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A network gateway is an internet working system capable of joining together two networks that use different base protocols. A network gateway can be implemented completely in software, completely in hardware, or as a combination of both. The key feature of a gateway is that it converts the format of the data, not the data itself.

Gateway functionality differs in many ways. For example, a router that can route data from an IPX network to an IP network is, technically, a gateway. The same can be said of a translational bridge that, converts from an Ethernet network to a Token Ring network and back again.

Software gateways can be found everywhere. Many companies use an email system such as Microsoft Exchange. These systems transmit mail internally in a certain format. When email needs to be sent across the Internet to users using a different email system, the email must be converted to another format, this conversion process is performed by a software gateway. In enterprises, the gateway often acts as a proxy server and a firewall. Gateways also associated with router-id switch.

Network Interface Cards:

The network interface card (NIC) provides the physical connection between the network and the computer workstation. Network interface cards are a major factor in determining the speed and performance of a network. The most common network interface connections are Ethernet cards.

1. Switches:

A switch is a hardware device that provides a central connection point for cables from workstations, servers, and peripherals, switch forwards data only to the port on which the destination system is connected.

Most switches are active, that is they electrically amplify the signal as it moves from one device to another. Switches manage the data flow on the connection, it can send and receive data on the connection at the same time. Switches use three methods to deal with data as it arrives. They are Cut-through, Store-and-forward, and Fragment-free.

2. Repeaters:
Since a signal loses strength as it passes along a cable, it is often necessary to boost the signal with a device called a repeater. The repeater electrically amplifies the signal it receives and rebroadcasts it.

3. Bridges:
Bridges are networking devices that connect networks. Sometimes it is necessary to divide networks into subnets to reduce the amount of traffic on each larger subnet or for security reasons. Once divided, the bridge connects the two subnets and manages the traffic flow between them.

Three types of bridges are used in networks are Transparent bridge, Translational bridge, Source-route bridge.

Most bridges can “listen” to the network and automatically figure out the address of each computer on both sides of the bridge. The bridge can inspect each message and, if necessary, broadcast it on the other side of the network. The bridge manages the traffic to maintain optimum performance on both sides of the network.

a. Routers:
Routers are network devices that route data around the network. By examining data as it arrives, the router can determine the destination address for the data; then, by using tables of defined routes, the router decides the best way for the data to reach a destination. The router can direct traffic to prevent a crash.

b. Hubs:
A network hub contains multiple ports. When a packet arrives at one port, it is copied to all ports of the hub for transmission.
The two types of hubs are active or passive hubs. Active hubs regenerate signal before forwarding it to all the ports and require a power supply. Passive hubs, do not need power and they don’t regenerate the data signal.

c. Gateways:
It is a device that connects dissimilar networks. The term gateway is applied to any device, system, or software application that can perform the function of translating data from one format to another. The key feature of a gateway is that it converts the format of the data, not the data itself. The conversion from one data format to another takes time, and so the flow of data through a gateway is always slower than the flow of data without one.

d. Modems:

The modem is a short form of the terms modulator and demodulator. Modems translate digital signals from a computer into analog signals that can travel across phone lines. The modem modulates the signal at the sending end and demodulates at the receiving end.

Modems provide a relatively slow method of communication. Modems are available as internal devices that plug into expansion slots in a system; external devices that plug into serial or USB ports;

The different measures for preventing virus are:

1. Install quality antivirus:

The users should install professional, business-grade antivirus software on their PCs. Pro-grade antivirus programs update more frequently throughout the, protect against a wider range of threats (such as rootkits), and enable additional protective features (such as custom scans).

2. Install real-time anti-spyware protection:
Use of professional (or fully paid and licensed) anti-spyware programs are required to prevent infections and fully remove those infections already present.

3. Keep anti-malware applications current:
Antivirus and anti-spyware programs require regular signature and database updates. Without these critical updates, anti-malware programs are unable to protect PCs from the latest threats. Computer users must keep their antivirus and anti-spyware applications up to date.

4. Perform daily scans:
Enabling complete, daily scans of a system’s on hard drive gives protection. These daily scans can be invaluable in detecting, isolating, and removing infections that initially escape security software’s attention.

5. Disable autorun:
Many viruses work by attaching themselves to a drive and automatically installing themselves. As a result, connecting any network drives, external hard disks, or even thumb drives to a system can result in the automatic propagation of such threats. The users can disable the Windows autorun feature to avoid.

6. Don’t click on email links or attachments:
Users should never click on email attachments without at least first scanning them for viruses using a business-class anti-malware application. As for clicking on links, users should access Web sites by opening a browser and manually navigating to the sites.

7. Use a hardware-based firewall:
The software-based firewall included with Windows isn’t sufficient to protect systems. For this reason, all PCs connected to the Internet should be secured behind a capable hardware-based firewall.

The differences between simplex, half-duplex and full-duplex are

SMS (Short Message Service), commonly referred to as “text messaging,” is a service for sending short messages of up to 160 characters (224 characters if using a 5-bit mode) to mobile devices, including cellular phones, smartphones and PDAs.

SMS messages do not require the mobile phone to be active and within range and will be held for a number of days until the phone is active and within range. SMS messages are transmitted within the same cell or to anyone with roaming service capability. They can also be sent to digital phones in a number of other ways, including:

• From one digital phone to another
• From Web-based applications within a Web browser
• From instant messaging clients like ICQ
• From VoIP applications like Skype ‘
• Enhanced messaging service (EMS), an adaptation of SMS that allows users to send and receive ringtones and operator logos, as well as combinations of simple media to and from EMS-compliant handsets.

Users can send messages from a computer via an SMS gateway. SMS gateways are Web sites that allow users to send messages to people within the cell served by that gateway. They also serve as international gateways for users with roaming capability.

1. Chat:
It is online communication between two users through a computer. Once a chat has been initiated, either user can enter text by typing on the keyboard and the entered text will appear on the other user’s monitor. Most networks and online services offer a chat feature.

2. Video Conferencing:
A video-conference (or Video Conference) is a live video connection between people in separate locations for the purpose of communication or interaction. Video-conferencing allows people to communicate visually from anywhere in the world.

There are three main types of video conference solutions for businesses: point-to-point, multipoint and streaming.

• Point-to-point (sometimes referred to as single call) is a direct connection between two locations. It’s like a telephone call, just with video.
• Multipoint lets three or more people or locations take part in the same video conference. Multiple parties can meet through HD video in a meeting room, from a desktop at work, from a home computer, or even over a smartphone or tablet when on the road.
• Streaming connects your video conference to others who may choose to view the meeting on a remote computer or mobile device using software instead of hardware.

The cables are said to be transmission media or communication channels of the network. The cables are used to connect two or more computers in the network.

Network Cables:

• Unshielded Twisted Pair Cable (UTP cable)
• Shielded Twisted Pair (STP) cable
• Coaxial Cable
• Fiber Optic Cable

Twisted-Pair Wire - The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch. 

They are used for both voice and data transmission. Cat 1 to Cat 5 is the different categories and the RJ-45 connector is used to connect a cable.

Coaxial Cable - Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield. Transmission speed range from 200 million to more than 500 million bits per second.

Fiber Optics - Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials. It transmits light rather than electronic signals eliminating the problem of electrical interference. Transmission speed could go up to as high as trillions of bits per second.

The networking techniques (topologies) are Bus topology, Ring topology, Star topology. Three topology, Mesh topology, Extended star topology.

A server is a computer program that provides services to other computer programs (and their users) in the same or other computers. The computer that a server program runs in is also referred to as a server.

Servers can be broadly classified into Dedicated servers and Non-dedicated servers.

1. Dedicated servers:

A computer exclusively reserved for the server’s job and its only job is to help workstations to access data, software and hardware resources. The term “dedicated server” can also mean a single computer within a network that is reserved for a specific purpose.

For example, within a network, you could have a computer dedicated to printer resources, another computer dedicated to Internet connections, another computer serving as a firewall, etc. These computers would all be dedicated servers, as the whole computer is allocated for a specific task within the network.

2. Non-dedicated servers:
A computer in a network acts as a server as well as a workstation is called a non-dedicated server. It is server upon which applications are available, and also network management software runs in the background. Non-dedicated servers are common in peer-to-peer networks. A peer to peer network is a network without a dedicated server. It is composed entirely of workstations that can be set up to share some of their services, like printers or files. These computers require more memory and work slower. It is suitable for small networks.

EDGE (Enhanced Data GSM Environment) is a faster version of GSM designed to deliver data at rates up to 384 Kbps and enable the delivery of multimedia and other broadband applications to mobile phone and computer users.

A specialized field in computer networking that involves securing a computer network infrastructure. It consists of the provisions and policies to prevent and monitor unauthorized access, misuse, modification, and network-accessible resources.

The goals of networking are resource sharing, reliability, cost factor, and communication medium.

The expansion of 2G is ‘second generation’.

The client is a user or a software who makes a request to the server.
A client is the requesting program or user in a client/server relationship.

A computer network is a group of autonomous computers that are connected to each other for the purpose of communication.

A computer network allows the sharing of resources and information among devices connected to the network.

A local Area Network (LAN) is a computer network covering a small physical area, like a home, office, or small group of buildings, such as a school, or an airport.

The characteristics of LANs:

• LAN’s enable the sharing of resources such as files or hardware devices that may be needed by multiple users
• Is limited in size, typically spanning a few hundred meters, and no more than a mile
• It is fast, with speeds from 10 Mbps to 10 Gbps.
• Requires little wiring, typically a single cable connecting to each device
• Has lower cost compared to MAN’S or WAN’s LAN’s can be either wired or wireless Twisted pair, coaxial or fiber optic cable can be used in wired LAN’s.
• Every LAN uses a protocol -a set of rules that governs how packets are configured and transmitted.
• Nodes in a LAN are linked together with a certain topology. These topologies include: Bus, Ring, Star
• LANs are capable of very high transmission rates (100s Mb/s to G b/s)

Metropolitan area network:

A metropolitan area network (MAN) is a network that connects two or more local area networks together but does not extend beyond the boundaries of the town/city.

• A MAN is covers larger geographical area than a LAN, ranging from several blocks of buildings to entire cities.
• A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations.
• A MAN often acts as a high speed network to allow sharing of regional resources.
• A MAN typically covers an area of between 5 and 50 km diameter.
• Examples of MAN: Telephone company network that provides a high-speed DSL to customers and cable TV network.

Wide area network:

A wide area network (WAN) is a computer network that covers a broad area. The largest and most well-known example of a WAN is the Internet. A WAN is a data communications network that covers a relatively broad geographic area (i.e. one city to another and one country to another country).

• To cover great distances, WANs may transmit data over leased high, speed phone lines or wireless links such as satellites.
• Multiple LANs can be connected together using devices such as bridges, routers, or gateways, which enable them to share data.
• It operates on a low data transfer rate.