WELCOME to COMP 421 /CMPET 401 COMMUNICATIONS and NETWORKING Class 1 COURSE OUTLINE Overview of Communications – Introduction – Protocols and Architecture Data Communications – – – – – Data Transmission Transmission Media Data Encoding Data Link Control Multiplexing 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 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. TELECOMMUNICATIONS The receiver has a decoding mechanism capable of recovering the message within certain limits of signal degradation by the communication channel. Telecommunication can be point-to-point or point-to-multipoint in which case it is called conferencing. Broadcasting is a particular form of telecommunication that is point-to-multipoint and goes predominantly from the transmitter to the receivers. Possible imperfections in a communication channel are: Shot noise Thermal noise Latency Non linear channel transfer function Sudden signal drops Bandwidth limitations Signal reflections TELECOMMUNICATIONS The art of the telecommunications engineer is to analyze the physical properties of the transmission channel, and the statistical properties of the message, in order to design the most effective coding and decoding mechanisms. Information theory enables us to evaluate the capacity of a communication channel according to its bandwidth and signal-tonoise ratio. The Communications Model input information Input device input data transmitted received signal signal Transmission Transmitter Receiver medium output information output data Output Devices Cloud Modem Modem Workstation Workstation Cloud Workstation Hub Hub Workstation 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 Data Communication Network Communication Network Node Communication Network Network Station 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) PSTN modem link via PSTN PSTN modem modem LAN hub station 4th floor hub station 3rd floor hub 2nd floor confined geographical area under single management high data rate station 1st floor server hub router Leased lines • Lease pubic circuits to connect different sites • Communication channel is private LAN leased circuit Voice LAN LAN Voice Voice PSDN • PSDN is designed specifically for the transmission of data rather than voice • Communication is shared PSDN= Public Switched Data Network LAN LAN PSDN LAN ISDN ISDN is an acronym for integrated Services Digital Network ISDN provides integrated voice and data over the Telephone company facilities. 3 Telephone Lines Computer Telco Central Office 1 ISDN Line Telephone Telco Central Office Fax Fax Telephone Computer 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 Standards ECMA EIA IEEE ITU-T CEPT ANSI Computer Industry Telecommunications Industry Proprietary standards (closed systems) Interface standards (multi-vendor systems) ISO ITU-T Integrated computer and telecommunications industry International Standards (Open Systems Interconnection) 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 Standards The process a specification goes through to become a standard is defined by RFC 2026 Proposed Standard Internet Draft Experimental Draft Standard Internet Standard Historic International An Example – 802.11 Wireless LAN 802.11 802.11a 802.11b 802.11c 802.11d 802.11e 802.11f 802.11g 802.11h 802.11i 802.11j 802.11k Initial 1 & 2 Mbps High Rate 5.7Ghz 5.5 and 11 Mbps MAC Bridge Regulating Domains Quality of Service Multi-Vendor Inter-Access Port High Rate 2.4Ghz Power Control/Frequency Selection Enhanced Security 4.9-5Ghz in Japan Radio Resonance Management 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. TOPOLOGY Bus topology. Mesh topology A network topology in which there are at least two nodes with two or more paths between them. Ring topology: A network topology in which every node has exactly two branches connected to it. Star topology: A network topology in which peripheral nodes are connected to a central node, which rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, including the originating node. . Hybrid topology A hybrid network accrues only when two basic networks are connected and the resulting network topology fails to meet one of the basic topology definitions. For example, two star networks connected together exhibit hybrid network topologies. Tree topology: A network topology that, from a purely topologic viewpoint, resembles an interconnection of star networks in that individual peripheral nodes are required to transmit to and receive from one other node only, toward a central node, and are not required to act as repeaters or regenerators. Computer Networks A computer network is a system for communication among two or more computers Computer network may be categorized by Range: PAN LAN MAN WAN Computer network applications may be categorized with respect to the functional relationships between components: •Client-server •Multi-tier architecture •peer to peer PANs A personal area network (PAN) is a computer network used for communication among computer devices (including telephones and personal digital assistants) close to one person. The devices may or may not belong to the person in question. The reach of a PAN is typically a few meters. PANs can be used for communication among the personal devices themselves (intrapersonal communication), or for connecting to a higher level network and the Internet (an uplink). Personal area networks may be wired with computer buses such as USB and Firewire. Wireless PANs can also be made possible with network technologies such as IrDA and Bluetooth. MANs Metropolitan area networks or MANs are large computer networks usually spanning a campus or a city. Common technologies used for this purpose are Asynchronous Transfer Mode, Fiber distributed data interface and Switched multimegabit data service and more recently gigabit Ethernet. Distances Data between 5 and 50 km rate above 1 Mbps Standards: IEEE 802.6 DQDB, FDDI, and ATM 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) 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. 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 WAN Usually separate communications functions from application functions Transmission Switching lines: circuits, channels or trunks elements: Specialized computers connecting two or more circuits Intermediate Systems, Packet Switching Node, Data Switching Exchange, Router, etc. Intermediate systems store a complete packet before forwarding it •store-and-forward; packet switched; point-to-point network 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: ARCNET DECNET Ethernet IP TCP AppleTalk Token Ring IPX FDDI HSSI ATM RS-232 USB Firewire X.25 Blue Tooth WiFi Frame Relay Network Software Network This The software is highly structured technique has been immensely successful 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 Nth layer on one machine “talks to” or interacts with the Nth layer on another machine The 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 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. Protocols A Structured Set of Modules implements the communications function File Transfer Application Files and file transfer commands File Transfer Application Communications Service Module Communications related data units Communications Service Module Network Access Module Network Interface Logic Network Access Module Comms \Network Network Interface Logic That structure is referred to as a Protocol Architecture 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 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 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 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 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 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) 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 The 3 Layer Model •Network access Layer - This layer is concerned with the exchange of data between the computer and the network •Transport Layer - This layer is concerned with reliable and orderly exchange of data •Application Layer - This layer provides the logic required to support the various user applications A Simple Architecture Application () () ()() Transport Network Access SAPs Network Address Application Comms Network () () ()() Transport Network Access Application () () ()() Transport Network Access •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) Simplified Architecture Computer A Computer B Application Protocol Application Application Transport Protocol Transport Transport Network Access Network Access Protocol Comms \Network Network Access Protocol Network Access PDUs Protocol Data Unit (PDU) - is the combination of data from the next higher layer and control information Application data Transport header Application data Transport header Application data Transport protocol data unit (TPDU) Network Transport header header Application data Network Transport header header Application data Network protocol data unit (NPDU) control info + data in each layer = protocol data unit (PDU) 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. 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) Operation of Protocol Architecture Source X Destination Y Record Application Transport Record DSAP DSAP Application Transport Transport PDU Network Access DHost DHost Packet Network Access 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 The components of a basic Network Why establish a computer network •Program and file sharing •Network resource sharing •Database sharing •Economical expansion of the PC base •Workgroup capabilities •Centralized management •Security •Interconnectivity •Enhancement of corporate structure Distributed computing Access methods in a distributed computing environment A local area network (LAN) and an internetwork A network communication model Circuit Switching Circuit-switched is a type of network in which a physical path is obtained for and dedicated to a single connection between two end-points in the network for the duration of the connection. Ordinary voice phone service is circuitswitched. The telephone company reserves a specific physical path to the number you are calling for the duration of your call. During that time, no one else can use the physical lines involved. Circuit Switching Circuit-switched networks have been rapped for not having the resiliency and redundancy to reroute traffic that runs into a fiber or wire cut, because they don't have as many dispersed points of presence as IP networks have. But the big problem for enterprises running circuit-switched networks is that first stretch that connects them to the public network - a vulnerable mile, or two or three, that links them to a solitary central office shared by several carriers and service providers That's a vulnerability that circuit-switched networks share with Ethernet, IP, data-only and sometimes even cable networks. If a tornado, earthquake, ice storm or terrorist attack disables that shared central office or the lines leading to it, all data and voice communications for miles around could stop dead in their routes. Circuit Switching Packet Switching Packet switching is a communications paradigm in which packets (messages or fragments of messages) are individually routed between nodes, with no previously established communication path Packet-switched describes the type of network in which relatively small units of data called packets are routed through a network based on the destination address contained within each packet. Breaking communication down into packets allows the same data path to be shared among many users in the network. This type of communication between sender and receiver is known as connectionless (rather than dedicated). Most traffic over the Internet uses packet switching and the Internet is basically a connectionless network. Packet Switching Another type of digital network that uses packet-switching is the X.25 network, a widely-installed commercial wide area network protocol. Internet protocol packets can be carried on an X.25 network. The X.25 network can also support a virtual circuit in which a logical connection is established for two parties on a dedicated basis for some duration. A permanent virtual circuit (PVC) reserves the path on an ongoing basis and is an alternative for corporations to a system of leased lines. A permanent virtual circuit is a dedicated logical connection but the actual physical resources can be shared among multiple logical connections or users. Packet Switching Analogous to a physical packet sent through the post with the address written on the outside, this provides the information the network (the postal service) needs to get the packet to the correct destination. Packets are routed to their destination through the most expedient route (as determined by some routing algorithm). Not all packets travelling between the same two hosts, even those from a single message, will necessarily follow the same route. The destination computer reassembles the packets into their appropriate sequence. Packet switching is used to optimize the use of the bandwidth available in a network and to minimize the latency. Ethernet, X.25 and Frame relay are international standard layer 2 packet switching networks. The Internet is a packet-switched network, running the Internet protocol layer 3 protocol over a variety of other network technologies. Also called connectionless. Internet The Internet is a system of linked networks that are worldwide in scope and facilitates data communication service such as remote login, file transfer, electronic mail, the World Wide Web and newsgroups. With the meteoric rise of demand for connectivity, the Internet has become the communications highway for millions of users. The Internet was initially restricted to military and academic institutions in its infancy but now it is a full-fledged information channel for any and all forms of information and commerce. Internet websites now provide personal, educational, political and economic resources to every corner of the planet. Intranet With the advancements made in browser-based software for the Internet, there is now a phenomenon developed by private organizations called an intranet. An intranet is a private network utilizing Internet-type tools, but available only within that organization. For large organizations, an intranet provides an easy access mode to corporate information for employees.
