Data and Computer Communications

1. Data and Computer Communications Chapter 2 – Protocol Architecture, TCP/IP, and Internet-Based Applications

2. Protocol Architecture, TCP/IP, and Internet-Based Applications • To destroy communication completely, there must be no rules in common between transmitter and receiver—neither of alphabet nor of syntax —On Human Communication, Colin Cherry

3. Need For Protocol Architecture • data exchange can involve complex procedures, file transfer example • better if task broken into subtasks • implemented separately in layers in stack • each layer provides functions needed to perform communications for layers above • using functions provided by layers below • peer layers communicate with a protocol

5. Functions of Protocol Architecture • breaks logic into subtask modules which are implemented separately • modules are arranged in a vertical stack • each layer in the stack performs a subset of functions • relies on next lower layer for primitive functions • changes in one layer should not require changes in other layers

6. Key Elements of a Protocol A protocol is a set of rules or conventions that allow peer layers to communicate. • syntax - data format • semantics - control info & error handling • timing - speed matching & sequencing

7. A Simple Protocol

8. Simplified Network Architecture ,Communications can be said to involve three agents

9. Communication Layers • communication tasks are organized into three relatively independent layers: • Network access layer • concerned with the exchange of data • Transport layer • provides reliable data transfer • Application layer • Contains logic to support applications

10. Network Access Layer The sending computer must provide the network with the address of the destination computer • exchange of data between an end system and attached network • concerned with issues like : • destination address provision • invoking specific services like priority • access to & routing data across a network link between two attached systems • allows layers above to ignore link specifics different standards have been developed for circuit switching, packet switching (e.g., frame relay), LANs (e.g., Ethernet), and others

11. Application Layer

12. Protocol Architecture and Networks

13. Protocols in a Simplified Architecture

14. Addressing and addressing Requirements every entity in the overall system must have a unique address. • two levels of addressing required • each host on a subnet needs a unique global network address • its IP address • each application on a (multi-tasking) host needs a unique address within the host • known as a port or SAP(service acces point)

15. Protocol Data Unit (PDU) • the combination of data and control information is a protocol data unit (PDU) • typically control information is contained in a PDU header • control information is used by the peer transport protocol at computer B • headers may include: • source port, destination port, sequence number, and error-detection code

16. Network Access Protocol • after receiving segment from transport layer, the network access protocol must request transmission over the network • the network access protocol creates a network access PDU (packet) with control information • header includes: • source computer address • destination computer address • facilities requests

17. TCP/IP Protocol Architecture • developed by US Defense Advanced Research Project Agency (DARPA) • for ARPANET packet switched network • used by the global Internet • protocol suite comprises a large collection of standardized protocols Built on the biases of the OSI Open System Interconnection Reference Model

18. TCP/IP Layers • no official model but a working one • Application layer • Host-to-host, or transport layer • Internet layer • Network access layer • Physical layer

19. TCP/IP Layers and Example Protocols

20. Physical Layer • concerned with physical interface between computer and network • concerned with issues like: • characteristics of transmission medium • signal levels • data rates • other related matters

21. Network Access Layer • covers the exchange of data between an end system and the network that it is attached to • concerned with issues like : • destination address provision • invoking specific services like priority • access to & routing data across a network for two end systems attached to the same network

22. Internet Layer (IP) This protocol is implemented not only in the end systems but also in routers • Covers routing functions across multiple networks • Used for systems attached to different networks • routers connect two networks and (main function) relays data between them

23. Host-to-Host (Transport) Layer

24. Operation of TCP and IP

25. TCP/IP Address Requirements Two levels of addressing are needed:

26. Operation of TCP/IP

27. Transmission Control Protocol (TCP) • usual transport layer is (TCP) • provides a reliable connection(temporary logic) for transfer of data between applications • a TCP segment is the basic protocol unit • TCP tracks segments between entities for duration of each connection

28. TCP Header minimum of 20 octets or 160 bits.

29. User Datagram Protocol(UDP) In addition to TCP, (UDP) is one other transport-level protocol that is in common use as part of the TCP/IP protocol suite. • an alternative to TCP • no guaranteed delivery • no preservation of sequence • no protection against duplication • minimum overhead • used in some simple transaction-oriented applications • adds port addressing to IP • it is connectionless

30. UDP Header UDP is connectionless and has very little to do Adds a port addressing capability to IP Optional to verify that no error occurs in the data

31. IP and IP v6 History • IP v4 header format was the keystone for decades • In 1995 the Internet Engineering Task (develops standards and protocols) issued specs for the next generation IP (IP ng). • IP ng became IPv6 in 1996. • IPv6 provided a number of functional enhancement over existing IP

32. IP v4 Header a minimum of 20 octets or 160 bits. used in the fragmentation and reassembly process includes 32-bit source and destination addresses Differentiated service field Explicit congestion field used to detect errors in the header to avoid misdelivery indicates which higher-layer protocol is using IP

33. IPv6 Provides enhancements over existing IP Designed to accommodate higher speeds and the mix of graphic and video data Driving force was the need for more addresses due to growth of the Internet IPv6 includes 128-bit source and destination address fields

34. IPv6 Header The current IP uses a 32-bit address to specify a source or destination(not sufficient anymore) all installations using TCP/IP are expected to migrate from the current IP to IPv6, but this process will take many years

35. TCP/IP Applications • have a number of standard TCP/IP applications such as (common ones) • Simple Mail Transfer Protocol (SMTP) • File Transfer Protocol (FTP) • Telnet (provides a remote logon capability)

36. Some TCP/IP Protocols Each layer in the TCP/IP protocol suite interacts with its immediate adjacent layers

37. The Open Systems Interconnection OSI • Open Systems Interconnection • developed by the International Organization for Standardization (ISO) • has seven layers • is a theoretical system delivered too late! • TCP/IP is the de facto standard

38. OSI Standardization framework for standardization was motivator lower layers are concerned with greater levels of details each layer provides services to the next higher layer three key elements:

39. OSI Layers

40. OSI v TCP/IP Please Do Not Thru Sausage Pizza Away

41. Standardized Protocol Architectures Lower layers are concerned with greater levels of detail; upper layers are independent of these details. Each layer provides services to the next higher layer and implements a protocol to the peer layer in other systems.

42. Layer Specific Standards and the nature of the standardization required at each layer. defines what services are provided, but not how the services are to be provided. indicates a transport entity that is a user of the network service. because two different open systems are involved

43. Service Primitives and Parameters services between adjacent layers in the OSI architecture are expressed in terms of primitives and parameters • primitives to specify function performed • parameters to pass data and control info

44. Primitive Types four types of primitives are used in standards to define the interaction between adjacent layers in the architecture (X.210)

45. Traditional vs Multimedia Applications • traditionally Internet dominated by info retrieval applications • typically using text and image transfer • eg. email, file transfer, web • see increasing growth in multimedia applications • involving massive amounts of data • such as streaming audio and video

46. Elastic and Inelastic Traffic • Traffic on a network or internet can be divided into two broad categories: elastic and inelastic. • elastic traffic • can adjust to delay & throughput changes over a wide range • eg. traditional “data” style TCP/IP traffic. • common Internet-based applications, such as file transfer, electronic mail, remote logon, network management, and Web access • some applications more sensitive though

47. Elastic and Inelastic Traffic • inelastic traffic • does not adapt to such changes • eg. “real-time” voice & video traffic • The requirements for inelastic traffic may include the following: • minimum throughput. • may be delay-sensitive • may require a reasonable upper bound on delay variation, may vary in the amount of packet loss • These requirements are difficult to meet in an environment with variable queuing delays and congestion losses.

48. Multimedia Technologies a list of technologies relevant to the support of multimedia applications. multimedia from the perspective of three different dimensions: type of media, applications, and the technology required to support the applications.

49. Summary • introduced need for protocol architecture • TCP/IP protocol architecture • OSI Model & protocol architecture standardization • traditional vs multimedia application needs