Data communication method csma/cd MAC ,Token ring and FDDI

Data communication method occurs in two ways:-

1. Broadcast
2. Tokenpass

Ethernet uses broadcast method of communication.

Logical Topologies:-

1. Bus topology   eg ethernet hub
2. Token ring topology
3. Hub and spoke topology.

Ethernet Hub is a shared media ,collision may happen in shared media

Collision Domain :-
Area affected(shared media) by unicast data or communication.To avoid collision,ethernet has adapted CSMA/CD(carrier sense multiple access/collision detction).

CSMA/CD (Carrier Sense Multiple Access / Collision Detection) is the protocol used in Ethernet networks to ensure that only one network node is transmitting on the network wire at any one time.Carrier Sense means that every Ethernet device listens to the Ethernet wire before it attempts to transmit. If the Ethernet device senses that another device is transmitting, it will wait to transmit.Multiple Access means that more than one Ethernet device can be sensing (listening and waiting to transmit) at a time.Collision Detection means that when multiple Ethernet devices accidentally transmit at the same time, they are able to detect this error.

How Collisions Occur under CSMA/CD

Imagine a very simple Ethernet network with only two nodes.

Each node, independently, decides to send an Ethernet frame to the other node.
Both nodes listen to the Ethernet wire and sense that no carrier is present.
Both nodes transmit simultaneously, causing a collision.
Both nodes detect the collision and each node waits a random amount of time before transmitting again.
Collisions are normal on an Ethernet network. A small amount of collisions are expected in the protocol design.
If too many nodes are transmitting on an Ethernet network the number of collisions can rise to an unacceptable level. This can reduce the amount of available bandwidth on an Ethernet network because so much bandwidth is lost in re transmission.
Ethernet switches greatly reduce the already minor difficulties experienced with the CSMA/CD protocol.

Types of Network:-

1. Broad cast Multi access network ---Ethernet lan 
2. Non Broadcast Multi access network
3. point to point network 
4. Point to multi point network.

 Micro segmentation:-The process of connecting source port and destination port in switch is known as micro segmentation.

Layer 2 broadcast addresses is FF-FF-FF-FF-FF-FF.

Mac Address Structure:-

A Media Access Control address (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802 network technologies including Ethernet. Logically, MAC addresses are used in the Media Access Control protocol sub-layer of the OSI reference model.

Token Ring:-

Token ring local area network (LAN) technology is a local area network protocol which resides at the data link layer (DLL) of the OSI model. It uses a special three-byte frame called a token that travels around the ring. Token-possession grants the possessor permission to transmit on the medium. Token ring frames travel completely around the loop.

This concept was introduced by physical topology ring topology.

FDDI:-

FDDI (Fiber-Distributed Data Interface) is a standard for data transmission on fiber optic lines in that can extend in range up to 200 km (124 miles). The FDDI protocol is based on the token ring protocol. In addition to being large geographically, an FDDI local area network can support thousands of users.

An FDDI network contains two token rings, one for possible backup in case the primary ring fails. The primary ring offers up to 100 Mbps capacity. If the secondary ring is not needed for backup, it can also carry data, extending capacity to 200 Mbps. The single ring can extend the maximum distance; a dual ring can extend 100 km (62 miles).

FDDI is a product of American National Standards Committee X3-T9 and conforms to the open system interconnect (OSI) model of functional layering. It can be used to interconnect LANs using other protocols. FDDI-II is a version of FDDI that adds the capability to add circuit-switched service to the network so that voice signals can also be handled. Work is underway to connect FDDI networks to the developing Synchronous Optical Network.