The School, University or venue where you study from
In a paragraph, describe yourself in relation to your learning or teaching
Click to select more than one option (multiple times)
In its simplest form, a network is a cluster of computers, with one computer acting as a server to provide network services such as file transfer, email and document printing to the client computers of that network. Using gateways and routers, a local area network (LAN) can be connected to other LANs to form a wide area network (WAN). These LANs and WANs can also be connected to the internet through a server that provides both the necessary software for the internet and the physical data connection (usually a high –bandwidth telephone line.) Individual computers not permanently part of a network (a home computer or a laptop) can dial up to one of these internet servers and , with proper identification and onboard client software, contain an IP address on the internet.
Computers connected over a network can make that information exchange easier and faster. The information moves directly from computer to computer rather than through a human intermediary.
3.1 TYPES OF NETWORK
Computer Networks are mostly classified on the basis of the geographical area that the network covers, the topology used, the transmission media used and the computing model used. Based on the geographical area covered the networks may be LAN, MAN, WAN.
3.1.1 METROPOLITAN AREA NETWORK (MAN)
Metropolitan Area Network is a Computer network designed for a town or city. In terms of geographic area MAN’s are larger than local-area networks (LANs), but smaller than wide-area networks (WANs). MAN’s are usually characterised by very high-speed connections using fibre optical cable or other digital media. It is designed for organisations who need a high – speed connectivity normally to the internet and have end point spread over a city or a part of the city.
Characteristics of a MAN are:
3.1.2 WIDE AREA NETWORK (WAN)
Wide Area Network is a computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more local-area networks (LANs). It provides a long distance transmission of data, image, audio and video information over large geographic areas that may comprise a country, a continent or even the whole world.
Computers connected to a wide-area network are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites.
Characteristics of a WAN are:
A WAN can range from 100krn to 1000krn and the speed between cities can vary forml.5 Mbps to 2.4 Gbps.
WAN supports large number of computers and multiple host machines.
Various segments of network are interconnected using sophisticated support devices like routers and gateways.
Usually the speed is much slower than LAN speed.
Highest possible error rate compared to LAN & MAN.
3.1.3 LOCAL AREA NETWORK (LAN)
A local Area network is usually privately owned and links the devices in a single office, building or campus. Depending o the needs of an organisation, and the type of technology used, a Local area network can be as simple as two PC or it can extend throughout a company and include audio and video peripherals.
LANS are designed to allow resources to be shared between personal computers or workstations. The resources to be shared can include hardware (e.g printer), software (e.g an application program) or data. A common example of a LAN, found in many business environment s, links a work group of task- related computers example engineering workstations or accounting PCs. One of the computers may be given a large capacity disk drive and may become a server to clients.
A local area network (LAN) is a number of computers connected to each other by cable in a single location , While local area network are perfect for sharing resources within a building or campus, they cannot be used to connect distant sites.
3.3 NETWORK TOPOLOGY
Topology refers to the shape of a network, or the network’s layout. How different nodes in a network are connected to each other and how they communicate with each other is determined by the network’s topology. Topologies are either physical or logical.
Some of the most common network topologies are:
3.2.1 BUS TOPOLOGY
Diagram of a Star Topology
In Bus topology, all devices are connected to a central cable, called the bus or backbone. The bus topology connects workstations using a single cable. Each workstation is connected to the next workstation in a point-to- point fashion. Nodes are connected to the bus cable by drop lines and taps. A drop line is a connection running between the device and the main cable. A tap is a connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core.
In this type of topology, if one workstation goes faulty all workstations may be affected as all workstations share the same cable for the sending and receiving of information. The cabling cost of bus systems is the least of all the different topologies. Each end of the cable is terminated using a special terminator.
The common implementation of this topology is Ethernet. Here, message transmitted by one workstation is heard by all the other workstations.
Advantages of Bus Topology
Installation is easy and cheap when compared to other topologies
Connections are simple and this topology is easy to use.
Less cabling is required. Disadvantages of Bus Topology
Used only in comparatively small networks.
As all computers share the same bus, the performance of the network deteriorates when we increase the number of computers beyond a certain limit.
·Difficulty in reconnection and fault isolation.
A single fault in the cable stops all transmission.
3.2.2 STAR TOPOLOGY
Star topology uses a central hub through which, all components are connected. In a Star topology, the central hub is the host computer, and at the end of each connection is a terminal. Nodes communicate across the network by passing data through the hub. A star network uses a significant amount of cable as each terminal is wired back to the central hub, even if two terminals are side by side but several hundred meters away from the host. The central hub makes all routing decisions, and all other workstations can be simple
An advantage of the star topology is that failure, in one of the terminals does not affect any other terminal; however, failure of the central hub affects all terminals. This type of topology is frequently used to connect terminals to a large time-sharing host computer.
Advantages of Star Topology
Installation and configuration of network is easy.
Less expensive when compared to mesh topology.
Faults in the network can be easily traced.
Expansion and modification of star network is easy.
Single computer failure does not affect the network.
Supports multiple cable types like shielded twisted pair cable, unshielded twisted pair cable, ordinary telephone cable etc.
Disadvantages of Star Topology
Failure in the central hub brings the entire network to a halt.
More cabling is required in comparison to tree or bus topology because each node is connected to the central hub.
3.2.3 RING TOPOLOGY
In Ring Topology all devices are connected to one another in the shape of a closed loop, so that each device is connected directly to two other devices, one on either side of it, i.e., the ring topology connects workstations in a closed loop, Each terminal is connected to two other terminals (the next and the previous), with the last terminal being connected to the first. Data is transmitted around the ring in one direction only; each station passing on the data to the next station till it reaches its destination.
Information travels around the ring from one workstation to the next. Each packet of data sent on the ring is prefixed by the address of the station to which it is being sent. When a packet of data arrives, the workstation checks to see if the packet address is the same as its own, if it is, it grabs the data in the packet. If the packet does not belong to it, it sends the packet to the next workstation in the ring.
Faulty workstations can be isolated from the ring. When the workstation is powered on, it connects itself to the ring. When power is off, it disconnects itself from the ring and allows the information to bypass the workstation.
The common implementation of this topology is token ring. A break in the ring causes the entire network to fail. Individual workstations can be isolated from the ring.
Advantages of Ring Topology
Easy to install and modify the network.
Fault isolation is simplified.
Unlike Bus topology, there is no signal loss in Ring topology because the tokens are data packets that are re-generated at each node.
Disadvantages of Ring Topology
Adding or removing computers disrupts the entire network.
A break in the ring can stop the transmission in the entire network.
Finding fault is difficult.
Expensive when compared to other topologies.
3.2.4 TREE TOPOLOGY
Tree topology is a LAN topology in which only one route exists between any two nodes on the network. The pattern of connection resembles a tree in which all branches spring from one root. Tree topology is a hybrid topology, it is similar to the star topology but the nodes are connected to the secondary hub, which in turn is connected to the central hub. In this topology groups of star-configured networks are connected to a linear bus backbone.
Advantages of Tree Topology
Faults in the network can be detected traced.
The addition of the secondary hub allows more devices to be attached to the central hub.
Disadvantages of Tree Topology
More cabling is required when compared to bus topology because each node is connected to the central hub.
3.2.5 MESH TOPOLOGY
Devices are connected with many redundant interconnections between network nodes. In a well-connected topology, every node has a connection to every other node in the network. The cable requirements are high, but there are redundant paths built in. Failure in one of the computers does not cause the network to break down, as they have alternative paths to other computers.
Mesh topologies are used in critical connection of host computers (typically telephone exchanges). Alternate paths allow each computer to balance the load to other computer systems in the network by using more than one of the connection paths available. A fully connected mesh network therefore has n (n-1)/2 physical channels to link n devices. To accommodate these, every device on the network must have (n-l) input/output ports.
Advantages of Mesh Topology
Use of dedicated links eliminates traffic problems.
Failure in one of the computers does not affect the entire network.
Point-to-point link makes fault isolation easy.
It is robust.
Privacy between computers is maintained as messages travel along dedicated path.
Disadvantages of Mesh Topology
The amount of cabling required is high.
A large number of I/O (input/output) ports are required.
Depending on the architecture used Networks can be classified as Client/Server or Peer-to-Peer Networks. Sever-based networks are the most typical in most organizations and represent the primary focus of the discussion here. It is essential to understand both types, especially as they compare and contrast with one another.
3.4.1 CLIENT/SERVER ARCHITECTURE
Client/Server Architecture is one in which the client (personal computer or workstation) is the requesting machine and the server is the supplying machine, both of which are connected via a local area network (LAN) or wide area network (WAN). Since the early 1990s, client/server has been the buzzword for building applications on LANs in contrast to centralised minis and mainframes with dedicated terminals. A client/server network is called Centralised or Server based network.
The client contains the user interface and may perform some or all of the application processing. Servers can be high-speed microcomputers, minicomputers or even mainframes. A database server maintains the databases and processes requests from the client to extract data from or update the database. An application server provides additional business processing for the clients.
The term client/server is sometimes used to contrast a peer-to-peer network, in which any client can also act as a server. In that case, a client/server entails having a dedicated server.
However, client/server architecture means more than dedicated servers. Simply downloading files from or sharing programs and databases on a server is not true client/server either. True client/server implies that the application was originally designed to run on a network and that the network infrastructure provides the same quality of service as traditional mini and mainframe information systems.
The network operating system (NOS) together with the database management system (DBMS) and transaction monitor (TP monitor) are responsible for integrity and security of these types of networks. Some of these products have gone through many client/server versions by now and have finally reached industrial strength.
3.4.2 PEER-TO-PEER ARCHITECTURE
A type of network in which each workstation has equal capabilities and responsibilities is called peer-to-peer network. Here each workstation acts as both a client and a server. There is no central repository for information and there is no central server to maintain.
Data and resources are distributed throughout the network, and each user is responsible for sharing data and resources connected to their system. This differs from client/server architectures, in which some computers are dedicated to serving the others. Peer-to-peer networks are generally simpler and less expensive, but they usually do not offer the same performance under heavy loads. A peer-to-peer network is also known as a Distributed network.
SELF ASSESSMENT EXERCISE
Identify the differences between the client Server and Peer-to-Peer network Architecture
In this unit you have learnt about networking and the different types of networks. You have also learnt that the primary motivation for networking arises from a need for individuals and programs to share data quickly and efficiently. How different nodes in a network are connected to each other and how they communicate with each other is determined by the network’s topology. Topologies are either physical or logical. Some of the most common network topologies are: Bus topology, Star topology, Ring topology, Tree topology and the Mesh topology
The most elementary of all networks consists of two computers, each connected to the other using some kind of cable to permit information exchange. No matter how many computers may be interlinked, or what kinds of connections may be in use, all networking derives from this basic description. In fact, when computers communicate, they frequently do so in pairs, with one machine sending information and the other receiving the information. Even though this may seem elementary, the introduction of computer networks represents significant step up from what any single computer can do alone.
6.0 TUTOR MARKED ASSIGNMENT
1).Distinguish between the different types of network
2) Describe the two types of network Architecture.
2).State three advantages and disadvantages of the WAN, LAN &MAN Networks
Enter the destination URL
Or link to existing content