Netwirk Layer

Question 1

Characteristics of subnet:

Answer 1

Error prone

Question 2

What is a Datagram:

Answer 2

An independent self contained message, whose arrival, arrival time and content are not guaranteed. Each packet is independently routed and contains address details.

Question 3

What protocol does network layer in the Internet use?

Answer 3

IP - the principal communications protocol in the Internet suite for relating datagrams

Question 4

What are the two main classes of routing algorithms:

Answer 4

Static (non adaptive) and dynamic (adaptive).

Question 5

What defines the best route:

Answer 5

Queues, cost, error rates as bandwidth.

Question 6

What are the properties for a good routing algorithm:

Answer 6

Correctness, simplicity, robustness, fairness and optimality.

Question 7

Characteristics of static routing:

Answer 7

Decisions made offline, current traffic/topology not considered. Examples: shortest path, flow based, flooding

Question 8

What algorithm is used I. Shortest path routing? Briefly explain…

Answer 8

Dijkstra’s Algorithm. At start no path known, mark first node, examine each node in turn, label shortest paths until destination reached.

Question 9

Characteristics of dynamic routing:

Answer 9

Decisions made online, current traffic/topology considered. Examples: distance vector, link state.

Question 10

Briefly describe vector routing:

Answer 10

Based on router tables, tables updated regularly, all routers talk to neigh out detailing best path to all routers, this plus own estimate is used to update own table. Initially used on Internet but reacts badly to bad news.

Question 11

What is the principal network layer protocol used?

Answer 11

IP RFC 760

Question 12

List IP protocol header format:

Answer 12

Version, IHL (header length), type of service, total length (length of Datagram - 65535), ID (to identify fragmented datagrams enroute), fragment offset (to rebuild Datagram), time to life (8 but lifetime allows 255 hops max), protocol (TCP/UDP), source / destination address.

Question 13

Options are at end of IP Datagram. Give 5 options:

Answer 13

Security, strict source routing (complete path), loose source routing (list of routers not to be missed), record route (each router appends IP address), time stamp ( each routers appends address and time stamp.

Question 14

What does the network layer do?

Answer 14

It is concerned with routing issues, getting packets from source to destination.