Networking Part - II

Classification of computer networks.

Geographical Distance: Computer networks may be classified according to the scale or extent of reach of the network as Local Area Network (LAN), Metropolitan Area Network (MAN) and Wide Area Network (WAN).

                         

Local Area Network (LAN): A network that is limited to a relatively small spatial area such as a room, a single building, a ship, or an aircraft is reffered as LAN. They are sometimes called a single location network. Eg. A small office network or two computers is a house connected using a cable.                           
                             




Metropolitan Area Network (MAN): A network that connects two or more Local Area Networks together but does not extend beyond the boundaries of the immediate town, city, or metropolitan area is called as MAN. eg. A branch office connected to the main office in the same city.


Wide Area Network (WAN):  A WAN is a data communications network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies etc. Eg. Internet or a branch office in India connected to its Corporate office in United States.

Peer to peer network

Advantages:

Low cost as expensive software and hardware are not required.

Easy to implement.

Resource sharing controlled by users.

No need of a dedicated network administrator.

Disadvantages:

Low level of security

Heavy load on computers because of resource sharing

Size of network limited to approximately 10 computers

Client – Server network

Advantages

Strong central security.

Central file storage.

Resource sharing controlled by administrators

Easy management of large number of users.

Disadvantages

Cost of server hardware and software.

Dedicated and well trained network administrator is needed to main this type of architecture.

Client:

A computer on the network that requests resources or services from another computer on a network. In some cases, a client could also act as a server. The term “client” may also refer to the human user of a client workstation.

Server.

A computer on the network that manages shared resources. Servers usually have more processing power, memory, and hard disk space than clients.They run network operating software that can manage not only data, but also users, groups, security, and applications on the network.

Workstation.

A desktop computer, which may or may not be connected to a network. Most clients are workstation computers.

Network operating system (NOS).

The software that runs on a server and enables the server to manage data, users, groups, security, applications, and other networking functions.The most popular network operating systems are Microsoft Windows NT,Windows 2000, Novell NetWare, and UNIX.

Host.

A server that manages shared resources.

Node.

A client, server, or other device that can communicate over a network and that is identified by a unique identifying number, known as its network address.

Topology.

The physical layout of a computer network. Typologies vary according to the needs of the organization and available hardware and expertise.

Transmission Basics:

Data transmission, whether analog or digital, may also be characterized by the direction in which the signals travel over the media.


Simplex, Half-Duplex and Duplex

In cases where signals may travel in only one direction, the transmission is considered simplex. For example, a football coach calling out orders to his team through a megaphone is using simplex communication. In this example, the coach’s voice is the signal, and it travels in only one direction—away from the megaphone’s mouthpiece and toward the team. Simplex is sometimes called one-way, or unidirectional, communication.

In half-duplex transmission, signals may travel in both directions over a medium but in only one direction at a time. Half-duplex systems contain only one channel for communication, and that channel must be shared for multiple nodes to exchange information. For example, Walkie – Talkie.

When signals are free to travel in both directions over a medium simultaneously, the transmission is considered full-duplex. Full-duplex may also be called bidirectional transmission or sometimes, simply duplex.

When you call a friend on the telephone, your connection is an example of a full-duplex transmission, because your voice signals can be transmitted to your friend at the same time your friend’s voice signals are transmitted in the opposite direction to you. In other words, both of you can talk and hear each other simultaneously.

Throughput:

The data transmission characteristic most frequently discussed and analyzed by networking professionals is throughput. Throughput is the measure of how much data is transmitted during a given period of time. It may also be called capacity or bandwidth. Throughput is commonly expressed as a quantity of bits transmitted per second, with prefixes used to designate different throughput amounts. For example, the prefix “kilo” combined with the word “bit” (as in “kilobit”) indicates a 1000 bits per second. Rather than talking about a transmission speed of 1000 bits per second, you would typically say the speed was 1 kilobit per second.

Bandwidth

Bandwidth and throughput are similar concepts, but strictly speaking, bandwidth is a measure of the difference between the highest and lowest frequencies that a medium can transmit. This range of frequencies, which is expressed in Hz, is directly related to throughput. The higher the bandwidth, the higher the throughput.

Baseband

Baseband is a transmission form in which (typically) digital signals are sent through direct current (DC) pulses applied to the wire.This direct current requires exclusive use of the wire’s capacity. As a result, baseband systems can transmit only one signal, or one channel, at a time. Every device on a baseband system shares the same channel.When one node is transmitting data on a baseband system, all other nodes on the network must wait for that transmission to end before they can send data. Baseband transmission supports bidirectional signal flow, which means that computers can both send and receive information on the same length of wire.

Ethernet is an example of a baseband system found on many LAN's.

Broadband

Broadband is a form of transmission in which signals are modulated as radio frequency (RF) analog pulses that use different frequency ranges. Unlike baseband, broadband technology does not involve digital pulses. Nevertheless, the use of multiple frequencies enables a broadband system to access several channels and, therefore, carry much more data than a baseband system.

As you may know, broadband transmission is used to bring cable TV to your home.Your cable TV connection can carry at least 25 times as much data as a typical baseband system (like Ethernet) carries, including many different broadcast frequencies (channels). In traditional broadband systems, signals travel in only one direction.Therefore, broadband cabling must provide a separate wire for the transmission and the receipt of data.

Broadband transmission is generally more expensive than baseband transmission because of the extra hardware involved. On the other hand, broadband systems can span longer distances than baseband.