Network Topologies
Network Topology is the study of the arrangement or mapping of the elements (links, nodes, etc.) of a network interconnection between the nodes. It also determines the strategy for physically expanding the network, in future. Common network topologies are Mesh, Ring, Bus, Star and Tree.
1. Bus Topology:
Bus topology is a single common communication to which all the computers are connected. It has a single length of cable with a termina or at each end.
F It is a passive topology which means only one computer at a time can send a message. Hence, the number of computers attached to a bus network can significantly affect the speed of the network.
F The bus topology is the simplest and most widely used with local area network design.
Advantages:
a. It is simple, reliable and easy to be used in a small sized local area network.
b. It requires least amount of cable to connect computers together and is therefore less expensive than other cabling arrangements.
c. It is easy to implement and extend using connectors.
d. If one computer on the bus fails, it does not affect the rest of the traffic on the bus.
Disadvantages:
a. In this topology, no two computers can transmit data at the same time.
b. It does not cope well with heavy load which can slow down a bus considerably.
c. Performance degrades as additional computers are added.
d. Terminators are required at both ends of the cable.
2. Ring Topology:
Ring topology is also known as circular topology. This layout is similar to the linear bus, except that the nodes are connected in a circle.
In this topology, each node is connected to two and only two neighbouring nodes. The ring does not have an end.
Advantages:
a. It is an orderly network where every device has access to the token (control signal) and the opportunity to transmit – because every computer is given equal access to the token, no computer can monopolize the network.
b. It performs better than a star topology under heavy network load.
c. It can create much larger network using Token Ring.
d. It does not require network server to manage the connectivity between the computers.
Disadvantages:
a. Network adapter cards and Multi Access Units used in this topology are much more expensive than Ethernet cards and hubs used in bus topology.
b. It is much slower than an Ethernet network under normal load.
c. It is difficult to troubleshoot.
d. One malfunctioning node or bad port in the Multi Access Units can create problems for the entire network.
3. Star Topology:
In star topology, each computer on a network communicates with a central hub (also called as a concentrator) that re-sends the message either to all the computers or only to the destination computer.
A hub expands one network connection into many. For example, a four-port hub connects up to four machines.
A single hub is sufficient for a small network; however large networks require multiple hubs. But, it increases hardware and cabling costs.
Advantages:
a. It is more reliable (if one connection fails, it does not affect others).
b. It is easy to replace, install or remove hosts or other devices, problem can be easily detected- It is easier to modify or add a new computer without disturbing the rest of the network by simply running a new line from the computer to the central location and plugging it to the hub.
c. Use of multiple cables types in a same network with a hub.
d. It has good performance.
Disadvantages:
a. It is expensive to install as it requires more cable, it costs more to cable a star network because all network cables must be pulled to one central point, requiring more cable length than other networking topologies.
b. Central node dependency, if central hub fails, the whole network fails to operate.
c. Many star networks require a device at the central point to rebroadcast or switch the network traffic.
4. Tree Topology:
It is a hierarchical topology, in which there are multiple branches and each branch can have one or more basic topologies like star, ring and bus.
Such topologies are usually realised in WANs where multiple LANs are connected. Those LANs may be in the form of a ring, bus or star.
In this type of network, data transmitted from source first reaches the centralised device and from there the data passes through every branch where each branch can havelinks for more nodes Network Classification There are various types of computer networks ranging from network of handhelddevices (like mobile phones or tablets) connected through Wi-Fi or Bluetooth within a single room to the millions of computers spread across the globe. Some are connected wireless while others are connected through wires.
Based on the geographical area covered and data transfer rate, computer networks are broadly categorised as:
1. Personal Area Network (PAN):
It is a network formed by connecting a few personal devices like computers, laptops, mobile phones, smart phones, printers etc.
All these devices lie within an approximate range of 10 meters.
A personal area network may be wired or wireless.
For example, a mobile phone connected to the laptop through USB forms a wired PAN while two smartphones communicating with each other through Bluetooth technology form a wireless PAN or WPAN.
2. Local Area Network (LAN):
LAN is a group of computers located in the same room, on the same floor or in the same building that are connected to form a single network as to share resources such as disk drives, printers, data, CPU, fax/ modem, applications etc. LAN is generally limited to specific geographical area less than 2 km, supporting high speed networks. The most widely used LAN system is the Ethernet system based on the bus topology.
Characteristics of LAN:
1. Network devices such as workstations, printers, file servers which are normally accessed by all other computers.
2. Network Communication Devices i.e., devices such as hubs, routers, switches etc. that are used for network connectivity.
3. Network Interface Cards (NICs) for each network device required to access the network. It is the interface between the machine and the physical network.
4. Cable as a physical transmission medium. However, present day LAN may not require the physical transmission media. It may be a wireless LAN.
5. Network Operating System
NETWORK DEVICES
1. Modem:
Modem stands for ‘MOdulator DEModulator’. It refers to a device used for conversion between analog signals and digital bits.
The modem at the sender’s end acts as a modulator that converts the digital data into analog signals.
r The modem at the receivers end acts as a demodulator that converts the analog signals into digital data for the destination node to understand.
2. Ethernet card:
Ethernet card, also known as Network Interface Card (NIC card in short) is a network adapter used to set up a wired network.
It acts as an interface between computer and the network. It is a circuit board mounted on the motherboard of a computer.
The Ethernet cable connects the computer to the network through NIC. Ethernet cards can support data transfer between 10 Mbps and 1 Gbps (1000 Mbps).
Each NIC has a MAC address, which helps in uniquely identifying the computer on the network.
3. Registered Jack-45:
RJ 45 or Registered Jack-45 is an eight-pin connector that is used exclusively with Ethernet cables for networking.
It is a standard networking interface that can be seen at the end of all network cables. Basically, it is a small plastic plug that fits into RJ-45 jacks of the Ethernet cards present in various computing devices.
4. Repeater:
Data are carried in the form of signals over the cable. These signals can travel a specified distance (usually about 100 m).
Signals lose their strength beyond this limit and become weak. In such conditions, original signals need to be regenerated.
A repeater is an analog device that works with signals on the cables to which it is connected. xw The weakened signal appearing on the cable is regenerated and put back on the cable by a repeater.
5. Hub:
An Ethernet hub is a network device used to connect different devices through wires.
Data arriving on any of the lines are sent out on all the others. The limitation of hub is that if data from two devices come at the same time, they will collide.
6. Switch:
A switch is a networking device that plays a central role in a Local Area Network (LAN). Like a hub, a network switch is used to connect multiple computers or communicating devices.
When data arrives, the switch extracts the destination address from the data packet and looks it up in a table to see where to send the packet.
Thus, it sends signals to only selected devices instead of sending to all. It can forward multiple packets at the same time.
A switch does not forward the signals which are noisy or corrupted. It drops such signals and asks the sender to resend it.
Ethernet switches are common in homes/ offices to connect multiple devices thus creating LANs or to access the Internet.
7. Router:
A router is a network device that can receive the data, analyse it and transmit it to other networks.
A router connects a local area network to the internet. A router can be wired or wireless.
A router has advanced capabilities as it can analyse the data being carried over a network, decide/ alter how it is packaged and send it to another network of a different type.
8. Gateway:
As the term “Gateway” suggests, it is a key access point that acts as a “gate” between an organisation's network and the outside world of the internet.
Gateway serves as the entry and exit point of a network, as all data coming in or going out of a network must first pass through the gateway in order to use routing paths.
For simple internet connectivity at homes, the gateway is usually the Internet Service Provider that provides access to the entire internet.
