Intro to WAN

Question 1

Circuit switching

Strengths\Weaknesses

Answer 1

1. Dedicated physical circuit path must exist between sender and receiver for duration of communication
2. Part of circuit can consist of time slots allocated using TDM on trunk links
3. Used extensively in the telephone network

Advantages of Circuit Switching:

1. The dedicated path/circuit established between sender and receiver provides a guaranteed data rate.
2. Once the circuit is established, data is transmitted without any delay as there is no waiting time at each switch.

Disadvantages of Circuit Switching:

1. As the connection is dedicated it cannot be used to transmit any other data even if the channel is free.
2. Dedicated channels require more bandwidth.

Question 2

Packet switching

Strengths\Weaknesses

Answer 2

1. Nodes share bandwidth with each other by sending packets/chunks of data with header/control info
2. Packets are routed independently - no bandwidth reservation
3. Used in modern data networks

Advantages of Packet Switching:

1. Efficient use of Network.
2. Easily get around broken bits or packets.
3. Circuit Switching charges user on the distance and duration of connection but Packet Switching charges users only on the basis of duration of connectivity.
4. High Data Transmission in a Packet Switching is very easy.

Disadvantages of Packet Switching:

1. In Packet Switching Packets arriving in wrong order.
2. Takes Transmission delay.
3. Requires Large amount RAM (Random Access Memory) to handle large amount of data communication in packets.

Question 3

Virtual Circuits

Strengths\Weaknesses

Answer 3

1. Packet-switched networks may establish routes through the switches for particular end-to-end connections. These routes are called virtual circuits – predefined pathways with QoS guarantees
2. A VC is a logical circuit created within a shared network between two network devices
3. Two types of VCs exist:
   Permanent - PVC
   Switched – SVC
4. Used in Frame Relay, ATM, MPLS

Advantages of using a virtual circuit:

1. Since the same direction is followed, the packets are delivered in proper order.
2. As there is no need for packets to contain the complete address, the overhead in the packets are comparatively smaller.

Disadvantages of using a virtual circuit:
1. Since each switch needs to allocate capacity for any generated traffic and also needs to store the call details, powerful switching equipment is essential in virtual circuits.

Question 4

WAN

Answer 4

1. Network that spans large geographical distance
2. Can be used to interconnect LANs
3. Predominately operate at the OSI physical and data link layers
4. Normally subscribe to a service provider to use network resources

Question 5

TDM

Answer 5

Shares available transmission time on a medium by assigning time-slots to users.