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Session 2. Application and Layered Architectures

Learn about communication networks, layered architectures, protocols, and various services in computer communication networks.

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Session 2. Application and Layered Architectures

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  1. Stephen Kim dskim@iupui.edu Session 2.Application and Layered Architectures

  2. Communication Networks • Various services and flexibility • Network architectures • Grouping a set of related function to a layer • A set of protocols • Advantage of layered architectures • Simplification • Flexibility Interface Interface Layered Monolithic Intro to Computer Communication Networks

  3. Example of Protocol • 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 Intro to Computer Communication Networks

  4. Example of Protocol, http (1) 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> … Interpret and display the html Disconnect the connection time Intro to Computer Communication Networks

  5. HTTP Server HTTP Client Protocol Interface Interface 80 #n TCP TCP Protocol Example of Protocol, http (2) • What if a request has a failure? Need a connection-oriented service & a reliable underlying layer Intro to Computer Communication Networks

  6. Other Examples • 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 Intro to Computer Communication Networks

  7. Terminal A Terminal B n-PDU n-SDU H Layer n Entity Layer n Entity H n-SDU n-PDU OSI Reference Model • International Organization for Standardization / Open System Interconnection (IOS/OSI) • Reference model, but not a real implementation • A process on one machine at layer n • Communicates with a peer process on the other machine • By exchanging PDU (Protocol Data Unit) • PDU contains a header and a payload called SDU (Service Data Unit) • Header – control information • Payload – do not care • Layer n protocol - A set of rules governing the behavior of the layer n Intro to Computer Communication Networks

  8. (n+1)-PDU layer n+1 layer n+1 (n+1)-PDU n-SAP n-SAP n-SDU H layer n layer n H n-SDU n-PDU Interface and Service • 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 B Terminal A Intro to Computer Communication Networks

  9. Host A Host B (n+1)-PDU (n+1)-PDU n-SDU H n-SDU H n-SDU H n-SDU H n-SDU H n-SDU H Segmentation and Reassembly • 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. Intro to Computer Communication Networks

  10. ISO/OSI Reference Model • 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 Intro to Computer Communication Networks

  11. Application Application Protocol Application Layer 7 Presentation Presentation Presentation Protocol Layer 6 Session Session Session Protocol Layer 5 Transport Transport Protocol Transport Layer 4 Communication network boundary Network Network Network Network Layer 3 Data Link Data Link Data Link Data Link Layer 2 Physical Physical Physical Physical Layer 1 Network layer host-router protocol Data link layer host-router protocol Physical layer host-router protocol OSI 7 Layer Reference Model Intro to Computer Communication Networks

  12. The Physical Layer (L1) • 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, Intro to Computer Communication Networks

  13. The Data Link Layer (L2) • Deal with the transfer of frames • Framing information • Boundary of the frame • attaching special bit patterns to the beginning and end of the frame • Control and address information • Check bit for recovering from transmission errors • acknowledge frames • handle with damaged, lost, and duplicate frames • Flow controls • prevent a fast transmitter from drowning a slow receiver in data • Broadcast networks • control access to the shared channel • LAN • Sub-layer: Medium Access Control layer (MAC) • One-to-one communication over broadcast medium • Examples • HDLC – High-level Data Link Control • PPP – Point-to-Point Protocol • SONET – Synchronous Optical Network Intro to Computer Communication Networks

  14. The Network Layer (L3) • 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 Intro to Computer Communication Networks

  15. The Transport Layer (L4) • 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 • Unix socket interface Intro to Computer Communication Networks

  16. The Session Layer (L5) • 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 Intro to Computer Communication Networks

  17. 32-bit word like an integers SUN Sparc, MIPS Intel x86, Dec Alpha 4 3 2 1 1 2 3 4 The POWER Processor can be configured as either big endian or little endian The Presentation Layer (L6) • 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 Intro to Computer Communication Networks

  18. The Application Layer (L7) • 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 Intro to Computer Communication Networks

  19. receivng process sending process data Application Application data AH Presentation Presentation data PH Session Session data SH Transport Transport data TH Network Network data NH Data Link Data Link DT data DH Physical Physical Bits actual data transmission path Data Transmission in OSI Model Intro to Computer Communication Networks

  20. TCP/IP Architecture • 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 • remote login, e-mail, file transfer, network management Intro to Computer Communication Networks

  21. OSI TCP/IP Application Application Presentation Session Transport TCP,UDP Network IP Data Link Network Interface Layer Physical OSI Model vs. TCP/IP Not present in the model Intro to Computer Communication Networks

  22. Protocols and Networks in TCP/IP Application TELNET FTP SMTP DNS RTP Transport TCP UDP Network IP ICMP Network Interface ARP X.25 ATM FR ETHER Intro to Computer Communication Networks

  23. APP APP router TCP TCP IP IP IP NI NI NI NI TCP/IP Protocol • 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 Intro to Computer Communication Networks

  24. TCP/IP in a Network data data IP (1,2) IP (1,3) data 1,2 data 1,2 1,3 1,3 NI 3487 NI 6537 data 3487 6537 Intro to Computer Communication Networks

  25. data data Router Host B Host A IP (1,2) IP (1,1) (2,3) IP (2,5) data 1,2 data 1,2 data 1,2 2,5 2,5 2,5 NI 3487 NI 6543 NI 1002 NI 3903 data 3487 data 1002 6543 3903 TCP/IP thru a Router Intro to Computer Communication Networks

  26. Data TCPHeader TCP Payload Source Port #, Destin Port # Source IP addr, Destin IP addr, Protocol type IP Header IP Payload Source PH addr, Destin PH addr, Network protocol type Ethernet Header Ethernet Payload Ethernet Tail TCP/IP in a System Intro to Computer Communication Networks

  27. Server in TCP/IP • A process waiting a packet on a specific port number • Duplicate a connection after establishing • Connection? • 5 tuple – (PT, SA, SP, DA, DP) • 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. Intro to Computer Communication Networks

  28. Berkeley Socket • 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 Intro to Computer Communication Networks

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