Lecture 2, 2010/3/4
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Stephen Kim dskim@iupui.edu Various services and flexibility Network architectures Grouping a set of related function to a layer A set of protocols Advantage of layered architectures Simplification Interface Flexibility Interface Monolithic ECE/IUPUI Intro to Computer Communication Networks Layered 2-2 Interaction between two peer entities Server/Client Server – a process waiting a request ▪ Listening a specific port in TCP/IP ▪ Httpd (Apache™) , telnetd, ftpd, … Client – a process making a request ▪ A request to server address and the port number ▪ Netscape™, telnet, gftp, ws_ftp, … A connection in a server/client model is a 5-tuple Protocol type, Source address, Destination address Source port number, destination port number ECE/IUPUI Intro to Computer Communication Networks 2-3 Server Client Listening on port 80 Request to 134.68.80.4:80 Connection established Connection established Send a request GET/index.html HTTP 1.0 Send a result code HTTP/1.1 200 Read and send the file <html> <head> … Disconnect the connection ECE/IUPUI Interpret and display the html time Intro to Computer Communication Networks 2-4 What if a request has a failure? Need a connection-oriented service & a reliable underlying layer HTTP Server Protocol HTTP Client Interface Interface 80 #n TCP ECE/IUPUI Protocol Intro to Computer Communication Networks TCP 2-5 DNS (Domain Name System) Convert an IP name to an IP address, or vice versa netlab.ece.iupui.edu 134.68.80.4 UDP/IP - Connectionless SMTP (Simple Mail Transfer Protocol) TCP connection to local SMTP server Work as if connectionless for forwarding the message to remote SMTP server ECE/IUPUI Intro to Computer Communication Networks 2-6 International Organization for Standardization / Open System Interconnection (IOS/OSI) Reference model, but not a real implementation A process on one machine at layer n PDU contains a header and a payload called SDU (Service Data Unit) Communicates with a peer process on the other machine By exchanging PDU (Protocol Data Unit) Header – control information Payload – do not care Layer n protocol - A set of rules governing the behavior of the layer n Terminal A Terminal B n-PDU n-SDU Layer n Entity H Layer n Entity H n-SDU n-PDU ECE/IUPUI Intro to Computer Communication Networks 2-7 Communication between two peer processes is not physical The layer n+1 uses the services provided by layer n through layer n interface, called SAP (Service Access Point). Terminal A Terminal B (n+1)-PDU layer n+1 layer n+1 (n+1)-PDU n-SAP n-SDU n-SAP H layer n layer n H ECE/IUPUI n-SDU n-PDU Intro to Computer Communication Networks 2-8 Maximum PDU size of Ethernet is 1500 bytes How can we send information larger than the maximum thru Ethernet? Segmentation The layer n in a terminal can segment its payload into small pieces Reassembly The layer n in the other terminal put together the small pieces in a payload. Host A Host B (n+1)-PDU n-SDU H ECE/IUPUI n-SDU H (n+1)-PDU n-SDU H Intro to Computer Communication Networks n-SDU H n-SDU H n-SDU H 2-9 International Standard Organization / Open Systems Interconnection Principles A layer should be created where a different level of abstraction is needed. Each layer should perform a well defined function. The function of each layer should be chosen with an eye toward defining internationally standardized protocols. The layer boundaries should be chosen to minimize the information flow across the interfaces. The number of layers should be large enough that distinct function need not be thrown together in the same layer out of necessity. The number of layers should be small enough that the architecture does not become unwieldy. 7 Layers ECE/IUPUI Intro to Computer Communication Networks 2-10 Application Protocol Layer 7 Application Layer 6 Presentation Layer 5 Session Presentation Protocol Session Protocol Transport Protocol Application Presentation Session Layer 4 Transport Layer 3 Network Network Network Network Layer 2 Data Link Data Link Data Link Data Link Layer 1 Physical Physical Physical Physical ECE/IUPUI Communication network boundary Network layer host-router protocol Data link layer host-router protocol Physical layer host-router protocol Intro to Computer Communication Networks Transport 2-11 Deal with the transfer of raw bits over communication channel Electrical aspects Voltage level Signal duration Mechanical aspects Socket type Number of pines Examples Twisted copper wire – telephone wire, 10/100BaseT, … Coaxial cable – CATV, 10Base2, 10Base5, … Radio – cellular phone, Wi-Fi, Bluetooth, Zigbee, WiMax, WiBro, … Optical fiber – WDM, DWDM, ECE/IUPUI Intro to Computer Communication Networks 2-12 Deal with the transfer of frames Framing information Boundary of the frame ▪ Control and address information Check bit for recovering from transmission errors ▪ ▪ prevent a fast transmitter from drowning a slow receiver in data Broadcast networks control access to the shared channel LAN ▪ ▪ acknowledge frames handle with damaged, lost, and duplicate frames Flow controls ▪ attaching special bit patterns to the beginning and end of the frame Sub-layer: Medium Access Control layer (MAC) One-to-one communication over broadcast medium Examples ECE/IUPUI HDLC – High-level Data Link Control PPP – Point-to-Point Protocol SONET – Synchronous Optical Network Intro to Computer Communication Networks 2-13 Transfer of data (packet) over networks Routing Select a path from the source to the destination thru many intermediate network components as switches and routers. Static routing vs. dynamic routing Deal with congestion – temporary traffic surges in a network components forming bottlenecks Differentiation of packet types Heterogeneous Network ▪ Different address scheme ▪ Maximum Transfer Unit (MTU) Political routing ▪ Inter-office emails between Microsoft branches shouldn’t pass through Netscape’s routers. Billing ECE/IUPUI Intro to Computer Communication Networks 2-14 Responsible for the end-to-end transfer of message Segmentation and reassembly Error-free transfer Error detection and recovery Sequencing Flow control Establishing and releasing connections Multiple connections for high throughputs Multiplexing a connection among many session layers for reducing the cost Type of Services Connection-oriented services – error-free point-to-point channel Connectionless services – no guarantee on the correct delivery of the message Example ECE/IUPUI Unix socket interface Intro to Computer Communication Networks 2-15 Enhance a reliable transfer service Control how data is exchanged manage dialogue control ▪ full duplex ▪ half duplex Examples Log in to a remote system Transfer a file between two machine Token management ▪ both side do not attempt the same operation at the same time. Synchronization ▪ Two-hour file transfer with one-hour mean time crashes ▪ The whole transfer would start over again ▪ Insert checkpoints into the data stream ▪ After a crash, continue after the last checkpoint ECE/IUPUI Intro to Computer Communication Networks 2-16 Concern with the syntax and sematic of the information Overcome the difference in data representation Resolve machine-dependencies Character code ASCII, EBCDIC, Unicode, … Big endian or little endian 32-bit word like an integers SUN Sparc, MIPS 4 3 2 1 Intel x86, Dec Alpha 1 2 3 4 The POWER Processor can be configured as either big endian or little endian ECE/IUPUI Intro to Computer Communication Networks 2-17 To provide network services Example HTTP – web browsing application FTP – File transfer between two different systems ▪ different file name convention ▪ different ways of representing text lines SMTP – Electronic mail Virtual terminals – vt100, TN 3270, xterm ECE/IUPUI Intro to Computer Communication Networks 2-18 sending process data Application data Presentation data DT Session SH data Network Presentation PH data Transport Physical Application AH data Session Data Link receivng process data Transport TH Network NH DH Bits Data Link Physical actual data transmission path ECE/IUPUI Intro to Computer Communication Networks 2-19 History Successor of ARPANET (Defense Advanced Research Project Agency) Principles Robustness ▪ If failures occurs in the network, the packets are routed around the failure point. ▪ Multiple paths and globally unique address. Flexibility – No Data link layer or physical layer defined Packet switching networks Best-effort connectionless in the Network layer ▪ “I will do my best to transfer your data, though I cannot guarantee their quality and delivery” ▪ IP packets are exchanged between routers without a connection setup. Two services in the Transport layer ▪ TCP – reliable connection-oriented transfer ▪ UDP – unreliable connectionless transfer Applications ECE/IUPUI remote login, e-mail, file transfer, network management Intro to Computer Communication Networks 2-20 OSI TCP/IP Application Application Presentation Not present in the model Session Transport TCP,UDP Network IP Data Link Network Interface Layer Physical ECE/IUPUI Intro to Computer Communication Networks 2-21 TELNET FTP SMTP TCP DNS RTP Application UDP IP Transport ICMP Network ARP X.25 ECE/IUPUI ATM FR ETHER Intro to Computer Communication Networks Network Interface 2-22 Each host (NIC) is assigned by a globally unique IP address (32-bit) IP address = network address + host address A net mask is used to calculate them Each host (NIC) is also assigned by a machine address, or a physical address Meaningful in one network by router Ethernet uses 6-octect (48-bit). ATM uses 16-octect. Router – consists of two or more network interfaces APP TCP IP NI ECE/IUPUI router IP NI NI Intro to Computer Communication Networks APP TCP IP NI 2-23 data data IP (1,2) IP (1,3) data 1,2 data 1,3 NI 3487 1,3 NI 6537 data ECE/IUPUI 1,2 3487 6537 Intro to Computer Communication Networks 2-24 data data Router Host A IP (1,2) data IP (1,1) 1,2 2,5 data NI 3487 data ECE/IUPUI Host B NI 6543 IP (2,5) (2,3) 1,2 data 2,5 NI 1002 3487 6543 Intro to Computer Communication Networks 1,2 2,5 NI 3903 data 1002 3903 2-25 Data Source Port #, Destin Port # Source IP addr, Destin IP addr, Protocol type Source PH addr, Destin PH addr, Network protocol type ECE/IUPUI Ethernet Header TCP Header IP Header TCP Payload IP Payload Ethernet Payload Intro to Computer Communication Networks Ethernet Tail 2-26 A process waiting a packet on a specific port number Duplicate a connection after establishing Connection? 5 tuple – (PT, SA, SP, DA, DP) ▪ ECE/IUPUI protocol type, source address, source port, destin address, destin port. A server waits on (pt, sa, sp, any-DA, any-DP) Upon a request from the client, any-DA and any-DP are filled with specific value. Server Port Number – 0 to 1023 are reserved to well-known services. Protocol Reserved Port # Comments FTP 21 File Transfer telnet 23 remote login SMTP 25 E-mail DNS 53 Domain name system HTTP 80 World Wide Web Intro to Computer Communication Networks 2-27 API – interface available to programmer socket(), bind(), listen(), accept(), connect(), sendto(), recvfrom(), htonl(), htons(), ntohl(), ntohs() Utility function - gethostbyname(), gethostbyaddr() Support multiple communication protocols Internet Domain Unix Domain Xerox NS Domain (XNS) ATM Domain (Recent progress in several implementation) References Richard Stevens, “Unix Network Programming”, or http://en.wikipedia.org/wiki/Internet_socket ECE/IUPUI Intro to Computer Communication Networks 2-28
