Lecture-5

Physical Structure:

Network attributes: Line Configuration / Type of connection, Topology

Line Configuration

Refers to the way the devices are connected by a link. A link is physical or wireless connection between one or more devices.

Types of line configuration

Point-to-Point

This type of configuration is used for line-of-sight communication when the two communicating devices are connected physically by a single wire or by a line-of-sight microwave link. Main characteristics are:

Dedicated link between two devices.

Whole capacity of the channel is reserved.

Uses actual length of wire or cable to connect two ends.

Microwave or satellite links can be established.

Examples:

Connection of devices in mesh topology.

Connection between remote control and operating device such as CD player, television set, home theater etc.

A simple example of type of connectivity between the two machines are:

  1. Straight Cable: Used for communication between two similar type of communicating device as computer to hub/switch. The CAT-5 cable connection to RJ45 is pin-to-pin
  2. Cross Cable: Used for communication between two similar type of communicating device as computer to computer. The CAT-5 cable connection to RJ45 is pin 1-3, 2-6 as shown below:

Point-to-Multipoint

This configuration is used when the medium is shared by multiple devices. This is also known as multi-drop configuration. A multipoint also called multi-drop is one in which more than two specific devices share a single link. In this connection the capacity of the channel is shared, either spatially or temporally. If several users can use the link simultaneously, it is spatially shared connection. If users must take turns, it is time shared connection. Figure shows the configuration.

More than two devices share the same link.

Capacity of channel is shared spatially or temporarily.

Allows broadcasting packets over the network.

Each device is able to communicate with each other.

Examples:

A radio station.

Video Conference.

Topology: It defines the way in which the devices are physically connected. Two or more devices connect to a link. Two or more link form a topology.

Type of topology:

  1. Mesh Topology: No. of point to point unidirectional links required = n(n-1) and bidirectional links = n(n-1)/2. Advantage: dedicated link guarantees fault tolerance. Robust, Privacy/Security,failure of one link does not only that device is affected not entire. The message is visible only to the recipient. Fault can be easily located.. Disadvantage: Large no. of cabling as the devices increase, costly, Space due to more cabeling.
  2. Star Topology : Dedicated point to point link to central controller called hub. Easy to install and reconfigure, Robustness. Less cabling than mesh but more than bus bus or ring). Used in LAN. Disadvantage-if hub goes down the whole network will go down.
  3. Bus Topology: Is multipoint which uses a long backbone cable. Nodes connected by tap and drop line. Some energy of signal is transformed into heat as it travels in long cable, so the signal gets weaker. So there is a limit on the number of taps or the distance between the taps. Advantage – easy to install, less cabling than mesh and star. Disadvantages- difficult fault isolation and reconnection. A fault or break in cable connection stops the communication. Difficult to add device as signal reflection at taps can degrade the quality.
  4. Ring Topology:- Each node has point-to-point connection. A signal is passed in one direction from device to device until it reaches the destination; each device acts as a repeater. Advantage:- easy installation and reconfiguration. Adding or deleting a device requires changing only two connections. If a device does not receive a signal in a specified time an alarm is generated for network operator. Disadvantage- A break in link can disable the whole network. This weakness can be overcome by using dual ring.

Type of Networks:

  1. LAN- were designed for resource sharing. It is limited in size and spanning a office, a building or campus
  2. MAN-Metro Area Network- It is spread across a big city, or a state.
  3. WAN:- Has a wide geographic span, a town, state or country or world.

LAN / MAN
A LAN connects the hosts / WAN connects the switches, routers or modems
A LAN is privately owned / WAN is run by communication companies
The company that owns it also uses it / Leased by an organization for use

Examples of WAN are :

  1. Point-to-point WAN: connects two communicating device through wire or air
  2. Switched WAN:

Questions:

  1. What do you understand by line configuration? What are it types?
  2. Explain various topology with advantage and disadvantage of Each.

Quiz:

Which of the following is/are example(s) of point-to-point topology.

(a)Bus Topoloy

(b)Start Topology

(c)Ring Topology

(d)Mesh Topology

Which of the following are robust topology

(a)Bus Topoloy

(b)Start Topology

(c)Ring Topology

(d)Mesh Topology