COP 4930 Computer Network Projects Summer C 2004 Prof. Roy B. Levow Lecture 9

IP Layer  IP provides connectionless service over the internet  IP Datagram consists of –Header: Control Information –Data Area: Application Data  Header and Data Area are variable length –Data can be from 1 to 64K octets

IP Datagram Header

IP Datagram Header.2  VERS = Version  H.LEN = Header Length, 32-bit multiples  TYPE = Type of data, TCP or UDP  TOTAL LENGTH = Octets in Header plus Data Area  TIME TO LIVE = # hops until death  PADDING = 0’s to make multiple of 32 bits

UDP: Datagram Transport  User Datagram Protocol characteristics –End-to-end –Connectionless –Message-oriented –Best-effort –Arbitrary interaction  1-1, 1-many, many-1, many-many –Boradcast and multicast –Operating system independent

UDP Datagram Format

UDP Datagram Format.2  Checksum is optional –If present, it checks a pseudo header including source and destination IP addresses and the IP type field  Message length is Header plus Data Area

UDP Encapsulation

TCP: Reliable Transport Service  Transmission Control Protocol –Connection Oriented –Point-to-point –Complete reliability –Full Duplex (both ways) –Stream Interface –Reliable Connection Startup –Graceful Connectin Shutdown

TCP Window  Window specifies how many octets may be sent –Specified by receiver  Window advisement –Based on buffer size –ACK specifies octets received in window –Window reduces until another window advisement allows more data

TCP Window.2

Three-Way Handshake  Guarantees connections are established reliably

Three-Way Handshake.2

TCP Segment Format

TCP Segment Format.2  Sequence Number = octet number of first byte of outgoing data  Ack Number = last octet acknowledged  Window = number of octets beyond Ack Number that can be sent

Ethereal  Packet sniffer 