ECS152BXin Liu 1 ECS 152B Computer Networks Fall 2003 Prof. Xin Liu

ECS152BXin Liu 2 Highlights prerequisites: ECS150 and ECS152A make sure to follow up the newsgroup messages ucd.class.ecs152b ucd.class.ecs152b.d grading Projects 40% Midterm 20% Homework 10% Final 30%

ECS152BXin Liu 3 Road Map I. Introduction Computer Networks Overview Layered architecture II. IP Protocols Internet Protocol Routing protocols ICMP and IGMP III. Transport Layer UDP TCP

ECS152BXin Liu 4 Road Map IV. Transport Layer Interfaces Socket Socket related system calls I/O Multiplexing V. Networking Applications Network Library Routines File Transfer Protocol (FTP) HyperText Transfer Protocol (HTTP) Telnet / Remote Login Domain Name System (DNS) Remote Procedure Calls (RPC) V. Other Topics

ECS152BXin Liu 5 Computer Networks local network local network Core network internet: network of networks

ECS152BXin Liu 6 Protocols A protocol defines: –the format and the order of the messages exchanged –the actions on receipt/transmission of a message host Network Adapter host Network Adapter Computer Network

ECS152BXin Liu 7 Protocol Example hello yes? 2:30pm time? Time request: TCP connection request TCP connection reply index.html get URL request: (not necessarily typical:)

ECS152BXin Liu 8 Protocols Why use a protocol? –to provide a common language There are so many protocols! Rules: –must be unambiguous and followed exactly e.g., TCP/IP, IP (Internet Protocol)

ECS152BXin Liu 9 The Protocol Stack Physical Transport Network Link Presentation Session Application Old Saying: If you know what you are doing, four layers is enough; if you don’t seven won’t help. Physical Transport Network Link Presentation Session Application TCP, UDP IPv4, IPv6 Ethernet… HTTP, FTP… OSI - 7 layers TCP/IP Suite – 4 layers

ECS152BXin Liu 10 Internet Protocol Suite Layers provide information hiding doesn’t matter what lower level layers use as long as higher layers use the same protocol Link Transport Network Application Link Transport Network Application e.g., supports network applications e.g., transports application-layer messages e.g., routes datagrams from one host to another e.g., transmits individual bits within the frame

ECS152BXin Liu 11 Link Layer: review Transfer datagram from one node to adjacent node over a link Involves device driver in OS and network interface card Physically connecting hosts: encoding, framing, error detection/correction, reliable delivery, access control Example: Ethernet, token rings, etc. “link”

ECS152BXin Liu 12 Network Layer Transport packet from sending to receiving hosts Network layer protocols in every host, router IP (Internet protocol): addressing, routing, forwarding Best effort, unreliable network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical application transport network data link physical application transport network data link physical

ECS152BXin Liu 13 Transport Layer provide logical communication between app processes running on different hosts transport protocols run in end systems –segments, reassembles more than one transport protocol available to apps Internet: TCP and UDP application transport network data link physical application transport network data link physical network data link physical network data link physical network data link physical network data link physical network data link physical logical end-end transport

ECS152BXin Liu 14 Household analogy 12 kids sending letters to 12 kids processes = kids app messages = letters in envelopes hosts = houses transport protocol = Alice to Bob network-layer protocol = postal service

ECS152BXin Liu 15 Protocol Layers Network Link Transport Network Link Application Transport Network Link Application HostA routerHostB Simplifies implementation segmentation/reassembly, error control, flow control, multiplexing, connection setup in different layers There also are some potential disadvantages may duplicate functionality may need info in a non-adjacent layer (e.g., timestamp) Network Link router

ECS152BXin Liu 16 Encapsulation source destination original message Transport Network Link Application Transport Network Link Application

ECS152BXin Liu 17 Demultiplexing source destination original message Transport Network Link Application

ECS152BXin Liu 18 The Internet Protocol Stack source original message Transport Network Link Application Protocol Data Units (PDU) message frame segment datagram software network interface card software mixed Implementation

ECS152BXin Liu 19 Client-Server Model server client client = host that initiates the session (e.g., asks for a Web page; browser) server = host that gives the requested service A typical network has two components: client and server

ECS152BXin Liu 20 Client-Server Model Client-server model: –Web, , file transfer, remote login, news group, p2p, etc. project –SETI: Search for ExtraTerrestrial Intelligence –3 million participants

ECS152BXin Liu 21 Our Class Upper layer protocols –Internet protocols –Transport protocols –Transport layer interface –Networking application Hands-on experience Transport Network Application client server

ECS152BXin Liu 22 Acronym Standardization –Internet Society (ISOC) –Internet Architecture Board (IAB) –Internet Engineering Task Force (IETF) –Internet Research Task Force (IRTF) RFC –Request for comments

ECS152BXin Liu 23 Suggested Reading TCP/IP Illustrated, Vol. 1, Chp. 1 Review ECS 150, 152A