A routing table required to find the output port for sending the information to its target device in datagram and virtual circuit switching. Show it complete process by diagram. And also write the reason that it is not required in circuit switching
Answers
Explanation:
Packet Switching don’t give packets in order, whereas Circuit Switching provides ordered delivery of packets because all the packets follow the same path.
Since the packets are unordered, we need to provide sequence numbers to each packet.
Complexity is more at each node because of the facility to follow multiple path.
Transmission delay is more because of rerouting.
Packet Switching is beneficial only for small messages, but for bursty data (large messages) Circuit Switching is better.
Modes of Packet Switching :
Connection-oriented Packet Switching (Virtual Circuit) :- Before starting the transmission, it establishes a logical path or virtual connection using signalling protocol, between sender and receiver and all packets belongs to this flow will follow this predefined route. Virtual Circuit ID is provided by switches/routers to uniquely identify this virtual connection. Data is divided into small units and all these small units are appended with help of sequence number. Overall, three phases takes place here- Setup, data transfer and tear down phase.
All address information is only transferred during setup phase. Once the route to destination is discovered, entry is added to switching table of each intermediate node. During data transfer, packet header (local header) may contain information such as length, timestamp, sequence number etc.
Connection-oriented switching is very useful in switched WAN. Some popular protocols which use Virtual Circuit Switching approach are X.25, Frame-Relay, ATM and MPLS(Multi-Protocol Label Switching).
Connectionless Packet Switching (Datagram) :- Unlike Connection-oriented packet switching, In Connectionless Packet Switching each packet contains all necessary addressing information such as source address, destination address and port numbers etc. In Datagram Packet Switching, each packet is treated independently. Packets belonging to one flow may take different routes because routing decisions are made dynamically, so the packets arrived at destination might be out of order. It has no connection setup and teardown phase, like Virtual Circuits.
Packet delivery is not guaranteed in connectionless packet switching, so the reliable delivery must be provided by end systems using additional protocols.
Average Queuing delay = (N-1)L/(2*R)
where N = no. of packets
L=size of packet
R=bandwidth
Processing Delay :
Processing delay is the time it takes routers to process the packet header. Processing of packets helps in detecting bit-level errors that occur during transmission of a packet to the destination. Processing delays in high-speed routers are typically on the order of microseconds or less.
In simple words, it is just the time taken to process packets.
Total time or End-to-End time
= Transmission delay + Propagation delay+ Queuing delay
+ Processing delay
For M hops and N packets –
Total delay
= M*(Transmission delay + propagation delay)+
(M-1)*(Processing delay + Queuing delay) +
(N-1)*(Transmission delay)
For N connecting link in the circuit –
Transmission delay = N*L/R
Propagation delay = N*(d/s)