Lecture 5 Flashcards
Network Layer
What does the network layer do?
Moves the packet from a sending host to a receiving host.
How does the network layer on each host sent/receive packets?
The sender will first encapsulate the segments into datagrams. This is sent to the receiver, which unwraps the segments and delivers it to the transport layer on its host.
What is routing?
Determining the path taken by the packets as they flow from sender to receiver.
What is forwarding?
When routers move packets from an input link to an appropriate output link.
What are forwarding tables? What hap
A router determines an index from the value of a field in the packets headers. This index is put into the router forwarding table. The forwarding table can use this value to determine the outgoing link the packet is to be forwarded to. The routing algorithm determines the output link the data is sent to.
What are connect and connectionless services called?
Connectionless services are called datagrams networks.
Connection services are called virtual-circuut networks.
What is the difference between virtual-circuit networks and transport layer networks?
VC networks are host to host, not socket to socket.
A network can provide both connection and connectionless services?
True or False
False. A network can only provide on of the two.
E.g. The internet it connectionless at the network layer, but an atm uses VC networks.
What does a Virtual-circuit consist of?
- A path between the source and destination hosts
- VC numbers (one number for each link along the path)
- The entries in the forwarding table in each router along the path
What always happens in the network layer wheen a new VC network is established?
A new entry for this VC network is added to the forwarding table.
What happens at the network layer when a VC network terminates?
All applicable entries in each forwarding table along the path are removed, as they are no longer needed.
What is VC setup?
When the sender specifies the receivers address and waits got he network to connect to the call.
What does data transfer mean?
Once the VC is established, packets are allowed to flow through the VC network.
What does it mean by VC teardown?
When the sender of receiver informs the network layer of its desire to terminate the VC network. The network will then inform the other end system and the network will update the routers forwarding tables.
Explain Datagram networks.
No setup is required by the network layer.
Packets are forwarded using the destination hosts address. Each router still has a forwarding table to map the destination addresses to link interfaces, to allows the path of the packet to be tracked.
