Catholic University College of Ghana FiapreSunyani Data Communications

Catholic University College of Ghana Fiapre-Sunyani Data Communications and Networks Internet INFORMATION TECHNOLOGY II Audrey Asante, Faculty of ICST

• Computer communication is the transmission of data and information over a communications channel between two computers, which can be several different things. • Communications between computers can be as simple as cabling two computers to the same printer. It can be as complex as a computer at NASA sending messages through an elaborate system of relays and satellites to tell a computer on Mars how to drive around without hitting the rocks.

• Depending on the context, for computer communications you might use the terms: • Data Communications for transmission of data and information over a communications channel Telecommunications for any long-distance communications, especially television Teleprocessing for accessing computer files located elsewhere

Communications Channel • A communications channel, also called a communications line or link, is the path that the data follows as it is transmitted from one computer to another.

COMPUTER NETWORK • A network is a system of interconnected computers, telephones, other communications devices that can communicate with one another and share applications and data

NETWORK MODEL • OSI (Open Systems Interconnect ) Reference Model • TCP/IP Reference Model

OSI MODEL 7

LAYERS’ FUNCTIONS Application (Layer 7) • This layer supports application and end-user processes. • Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. • Everything at this layer is application-specific. • This layer provides application services for file transfers, email, and other network software services. 8

LAYERS’ FUNCTIONS Presentation (Layer 6) • This layer provides independence from differences in data representation (e. g. , encryption) by translating from application to network format, and vice versa. • The presentation layer works to transform data into the form that the application layer can accept. • This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer. 9

LAYERS’ FUNCTIONS Session (Layer 5) • This layer establishes, manages and terminates connections between applications. • The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. • It deals with session and connection coordination. 10

LAYERS’ FUNCTIONS Transport (Layer 4) • This layer provides transparent transfer of data between end systems, or hosts • The layer is responsible for end-to-end error recovery and flow control. • It ensures complete data transfer. 11

LAYERS’ FUNCTIONS Network (Layer 3) • The layer provides switching and routing technologies • Creates logical paths, known as virtual circuits, for transmitting data from node to node • Provides routing and forwarding functions • Transforms the Logical Names into Physical Addresses • Provides internetworking, error handling, congestion control and packet sequencing. 12

LAYERS’ FUNCTIONS Physical (Layer 1) • This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level • It defines the electrical characteristics of the signals • It provides the hardware means of sending and receiving data on a carrier • It defines Network Interface Cards (NIC), cables, and connectors 13

TYPES OF NETWORKS • Local network – It is a privately owned communications network that serves users within a confined geographical area. The range is usually within a mile-an office, a building, a campus. There are two types-private branch exchanges (PBXs) and Local area networks • Metropolitan area network – It is a communications network covering a geographic area the size of a city or suburb. The purpose is often to bypass local telephone companies when accessing long-distance services.

• Wide area network – It is a communications network that covers a wide geograhical area, such as a state or a country. The internet links together hundreds of computer WANs. Most telephone systems are WANs. • Global area network – It is a communications network that covers the world. An examples is the internet.

Advantages • • • Sharing of peripheral devices Sharing of programs and data Better communications Security of information Access to databases

DISADVANTAGES • More complexity adds new problems to handle. Less customization is possible for shared programs and folders. Everyone will have to follow the same conventions for storing and naming files so others can find the right files. Sharing is hard for some people

LAN • They are local networks consisting of a communications link, network operating system, microcomputers or workstations, servers, and other shared hardware.

TYPES OF LAN • Client/Server LAN • Peer-to-peer: they don’t rely on a server.

TOPOLOGY OF LANs • Topology is the logical layout or shape of a network. The five basic topologies are star, ring, bus, hybrid, FDDI, Mesh

STAR TOPOLOGY • All microcomputers and other communication devices are connected to a central server. If the server goes down, the entire network will go off because it handles the flow of information. The maximum number of network devices is 1, 024. This configuration is good for businesses that have large amounts of rapidly changing data, like banks and airline reservation. Standard twisted-pair Ethernet uses a star topology

ADVANTAGES OF STAR TOPOLOGY • The server prevents collisions between messages. • If a connection is broken between any communications device and the server, the rest of the devices on the network will continue operating. • It's easy to add and remove nodes.

DISADVATANGES OF STAR TOPOLOGY • They require more cabling than other topologies

RING TOPOLOGY • All microcomputers and other communication devices are connected in a continuous loop. Each device is connected directly to two other devices, one on either side of it. There is no central server. Electronic messages are passed around the ring until they reach the right destination. Messages travel around the ring, with each node reading those messages addressed to it.

Ring Topology • The most common type of cabling used for token ring networks is twisted pair. Transmission rates are at either 4 or 16 megabits per second

ADVANTAGES OF THE RING TOPOLOGY • • Messages flow in only one direction. There is no collisions Requires less cabling. They offer high bandwidth and can span large distances

DISADVANTAGES OF RING TOPOLOGY • If the connection is broken, the entire network stops working. • Ring topologies are relatively expensive and difficult to install • Moves, adds and changes of devices can affect the network • Much slower than an Ethernet network under normal load

BUS TOPOLOGY • All communications devices are connected to a common channel called the bus or backbone. There is no central server. Each communications device transmits electronic messages to other devices. If some of those messages collide, the device waits and tries to retransmit. Ethernet 10 Base-2 and 10 Base-5 networks are bus networks.

Disadvantages • If a connection in the bus is broken, the entire network may stop working. • Extra circuitry and software needed to avoid collisions between data • Can't connect a large number of computers this way. It's physically difficult to run the one communications line over a whole building, for example.

ADVANTAGES OF BUS NETWORK • It may be organized as a client/server or peerto-peer network • Any one computer or device being down does not affect the others. • Bus networks are relatively inexpensive and easy to install for small networks.

MIXED/HYBRID TOPOLOGIES • The purpose of such topologies is to avoid some of the inconveniencies of the simple topologies and to use more effectively their advantages. • In such topologies, there at least one station, which belongs to the both topologies. Its role is to transform the signals and the protocols of the both networks. 31

RING – BUS TOPOLOGY • An interesting example is the mixed topology, based on token ring (optical cable) and star topology is very often used. • The optical ring can cover more long distances (between different buildings), and within each building – the topology can be either star or bus. 32

RING – BUS TOPOLOGY 33

FDDI • Fiber distributed data interface uses fiberoptic cable with an adaptation of ring topology using not one but two token rings. It is costly and fragility because fiber-optic cables are fragile. It overcomes the vulnerability by sending data on a clockwise and a counterclockwise ring:

• in the event of a break data is wrapped back onto the complementary ring before it reaches the end of the cable, maintaining a path to every node along the resulting "C-Ring • In addition to covering large geographical areas, FDDI local area networks can support thousands of users.

ADVANTAGES OF FDDI • High speed • Because of the adaptation of two token rings, if one should fail, the network can continue operating with the second ring.

MESH TOPOLOGY This is a network topology in which devices are connected with many redundant interconnections between network nodes. There are two types of mesh topologies: • full mesh • partial mesh. 37

FULL MESH TOPOLOGY • Every node has a circuit connecting it to every other node in a network. • Very expensive to implement but yields the greatest amount of redundancy • If one of those nodes fails, network traffic can be directed to any of the other nodes. • Full mesh is usually reserved for backbone networks 38

PARTIAL MESH TOPOLOGY • Less expensive to implement and yields less redundancy than full mesh topology. • With partial mesh, some nodes are organized in a full mesh scheme but others are only connected to one or two in the network. • Partial mesh topology is commonly found in peripheral networks connected to a full meshed backbone. 39

COMPONENTS OF LAN • Connection or cabling system: Cabling or connection system is either wired or wireless. Wired connections may be done by twistedpair, coaxial or fiber-optic cables. Wireless connections may be infrared or radio-wave transmission. Wireless are essential if computers are portable.

• Transmission media just means the physical materials that are used to transmit data between computers.

Twisted wire(phone line) • Advantage: Easy to string Cheap Disadvantage: Subject to interference = static and garble. attenuation

Fiber optic line (glass fibers) • Advantage: Smaller Lighter Faster (speed of light!) No interference • Disadvantage: Expensive Harder to install and modify

Wireless(infrared, light, radio) • Advantage: Flexible Portable • Disadvantage: Slower data transfer than hardwired methods Subject to interference

Microwave • Advantage: Speed of light Uses a few sites • Disadvantage: Line-of-sight only

Satellite • Advantage: Always in sight • Disadvantage: Expensive uplink and downlink facilities

Signals • Two types of signals are used for data transmission: Digital and Analog.

• A digital signal is a stream of 0's and 1's. So this type is particularly appropriate for computers to use. An analog signal uses variations (modulations) in a signal to convey information. It is particularly useful for wave data like sound waves. Analog signals are what your normal phone line and sound speakers use.

Coaxial cable (round insulated wire) • Advantage: Not susceptible to interference Transmits faster • Disadvantage: Heavy & bulky Needs booster over distance • Cross talk

COMPONENTS OF LAN cotn • Microcomputers with network interface cards. For communication to go on between two or more computers, they should have network interface cards • Network Operating System: NOS manages the activities of the network. Example Windows Server 2003 • Other shared devices: printers, fax, scanners, peripherals

COMPONENTS OF LAN cotn • Bridges, routers, and gateways: LANs can be stand alone but to connect to other networks you can make use of other types of hardware and software devices as an interface to make these connections. • A bridge is a hardware and software combination used to connect the same types of networks • A router is a special computer that directs communicating messages when several networks are connected together. • A gateway is an interface that enables dissimilar networks to communicate, such as a LAN with a WAN or two LANs based on different topologies or network operating systems.

NETWORK SERVERS • File Server: it is a computer that stores the programs and data files shared by users on a LAN. • It provides global disk space for users which have certain access and directories • It organize access rights and allocate resources to the users

Database Server • It is a computer in a LAN that stores data. Unlike a file server, it does not store programs.

PRINT SERVER • It is a computer in a LAN that controls one or more printers. It stores the print-image output to the printer or printers one document at a time. • Printer is shared on the network • They are for cost efficiency since not every station needs its own printer

COMMUNICATION SERVER • It handles data exchange with the outside world as well as internal data exchange • They usually provide – Sending and reception of email – Sending and reception of fax messages – Connection to the internet – Connection to other networks

FAX AND MAIL SERVERS • Fax servers are dedicated to managing fax transmissions • Mail servers manage email

BACK UP SERVER • It is important to backup workstation or server data. • They are mainly performed in the nights

INTERNET • • What is Internet Connecting to the Internet Addresses Features of the Internet

INTERNET • It is the global interconnection of networks. • TCP/IP is the standardized set of computer guidelines (protocols) that allow different computers on different networks to communicate with each other efficiently.

Connecting to the Internet • Through school or work • Online information services • Internet service providers

INTERNET ADDRESS • • dasoul@cug. edu. gh Dasoul: userid @: separator Cug. edu. gh: domain

TOP LEVEL DOMAINS • • • . com: commercial organizations. edu: educational and research organizations. firm. gov. info. org. int. mil. net

SERVICES OF THE INTERNET • • • Email Telnet File Transfer Gopher Chat World Wide Web (WWW)