Data Communication NetworksLec 3

Physical Structure

• Point-to-point• Multipoint

Point-to-point

Multipoint

Physical Topology

• Refer to way in which network is laid out physically.– Mesh– Star– Bus– Ring

Mesh topology

• In mesh, every device has a dedicated point-to-point link to every other device.

• Link carries traffic only between the two devices it connects.

Advantages of Mesh Topology

• Each connection carries its own data load, eliminate traffic problems.

• robust• Privacy and security

Disadvantages of Mesh topology

• Amount of cabling.• Installation and reconnection.• Expensive.

Mesh topology

Star topology

• Each device has dedicated point-to-point link only to a central controller, using a hub.

• Does not allow direct traffic between devices.• All communication is through controller.

Advantages of Star Topology

• Each device needs one link and one port to connect to any number of others.

• Easy to install and reconfigure.• Less cabling. • Robustness, one link fails, only that is affected.• Hub can monitor link problems and bypass

defective links.

Disadvantage of Star Topology

• Dependency on a single point, the hub.

Star Topology

Bus Topology

• One long cable acts as a backbone to link all devices in the network.

• Nodes are connected to the bus cable by drop lines and taps.

Advantages of Bus Topology

• Ease of installation.• Less cabling.

Disadvantages of Bus topology

• Difficult to add new devices.• Signal reflection at the taps cause degradation

in quality.• Adding new device require modification or

replacement of the backbone.• Damaged area causes noise.

Bus topology

Ring topology

• Each device has a dedicated point-to-point connection with only the two devices on either side.

• Signal is passed along the ring in one direction, from device to device, until reaches destination.

• repeater

Advantages of Ring topology

• Easy to install and reconfigure.• Device is linked to only immediate neighbors,

add or remove require changing two connections.

Disadvantages of Ring Topology

• Break in ring , can disable entire network.

Ring topology

Hybrid topology

Network Models

• Networks are created by different entities.• Standards are needed.• OSI model and internet model.• OSI(open systems interconnection) define 7

layer network.• Internet model defines 5 layer network.

Categories of Networks

• LAN• MAN• WAN

Local Area Network(LAN)

• Privately owned and link the devices in a single office, building or campus.

• Designed to allow resources to shared personal computers e.g. hardware, printer data etc.

• Engineering workstations or accounting PCs.• Servers to clients.• Restrictions for number of users.• LAN topologies.• Data rates

LAN

Wide area Network(WAN)

• Provides long distance transmission of data.• Large geographical area that comprise of

country or even whole world.• Switched WAN and point-to-point WAN.• Switched WAN connects the end systems,

usually a router that connects to LAN or WAN.• Point-to- point WAN is a leased line from

telephone or cable TV , that connects to ISP.

WAN

Metropolitan Area Network(MAN)

• Lies between size of LAN and WAN.• Covers the area inside city or a town.

Internetwork

• LAN , WAN and MAN are not seen in isolation.• Mostly are interconnected, form an

internetwork or a internet.

internetworks