Networking: Network Topology

The arrangement of a network which comprises of nodes and connecting lines via the sender and receiver is referred as Network Topology. The various network topologies are:

1) Mesh Topology :

In a mesh topology, every device is connected to another device via the particular channel.

  • If suppose, N number of devices are connected with each other in mesh topology, then total number of ports that is required by each device is ​ N-1. In the Figure 1, there are 5 devices connected to each other, hence total number of ports required is 4.
  • If suppose, N number of devices are connected with each other in mesh topology, then total number of dedicated links required to connect them is NC2 i.e. N(N-1)/2. In the Figure 1, there are 5 devices connected to each other, hence total number of links required is 5*4/2 = 10.

Advantages of this topology :

  • It is robust.
  • A fault is diagnosed easily. Data is reliable because data is transferred among the devices through dedicated channels or links.
  • Provides security and privacy.

Problems with this topology :

  • Installation and configuration are difficult.
  • Cost of cables is high as bulk wiring is required, hence suitable for less number of devices.
  • Cost of maintenance is high.

2) Star Topology :

​ In the star topology, all the devices are connected to a single hub through a cable. This hub is the central node and all others nodes are connected to the central node. The hub can be passive ​in nature i.e., not intelligent hub such as broadcasting devices, at the same time the hub can be intelligent known as active ​hubs. Active hubs have repeaters in them.

Advantages of this topology :

  • If N devices are connected to each other in the star topology, then the number of cables required to connect them is N. So, it is easy to set up.
  • Each device requires only 1 port i.e. to connect to the hub.

Problems with this topology :

  • If the concentrator (hub) on which the whole topology relies fails, the whole system will crash down.
  • Cost of installation is high.
  • Performance is based on the single concentrator i.e. hub.

3) Bus Topology :

​ Bus topology is a network type in which every computer and network device is connected to a single cable. It transmits the data from one end to another in the single direction. No bi-directional feature is in the bus topology.

Advantages of this topology :

  • If N devices are connected to each other in a bus topology, then the number of cables required to connect them is 1 ​which is known as backbone cable and N drop lines are required.
  • Cost of the cable is less as compared to other topology, but it is used to build small networks.

Problems with this topology :

  • If the common cable fails, then the whole system will crash down.
  • If the network traffic is heavy, it increases collisions in the network. To avoid this, various protocols are used in the MAC layer known as Pure Aloha, Slotted Aloha, CSMA/CD etc.

4) Ring Topology :

​ In this topology, it forms a ring connecting devices with its exactly two neighboring devices.

The following operations take place in ring topology are :

  1. One station is known as a monitor station which takes all the responsibility to perform the operations.
  2. To transmit the data, a station has to hold the token. After the transmission is done, the token is to be released for other stations to use.
  3. When no station is transmitting the data, then the token will circulate in the ring.
  4. There are two types of token release techniques: Early token release releases the token just after the transmitting the data and Delay token release releases the token after the acknowledgment is received from the receiver.

Advantages of this topology :

  • The possibility of collision is minimum in this type of topology.
  • Cheap to install and expand.

Problems with this topology :

  • Troubleshooting is difficult in this topology.
  • Addition of stations in between or removal of stations can disturb the whole topology.

5) Hybrid Topology :

​This topology is a collection of two or more topologies which are described above. This is a scalable topology which can be expanded easily. It is a reliable one but at the same, it is a costly topology.

The Network allows Computersto connect and communicate with different computers via any medium. LAN, MAN, and WAN are the three major types of the network designed to operate over the area they cover. There are some similarities and dissimilarities between them. One of the major difference is the geographical are they cover, i.e. LAN covers the smallest area; MAN covers an area longer than LAN ad WAN comprises the largest of all.

There are other types of Computer Networks also, like :

  • PAN (Personal Area Network)
  • SAN (Storage Area Network)
  • EPN (Enterprise Private Network)
  • VPN (Virtual Private Network)

Local Area Network (LAN) –

LAN or Local Area Network connects network devices in such a way that personal computer and workstations can share data, tools, and programs. The group of computers and devices are connected together by a switch, or stack of switches, using a private addressing scheme as defined by the TCP/IP protocol. Private addresses are unique in relation to other computers on the local network. Routers are found at the boundary of a LAN, connecting them to the larger WAN.

Data transmits at a very fast rate as the number of computers linked are limited. By definition, the connections must be high speed and relatively inexpensive hardware (Such as hubs, network adapters, and Ethernet cables). LANs cover smaller geographical area (Size is limited to a few kilometers) and are privately owned. One can use it for an office building, home, hospital, schools, etc. LAN is easy to design and maintain. A Communication medium used for LAN has twisted pair cables and coaxial cables. It covers a short distance, and so the error and noise are minimized.

Early LAN’s had data rates in the 4 to 16 Mbps range. Today, speeds are normally 100 or 1000 Mbps. Propagation delay is very short in a LAN. The smallest LAN may only use two computers, while larger LANs can accommodate thousands of computers. A LAN typically relies mostly on wired connections for increased speed and security, but wireless connections can also be part of a LAN. The fault tolerance of a LAN is more and there is less congestion in this network. For example A bunch of students playing Counter-Strike in the same room (without internet).

Metropolitan Area Network (MAN) –

MAN or Metropolitan area Network covers a larger area than that of a LAN and smaller area as compared to WAN. It connects two or more computers that are apart but resides in the same or different cities. It covers a large geographical area and may serve as an ISP (Internet Service Provider). MAN is designed for customers who need high-speed connectivity. Speeds of MAN range in terms of Mbps. It’s hard to design and maintain a Metropolitan Area Network.

The fault tolerance of a MAN is less and also there is more congestion in the network. It is costly and may or may not be owned by a single organization. The data transfer rate and the propagation delay of MAN are moderate. Devices used for transmission of data through MAN are Modem and Wire/Cable. Examples of a MAN are the part of the telephone company network that can provide a high-speed DSL line to the customer or the cable TV network in a city.

Wide Area Network (WAN) –

WAN or Wide Area Network is a computer network that extends over a large geographical area, although it might be confined within the bounds of a state or country. A WAN could be a connection of LAN connecting to other LAN’s via telephone lines and radio waves and may be limited to an enterprise (a corporation or an organization) or accessible to the public. The technology is high speed and relatively expensive.

There are two types of WAN: Switched WAN and Point-to-Point WAN. WAN is difficult to design and maintain. Similar to a MAN, the fault tolerance of a WAN is less and there is more congestion in the network. A Communication medium used for WAN is PSTN or Satellite Link. Due to long distance transmission, the noise and error tend to be more in WAN.

WAN’s data rate is slow about a 10th LAN’s speed since it involves increased distance and increased number of servers and terminals etc. Speeds of WAN ranges from few kilobits per second (Kbps) to megabits per second (Mbps). Propagation delay is one of the biggest problems faced here. Devices used for transmission of data through WAN are Optic wires, Microwaves, and Satellites. Example of a Switched WAN is the asynchronous transfer mode (ATM) network and Point-to-Point WAN is the dial-up line that connects a home computer to the Internet.

Conclusion –

There are many advantages of LAN over MAN and WAN, such as LAN’s provide excellent reliability, high data transmission rate, they can easily be managed and shares peripheral devices too. Local Area Network cannot cover cities or towns and for that Metropolitan Area Network is needed, which can connect city or a group of cities together. Further, for connecting Country or a group of Countries, one requires Wide Area Network.

An access network is a type of network which physically connects an end system to the immediate router (also known as the “edge router”) on a path from the end system to any other distant end system. Examples of access networks are ISP, home networks, enterprise networks, ADSL, mobile network, FITH etc.

Types of access networks:

  • Ethernet –
    It is the most commonly installed wired LAN technology and it provides services on the Physical and Data Link Layer of OSI reference model. Ethernet LAN typically uses coaxial cable or twisted pair wires.

  • DSL –
    DSL stands for Digital Subscriber Line and DSL brings a connection into your home through telephone lines and a DSL line can carry both data and voice signals and the data part of the line is continuously connected. In DSL you are able to use the Internet and make phone calls simultaneously. DSL modem uses the telephone lines to exchange data with digital subscriber line access multiplexer (DSLAMs). In DSL we get 24 Mbps downstream and 2.5 Mbps upstream.

  • FTTH –
    Fiber to the home (FTTH) uses optical fiber from a Central Office (CO) directly to individual buildings and it provides high-speed Internet access among all access networks. It ensures high initial investment but lesser future investment and it is the most expensive and most future-proof option amongst all these access networks.

  • Wireless LANs –
    It links two or more devices using wireless communication within a range. It uses high-frequency radio waves and often includes an access point for connecting to the Internet.

  • 3G and LTE –
    It uses cellular telephony to send or receive packets through a nearby base station operated by the cellular network provider. The term “3G internet” refers to the third generation of mobile phone standards as set by the International Telecommunications Union (ITU). Long Term Evolution (LTE) offers high-speed wireless communication for mobile devices and increased network capacity.

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