28-03-2012, 04:30 PM
PACKET overview
PACKET OVERVIEW.pptm (Size: 161.6 KB / Downloads: 29)
WHAT IS PACKET-
A packet is the unit of data that is routed between an origin and a destination on the internet and any other packet-switched network.
Packet is the smallest unit of data that travels across a network.
For example-Internet is a packet-switched network in which data flows in the form of a packet.
Identification
A source node gives a unique ID to each packet.
Identification, Flags, Fragmentation offset fields are used for fragmentation (will be covered later)
Time to Live (TTL)
A packet has a limited lifetime in the network to avoid zombie packets.
Designed to hold a timestamp, and decreased by each router. A packet is discarded by a router if TTL is zero.
Revised to hold the maximum number of hops the packet can travel thru the network. Each router decrements it by one.
Header checksum
Refer RFC 1071
An IP header is slightly modified by each router. At least TTL field.
The checksum must be re-calculated by routers which is a kind of general compuers with more than one network interface.
The checksum must be efficiently calculated with no need of special hardware.
SUMMARY
A packet is the smallest unit of data that travels across a network.
Routing the packet by consulting the routing table for each incoming packet and find the i/f that the packet must be sent to
When all the packets reach the destination then packets are reassembled to get the original data.