Tuesday 18 December 2012

Lan Topologies

The shape of a network, and the relationship between the nodes in that network is known as the Network Topology. The network topology determines, in large part, what kinds of functions the network can perform, and what the quality of the communication will be between nodes.

Start Topology:
A star topology creates a network by arranging 2 or more host machines around a central hub. A variation of this topology, the 'star ring' topology, is in common use today. The star topology is still regarded as one of the major network topologies of the networking world. A star topology is typically used in a broadcast or SIMO network, where a single information source communicates directly with multiple clients. An example of this is a radio station, where a single antenna transmits data directly to many radios.

Ring Topology:
A ring topology (more commonly known as a token ring topology) creates a network by arranging 2 or more hosts in a circle. Data is passed between hosts through a 'token.' This token moves rapidly at all times throughout the ring in one direction. If a host desires to send data to another host, it will attach that data as well as a piece of data saying who the message is for to the token as it passes by. The other host will then see that the token has a message for it by scanning for destination MAC addresses that match its own. If the MAC addresses do match, the host will take the data and the message will be delivered. A variation of this topology, the 'star ring' topology, is in common use today.

Mesh Network:
A mesh topology creates a network by ensuring that every host machine is connected to more than one other host machine on the local area network. This topology's main purpose is for fault tolerance as opposed to a bus topology, where the entire LAN will go down if one host fails. In a mesh topology, as long as 2 machines with a working connection are still functioning, a LAN will still exist. The mesh topology is still regarded as one of the major network topologies of the networking world.

Bus Topology:
A bus topology creates a network by connecting 2 or more hosts to a length of coaxial backbone cabling. In this topology, a terminator must be placed on the end of the backbone coaxial cabling.
The bus topology is still regarded as one of the major network topologies of the networking world.






Best Regards,


S. N. Jafar


Monday 18 June 2012

Network Cables

Straight through Cable: is a network cable that connects a computer to a network device. For example, straight through cables are cables that connect a computer to a network hub, network switch, and network routers. (To connect Different devices)
Color sequence in straight cables are:
1-White Orange
2-Orange
3-White Green
4-Blue
5-White Blue
6-Green
7-White Brown
8-Brown
Note: same color combination on both Ends of the cable
Cross-Over Cable: Networking cable that connects two computers or network devices directly to one another, crossover cables are used to connect two computers (or same devices) with network cards together without using a network hub, network router, or network switch.
Color sequence in cross-over cables are:
1-White Green
2-Green
3-White Orange
4-Blue
5-White Blue
6-Orange
7-White Brown
8-Brown
Note: just replace 1 with 3 and 2 with 6.
Roll-Over cable: Both the combination are opposite to each other like if, straight combination at one end than on the other end it must be opposite.
i.e. Used to connect router to PC.


Thanks.

S. N. Jafar

Saturday 16 June 2012

Network Communication Media

There are two mediums for network communication.
1-Cable Media (Guided Media)
2-Wireless Media (Un-guided Media) (will discuss later)

Cable Media (Guided Media)
i.e: co-axial cable, UTP (un-shielded twisted Pair), STP (Shielded Twisted Pair) and Fiber Optics.

Co-axial cable

Coaxial cables are a type of cable that is used by cable TV and that is common for data communications. Data is transmitted through the center wire, while the outer braided layer serves as a line to ground. Both of these conductors are parallel and share the same axis. This is why the wire is called coaxial!
There are two types of co-axial cables
1- Thin-net co-axial cable (Speed 10 Mbps, Range 185 meter)
2- Thick-net  co-axial cable (Speed 10 Mbps, Range 500 meter)

UTP (unshielded twisted pair)

Short form of Unshielded Twisted Pair cable, UTP cable is a popular cable used in computer networking that consists of two shielded wires twisted around each other. In the image to the right, is an example of the different network cables you’re likely to encounter.
UTP cables are twisted to cancel the EMI (Electro-magnetic interference), it has four pairs which are twisted so that magnetic and electric fields are opposite and it cancels EMI.
Given below is the Categories of UTP:
CAT 1                     Used for only voice communication
CAT 2                     Used for only voice communication
CAT 3                     Data + Voice both, Speed 4 Mbps, Range 100m
CAT 4                     Data + Voice both, Speed 10 Mbps, Range 100m
CAT 5                     Data + Voice both, Speed 100 Mbps, Range 100m
CAT 6                     Data + Voice both, Speed 1000 Mbps, Range 100m
CAT 6A                  Data + Voice both, Speed 10 Gbps, Range 10 to 15 meter

STP (Shielded Twisted Pair)

Short form of Shielded Twisted-Pair cable, STP is a cable originally developed by IBM for Token Ring that consists of two individual wires wrapped in a foil shielding to help provide a more reliable data communication.


FIBER OPTIC CABLE:
In fiber optic cables data transmit in the form of light only. There are two types of fiber optic cables which are:

1- Single Mode Fiber:
In single mode fiber, light inject through a Laser and only single ray of light travels on theory of total internal reflection (Stimulated Emission)
Maximum Bandwidth/Data rate on fiber cable   = 40 Gbps (Giga-bps)
Range ( after which signal drops)                              = up to 1 k.m (on 10 Gig)

2- Multi Mode Fiber:
In multi mode fiber, Light inject through LED ( Light Emitting Diode) and so many rays can travel simultaneously on total internal reflection (Spontaneous Emission Theory)
Maximum Bandwidth/Data rate on fiber cable   = 10 Gbps (Giga-bps)
Range ( after which signal drops)                              = 500 m



Best Regards,

S. N. Jafar

Friday 15 June 2012

Types of Network

There are two types of Network
1- Distributed Network: which is costly and its even hard to troubleshoot. its also not easy to manage these type of networks. for example if we have three different locations of our office than we need to have a data center on all three locations which would be synchronized to Head Office in respective time period (Scheduled)  see below the diagram of Distributed Network. For Big organizations distributed network is highly not recommended.
2-Centralized Network: In a centralized network design, every branch is directly connected to a HO. online synchronization, Centralized data, no need to have Data Centers on all locations. Management and troubleshooting will become easier. very cost effective. It is recommended for Mid-size/large organizations but DRP (Disaster Recovery Plan) should be a necessary part of this network design to prevent form Data and connectivity losses. see below an example of Centralized Network.


Thank you

Best Regards,

S. N. Jafar