WELCOME to COMP 421 /CMPET 401

1. WELCOME to COMP 421 /CMPET 401 COMMUNICATIONS and NETWORKING Class 1

2. COURSE OUTLINE • Overview of Communications • Introduction • Protocols and Architecture • Data Communications • Data Transmission • Transmission Media • Data Encoding • Data Link Control • Multiplexing

3. COURSE OUTLINE (continued) • Local and Wide Area Networks • LAN & WAN Protocols • Switching Techniques • Bridges and Routers • High Speed Networks • Internetworking • Internet Resources • Network Operating Systems

4. TELECOMMUNICATIONS • Telecommunications is the technique of transmitting a message from one point to another • knowing how much information, if any, is likely to be lost in the process. • Hence the term TELECOMUNICATIONS covers all forms of distance communications • including: • Radio • Telegraph • Television • Telephony • Data Communications • Computer Networking • The elements of a telecommunication system are: • Transmitter • Channel • Line • Receiver • The transmitter is a device that transforms or codes the message into a physical • phenomenon called the transmission channel, by its physical nature it is likely to • modify or degrade the signal on it path from the transmitter to the receiver.

5. TELECOMMUNICATIONS

6. TELECOMMUNICATIONS

7. output data input data transmitted signal received signal input information Transmission medium Input device Output Devices Transmitter Receiver The Communications Model output information

8. Communication Tasks • Communication Tasks Include: • Transmission System Utilization • Interfacing • Signal Generation • Synchronization • Exchange Management • Error Correction and Detection • Flow Control • Addressing • Routing • Recovery • Message Formatting • Security • Network Management

9. Data Communication Network Communication Network Node Network Station Communication Network

10. Data Communication Networking • Networks are used to link devices together • Distant - Network is called a Wide Area Network (WAN) • Circuit Switched • Packet Switched • Frame Relay • ATM • Public Switched Telephone Network (PSTN) • Leased lines • Public switched data network (PSDN) • Integrated services digital network (ISDN) • Local - Network is called a Local Area Network (LAN) • Intermediate - Network is called a Metropolitan Area Network (MAN)

11. PSTN • modem link via PSTN PSTN modem modem

12. hub hub hub hub LAN station 4th floor • confined geographical area • under single management • high data rate station 3rd floor station 2nd floor 1st floor server router

13. LAN Voice Leased lines • Lease pubic circuits to connect different sites • Communication channel is private LAN leased circuit Voice LAN Voice

14. PSDN • PSDN is designed specifically for the transmission of data rather than voice • Communication is shared LAN PSDN= Public Switched Data Network LAN PSDN LAN

15. ISDN ISDN is an acronym for integrated Services Digital Network ISDN provides integrated voice and data over the Telephone company facilities. 3 Telephone Lines 1 ISDN Line Telco Central Office Telco Central Office

16. Standards • Standards are required in the telecommunications industry to govern • the physical, electrical and procedural characteristics of communications • equipment. • Some organizations whom exist, at least partially, to create these • standards are: • The Internet Society • ISO • ITU-T (formerly CCITT) • The ATM Forum • IEEE RFC - Request for Comment

17. ECMA EIA IEEE ITU-T CEPT ANSI Computer Industry Telecommunications Industry Proprietary standards (closed systems) Interface standards (multi-vendor systems) Standards ISO ITU-T Integrated computer and telecommunications industry International Standards (Open Systems Interconnection)

18. Standards • The Standardization Process of the Internet Organizations is • Be stable & well understood • Be technically competent • Have multiple independent and interoperable • implementations with substantial operational experience • Enjoy significant public support • Be recognizable useful in some or all parts of the Internet The key difference between theses criteria and this used for the international standards from ISO and ITU-U is the emphasis on operational experience

19. Standards The process a specification goes through to become a standard is defined by RFC 2026 Internet Draft Proposed Standard Experimental International Draft Standard Internet Standard Historic

20. An Example – 802.11 Wireless LAN 802.11 Initial 1 & 2 Mbps 802.11a High Rate 5.7Ghz 802.11b 5.5 and 11 Mbps 802.11c MAC Bridge 802.11d Regulating Domains 802.11e Quality of Service 802.11f Multi-Vendor Inter-Access Port 802.11g High Rate 2.4Ghz 802.11h Power Control/Frequency Selection 802.11i Enhanced Security 802.11j 4.9-5Ghz in Japan 802.11k Radio Resonance Management

21. TOPOLOGIES • A network topology is the geometric arrangement of nodes and cable links in a LAN, and is used in two general configurations: bus and star. These two topologies define how nodes are connected to one another. A node is an active device connected to the network, such as a computer or a printer. A node can also be a piece of networking equipment such as a hub, switch or a router. • A bus topology consists of nodes linked together in a series with each node connected to a long cable or bus. Many nodes can tap into the bus and begin communication with all other nodes on that cable segment. A break anywhere in the cable will usually cause the entire segment to be inoperable until the break is repaired. Examples of bus topology include 10BASE2 and 10BASE5.

22. TOPOLOGY

23. Computer Networks • A computer network is a system for communication among two or more computers • Computer network may be categorized by Range: • PAN • LANMANWAN • Computer network applications may be categorized with respect to the functional • relationships between components: • Client-server • Multi-tier architecture • peer to peer

24. PANs

25. MANs • Distances between 5 and 50 km • Data rate above 1 Mbps • Standards: IEEE 802.6 DQDB, FDDI, and ATM

26. LANs (Local Area Networks) • Maximum distance not more than a few kms • Ownership by a single organization • Transmission speed of at least several Mbps (tens to hundreds are economical) • Some widely used standards include: • IEEE 803.3 - Ethernet • IEEE 803.5 - Token ring • FDDI • ATM • An important issue in broadcast LANs is the allocation of the shared channel (media access control) • Control may be static (time division multiplexing) or dynamic (contention or arbitration)

27. WANs (Wide Area Networks) Often a network is located in multiple physical locations. Wide area networking combines multiple LANs that are geographically separate. This is accomplished by connecting the different LANs using services such as dedicated leased phone lines, dial-up phone lines both synchronous and asynchronous, satellite links, and data packet carrier services. Wide area networking can be as simple as a modem and remote access server for employees to dial into, or it can be as complex as hundreds of branch offices globally linked using special routing protocols and filters to minimize the expense of sending data sent over vast distances.

28. WAN • WAN (Wide Area Network) • Spans entire states or countries • Data rate of 1.544 (T1), and 45 (T3) Mbps common • Higher data rates are available with the wide deployment of ATM backbone networks • Often owned by multiple organizations

29. WAN • Usually separate communications functions from application functions • Transmission lines: circuits, channels or trunks • Switching elements: • Specialized computers connecting two or more circuits • Intermediate Systems, Packet SwitchingNode, Data Switching Exchange, Router, etc. • Intermediate systems store a complete packet before forwarding it • store-and-forward; packet switched; point-to-point network

30. Computer Networks • Computer Networks may be implemented using a variety of network protocol • stack architectures computer buses or combinations of media and protocol layers • incorporating one or more of the following: • ARCNETDECNETEthernet • IP • TCP • AppleTalk • Token Ring • IPX • FDDIHSSI • ATM • RS-232 • USBFirewire • X.25 • Blue Tooth • WiFi • Frame Relay

31. Network Software • Network software is highlystructured • This technique has been immensely successful • The key is Layered design • Each layer provides a service to the layer above • Each layer hides details of how the service is provided to the layer above • The Nth layer on one machine “talks to” or interacts with the Nth layer on another machine

32. Understanding Services and Protocols • Protocol is set of rules about the format and meaning of data units exchanged by peers • Protocol is used by entities to implement services • Protocol and/or its implementation can change and as long as the Service (interface) remains unchanged, higher layers are happy and continue to work • Like in abstract data types or object orientation, we decouple interface and implementation

33. Protocols Although each network protocol is different, they all share the same physical cabling. This common method of accessing the physical network allows multiple protocols to peacefully coexist over the network media, and allows the builder of a network to use common hardware for a variety of protocols. This concept is known as "protocol independence," which means that devices that are compatible at the physical and data link layers allow the user to run many different protocols over the same medium.

34. Files and file transfer commands File Transfer Application File Transfer Application Communications related data units Communications Service Module Communications Service Module Network Access Module Network Access Module Comms \Network Network Interface Logic Network Interface Logic Protocols A Structured Set of Modules implements the communications function That structure is referred to as a Protocol Architecture

35. Protocols • The Key Elements of Protocols are: • SYNTAX - Data format and signal levels • SEMANTICS- Control information for coordination • & error handling • TIMING - speed matching and sequencing

36. Network Software - Protocols • Conventions and rules governing this interaction are specified by the Layer N Protocol • A protocol is an agreement about how communications are to proceed • Without a protocol, communication can be difficult or even impossible • E.g. Telephone conversation, Postal addresses

37. Network Software - Protocols • The set of protocols and layers together make up the Network Architecture • A Network Architecture Specification must provide enough information to allow implementation in hardware/software • Implementation specific details are not part of the architecture and should be irrelevant for inter-operation • With one protocol per layer we have a Protocol Stack

38. Network Software - Protocols • Information is not actually transferred directly between peer layer N entities • Peer layer N entities carry on a virtual communication using the services of the layers below • Layer N passes data and control information down to (or receives data and control from) Layer N-1 until the physical medium is reached

39. The benefits of Layered Protocols • Network Architectures, Protocols and Protocol stacks are the Fundamentals of Computer Networks • They form the foundation for the very considerable success of computer networks in the real world • Multilayer communications protocols allow • ready adaptation of successful protocols to new technology (prevent obsolescence) • migration of protocols from software implementation (slow) to hardware (fast) as they evolve

40. More Benefits of Layered Protocols • Separate data and control information • Support differing levels of abstraction (message, packet, frame) with different sizes • Allow segmentation of large messages • Peer process abstraction facilitates reduction of difficult design task (a network architecture) into smaller manageable tasks (protocol layer architecture) • Typically lower layer protocols of “network software” are implemented in silicon (hardware)

41. Network Software - Interfaces & Services • Interfaces exist between each layer • Interface defines which primitive functions and services layer N-1 provides to layer N • Want layers to: • Perform a well defined, logically related set of functions • Minimize the amount of information needed to pass between layers • Keep interfaces “clean” to allow easy and transparent replacement of layers

42. The 3 Layer Model • Network access Layer - • Transport Layer - • Application Layer - This layer is concerned with the exchange of data between the computer and the network This layer is concerned with reliable and orderly exchange of data This layer provides the logic required to support the various user applications

43. Application Application Application Transport Transport Transport Network Access Network Access Network Access A Simple Architecture SAPs ( ) ( ) ( ) ( ) Network Address Comms Network ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) • Each computer contains software at all three layers. • Every entity on the network must have a unique address • Actually two layers of addressing are required • A unique network address • Each application of the computer must have a unique address • This application address allows the transport layer to support • applications on each computer and are known as • Service Access Points (SAPs)

44. Application Application Transport Transport Network Access Network Access Simplified Architecture Computer A Computer B Application Protocol Transport Protocol Comms \Network Network Access Protocol Network Access Protocol

45. PDUs Protocol Data Unit (PDU) - is the combination of data from the next higher layer and control information Application data Transport protocol data unit (TPDU) Transport header Application data Transport header Application data Network protocol data unit (NPDU) Network header Transport header Application data Network header Transport header Application data • control info + data in each layer = protocol data unit (PDU)

46. Network Operation Information in Transport Header Destination SAP - Tells the destination Transport layer to whom to deliver the message Sequence Number - Tells the destination what order the PDU was sent by numbering them Error-Detection Code - The sending transport sends a code that is a function of the contents of the PDU. The receiving entity performs the same calculation and compares the two numbers.

47. Network Operation Information in Network Header Destination Computer Address - Tells the network to which computer the data is to be delivered Facilities Requests - Tells the network to make use of certain facilities (i.e. Priority)

48. Operation of Protocol Architecture Source X Destination Y Application Application Record Record Transport Transport DSAP DSAP Transport PDU Network Access Network Access DHost DHost Packet

49. Network Operation • Computer X desires to send a record to computer Y • Computer X hands the record via a procedure call to the Transport layer • The Transport layer adds its header creating the Transport PDU • This is passed down to the Network layer • The Network layer adds its header creating the Network PDU • The Network accepts the network PDU from X and delivers it to Y • The network access module in Y receives the PDU and strips off the header • It transfers the transport PDU to its transport layer • The Transport layer examines the transport header and on the basis of the • SAP field delivers the enclosed record

50. The components of a basic Network