Data Segmentation and Token Ring For Networking.

Segmentation:

• As an Ethernet network grows and more stations are added to the LAN, performance can drop significantly.
• Ethernet is a shared media network; when a lot of stations have data to transmit, the net gets congested and many collision occur.
• Segmentation is the solution.
• Segmentation is the process of splitting a larger Ethernet network into two or more segments linked by brides or routers.
• The resulting segments have fewer stations to contend with for access to the net and the router or bride transfer data from one segment to the other only when the destination for the data is on the other segment. The rest of the net traffic stays in the segment where it belongs.

Token Ring:

Token Ring was developed by IBM as a robust and highly reliable network.

Specification:

Cable type                                                                  UTP, STP or fiber-optic

Maximum MSAUs                                                      33

Maximum nodes                                                         260

Max dist between node and MSAU                            45.5 m for UTP, 100m

Max patch cable distance connecting MSAUs             45.5m UTP, 200m STP, 1 Km fiber-optic

Min patch cable dist connecting MSAUs                      2.5m

Max cumulative patch cable dist connecting all MSAUs   121.2m UTP, several Km for fiber-optic

How Token Ring Works:

• The ring passes a free token around the ring in one consistent direction.
• A node receives the token from its nearest active upstream neighbor and passes it to its nearest active downstream neighbor.
• If a station receives a free token, it knows it can attach data and send it on down the ring.
• Each station is given an equal chance to have the token and take control in order to pass data.
• Each station in the ring receives the data from the busy token with data attached and repeats the token
• and data, exactly as it received them, to the next active downstream neighbor on the ring.
• The data is received and retransmitted by each node on the network until it has gone full circle.

Advantages and Disadvantages:

• Token Rings continues to operate reliably under heavy loads
•  Built-in diagnostic and recovery mechanisms
• Token Ring makes connecting a LAN to an IBM mainframe easier
• Fault-tolerance features are provided through ring configuration

Disadvantages:

• Token Ring cards and equipments are more expensive than Ethernet
• Token Ring can be very difficult to troubleshoot and requires considerable expertise

FDDI

FDDI:

• Fiber Distributed Data Interface (FDDI) is another ring-based network.
• FDDI uses fiber-optic cables to implement very fast, reliable networks.
• FDDI uses a token-passing scheme to control network access.
• Several FDDI devices can transmit data simultaneously.
• A token is passed around the ring, and the possessor of the token is allowed to transmit FDDI frames.
•  A FDDI network may have several frames simultaneously circulating on the network.
• This is possible bcz the possessor of the token may send multiple frames, without waiting for the first frame to circulate all the way around the ring before sending the next frame.
• The possessor of the FDDI token is also allowed to release the token and send it to the next station in the ring as soon as it is through transmitting frames, rather than having to wait for the frames to make it all the way around the ring.

Different Kinds Of Network Topology In Computer Networks

The way in which the connections are made is called the topology of the computer network. Now I am discussing about network topology, Network topology specifically refers to the physical layout of the network, especially the locations of the computers and how the cable is run between them.

Four most common topologies are:

• Bus                       
•  Star
•  Ring
• Mesh

 Bus Topology:

Bus topologies

 All the devices on a bus topology are connected by one single cable. When one computer sends a signal up the wire, all the computers on the network receive the information, but only one accepts the information. The rest regrets the message. One computer can send a message at a time. A computer must wait until the bus is free before it can transmit. When the signal reaches the end of the wire, it bounces back and travels back up the wire. When a signal echoes back and forth along an unterminated bus, it is called ringing. To stop the signals from ringing, attach terminators at either end of the segment. The terminators absorb the electrical energy and stop the reflection.

Advantages and disadvantages of network topology:

• advantage of network topology

1. The bus is simple, reliable in small network, easy to use and understand
2. Requires the least amount of cable to connect the computers and less expensive
3.  Easy to extend the bus

• Disadvantage of network topology

1. Heavy network traffic can slow a bus considerably
2. Each barrel connector weakens the electrical signal
3.  Difficult to troubleshoot a bus

  Star Topology:

Star Topology 

 All the cables run from the computers to a central location, where they are all connected by a device called a hub. Each computer on a star network communicates with a central hub that resends the message either to all the computers or only to the destination computers. Hub can be active or passive in the star network Active hub regenerates the electrical signal and sends it to all the computers connected to it. Passive hub does not amplify or regenerate signal and does not require electrical power to run. We can expand a star network by placing another star hub.

Advantages:

• Easy to modify and add new computers to a star net
• Center of a star net is a good place to diagnose network faults
• Single computer failure do not necessarily bring down the whole net
• Several cable types can be used with the hub

Disadvantages:

• Central hub fails, the whole network fails to operate
• Many star networks require a device at the central point to rebroadcast or switch network traffic.
• Costs more for cabling in star net than bus.

Ring Topology:

Ring Topology 

 Each computer is connected to the next computer ,with the last one connected to the first. Every computer is connected to the next computer in the ring, and each retransmits what it receives from the previous computer. The message flow around the ring in one direction. Some ring networks do token passing. It passes around the ring until a computer wishes to send information to another computer. The computer adds an electronic address and data and sends it around the ring. Each computer in sequence receives the token and the information and passes them to the next until either the electronic address matches the address of the computer or the token returns to the origin. The receiving computer returns a message to the originator indicating that the message has been received. The sending computer then creates another token and place it on the network, allowing another station to capture the token and being transmitted.

Advantages:

• No computer can monopolize the network
• The fair sharing of the network allows the net to degrade gracefully as more user are added. 

Disadvantages:

• Failure of one compute can affect the total network
• Difficult to troubleshoot
• Adding or removing Computers disrupts the network 

Mesh Topology:

Mesh Topology

 The mesh topology connects all devices (nodes) to each other for redundancy and fault tolerance. It is used in WANs to interconnect LANs and for mission critical networks like those used by banks and financial institutions. Implementing the mesh topology is expensive and difficult.

 Advantages:

• Fault tolerance
• Guaranteed communication channel capacity
• Easy to troubleshoot

Disadvantages:

• Difficulty of installation and reconfiguration
• Cost of maintaining redundant link