Saturday, April 25, 2015

Let us know Computer Networkings that are behind the Internet(an update)




Computer network means a collection of autonomous computers interconnected by a single technology.
The internet is a network of networks & the web is a distributed system that runs on top of the internet.

Examples of Networks-
1.Communication
2.Transportation
3.Social
4.Biological
5.Utilities

Components of a network-


  • Server                           

1.Dedicated Server
2.Non Dedicated Server

Dedicated Server
We cannot use dedicated servers as a workstation & they are entirely dedicated to their connected workstations. Users access shared directories & resources on dedicated server.Eg. Novel NetWare.

Non dedicated Server
The machine used as a server can also operate as a workstation.


  • Workstation


When a computer is connected to a network, it becomes a node on the network & is called a workstation or client.


  • Network Interface Card(NIC)

Each computer attached to a network requires a network interface card(NIC) that supports a specific networking scheme such as Ethernet, ArcNet or Token Ring.


  • Cabling System



Shared Resources & Peripherals


Network Fundamentals

1.
Local Area Network(LAN)
LAN
a)single building LAN
b)Multiple building LAN


LAN are privately owned networks within a single building or campus of up to a few kilometers in size.
LANs are distinguished from other kinds of networks by 3 characteristics
1)their size
2)their transmission technology
3)their topology

1.LANs are restricted size,which means that the worst-case transmission time is bounded.

2.LANs may use a transmission technology consisting of a cable to which all the machines are attached like the telephone company. Traditional LANs run at speed of 10 Mbps to 100 Mbps,have low delay(microseconds or nanoseconds) & make very few errors.Newer LANs operate at up to 10 Gbps.
3.Topologies for broadcast LANs are bus and ring.
Bus network

In a bus network, at any instant at most 1 machine is the master & is allowed to transmit. All other machines are required to refrain from sending. An arbitration mechanism is needed to resolve conflicts when 2 or more machines want to transmit simultaneously.
IEEE 802.3,popularly called Ethernet is a bus based broadcast network with decentralized control, usually operating at 10Mbps to 10Gbps.


Advantages of bus n/w

1)Short cable length & simple wiring layout because there is a single common data path connecting all nodes.

2)Resilient Architecture
Simplicity in architecture that makes it very reliable from a h/w point of view.

3)Easy to Extend
Additional node can be connected at any point along its length.

Disadvantage
1)Fault diagnosis is difficult
Control of n/w is not centralized. This means that detection of a fault may be performed from many points in the n/w.

2)Fault isolation is difficult
In case where the fault is in the n/w medium itself,an entire segment of the bus must be disconnected.

3)Repeater configuration
When a bus n/w has its backbone extended using repeaters,reconfiguration may be necessary.


Ring

In a ring n/w (loop n/w),several devices or computers are connected to each other in a closed loop by a single communication cable. Here data must travel around the ring to each station in turn until they arrive at the station.A ring can be unidirectional or bidirectional.

    Broadcast n/w can be further divided into static & dynamic, depending on how the channel is allocated.

   Static allocation uses round robin algorithm, allowing each machine to broadcast only when its time slot comes up.

Dynamic allocation method for a common channel are either centralized-there is eg. a bus arbitration unit,which determines who goes next or decentralized -there is no central entity, each machine must decide for itself whether to transmit.

Advantages of Ring n/w

1)Short cable length-A ring topology, is comparable to that of bus & is small relative to that of star.Less connection will be needed,which will in turn increase n/w reliability.

2)No wiring closet space required:since there is only 1 cable connecting each node.

3)Suitable for optical fibre:because traffic on a ring travel in 1 direction.


Disadvantage of Ring n/w

1)Node failure causes n/w failure. If 1node fails to pass through itself,entire n/w has failed & no traffic can flow until the defective node has been removed from the ring.

2)Difficult to diagnose fault:The fault if 1 node will affect all others.

3)N/w reconfiguration is difficult: For a very big ring n/w it is not possible to shut down a small section of a ring.Reconfiguration will have to be done.


Continued on Page 2 - MAN