Allows applications on different systems to communicate by defining rules for exchanging data between them. It uses a modular approach that breaks tasks into subtasks handled by separate modules, making applications easier to develop and networks more flexible. The three-layer TCP/IP and seven-layer OSI models both describe a standardized architectural approach to protocol design.

1. IE 20303

2. What is a Protocol?Allows entities (i.e. application programs) from different systems to communicateShared conventions for communicating information are called protocolsDefines a set of rules that govern the exchange of dataIncludes syntax, semantics, and timing

3. Why Use Protocol Architecture?Data communications requires complex proceduresSender identifies data path/receiverSystems negotiate preparednessApplications negotiate preparednessTranslation of file formatsFor all tasks to occur, high level of cooperation is required

4. Modular ApproachBreaks complex tasks into subtasksEach module handles specific subset of tasksCommunication occursbetween different modules on the same systembetween similar modules on different systems

5. Advantages of ModularityEasier application developmentNetwork can change without all programs being modified

6. Three-Layer ModelDistributed data communications involves three primary components:NetworksComputersApplicationsThree corresponding layersNetwork access layerTransport layerApplication layer

7. Network Access LayerConcerned with exchange of data between computer and networkIncludes addressing, routing, prioritizing, etcDifferent networks require different software at this layerExample: X.25 standard for network access procedures on packet-switching networks

8. Transport LayerConcerned with reliable transfer of information between applicationsIndependent of the nature of the applicationIncludes aspects like flow control and error checking

9. Application LayerLogic needed to support various applicationsEach type of application (file transfer, remote access) requires different software on this layer

10. AddressingEach computer on a network requires a unique address on that networkEach application requires a unique address within the computer to allow support for multiple applications (service access points, or SAP)

11. Data TransmissionApplication layer creates data blockTransport layer appends header to create PDU (protocol data unit)Destination SAP, Sequence #, Error-Detection CodeNetwork layer appends another headerDestination computer, facilities (e.g. “priority”)

12. Protocol Architectures

13. Protocols in a Simplified Architecture

14. Transport PDU HeadersSource port: indicates the application that sent the dataDestination port: the appplication that the data is to be delivered toSequence number: provides sequential ordering of segments Error-detection code: code that is a function of the contents of a segment (e.g., checksum or frame check sequence)

15. Network Access PDU (Packet Header)Source computer address: indicates the source of the packetDestination computer address: indicates the computer that the data is to be delivered toFacilities requests: indicates if the network is to make use of certain facilities such as priority

16. Standardized Protocol ArchitecturesVendors like standards because they make their products more marketableCustomers like standards because they enable products from different vendors to interoperateTwo protocol standards are well-known:TCP/IP: widely implementedOSI: less used, but widely known and still useful for modeling/conceptualizing

17. TCP/IPTransmission Control Protocol/Internet ProtocolDeveloped by DARPANo official protocol standardIdentifies 5 LayersApplicationHost-to-Host (transport)InternetNetwork AccessPhysical

18. TCP/IP Physical LayerPhysical interface between a DTE (e.g. computer or terminal) and a transmission medium Specifies:Characteristics of mediumNature of signalsData rate

19. TCP/IP Network Access LayerExchange of data between systems on a shared networkUtilizes address of host and destinationCan also prioritize transmissionSoftware at this layer depends on network (e.g. X.25 vs. Ethernet)Segregation means that no other software needs to be concerned about net specifics

20. TCP/IP Internet LayerAn Internet is an interconnection of two or more networksInternet layer handles tasks similar to network access layer, but between networks rather than between nodes on a networkUses IP for addressing and routing across networksImplemented in workstations and routers

21. TCP/IP Transport LayerAlso called host-to-host layerReliable exchange of data between applicationsUses TCP protocols for transmission

22. TCP/IP Application LayerLogic needed to support variety of applicationsSeparate module supports each type of application (e.g. file transfer)

23. Operation of TCP/IP

24. TCP & UDPMost TCP/IP applications use TCP for transport layerTCP provides a connection (logical association) between two entities to regulate flow check errorsUDP (User Datagram Protocol) does not maintain a connection, and therefore does not guarantee delivery, preserve sequences, or protect against duplication

25. TCP & UDP

26. IP and IPv6IP provides for 32-bit source and destination addressesIPv6 (1996 standard) provides for 128-bit addressesMigraqtion to IPv6 will be a very slow process

27. IP Headers

28. TCP/IP ApplicationsSMTP (Simple Mail Transfer Protocol)Basic e-mail facility, transferring messages among hostsFTP (File Transfer Protocol)Sends files from one system to another on user commandSSH (Secure Shell)Secure remote login capability, allowing a user to remotely logon to a computer

29. InternetworkingInterconnected networks, usually implies TCP/IPCan appear to users as a single large networkThe global Internet is the largest example, but intranets and extranets are also examples

30. RoutersEquipment used to interconnect independent networksSeveral essential functionsProvide a link between networksProvide routing and delivery of data between processes on systems from different networksProvide these functions without requiring modification of networking architecture

31. Router IssuesAddressing schemesMaximum packet sizeInterfacesReliability

32. Operation of TCP/IP: Action at the Sender

33. Operation of TCP/IP: Action at the Router

34. Operation of TCP/IP: Action at the Receiver

35. Why Study OSI?Still an excellent model for conceptualizing and understanding protocol architecturesKey points:ModularHierarchicalBoundaries between layers=interfaces

36. OSIOpen Systems InterconnectionDeveloped by ISOContains seven layers

37. OSI Lower LayersPhysicalData LinkNetwork

38. OSI Physical LayerResponsible for transmission of bitsAlways implemented through hardwareEncompasses mechanical, electrical, and functional interfacese.g. RS-232

39. OSI Data Link LayerResponsible for error-free, reliable transmission of dataFlow control, error correctione.g. HDLC

40. OSI Network LayerResponsible for routing of messages through networkConcerned with type of switching used (circuit v. packet)Handles routing between networks, as well as through packet-switching networks

41. OSI Upper LayersTransportSessionPresentationApplication

42. OSI Transport LayerIsolates messages from lower and upper layersBreaks down message sizeMonitors quality of communications channelSelects most efficient communication service necessary for a given transmission

43. OSI Session LayerEstablishes logical connections between systemsManages log-ons, password exchange, log-offsTerminates connection at end of session

44. OSI Presentation LayerProvides format and code conversion servicesExamples File conversion from ASCII to EBDICInvoking character sequences to generate bold, italics, etc on a printer

45. OSI Application LayerProvides access to network for end-userUser’s capabilities are determined by what items are available on this layer

46. The OSI Environment

47. TCP/IP - OSI Comparison

48. IPSecDeveloped by the Internet Architecture Board in 1994 (RFC 1636)Examples of Applications include:-Secure branch office connectivity over the Internet-Secure remote access over the Internet-Establishing extranet and intranet connectivity with partners-Enhancing electronic security

49. Benefits of IPSecProvides stronger secuirty to routers and firewallsIs resistant to bypass within a firewallIs transparent to applications Is transparent to end usersCan provide security to end-users