Quinn sell TCP/IP software customized for specific computers and controller cards. These software modules communicate through the network, recognize each other and pass messages in common format generated by the higher-level Session layer and application programs. TCP/IP software is popular on large networks because it works and is available for practically in all computers.

X.25 Protocol:- X.25 protocol defines how communication devices such as routers package and route data over a connecting circuit. X.25 data packaging and routing can be used over any satellite or Integrated Services Digital Network (ISDN) communication circuits. It can also be used over any type of point-to-point circuits but the protocol is better known for its packet-switching capabilities.

There are two main types of Public Data Networks (PDN), circuit switched and packet switched each with its own standards. Since the Public Switched Telephone Network (PSTN) is still widely used for data communication, standards have been established for interfacing to this type of network. In general, the standards for each of these networks refer to the lowest three layers of the OSI model. Let us outline the differences between the two types of switching used in PDNs.