Computer Networks

Ethernet and token bus are protocols at the data link layer and a bridge is used when two networks have different data link layers but the same network layer.

Its main task is routing and congestion control.

It is used at the physical layer and just forwards bits from one network to another.

It is concerned with all aspects of information representation including data encoding and compression.

Upon detecting a collision, stations abort the transmission and saves time and bandwidth.

Collision occurs during the contention period.

This ensures low delay at low loads and good channel efficiency at high loads.

It multiplexes several transport connections onto the same network connection to reduce cost and is a true end-to-end layer.

This layer solves the problems caused by lost, damaged and duplicate frames.

When the token holder crashes along with the token, the ring initialisation algorithm is used and Claim_token control frame is sent.

Crash recovery is a function of the transport layer.

The delaying acknowledgements to be sent with next frame is piggybacking.

Both (1) and (2) use pipelining.

It is also known as polynomial code.

It always chooses the shortest path because it chooses every possible path in parallel.

It uses both global and local information.

Router is needed when two networks use the same transport layer but have different network layers. A router can convert token bus frames to the form required by X.25 n/w.

This station transmits with probability p if channel is idle with probability q = 1 - p. It defers until the next slot and so is applied to slotted channels.

Based on the optimality principle that set of optimal routes from all sources to a given destination form a tree rooted at the destination called sink tree.

X.21 is a digital signaling interface.

IMPs are divided into regions with each IMP knowing all details of routing in its own region and nothing about other regions; is effective for large networks.

Idempotent operations can be repeated over and over with no harm and hence this semantics is ideal where client keeps trying until it gets a proper reply so that it knows the operation is performed one or more times.

It cannot really solve congestion problems because computer traffic is bursty.

Three-way handshake is useful to solve the problem of duplicate connection requests.

It measures number of bytes of user data transferred per sec, over a time interval.

When a client crashes after starting a RPC , the server whose process continues to run is called an orphan and causes wastage of CPU cycles and other resources.

It is a context dependent encoding.

It is measured by Connection Release Failure Probability.

Both vigenere cipher and transposition cipher are block ciphers.

The most sophisticated terminals with built-in microprocessors and allow local editing, macros and other facilities.