Networking Protocol
A protocol is a set of rules that governs the communications between computers on a network. These rules include guidelines that regulate the following characteristics of a network:
There are 5 most common protocols:
Ethernet
LocalTalk
Token Ring
FDDI
ATM
Ethernet
The Ethernet protocol is the most widely used. It is based on the use an access method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection). In this system each computer "listens" to the cable before sending anything through the network. If the network is clear, the computer will transmit. In the event that some other node is transmitting at that time, the computer will wait and try again when the line is clear.
Sometimes two computers attempt to transmit at the same time. In this case a collision occurs. Each computer then back off and waits a random amount of time before attempting to retransmit.
Collisions are normal to this access method. However, the delay caused by collisions and retransmitting is very small and does not normally effect the speed of transmission on the network.
The Ethernet protocol allows for linear bus, star, or tree topologies. The cable used for data transmission is twisted pair, coaxial, or fiber optic. The speed of transmission is 10 Mbps to 1000 Mbps.
To increase speed of transmission, the Ethernet has developed a new standard that supports 100 Mbps. This protocol is known as Fast Ethernet Fast Ethernet requires a higher end, that is more expensive, network concentrators (hubs or switches), and network interface cards. To impliment this protocol, category 5 twisted pair or fiber optic cable is required.
One of the recent developments in the Rhernet standard is Gigabit Ethernet. This protocol has a transmission speed of 1 gigabit (Gbps). Gigabit Ethernet can be used with both fiber optic cabling and copper.
LocalTalk
LocalTalk is a network protocol that was developed by Apple Computer, Inc. for Macintosh computers. The method used by LocalTalk is called CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance). This method is similar to CSMA/CD used by Ethernet. The only difference is that a computer signals its intent to transmit before it actually does so.
LocalTalk adapters and special twisted pair cable can be used to connect a series of computers through the serial port. The Macintosh operating system allows a peer-to-peer network without additional software. With the addition of the server version of AppleShare software, a client/server network can be established.
The LocalTalk protocol allows for linear bus, star, or tree topologies using twisted pair cable. A primary disadvantage of LocalTalk is its speed of transmission - only 230 kilobits per second (Kbps).
Token Ring
Token Ring protocol was developed by IBM in the mid-1980s. The access method used involves token-passing. In token Ring, the computers of the network are so that the signal travels around the network from one computer to another in a logical ring. A signal electronic token moves around the ring from one computer to next. If a computer does not have information to transmit, it simply passes the token to the next workstation. If a computer wishes to transmit and it receives an empty token, it attaches data to the token. The token then is being passed around the ring until it comes to the computer for which the data was sent. In its turn, this computer will capture the data.
The Token Ring protocol requires a star-wired ring using twisted pair or fiber optic cable. It can operate at transmission speeds of 4 Mbps or 16 Mbps. Due to the limitation in speed and increasing popularity of Ethernet, the use of Token Ring has dramatically decreased.
FDDI
Fiber Distributed Data Interface (FDDI) is a network protocol that is primarily used to interconnect two or more local area networks. These networks are often spread over large distances. The access method used by FDDI involves token-passing. FDDI uses a dual ring physical topology.
Transmission normally occurs on one of the rings. If a break occurs, the system keeps information moving by automaticaly using portions of the second ring to create a new complete ring.
This protocol has a great advantage - its speed. FDDI operates over fiber optic cable at 100 Mbps.
ATM
Asynchronous Transfer Mode (ATM) is a network protocol that transmits data in small packet of a fixed size, unlike other protocols that transfer data in variable length packets. ATM suppots different media, such as video, CD-quality audio, and imaging.
Atm is most often used to interconnect two or more local networks. It employs a star topology. The cable used for data transmission is twisted pair or fiber optic.The speed of data transmission aloowed by ATM protocol is 155 Mbps or higher.
OSI Model
When diffrent types of microcomputers are connected in a network, the protocols can become very complex. Obviously, for the conection to work, these network protocols must adhere to certain standards.
The International Standards Organization has defined a set of communications protocols called Open Systems Interconnection (OSI). The purpose of the OSI model is to identify functions provided by any network. It separates each network's funcion into seven "layers" of protocols, or communication rules. When two network systems communicate, their corresponding layers may exchange data. This assumes that the microcomputers and other equipment on each network have implemented the same functions and interfaces.
