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 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 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

TELECOMMUNICATIONS

TELECOMMUNICATIONS

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

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 Communication Network Node 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 modem link via PSTN PSTN

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

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

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

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

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

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

An Example – Wireless LAN Initial 1 & 2 Mbps aHigh Rate 5.7Ghz b5.5 and 11 Mbps c MAC Bridge dRegulating Domains eQuality of Service fMulti-Vendor Inter-Access Port gHigh Rate 2.4Ghz h Power Control/Frequency Selection iEnhanced Security j4.9-5Ghz in Japan kRadio 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

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

MANs u Distances between 5 and 50 km u Data rate above 1 Mbps u Standards: IEEE DQDB, FDDI, and ATM

LANs (Local Area Networks) u Maximum distance not more than a few kms u Ownership by a single organization u Transmission speed of at least several Mbps (tens to hundreds are economical) u Some widely used standards include: F IEEE Ethernet F IEEE Token ring F FDDI F ATM u An important issue in broadcast LANs is the allocation of the shared channel (media access control) u 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 a WAN (Wide Area Network) u Spans entire states or countries u Data rate of (T1), and 45 (T3) Mbps common u Higher data rates are available with the wide deployment of ATM backbone networks u Often owned by multiple organizations

WAN u Usually separate communications functions from application functions u Transmission lines: circuits, channels or trunks u Switching elements: F Specialized computers connecting two or more circuits F Intermediate Systems, Packet Switching Node, Data Switching Exchange, Router, etc. F Intermediate systems store a complete packet before forwarding it store-and-forward; packet switched; point-to-point networkstore-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 a Network software is highly structured a This technique has been immensely successful a The key is Layered design u Each layer provides a service to the layer above u Each layer hides details of how the service is provided to the layer above u The N th layer on one machine “talks to” or interacts with the N th layer on another machine

Understanding Services and Protocols n Protocol is set of rules about the format and meaning of data units exchanged by peers u Protocol is used by entities to implement services u Protocol and/or its implementation can change and as long as the Service (interface) remains unchanged, higher layers are happy and continue to work u 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 File Transfer Application Communications Service Module Network Access Module File Transfer Application Communications Service Module Network Access Module Comms \Network Network Interface Logic Network Interface Logic Communications related data units Files and file transfer commands A Structured Set of Modules implements the communications function 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 a Conventions and rules governing this interaction are specified by the Layer N Protocol u A protocol is an agreement about how communications are to proceed u Without a protocol, communication can be difficult or even impossible u E.g. Telephone conversation, Postal addresses

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

Network Software - Protocols a Information is not actually transferred directly between peer layer N entities u Peer layer N entities carry on a virtual communication using the services of the layers below u 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 a Network Architectures, Protocols and Protocol stacks are the Fundamentals of Computer Networks u They form the foundation for the very considerable success of computer networks in the real world u Multilayer communications protocols allow F ready adaptation of successful protocols to new technology (prevent obsolescence) F migration of protocols from software implementation (slow) to hardware (fast) as they evolve

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

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

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

A Simple Architecture Application Transport Network Access Application 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) SAPs Network Address Comms Network ( ) ( )

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

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

Network Operation 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. Information in Transport Header

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 Network Access Transport Application Transport Network Access Source X Destination Y Record DSAP DHost Packet Transport PDU

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

Packet Switching

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.