Computer Network Unit 1 q what are the topologies in computer n/w ?

Unit 3
Q 1. What do you mean by Virtual circuit and Datagram ?
Ans:
Datagram :
a self-contained, independent entity of data carrying sufficient information to be routed from the source to the destination computer without reliance on earlier exchanges between this source and destination computer and the transporting network.

Virtual ckt :

In telecommunications and computer networks, a virtual circuit (VC), synonymous with virtual connection and virtual channel, is aconnection oriented communication service that is delivered by means of packet mode communication. After a connection or virtual circuit is established between two nodes or application processes, a bit stream or byte stream may be delivered between the nodes; a virtual circuit protocol allows higher level protocols to avoid dealing with the division of data into segments, packets, or frames.


Q 2. What is Adaptive and Non adaptive algorithm ?
Ans: Adaptive Algorithm :
An adaptive algorithm is an algorithm that changes its behavior based on the resources available. For example, stable partition, using no additional memory is O(n lg n) but given O(n) memory, it can be O(n) in time.

Non adaptive algorithm :

When a ROUTER uses a non-adaptive routing algorithm it consults a static table in order to determine to which computer it should send a PACKET of data. This is in contrast to an ADAPTIVE ROUTING ALGORITHM, which bases its decisions on data which reflects current traffic conditions.


Q 3. What is responsibility of network layer ?
Ans : following responsibilities,

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  Routing: routes frames among networks.
  
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  Subnet traffic control: routers (network layer intermediate systems) can instruct a sending station to "throttle back" its frame transmission when the router's buffer fills up.
  
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  Frame fragmentation: if it determines that a downstream router's maximum transmission unit (MTU) size is less than the frame size, a router can fragment a frame for transmission and re-assembly at the destination station.
  
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  Logical-physical address mapping: translates logical addresses, or names, into physical addresses.
  

Subnet usage accounting: has accounting functions to keep track of frames forwarded by subnet intermediate systems, to produce billing information