Forwarding Approaches

Question 1

What is a datagram/connectionless?

Answer 1

Is a self contained, independent unit of data, has complete destination address, uses a forwarding table. Easy to figure out for small networks, but harder for larger networks since it can contain multiple paths between a pair of hosts. Data is routed independently.

Question 2

How does a datagram work?

Answer 2

1. Host can send packet anywhere, anytime
2. Any packet arrives can be forwarded by switch
3. Sender won’t know if network can deliver
4. Packets are forwarded independently but packets can use different paths between source and destination

Question 3

What is virtual circuit/connection oriented?

Answer 3

Virtual circuit is connection oriented, needs a connection state in each switch between source and destination using a VC table. New connection link is assigned a new VCI for connection, as routes are established before data transfer.

Question 4

VC vs. Datagram

Answer 4

VC:
- setup needed before sending data
- less overhead packet
- all packets follow same route
- fail = connection breaks
- after fail, needs clean up
Datagram:
- can send anytime
- more overhead packet
- packets take different routes
- can handle fails
- no clean up after fail

Question 5

What is source routing?

Answer 5

Information about network topology from source host, assumes that switch knows topology but doesn’t know where big header is. Sender will specify the path through network for packet to follow.