Notes on Computer Networking

Hybrid Star Bus & Star Ring: When more than one topology is combined together that forms the Hybrid topology. In hybrid topology it is not just combining topologies together but combining the features or advantages. The hybrid topology is confined when a single network grows beyond the limitation.

Mesh: According to mesh every device needs to have point to point link with every other device on the network. It is the most commonly used topology in WAN and is often seen in public network like, Internet. But in practice, this network is used in a hybrid approach with only the most important devices interconnected in the mesh.

Star: In this type each PC is connected to a central device called ‘Hub’ or ‘Switch’ via a point to point link. When a PC sends any data on the network, then the central device use to sends the data to all the PCs on the network. It is similar to an EPBAX telephone system.

Advantages:
1. In Star it is very easy to configure & reconfigure the network settings.
2. In this type it is very easy to monitor the network functions. And easy to locate any problem in the network.

Disadvantages:
1. Adding or removing a device can affect the network making it difficult to reconfigure the network. 2. All devices will be affected by media or central device failure on the network.

Ring: In this type, the PCs are connected in a circle in a series of point-to-point links between each device. The Ring topology can be implemented by direct link using cable or using intermediary device called “Multi Station Access Unit” (MSAU). In this network a signal emit by one computer is passed from one device to another in a single direction and the signal is regenerated each time at each device. It can be implemented commonly as IBM’s token ring, Fiber Distributed Data Interference (FDDI), & Copper Distributed Data Interference (CDDI).

Advantages:
1. It uses least amount of cable for networking after bus topology.
2. It is relatively simple to install.
3. You can make a fault tolerance network by using dual ring system via dual counter rotating rings.

Disadvantages:
1. Adding and removing a device can affect the network making it difficult to reconfigure.
2. All devices will be affected by media or device failure.
3. It is difficult to troubleshoot any problems in this topology.

Bus: In this topology all PCs are attached directly to the main or backbone cable in a linear method. The BUS needs to be terminated at both ends of the cable so that the signal is reflected back when it has gone through all the devices attached to the network. In this network the data signal will travel both the directions of the network.

Advantages:
1. It is relatively simple to install.
2. It uses the least amount of cable among all other topologies.
3. It is the cheapest of all other topology.
4. It is not dependent on any one device for its function.

Disadvantages:
1. It is relatively hard to reconfigure.
2. The No of PCs connection is limited as because the signal will degrades as the traffic increases.
3. It is difficult to locate or to troubleshoot the problems.

Network Topology: In order to make computer network one can use either of the two connections. Point to Point connection: It is a one to one connection where only two devices can share connection. Since only two devices on the network so a level of bandwidth is assured to the user. Multipoint connection: It is a connection where more than three computers share the connection and is also called as multi drop connection. Here the amount of bandwidth that available to the user is purely depends on the load of the network. Topology: The structure or the layout of the network is called as the topology of the network.

Or
The topology describes the way of interconnecting of the computers.
Physical Topology: It explains the actual physical layout of the network. Logical Topology: It explains the logical flow of the data through the network. There are 3 core topologies and 2 other topologies

Unguided Media: It is one that does not guide the data signals instead it uses the multiple paths for transmitting data signals. In this type the data cable are not bounds to a cable media. So it is called “Unbound media” basically there are 2 types.
a) Microwave, b) Satellite Technology.

a) Microwave: Microwave lies on the electromagnetic spectrum between radio waves and light waves. As a means of carrying data, microwave offers advantages because their high frequency is less affected by atmospheric conditions. Technically speaking, microwave lies between 890 MHz to 5 GHz. A common use for microwave technology in data network where using physical media would be difficult & some time may impossible. It is also used in satellite technology. They constitute an excellent choice for broadcasting to satellite & back to earth. From security point of view MW may not be that safe. Because anyone may intercept jam, or in some cases. It is also not cent percent reliable. Though it would get less affected by atmospheric condition.

Advantages:
1. It has the medium capacity slightly higher than “Bound Media”
2. Medium cost.
3. It can cover longer distance that cannot be possible by bound media.

Disadvantages:
1. Noise interference is more.
2. Since it uses less susceptible signal so it has got greater influence from rain & fog.
3. It is not secure & reliable.

b) Satellite Communication: Satellite is a celestial body that revolves around the earth in a specific orbit & mean while establishes a non terrestrial means of communication. It has a unit called “Transponder” that is responsible for transmission, reception, & amplification, of the signal which is being sent from the earth. The term uplink describes the transmission of signals from earth station to satellite, while the term down link describes the retransmission of the signal from satellite to earth station. Each channel is managed by a transponder, which can support thousands of speech channels and about 4 TV channels simultaneously. It’s primary use to link between countries and even continents.

Advantages:
1. Low cost per user (for pay TV)
2. High Capacity
3. Very large coverage area.

Disadvantages:
1. High Installing & managing cost.
2. Receive dishes & decoders required.
3. Delays involved in the reception of the signal.

Fiber Optic Cable: It uses light signals instead of electrical signals & comprises of glass core, which is surrounded by a glass layer known as cladding. The light traveling along the cable core is called waveguide. Cladding is used to reflect the signals back into the waveguide the by multiple internal reflections.
Categories of FOC:
a) Monomode: It is a single wavelength, which follows the same path along the fiber. It supports higher transmission speeds over long distance. It is very expensive.

b) Multimode: It is a multiple wavelength, which follows the multiple light paths along the fiber. The light pulse at the receiving end is more blurred than the light source created by Monomode system.

Advantages:
1. It is very reliable and secure transmission medium as it is immune to EMI or eavesdropping.
2. It supports comparatively high bandwidth upto 2Gbps.
3. It can be used over large distance as it has low attenuation level.
4. Due to its non use of electrical signals it can be used in hazards condition, which are highly inflammable.
5. It has a long life & thus does not require to be reinstalled.

Disadvantages:
1. The connectivity devices & installation of the cable is relatively expensive.
2. Because of the need of high degree of precision & careful handling of the cable, the installation has to be done by a very experienced person & costs a lot.
3. Compare to other cables, it is relatively complex to configure & reinstall.

Coaxial Cable: Co axial or co-ax cable is made up of two conductors, which share the same axis due to which they have been named as ‘co’ and ‘ax’ “coax”. The copper wire enclosed in a plastic insulation is the main conductor of the cable while the wire mesh acts as the second conductor. The wire mesh is also acts as a shield against EMI and a grounded point. It can be categorized according to the Radio Grade Standard:

Rating Impedance (ohms) Description
RG- 8 50 Thick net
RG-58 50 Thin net
RG-59 75 Cable Net
RG-62 93 ARC net

Thick coax cable: It requires a hole to be drilled into the cable through a device called vampire tap which is clamped around the cable. To receive and handle signals on the network, the tap also contain a transceiver. Thin coax cable: It can be cut at the position which you want to attach a device to it. It is crimped with BNC connectors at both the ends of the cable.

Advantages:
1. Thin coax cable is relatively cheap & in the same price range of UTP.
2. It is compatible and has interoperability with different vendor’s equipment. 3. The installation is relatively simple.

Disadvantages:
1. Coax cables are prone to EMI and eavesdropping.
2. It may be difficult to reconfigure the coax network.

Twisted Pair: A pair of insulated wires twisted together forms a twisted pair (TP). The wires are twisted so that the signal emitted by one wire is cancelled by the signal emitted by other wire there by reducing interference & cross talk. In TP there are mainly two types. STP & UTP.

Shielded Twisted Pair (STP): Earlier the twisted pair cable was shielded because of its greater resilience to EMI while the latest twisted pair cabling is unshielded. It consists of 2 pairs of wires each pair is wrapped in metallic foil. The two pairs are wrapped in an overall metallic braid or foil.

Unshielded Twisted Pair (UTP): Most of the current twisted pair cables used in the network is UTP. Because of its large success in telephone systems. This cable supports both the telephone system and PC network.

Advantages:
1. Using this cable makes the network reconfiguration simple & easy.
2. The cable can be easily & cheaply installed with the help of various equipments.
3. STP is cheaper than Co-ax and FOC cable.

Disadvantages:
1. Both the formats have high attenuation levels causing data loss or corruption over larger networks. 2. It is susceptible to EMI and eavesdropping.
3. It can only transfer data at a speed of up to 155 Mbps.

Connectors: RJ-45/RJ-11 RJ stands for Registered Jack. These two connectors are used by TP cable. RJ-11 has 4 contacts and it is used for telephone system, while RJ-45 has 8 contacts which is used for data network.

Types of networking:
LAN: It is a local area network it is a type of network that covers the distance of not more 1.25 mile from one end to other end. It is popularly used in an office, factory etc.

MAN: It is a Metropolitan area network. It is a type of network that covers a city of not
more than tens of miles or kilometers. Normally it is confined in an area like a metropolitan city.

WAN: It is wide area network. It is a network that covers countries & even continents. It is often made up of multiple LANs joined together for ex: Internet.

Transmission Media:
Transmission media is a physical or virtual path that allows data signal to flow along with it.
There are mainly two types.
a) Guided Media,
b) Unguided Media.
Guided Media: It is one that guides the data signals along a specific path. In this type the data signals are bound by the cabling system. In guided media basically 3 types.
1. Twisted Pair, 2. Co-Axial cable, 3. Fiber Optic Cable

Definition:
Computer network in the sense connecting two are more computers together via a transmission media so that they can share information & resources.

Necessity of Networking:
In an organization there may be thousands employees working together and information need to be shared among themselves for better co-ordination & performance. And it is also difficult for an organization to spend lot of money for purchasing of peripheral resources like printer, CD-ROM, etc. Through the network we can share these resources among the multiple users there by it reduces the cost & saves the time. These points describe the necessity for making computer network.

Advantages:
1. Information & Resources can be shared.
2. It saves the time & cost through sharing of the information & Resources.
3. It is secure & reliable media.
4. It enables efficient communication.
5. Network administration is easy & centralized. 6. It standardizes the application.

Application:
1. Electronic mail (Email).
2. Web Browsing.
3. Internet chatting.
4. Video conference Etc