Networks Types. Spring 2002Computer Network Applications Data Transfer During the ’70s: Minicomputers became affordable; Need to communicate information;

Networks Types

Spring 2002Computer Network

Applications

Data Transfer During the ’70s:

Minicomputers became affordable; Need to communicate information; Data transferred using removable

storage device---tapes, floppy. Drawback:

(very) slow


Applications

Point-to-Point (Direct) Connection Dedicated circuit boards connected by cable; To transfer data from A to B:

A writes on its circuit board; A’s board transfers data to B’s board; B reads data from its board.

A B


Applications

Point-to-Point Connection (cont.) Pros:

High transfer speed; Secure connection;

Cons: Difficult to add a new computer to a set of

communicating computers. Difficult if communication is between heterogeneous

computers; Expensive: circuit boards needed for every pair of

communicating computers;

How many boards would you need to connect 5 computers via this method?


Applications

PC 1

PrinterPC 2

File ServerPC n

Local Area Network (LAN) A single shared medium, usually a

cable, to which computers can attach.


Applications

Local Area Networks (cont.) Designed and developed for communications

and resource sharing in a local work environment (room, campus, building).

Because sharing occurs: Cost decreases Computers have to coordinate the use of the

network; Overall, LANs connect more computers than

any type of network.


Applications

Connecting a Computer to a LAN Requires a network interface; A network interface consists of:

a circuit board that plugs into the computer A cable that connects the circuit board to

the LAN; The network interface isolates a

computer from the LAN heterogeneous computers can communicate across the LAN.


Applications

LAN Topologies

Star Topology Bus Ring


Applications

Star Topology Connections are made from all connected machines to one central

place, called a hub. The hub: accepts messages from the sending computer, and sends

data to recipient.


Applications

Star Topology (cont.) Pros:

Some degree of fault tolerance: the failure of any link does not affect the other computers;

Cons: Expensive (the hub is a dedicated

computer); If the hub fails, no connection is

possible.


Applications

Ring Topology Messages in the network are passing from machine to machine. This gives controlled and stable data traffic in the network. No central control or configuration of the traffic.

RING


Applications

Ring Topology (cont.) Sending a message:

There is a special message, called token; Exactly one token exists on the ring at any time

which is passed along the ring; To send data, a computer waits for the token to

arrive, and then transmits one message; The message is transmitted to the next computer,

and then to the next, until it arrives back to the sender.

After the message is transmitted, the computer holding the token, passes the token to the next computer in the ring.


Applications

Ring Topology (cont.) Pros:

Requires less wire than star; Less expensive;

Cons: If any cable is cut, the entire network is

disabled. May incur delays: A computer has to

pass the token even if it has more messages to transmit and nobody else does.


Applications

Bus Topology Each unit is connected to a cable. Ex: Ethernet network; original transmission rate: 10 Megabits/s;

now: 1000Megabit/s.

BUS


Applications

Bus Topology (cont.) Sending a message:

The sender sends a message only when the cable is not in use;

The message propagates to both ends of the cable; The receiver process the message (all computers

have to check if they are the intended destination)

Collisions: A collision occurs when two computers try to send in

the same time garbled transmission; When a collision is detected; each computer have to

wait a randomly chosen time before retransmitting.


Applications

Bus Topology (cont.) Pros:

No delays when only one computer wants to transmit;

Cons: If the bus fails, no transmission possible. Limited number of communicating parties

(the bus < 500 m, >3m between two connections)

Generally: each topology has adv. and disadv.;


Applications

Wide Area Networks (WANs) Span a large geographic area, cross public

property; Scalable: allow many computers to send

data simultaneously; Often based on services provided by 3rd

party companies, like telephone networks, for transmission from one node to another;

Can be used to connect several LANs together;


Applications

Packet Switches A WAN is constructed from many switches; A switch moves message fragments called

packets from one connection to the other; A switch is a dedicated computer, with two

types of connections: High-speed connections with other switches; they

can be: leased phone lines, optical fibers, microwave, satellite.

Low-speed connection: used to connect with an individual computer, or a LAN.


Applications

Switched Network

SwitchSwitch

Switch

High speed connection


Applications

Transmitting messages across a WAN Store and forward technique:

When a packet arrives at a switch: it is stored into its internal memory; the processor is informed of its arrival;

The processor examines the packet and if the destination is idle, then the packet is

forwarded to the destination. Otherwise, it places the packet in a queue---

it will be sent when the destination is idle.


Applications

WAN (cont.) Pros:

Scalable Many messages can be sent simultaneously; A message passes only through switches Fault tolerant: if a switch fails, another route

can be found; Cons:

expensive

Documents

Networks Types. Spring 2002Computer Network Applications Data Transfer During the ’70s: Minicomputers became affordable; Need to communicate information;