Saturday, 26 May 2012


• 10/100/1000 Mbps Ethernet
• 100 Mbps FDDI
• 155/620 Mbps ATM
• 4/10/45 Mbps Wireless

What is a 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:
– Access method,
– allowed physical topologies,
– Types of cabling, and
– Speed of data transfer
• Protocol (communications protocol) = standards that specifically address how the devices on a network communicate, i.e
– How the data is packaged for transmission
– How receiving devices acknowledge signals from sending devices
– How errors are detected and handled

Logical topologies are bound to network protocols and describe how data is moved across the network.
Ethernet, Local Talk, Token ring for wired networks
• TCP/IP and WAP for internet
• Wi-Fi for wireless networks
• Bluetooth, for short range wireless network

     A)    Ethernet

• The most widely used wired networks protocol
• Early Ethernet network were half duplex, uses an access method called CSMA/CD (Carrier Sense Multiple Access/Collision Detection) a system where each computer listens to the cable before sending anything through the network to avoid collisions.
• Since 1997 Ethernet uses full duplex communication, that does not require listening to other messages and no collisions occur.
• The Ethernet protocol allows for linear bus, star, or tree topologies. Data can be transmitted over wireless access points, twisted pair, coaxial, or fiber optic cable.
• Early Ethernet protocols (10BASE-T) support 10BASE transmissions rate 10 Mbps
• Today
– 100BASE-T or 100BASE-TX – 1000Mbps (1Gbps
– 10Gigagbit Ethernet – 10Gbps

     B)    LOCALTALK

• A network protocol that was developed Macintosh computers.
• Used a method called CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance), where a computer signals its intent to transmit before it actually does so.
• Allows for linear bus, star, or tree topologies using twisted pair cable.
Disadvantage: slow speed (only 230 Kbps).

     C)    TOKEN RING

• developed by IBM in the mid-1980s.
Access method involves token-passing.
• The computers are connected so that the signal travels around the network from one computer to another in a logical ring.
• A single electronic token moves around the ring from one computer to the next. If a computer does not have information to transmit, it simply passes the token on to the next workstation. If a computer wishes to transmit and receives an empty token, it attaches data to the token. The token then proceeds around the ring until it comes to the computer for which the data is meant- the data is captured by the receiving computer.
-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.

     D)    FDDI

• Fiber Distributed Data Interface - a network protocol that is used primarily to interconnect two or more local area networks, often over large distances.
Access method involves token-passing.
Uses a dual ring physical topology. Transmission normally occurs on one of the rings; if a break occurs, the system keeps information moving by automatically using portions of the second ring to create a new complete ring.
• A major advantage of FDDI is speed. It operates over fiber optic cable at 100 Mbps.

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