IP datagram format IP protocol version number 32 bits total datagram header length head. type of length (bytes) (bytes) ver length service for “type"of data 16-bit identifier- fHg到 fragment- -fragmentation/ offset max number time to upper header reassembly remaining hops live layer checksum (decremented at each router) 32 bit source IP address upper layer protocol 32 bit destination IP address to deliver payload to Options(if any) E.g.timestamp, record route how much overhead data taken,specify with TCP? (variable length, list of routers 20 bytes of TCP typically a TCP to visit. ▣20 bytes of IP or UDP segment) =40 bytes app layer overhead Network Layer 4-33 Network Layer 4-33 IP datagram format ver length 32 bits data (variable length, typically a TCP or UDP segment) 16-bit identifier header checksum time to live 32 bit source IP address IP protocol version number header length (bytes) max number remaining hops (decremented at each router) for fragmentation/ reassembly total datagram length (bytes) upper layer protocol to deliver payload to head. len type of service “type” of data flgs fragment offset upper layer 32 bit destination IP address Options (if any) E.g. timestamp, record route taken, specify list of routers to visit. how much overhead with TCP?  20 bytes of TCP  20 bytes of IP  = 40 bytes + app layer overhead