EE450, USC, Zahid 1Layered Architecture and Network ProtocolsEE450: Introduction to Computer NetworksProfessor A. ZahidEE450, USC, Zahid 2ProtocolsHuman Protocols:z what’s the time?z I have a questionz Introductions… specific msgs sent… specific actions taken when msgs received, or other eventsNetwork Protocols:z Machines rather than humansz All communication activity in Internet governed by protocolsProtocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receiptEE450, USC, Zahid 3Human vs. Network ProtocolsHiHiGot thetime?2:00TCP connectionrequestTCP connectionreply<file>timeGet http://www.usc.com/grades.htmlEE450, USC, Zahid 4Key Elements of a Protocolz Syntaxz Data formats, compression, encryption, etc..z Signal levelsz Semanticsz Control information such as flow & congestionz Error detection and control mechanismsz Timingz Speed matchingz Sequencingz FairnessEE450, USC, Zahid 5Standardsz Required to allow for interoperability between equipmentz Advantagesz Ensures a large market for equipment and softwarez Allows products from different vendors to communicatez Disadvantagesz Freeze technologyEE450, USC, Zahid 6OSI Reference ModelEE450, USC, Zahid 7Data Transfer in OSIEE450, USC, Zahid 8Layered Communicationsz Peer layers communicate via protocolsz Adjacent layers communicate via service interfacesz Protocol control information (PCI) is added to Service data unit (SDU) at each layer to form a Protocol data unit (PDU)z (SDU)N= (PDU)N+1z (PDU)N= (SDU)N+(PCI)NEE450, USC, Zahid 9Why Layering?Dealing with complex systems:z explicit structure allows identification, relationship of complex system’s piecesz layered reference model for discussionz Modularization eases maintenance, updating of systemz change of implementation of layer’s service transparent to rest of systemz change in one layer doesn’t affect rest of systemEE450, USC, Zahid 10Summary of Layers FunctionalityEE450, USC, Zahid 11The Internet and TCP/IPEE450, USC, Zahid 12Internet Protocol Stackz Application: supporting network applicationsz FTP, SMTP, HTTPz Transport: process-process data transferz TCP, UDPz Network: routing of datagrams from source to destinationz IP, routing protocolsz Link: data transfer between neighboring network elementsz PPP, Ethernetz Physical: bits “on the wire”applicationtransportnetworklinkphysicalDeveloped by the US Defence Advanced Research Project Agency (DARPA) for its packet switched network (ARPANET)EE450, USC, Zahid 13TCP/IP ModelEE450, USC, Zahid 14Message Transmission using TCP/IPEE450, USC, Zahid 15TCP/IP vs. OSI ModelsEE450, USC, Zahid 16EncapsulationsourceapplicationtransportnetworklinkphysicalHtHnMsegmentHtpacketdestinationapplicationtransportnetworklinkphysicalHtHnHlMHtHnMHtMMnetworklinkphysicallinkphysicalHtHnHlMHtHnMHtHnMHtHnHlMrouterswitchmessageMHtMHnframeSwitchRouterEE450, USC, Zahid 17Communications between Networked ApplicationsEE450, USC, Zahid 18Communications between Transport LayersEE450, USC, Zahid 19Network Layer CommunicationsEE450, USC, Zahid 20Link Layer CommunicationsEE450, USC, Zahid 21Addressing in TCP/IPEE450, USC, Zahid 22TCP/IP Layers and AddressesEE450, USC, Zahid 23Link Layer (MAC) AddressesMost local area networks use a 48-bit (6 Bytes) physical address written as 12 hexadecimal digits, with every 2 Bytes separated by a hyphen for example “07-01-02-01-2C-4B”a node with MAC address 10 sends a frame to a node with MAC address 87. The two nodes are connected by a link. At the data link level this frame contains MAC addresses in the header. These are the onlyaddresses needed. The header contains other information needed @ this level. The trailer contains extra bits needed for error detectionEE450, USC, Zahid 24Internetwork Communications An Internet address (in IPv4) is 32 bits in length written as four decimal numbers, with each number representing 1 Byte. The numbers are separated by a dot. For example 128.125.75.9A node with an IP address A and MAC address 10, located on one LAN, to a node with an IP address P and MAC address 95, located on another LAN. Because the two devices are located on different networks, we cannot use MAC addresses only; the MAC addresses only have local significance. What we need here are universal addresses that can pass through the LAN boundaries. The IP address has this characteristic.EE450, USC, Zahid 25Port AddressesA port address is a 16-bit address represented by one decimal number for example 750Data coming from the upper layers have port addresses j and k (j is the address of the sending process, and k is the address of the receiving process). Data are split into two Packets, each retaining the port addresses (j and k). Then in the network layer, IP addresses (A and P) are added to each packet.EE450, USC, Zahid 26Layered Architecture and Networks• Each host needs a unique global address referred to as the IP address• Each application on a multitaskingcomputer needs a unique address, referred to as the Port number, within the computerEE450, USC, Zahid 27Overview of Network Programming: Sockets EE450: Introduction to Computer NetworksProfessor A. ZahidEE450, USC, Zahid 28Application Programming Interfacez The services provided by the operating system that provide the interface between application and the TCP/IP Protocol Suite.ApplicationApplicationNetwork APINetwork APIProtocol AProtocol AProtocol BProtocol BProtocol CProtocol CEE450, USC, Zahid 29API: Socketsz TCP/IP does not include an API definition.z There are a variety of APIs for use with TCP/IP:z UNIX Sockets z Winsock (Windows Sockets)z A socket is an abstract representation of a communication endpoint.z A socket allows the application to “plug in” to the network and communicate with other applicationsz A socket is uniquely identified by the IP address, Port number and the underlying transport layer protocolEE450, USC, Zahid 30Socket TypesEE450, USC, Zahid 31Socket StructureEE450, USC, Zahid 32Socket Descriptor Data StructureDescriptor TableDescriptor Table01234Family: PF_INETFamily: PF_INETService: SOCK_STREAMService: SOCK_STREAMLocal IP: 111.22.3.4Local IP: 111.22.3.4Remote IP: 123.45.6.78Remote IP: 123.45.6.78Local Port: 2249Local Port: 2249Remote Port: 3726Remote Port: 3726EE450, USC, Zahid 33Basic Sockets APIz Clients and Servers differ in some aspects of their use of API and they are the same in other aspectsz Both client and server programs begin by