Chapter 2 Communicating Over the Network

1. Chapter 2Communicating Over the Network CIS 81 Networking Fundamentals Rick Graziani Cabrillo College graziani@cabrillo.edu Last Updated: 2/17/2008

2. This Presentation • For a copy of this presentation and access to my web site for other CCNA, CCNP, and Wireless resources please email me for a username and password. • Email: graziani@cabrillo.edu • Web Site: www.cabrillo.edu/~rgraziani

3. The Platform for Communications

4. Elements of Communication

5. Communicating the Messages Continuous stream of bits 00101010100101010101010101010101010 I have to wait… • Theoretically, single communication, such as a music video or an e-mail message, could be sent across a network from a source to a destination as one massive continuous stream of bits. • No other device would be able to send or receive messages on the same network. • Results in significant delays. • Inefficient use of channel or link. • Any loss in data, entire message would have to be resent.

6. Communicating the Messages Segmentation • Better approach – segmentation. • Division of the data stream into smaller pieces is called segmentation. • Segmentation has two benefits…

7. Communicating the Messages Segmentation Benefits of segmentation: • Multiplexing: • Different conversations can be interleaved on the network.

8. Communicating the Messages X • Reliability • Increase the reliability of network communications. • Separate pieces of each message can travel across different paths to destination. • Path fails or congested, alternate path can be used. • Part of the message fails to make it to the destination, only the missing parts need to be retransmitted.

9. Disadvantage of Segmentation • Disadvantage – added level of complexity. • Like sending a 100 page letter one page at a time. • All of the separate envelopes needed • Need to label the pages with a sequence number. • This extra overhead is handled by protocols used to format and address these messages (later).

10. Components of the Network • Devices (hardware) • End devices, switch, router, firewall, hub • Media (wired, wireless) • Cables, wireless mediums • Services (software) • Network applications, routing protocols, processes, algorithms

11. End devices • End devices: • Computers (work stations, laptops, file servers, web servers) • Network printers • VoIP phones • Security cameras • Mobile handheld devices (such as wireless barcode scanners, PDAs) • End devices are referred to as hosts. • A host device is either the source or destination of a message.

12. Source Address: 209.67.102.55 Destination Address: 107.16.4.21 209.67.102.55 107.16.4.21 • Each host on a network is identified by an address. • IP (Internet Protocol) address (later)

13. Servers and Clients Client Server • A host can act as a client, a server, or both. • Software installed on the host determines the role. • Servers are hosts that have software installed that enables them to provide information and services, like e-mail or web pages, to other hosts on the network. • Clients are hosts that have software installed that enables them to request and display the information obtained from the server.

14. Intermediary Devices switch or hub switch or hub routers • Intermediary devices: • Provide connectivity to the network (switches/hubs) • Connect individual networks (routers) • Connect segments (links) within the same network (switches/hubs) • Examples: • Network Access Devices (Hubs, switches, and wireless access points) • Internetworking Devices (routers) • Communication Servers and Modems • Security Devices (firewalls)

15. Network Media • Network media: The medium provides the channel over which the message travels from source to destination. • Metallic wires - encoding into patterns of electrical impulses. • Fiber optics – encoding into pulses of light (infrared or visible light ranges) • Wireless – encoding patterns of electromagnetic waves. • (Later: OSI Physical Layer)

16. Network Media • Different media considerations: • Distance it can carry the signal • Environment it works in • Bandwidth • Cost of medium and installation • Cost of connectors and equipment

17. Local Area Network (LAN) • Local Area Network (LAN) • An individual network usually spans a single geographical area, providing services and applications to people within a common organizational structure, such as a single business, campus or region. • LAN devices • Switches (and hubs) • Routers • Multilayer switches

18. Wide Area Network (WAN) • T1, DS3, OC3 • PPP, HDLC • Frame Relay, ATM • ISDN, POTS • Wide Area Networks (WANs) • Leased connections through a telecommunications service provider network. • Networks that connect LANs in geographically separated locations • Telecommunications service provider (TSP)interconnect the LANs at the different locations. • TSPs transported voice and data communications on separate networks. • Providers are now offering converged information network services to their subscribers.

19. The Internet – A Network of Networks • ISPs (Internet Service Providers) are often also TSPs. • Connect their customers to the Internet. • The Internet is created by the interconnection of networks belonging to ISPs. • ISPs cooperate with other ISPs and TSPs to make sure their customers have access to all Internet networks. • BGP peering and routing is used.

20. CENIC – ISP for K-12, Community Colleges, CSU and UC • ISPs route traffic within their own group of networks (autonomous system). • ISPs connect their networks to other ISPs networks. • Within the ISP’s networks are both WANs and customer LANs

21. Network Representations • Network Interface Card (NIC) - Provides the physical connection to the network at the PC or other host device. • Physical Port - A connector or outlet on a networking device where the media is connected to a host or other networking device. • Interface - Specialized ports on an internetworking device that connect to individual networks. • Because routers are used to interconnect networks, the ports on a router are referred to network interfaces.

22. Protocols

23. Protocol • Protocol – Rules that govern communications. • Protocol suite - A group of inter-related protocols that are necessary to perform a communication function.

24. Multiple protocols (encapsulated) HTTP Header Data Protocols • The message received by the host usually contains multiple protocols, plus the actual data. • Note: Application Header (HTTP) may or may not exist. Typically Application Header or Data. (later) App Header Frame Header IP Header TCP Header Frame Trailer Data

25. Multiple protocols (encapsulated) HTTP Header Data Protocols • Encapsulation – Process of adding a header to the data or any previous set of headers. • Decapsulation – Process of removing a header. • More later. App Header Frame Header IP Header TCP Header Frame Trailer Data

26. Example: Protocol – IPv4 HTTP Header Frame Header IP Header TCP Header Frame Trailer Data • Example of IPv4 • More later

27. 209.67.102.55 107.16.4.21 HTTP Header Frame Header IP Header TCP Header Frame Trailer Data 209.67.102.55 107.16.4.21

28. Protocols • Networking protocols suites describe processes such as: • The format or structure of the message • The process by which networking devices share information about pathways with other networks • How and when error and system messages are passed between devices • The setup and termination of data transfer sessions

29. Protocol Suites and Standards • Early days – proprietary network equipment and protocols. • Now – Industry standards • Institute of Electrical and Electronics Engineers (IEEE) • Develops standards in telecommunications, information technology and power generation. • Examples: 802.3 (Ethernet), 802.11 (WLAN) • Internet Engineering Task Force (IETF) • Internet standards • RFCs (Request for Comments) • Example: TCP, IP, HTTP, FTP

30. Interaction of Protocols Hypertext Transfer Protocol (HTTP) • Common protocol that governs interaction between web server and a web client. • Defines the content and formatting of the requests and responses between the client and server. • Both the client and the web server software implement the HTTP application. • HTTP relies on other protocols to govern how the messages are transported between client and server.

31. Interaction of Protocols segment Transmission Control Protocol (TCP) • Transport protocol that manages the individual conversations between servers and clients (not just web servers and web clients) • TCP divides the HTTP messages into smaller pieces, called segments • Responsible for controlling the information exchanged between the server and the client: • Size of data • Flow control – how much is sent and received • Reliability – Sequence numbers in case lost or missing

32. packet Internetwork Protocol (IP) • Responsible for taking the formatted segments from TCP, encapsulating them into packets. • Assigns the appropriate source and destination addresses, • Original source address of host • Final destination address of host • Used by routers in selecting the best path to the destination host.

33. Interaction of Protocols frame Network access protocols (Data link and Physical layer protocols) • Physical transmission of data on the media. • Take the packets from IP and format them to be transmitted over the media.

34. Interaction of Protocols 209.67.102.55 107.16.4.21 Network access protocols (Data link and Physical layer protocols) • Responsible for addressing and sending the IP packet between two devices on the same network. • Host to router • Router to router • Router to host

35. Technology-Independent Protocols HTTP Header Frame Header IP Header TCP Header Frame Trailer IP Packet IP Packet Ethernet Ethernet • T1, DS3, OC3 • PPP, HDLC • Frame Relay, ATM • ISDN, POTS • Protocols are not dependent upon any specific technology. • For example: • Our IP Packet (IP + TCP + HTTP + Data) can be delivered over various types of networks using a variety of data link frames. • More later! – Herding cats.

36. Using Layered Protocols

37. Layered Model • Layered Models separate the functions of specific protocols.

38. Benefits of a Layered Model • Using a layered model: • Have defined information that they act upon and a defined interface to the layers above and below. • Fosters competition because products from different vendors can work together. • Prevents technology or capability changes in one layer from affecting other layers above and below. • Provides a common language to describe networking functions and capabilities.

39. Protocol and Reference Models • A protocol model provides a model that closely matches the structure of a particular protocol suite. • A reference model provides a common reference for maintaining consistency within all types of network protocols and services. • Not intended to be an implementation specification.

40. Protocol and Reference Models • The Open Systems Interconnection (OSI) model is the most widely known internetwork reference model. • OSI is also a protocol suite or protocol model. • OSI lost out to TCP/IP as the protocol suite of the Internet. • OSI protocol suite includes layers 3 through 7

41. TCP/IP Model • TCP/IP Model and Protocol Suite is an open standard. • No one company controls it. • Governed by IETF Working Groups with standards proposed using Request for Comments (RFCs).

42. Example: RFC 791 IPv4

43. The Communication Process - Encapsulation Data Link Trailer Data Link Header IP Header TCP Header HTTP Header Data Server HTTP Data • Encapsulation – Process of adding control information as it passes down through the layered model. • Note: Application Header (HTTP) may or may not exist. (later)

44. The Communication Process - Decapsulation Data Link Trailer Data Link Header IP Header TCP Header HTTP Header Data • Client HTTP Data • Decapsulation – Process of removing control information as it passes upwards through the layered model.

45. Wireshark will let us examine protocols!

46. The Communication Process • Protocol Data Unit (PDU) - The form that a piece of data takes at any layer. • At each stage of the process, a PDU has a different name to reflect its new appearance. • PDUs are named according to the protocols of the TCP/IP suite. • Data - The general term for the PDU used at the Application layer • Segment - Transport Layer PDU • Packet - Internetwork Layer PDU • Frame - Network Access Layer PDU • Bits - A PDU used when physically transmitting data over the medium

47. ISO and the OSI Model • The International Organization for Standardization(ISO) released the OSI reference model in 1984, was the descriptive scheme they created. • “ISO. A network of national standards institutes from 140 countries working in partnership with international organizations, governments, industry, business and consumer representatives. A bridge between public and private sectors.” www.iso.ch

48. OSI Model • It breaksnetwork communication into smaller, more manageable parts. • It standardizes network components to allow multiple vendor development and support. • It allows different types of network hardware and software to communicate with each other. • It prevents changes in one layer from affecting other layers. • It divides network communication into smaller parts to make learning it easier to understand.

49. OSI Model • Presentation and Session layers are not commonly referred to in most instances.

50. Comparing OSI and TCP/IP Models