1 ITC242 – Introduction to Data Communications TCP/IP and OSI

2 “Study algorithm for this unit” Make up the background knowledge for this unit. The subsequent chapter is related logically to the previous chapters This means that you must make up them if you miss one or more. You cannot fully understand the contents being covered by only attending the class ! The content I am lecturing in the classes is harder than that of the text Different learning outcomes, depending on the degree for which you are studying The exam is relatively easier than….. Before coming to my classes (1) Read the corresponding chapter(s) to be covered (2) Read my PowerPoint slides published on the course website (3) Write down the questions you have If you have not done the above, then …… During my classes Concentrate on listening and thinking rather than talking ! Concentrate on understanding rather than writing ! ( make notes) After my classes Read the text and the slides again ! If you still have questions, then go to my office If you still have questions, then read the reference book(s) If you still have questions, then consider withdrawing from this unit

3 Last Week Topic 3 – Distributed Data Processing Describe the differences between centralised and distributed data processing Describe different types of distributed data processing for applications and distributed databases Describe the implications for data comms of distributed data processing Understand the motivation towards client server architectures

4 Last Week Topic 4 – The Internet Discuss the history of the Internet and explain it’s explosive growth Describe the overall Internet architecture including key components Explain the components and operation of the Domain Name System

5 Topic 5 – TCP/IP and OSI Learning objectives Describe the definition of a protocol; Discuss the need and benefits of using protocol architectures; Describe the TCP/IP protocol architecture Describe the OSI reference model.

6 What’s a protocol? human protocols: “what’s the time?” “I have a question” introductions … specific msgs sent … specific actions taken when msgs received, or other events network protocols: machines rather than humans all communication activity in Internet governed by protocols protocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, receipt

7 What’s a protocol? a human protocol and a computer network protocol: Hi Got the time? 2:00 TCP connection request TCP connection response Get time

8 Protocol Architecture – Modular Approach Breaks complex tasks into subtasks Each module handles specific subset of tasks Communication occurs –between different modules on the same system –between similar modules on different systems

9 Advantages of Modularity Easier application development Network can change without all programs being modified

10 Organization of air travel a series of steps ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing

11 ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing Layering of airline functionality Layers: each layer implements a service –via its own internal-layer actions –relying on services provided by layer below

12 Three-Layer Model Distributed data communications involves three primary components: –Networks –Computers –Applications Three corresponding layers –Network access layer –Transport layer –Application layer

13 Network Access Layer Concerned with exchange of data between computer and network Includes addressing, routing, prioritizing, etc Different networks require different software at this layer Example: X.25 standard for network access procedures on packet-switching networks

14 Transport Layer Concerned with reliable transfer of information between applications Independent of the nature of the application Includes aspects like flow control and error checking

15 Application Layer Logic needed to support various applications Each type of application (file transfer, remote access) requires different software on this layer

16 Addressing Each computer on a network requires a unique address on that network Each application requires a unique address within the computer to allow support for multiple applications (service access points, or SAP)

17 Data Transmission Application layer creates data block Transport layer appends header to create PDU (protocol data unit) –Destination SAP, Sequence #, Error-Detection Code Network layer appends another header –Destination computer, facilities (e.g. “priority”)

18 Simplified Architecture

19 Protocol Architecture Operation

20 Standardised Protocol Architectures Vendors like standards because they make their products more marketable Customers like standards because they enable products from different vendors to interoperate Two protocol standards are well-known: –TCP/IP: widely implemented –OSI: less used, but widely known and still useful for modeling/conceptualizing

21 TCP/IP Transmission Control Protocol/Internet Protocol Developed by DARPA No official protocol model Identified by 5 Layers –Application –Host-to-Host (transport) –Internet (Network) –Network Access (link) –Physical

22 source application transport network link physical HtHt HnHn M segment HtHt datagram destination application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M network link physical link physical HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn M HtHt HnHn HlHl M router switch Encapsulation message M HtHt M HnHn frame

23 TCP/IP Physical Layer Physical interface between a DTE (e.g. computer or terminal) and a transmission medium Specifies: –Characteristics of medium –Nature of signals –Data rate

24 TCP/IP Network Access (link) Exchange of data between systems on a shared network Utilizes address of host and destination Can also prioritize transmission Software at this layer depends on network (e.g. X.25 vs. Ethernet)

25 TCP/IP Internet Layer An Internet is an interconnection of two or more networks Internet layer handles tasks similar to network access layer, but between networks rather than between nodes on a network Uses IP for addressing and routing across networks Implemented in workstations and routers

26 TCP/IP Transport Layer Also called host-to-host layer Reliable exchange of data between applications Uses TCP protocols for transmission

27 TCP/IP Application Layer Logic needed to support variety of applications Separate module supports each type of application (e.g. file transfer)

28 TCP & UDP Most TCP/IP applications use TCP for transport layer TCP provides a connection (logical association) between two entities to regulate flow check errors UDP (User Datagram Protocol) does not maintain a connection, and therefore does not guarantee delivery, preserve sequences, or protect against duplication

29 TCP service Reliable, in-order byte-stream data transfer –loss: acknowledgements and retransmissions Flow control: –sender won’t overwhelm receiver Congestion control: –senders “slow down sending rate” when network congested

30 UDP Goal: data transfer between end systems –same as TCP UDP - User Datagram Protocol : –connectionless –unreliable data transfer –no flow control –no congestion control App’s using TCP: HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP ( ) App’s using UDP: streaming media, teleconferencing, DNS, Internet telephony

31 IP and IPv6 IP provides for 32-bit source and destination addresses IPv6 (1996 standard) provides for 128-bit addresses Migration to IPv6 will be a very slow process

32 TCP/IP Applications SMTP (Simple Mail Transfer Protocol) –Basic facility, transferring messages among hosts FTP (File Transfer Protocol) –Sends files from one system to another on user command Telnet –Remote login capability, allowing a user to emulate a terminal on the remote system

33 Internetworking Interconnected networks, usually implies TCP/IP Can appear to users as a single large network The global Internet is the largest example, but intranets and extranets are also examples

34 Origins of the OSI reference model The early development of LANs, MANs, and WANs was chaotic in many ways. The early 1980s saw tremendous increases in the number and sizes of networks. As companies realized that they could save money and gain productivity by using networking technology, they added networks and expanded existing networks as rapidly as new network technologies and products were introduced. By the middle of the 1980s, companies began to experience difficulties from all the expansions they had made. It became more difficult for networks using different specifications and implementations to communicate with each other. To address the problem of networks being incompatible and unable to communicate with each other, the International Organization for Standardization (ISO) researched different network schemes. As a result of this research, the ISO created a model that would help vendors create networks that would be compatible with, and operate with, other networks. the OSI reference model describes how data travels from application programs (for example, spreadsheets), through a network medium, to an application program located in another computer, even if the sender and receiver are connected using different network media.

35 OSI Open Systems Interconnection Developed by ISO Contains seven layers

36 OSI Lower Layers Physical Data Link Network

37 OSI Physical Layer Responsible for transmission of bits--binary transmission Always implemented through hardware This layer outlines the functional, procedural, electrical, and mechanical specifications for controlling physical links. The specifications relate to the activation, maintenance, and deactivation of physical links. It also controls the transmitting of data onto physical media. e.g. RS-232 A “hub” operates at this layer

38 OSI Data Link Layer The data-link layer arranges bits from the physical layer into logical chunks of data, known as frames. A frame is a contiguous series of data with a common function. Framing enables the network to organize bits into a logical data format and send them to the correct computer. This layer controls how data is formatted and how transmission on the network is controlled Responsible for error-free, reliable transmission of data Flow control, error correction Controls access to the medium e.g. HDLC, ethernet A “switch” operates at this layer

39 OSI Network Layer Responsible for routing of messages through network ensures data delivery by providing connectivity and path selection between two host systems. selects the most appropriate path for sending data, and routes data packets Concerned with type of switching used (circuit v. packet) Handles routing between networks, as well as through packet-switching networks provides logical LAN-to-LAN communications by supporting the routing of data between different networks IP protocol and IP addressing at this layer A “router” operates at this layer

40 OSI Upper Layers Transport Session Presentation Application

41 OSI Transport Layer Aids point-to-point communications Isolates messages from lower and upper layers Provides reliability in the transportation of data between hosts and ensures complete data transfer. The transport layer uses error detection and recovery information flow control to establish, maintain, and terminate all virtual circuits. Breaks down message size Monitors quality of communications channel Selects most efficient communication service necessary for a given transmission TCP/UDP operate at this layer

42 OSI Session Layer Establishes logical connections between hosts:connection establishment, data transfer, and connection release Manages log-ons, password exchange, log-offs Terminates connection at end of session

43 OSI Presentation Layer manages data representation transforms data into a mutually agreed format that each application can understand Provides format and code conversion services Examples –File conversion from ASCII to EBDIC(Extended Binary-Coded Decimal Interchange Code ) –Encryption and compression –Invoking character sequences to generate bold, italics, etc on a printer

44 OSI Application Layer Provides access to network for end-user User’s capabilities are determined by what items are available on this layer

45 Layering: The OSI Model Session Network Link Physical Application Presentation Transport Network Link Network Transport Session Presentation Application Network Link Physical Peer-layer communication layer-to-layer communication Router

46 Network Link Transport Application Presentation Session Transport Network Link Physical The 7-layer OSI Model The 4-layer Internet model Application FTP ASCII/Binary IP TCP Ethernet TCP/IP - OSI Comparison

47 Example: FTP over the Internet Using TCP/IP and Ethernet App OS R2 R3 R4 R1 R5 Ethernet “A” Stanford “B” (MIT) Ethernet App OS

48 In the sending host 1.Application-Programming Interface (API) –Application requests TCP connection with “B” 2.Transmission Control Protocol (TCP) –Creates TCP “Connection setup” packet –TCP requests IP packet to be sent to “B” TCP Data TCP Header TCP Packet Type = Connection Setup Empty

49 In the sending host (2) 3. Internet Protocol (IP) –Creates IP packet with correct addresses. –IP requests packet to be sent to router. IP Data TCP Packet Encapsulation IP Header IP Packet Destination Address: IP “B” Source Address: IP “A” Protocol = TCP TCP Data TCP Header

50 In the sending host (3) 4. Link (“MAC” or Ethernet) Protocol –Creates MAC frame with Frame Check Sequence (FCS). –Wait for Access to the line. –MAC requests PHY to send each bit of the frame. Ethernet Data IP Packet Ethernet FCS Ethernet Header Ethernet Packet Destination Address: MAC “R1” Source Address: MAC “A” Protocol = IP IP Data IP Header Encapsulation

51 In Router R1 5. Link (“MAC” or Ethernet) Protocol –Accept MAC frame, check address and Frame Check Sequence (FCS). –Pass data to IP Protocol. Ethernet Data IP Packet Ethernet FCS Ethernet Header Ethernet Packet Destination Address: MAC “R1” Source Address: MAC “A” Protocol = IP IP Data IP Header Decapsulation

52 In Router R1 6. Internet Protocol (IP) –Use IP destination address to decide where to send packet next (“next-hop routing”). –Request Link Protocol to transmit packet. IP Data IP Header IP Packet Destination Address: IP “B” Source Address: IP “A” Protocol = TCP

53 In Router R1 7. Link (“MAC” or Ethernet) Protocol –Creates MAC frame with Frame Check Sequence (FCS). –Wait for Access to the line. –MAC requests PHY to send each bit of the frame. Ethernet Data IP Packet Ethernet FCS Ethernet Header Ethernet Packet Destination Address: MAC “R2” Source Address: MAC “R1” Protocol = IP IP Data IP Header Encapsulation

54 In Router R5 16. Link (“MAC” or Ethernet) Protocol –Creates MAC frame with Frame Check Sequence (FCS). –Wait for Access to the line. –MAC requests PHY to send each bit of the frame. Ethernet Data IP Packet Ethernet FCS Ethernet Header Ethernet Packet Destination Address: MAC “B” Source Address: MAC “R5” Protocol = IP IP Data IP Header Encapsulation

55 In the receiving host 17. Link (“MAC” or Ethernet) Protocol –Accept MAC frame, check address and Frame Check Sequence (FCS). –Pass data to IP Protocol. Ethernet Data IP Packet Ethernet FCS Ethernet Header Ethernet Packet Destination Address: MAC “B” Source Address: MAC “R5” Protocol = IP IP Data IP Header Decapsulation

56 In the receiving host (2) 18. Internet Protocol (IP) –Verify IP address. –Extract/decapsulate TCP packet from IP packet. –Pass TCP packet to TCP Protocol. IP Data TCP Packet Decapsulation IP Header IP Packet Destination Address: IP “B” Source Address: IP “A” Protocol = TCP TCP Data TCP Header

57 In the receiving host (3) 19. Transmission Control Protocol (TCP) –Accepts TCP “Connection setup” packet –Establishes connection by sending “Ack”. 20. Application-Programming Interface (API) –Application receives request for TCP connection with “A”. TCP Data TCP Header TCP Packet Type = Connection Setup Empty

58 Topic 5 Summary Looked at what a protocol is Discuss the need for and benefits of using protocol architectures; Describe the TCP/IP protocol architecture Describe the OSI reference model.