Data Communication Networks
Lec 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 pointto-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.

• LAN
• MAN
• WAN
Categories of Networks

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