台北科技大学：《计算机网络》（英文版） NP04 8 Internet Protocol (IP)

Internet Protocol (P) Chuan-Ming liu CSIE NTUT Spring04, TAIWAN CSIE NTUT TANAN

CSIE, NTUT, TAIWAN 1 Internet Protocol (IP) Chuan-Ming Liu CSIE, NTUT Spring ’04, TAIWAN

CONTENTS DATAGRAM FRAGMENTATION OPTIONS CHECKSUM IP PACKAGE CSIE NTUT TANAN

CSIE, NTUT, TAIWAN 2 CONTENTS • DATAGRAM • FRAGMENTATION • OPTIONS • CHECKSUM • IP PACKAGE

Position of Ipin TcP/ip protocol suite pplicationSMTP‖ FTPTFTP‖DNs|SNMP IBOOTP layer Transport TCP UDP IGMP ICMP Network IP ayer ARP RARP Data link laver Underlying LAN or WAN technolog eI

CSIE, NTUT, TAIWAN 3 Figure 8-1 Position of IP in TCP/IP protocol suite

Internet Protocol (IP) Unreliable Connectionless Best-effort delivery No error checking CSIE NTUT TANAN

CSIE, NTUT, TAIWAN 4 Internet Protocol (IP) • Unreliable • Connectionless • Best-effort delivery • No error checking

8. DATAGRAM CSIE NTUT TANAN

CSIE, NTUT, TAIWAN 5 DATAGRAM 8.1

Datagram Packets in the ip layer are called datagrams The lengths of different datagrams vary a datagram consists of two parts Header Data The header is 20-60 bytes in length contains information for routing CSIE NTUT TANAN

CSIE, NTUT, TAIWAN 6 Datagram • Packets in the IP layer are called datagrams. • The lengths of different datagrams vary • A datagram consists of two parts: – Header – Data • The header – is 20-60 bytes in length – contains information for routing

IP datagram 20-65536 bytes 20-60 bytes Header Data VER HLEN Service type Total length 4 bits 4 bits 8 bits 16 bits Identification Flags Fragmentation offset 16 bits 3 bits 13 bits Time to live Protocol Header checksum 8 bits 8 bits 16 bits Source ip address Destination ip address Option Figure 8-2

CSIE, NTUT, TAIWAN 7 Figure 8-2 IP datagram

IP Headers 4-byte section presentation ●上1 elds includes Version (ver) Header length(HLEN Differential Services(DS), or service types (ST) Total length Identification Flags Fragmentation offset Time to live Protocol Checksum Source and destinati6FⅠP冱dres

CSIE, NTUT, TAIWAN 8 IP Headers • 4-byte section presentation • Fields includes: – Version (VER) – Header length (HLEN) – Differential Services (DS), or service types (ST) – Total length – Identification – Flags – Fragmentation offset – Time to live – Protocol – Checksum – Source and Destination IP address

IP datagram 20-65536 bytes 20-60 bytes Header Data VER HLEN Service type Total length 4 bits 4 bits 8 bits 16 bits Identification Flags Fragmentation offset 16 bits 3 bits 13 bits Time to live Protocol Header checksum 8 bits 8 bits 16 bits Source ip address Destination ip address Option Figure 8-2

CSIE, NTUT, TAIWAN 9 Figure 8-2 IP datagram

IP Headers 0 8 1619 24 31 VER HLEN DS(ST) TOTAL LENGTH IDENTIFICATION FLAGS FRAGMENT OFFSET TIME TO LIVE PROTOCOL HEADER CHECKSUM SOURCE IP ADDRESS DESTINATION IP ADDRESS OPTIONS CSIE NTUT TANAN

CSIE, NTUT, TAIWAN 10 IP Headers VER HLEN DS(ST) TOTAL LENGTH FLAGS TIME TO LIVE IDENTIFICATION PROTOCOL HEADER CHECKSUM FRAGMENT OFFSET SOURCE IP ADDRESS DESTINATION IP ADDRESS OPTIONS 0 4 8 16 19 24 31