Network Transmission Devices

INTRODUCTION

Network transmission devices connect individual workstations and servers into a synergistic LAN. These devices start simple connectors and evolve in complexity and sophistication. The following are the transmission devices:

1. Media Connectors
2. Network Interface Card (NIC)
3. Repeaters
4. Hubs

Media Connectors

Transmission media connectors attach directly to the medium itself and serve as the physical interface between cabling and network nodes. BNC T-connector, RJ- 45 Connector for UTP, IBM data connector for STP and DIX connector for thick coaxial cabling are media connectors. Some of the media connector are described below:

• BNC T-connector for Thin Coaxial Cabling

The BNC connector was one of the first for network communications. It was introduced so long ago that none is really sure what the letters stand for. Some authorities claim that it means “British Naval Connector”, whereas others insist that it stands for “Bayonet Nut Coupler”. BNC has become part of standard networking language.

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• RJ-45 Connector for UTP (Unshielded Twisted Pair)

In the business world, coaxial cabling is one way out, but manufacturers are still using it. Nearly, all new cable installations use twisted-pair cabling with eight wires per cable. The eight wires are separated into four twisted pairs.

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The pairs are then terminated in and RJ-45 connector. This port looks like the one attached to your home telephone except that it is a bit larger with room for eight for wires instead of four.

• DIX Connector for Thick Coaxial Cabling

DIX is an acronym for Digital, Intel and Xerox. The companies that invented Ethernet these early connectors are D-shell shaped with 15 pins each (organized in two rows and eight pins, respectively). The drop cable that plugs into this port looks a lot like your video connector except that it is little longer and narrower.

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Network Interface Boards or Network Interface Card (NIC)

The NIC contains the electronic circuitry needed to ensure the reliable communications between workstations and servers. The NIC is the electronic interface between the computer and the LAN cabling.

The card itself uses a bus-specific edge connector to plug into the computer motherboard. On the exposed side of the NIC, there are cabling ports that plug directly into the LAN cabling.

Repeaters

As the name implies, repeaters repeat network data. In general, repeaters operate at the electronic level and contain no real intelligence. A repeater accepts weak signals, electrically regenerates them and then sends the messages on their way. There are two types of repeaters: amplifiers and signal-regenerating repeaters.

Hubs

Technically speaking, a hub is simply a multi-port repeater. In addition to regenerating network data, hubs add form and function to the layout of the LAN. In many topologies, the hub is the central component of the network transmission media. There are three types of hubs. They are the passive hub, active hub and intelligent hub.

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Internetwork Transmission Devices

A LAN links a small group of functionally similar workstations within a local geographic area. Once your network expands to include other floors or even other LANs, it ceases to be local and becomes a WAN. To connect multiple LANs into a WAN, you need flexible advanced internetwork transmission devices such as:

1. Bridges
2. Routers
3. Gateways

1. Bridges

Like repeaters, bridges extend the maximum distance of your network by connecting separate segments together. However, unlike repeaters, bridges do it intelligently. Bridges analyze network packets from multiple segments and determine who gets through and who doesn’t. This is based on physical address.

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2. Routers

Routers are more intelligent than bridges. Instead of being limited to the physical address, routers can use both physical and logical addressing, which allows you to break your internetwork into logical subnets.

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3. Gateways

Gateways represent the pinnacle of internetwork transmission devices. They perform more software translation than anything. Routing capabilities which are built into the gateway device do the packet routing. Gateways are required when network messages travel between two entirely different systems.

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A classic example is the exchange of data between centralized and distributed CPUs. The gateway needs to read the network address, reconfigure the packet protocols from IPX to SNA, translate the operating software and in most cases, completely rewrite the data alphabet.

Communication Transmission Devices & Techniques

Communication devices provide basic data communications functions. They transmit, translate and transform data into signals that can be transmitted into the physical world. The most common communication devices are:

1. Modems
2. Multiplexers
3. CSU/DSU (Channel Service Unit/Digital Service Unit)
4. Circuit Switching
5. Message Switching
6. Packet Switching

1. Modems

Modems are necessary because computers and transmission media speak completely different languages. Computers are digital (0s and 1s) and most transmission media are analog (UTP or radio waves). For digital computers to communicate over analog media, they need translation device.

That’s where a modem comes in. The modem actually performs two distinct tasks: modulation and demodulation. During modulation, the modem translated digital information into an analog waveform. Next, the data travels along the medium to the destination device. There, the analog wave is demodulated into digital 0s and 1s.

Modem speeds are typically measured in baud (or loosely but per second). Today’s faster modems can support speed up to 96,000 bps (96kbps).

2. Multiplexers

Multiplexers allow you to send multiple signals across the single transmission medium. Multiplexing (or mixing) refers to the process of funneling multiple data connections into one circuit for transport across a single medium. An excellent example can be found in TV cabling.

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If you think about it for a moment, you have 100 or more channels arriving through one piece of coaxial cabling. Your cable box or VCR demultiplexes the signal and separates the channels.

3. CSU/DSU

Modems allows you to connect digital computers to analog transmission media. Most WAN providers require that you lease the CSU/DSU device from them. This ensures system-wide continuity and safety.

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4. Circuit Switching

Circuit switching connects the sender and receiver by a single path during the conversion. Telephone switching equipment, for example, uses address number (in the form of a country area, office, trunk codes, etc) to establish a path that connects the sender’s telephone to the receiver’s telephone.

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In circuit switching, a complete path must exist before communications can take place. The computer which is initiating the data transfer establishes the dedicated path and ensures reliable packet delivery.

5. Message Switching

Message switching does not establish a dedicated path between two stations. Instead, conversions are divided into messages. Each message is packaged with its own destination address and then transmitted from the router through the internetwork.

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Each router receives the messages, stories briefly and then transmits it to the next device. This type of network is sometimes called a store-and-forward WANs.

6. Packet Switching

Packet switching combines the advantage of both circuit and message switching. Packet switching breaks the datagrams into small parts called packets. Each packet is constructed with source and destination address that allow it to work its way through internetwork and find its destination.

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Because packets have strictly defined maximum lengths, they can be stored in RAM instead of disk, which makes store-and-forwarding faster and easier. In general packet switching routers use one of the two different Strategies:

1. Datagram packet switching
2. Virtual packet switching

Advantages & Disadvantages of Network

The following are the distinct notes in favor of networking:

1. The computers, staff and information can be well managed.
2. A network provides the means to exchange data among the computers and to make programs and data available to the people.
3. It permits the sharing of the resources of the machine.
4. Networking also provides the function of back-up. The backup capability is especially useful in systems like air traffic control where the counterpart can assume its functions and workload.
5. Networking provides a flexible networking environment. Employees can work at home by using through networks tied through networks into the computer at the office.

References:

Khanal, R.C. Khanal, R.C. Computer Concept for XII. Pashupatigriha Marga, Thapathali, Kathmandu, Nepal: Ekta Books Distributors Pvt. Ltd., 2010. 73-88.

Adhikari, Deepak Kumar.,et.al., Computer Science XII,Asia Publication Pvt.Ltd