1. LO1 – Understand Computer Hardware
1.5 Communication Hardware

2. Communication Hardware
These devices allow one computer device to communicate with another. A communication device is a hardware device capable of transmitting an analog or digital signal over the telephone, other communication wire, or wirelessly. The best example of a communication device is a computer Modem, which is capable of sending and receiving a signal to allow computers to talk to other computers over the telephone. Other examples of communication devices include a network interface card (NIC), Wi-Fi devices, and an access point. A modem is used to connect to the Interenet.
A modem converts the digital data from the computer into a continuous analogue waveform that the telephone system is designed to deal with (This is the MODulation part of a modem).
The reason for this is that the telephone system was originally designed for the human voice i.e. continuous signals. The modem also converts the analogue signal *from* the telephone network back into digital data that the computer can understand. (DEModulation).
Hence the word MODEM (Short for MODulation and DEModulation)
Standard ADSL modems come in two forms. An external box that links to your computer through an USB port or a network cable (like the one above), or an internal modem that is plugged directly to the motherboard inside the computer.
Wi-Fi modems – in addition to telephone modems, radio has not become very popular as means of connecting to the Internet. The device that allows you to do this is call the Wi-Fi modem. Many home units combine a router, and ADSL modem and a wireless access point into one box.
A computer can work fine without a communication device. However, for a computer to communicate with other computers they need a communication device. For example, for your computer to connect to the Internet to view a web page it needed a communication device (modem) and to connect to a network it needs a rounter

3. Communications Hardware continued…
A hub is a hardware device that connects multiple computers together in a network and allows them to share data packets. Each computer will be connected to a single 'port' on the hub. So if you purchase an '8 port hub', you will be able to connect up to eight computers together. Every node on a wired network is connected to the hub by a cable.
Hubs transmit data from one node, to another, in the form of data packets. A data packet is a small
chunk of data. It has a destination address included. When a data packet arrives at the hub, it is
transmitted to every other node on the network. Used in Star Network Topology.
This is not very secure as every node can view the data, whether it was intended for them, or not.
Another issue with using a hub is the high risk of a data collision.
Data collisions happen because a network cable can only have one data packet in it at any instant.
So, if two or more computers on the network transmit data at exactly the same time, a data collision will occur.
The collided data is marked as unusable and the data has to be transmitted again.
This can lead to a delay and the network slowing down.
For larger networks, or networks where security is important, a switch is a better option than a hub. A switch is similar to a hub as it allows computers to be linked together to exchange data. But, unlike a hub, a switch sends the data packet only to the intended node. It does this by reading the destination information within the data packet. The switch knows the location of every node on the network because of their individual MAC addresses. Because data is only sent to the intended devices, security is improved. There is also a much lower risk of data collisions when switches are used. The disadvantage of switches are that they cost more than hubs.
So they only tend to be used in high bandwidth, high performance networks.

4. Communications Hardware continued…
A router is a device which transfers data from one network to another i.e. between networks. Routers are used to
connect Local Area Networks (LANs) together to form a Wide Area Network (WAN). A router can form a LAN by connecting devices within a building. It also makes it possible to connect different networks together. Homes and businesses use a
router to connect to the internet. A router can often incorporate a modem within the hardware. Here is a simplified
overview of how a router works:
A data packet arrives from the node or hub
The router reads the data packet’s destination IP address (internet protocol address) – this is not the same as the MAC address.
The router uses a database to look up where the IP address is located.
It identifies all of the different routes that could be used to send the data packet through.
It checks how busy each route is at that very moment.
It sends the data packet via the fastest route/ path.

5. Communications Hardware continued…
Network Interface Card (NIC) - Sometimes known as a network interface controller. Every device on the network needs an NIC. It is found inside the device, sometimes as a dedicated card, sometimes as a chip on the motherboard. Each NIC has its own individual MAC address (Media Access Control). The MAC address enables every device on the network to be uniquely identified. Because of this, data can be sent to the correct device. The NIC converts data from the nodes into a format that is compatible with the network. In order to do this, it follows the network protocol (set of rules).

6. Communications Hardware continued…
Network Card/Chip
If the computing device is big enough, Network connectora network card or chip is often fitted within it.
For example a desktop, laptop or games console usually has the physical size to include one.
If it has, you will see a standard network connector with the graphic of a network next to it, as shown in the picture opposite (little pc's stacked).
There are also two tiny LEDs in the socket that light up and flash green when the network is working and active. They light orange if the network is not working.
A network cable is inserted into the socket and the other end is connected to a modem.
However, many devices are just too thin or too small to include a network socket. For example a tablet computer or e-reader such as the Kindle. In which case the only option is to use Wi-Fi.
If the communication device is integrated it can make portable devices easier to use e.g. voice recognition to unlock phone or SIRI to answer questions, but voice recognition may not work well in a noisy environment or with strong accents.
More on connecting to the Internet Here

7. Communications Hardware continued…
Hybrid network hub: includes internet access, wireless and wired LANs. They have a fixed number of Ethernet ports for wired devices and also broadcast a Wi-Fi signal. A device used to interconnect different types of cables and to maximize network efficiency. Used to create a network which includes a mixture of wired and wireless devices.
Advantages of Hybrid Network Topology
Reliable : Unlike other networks, fault detection and troubleshooting is easy in this type of topology. The part in which fault is detected can be isolated from the rest of network and required corrective measures can be taken, WITHOUT affecting the functioning of rest of the network.
Scalable: Its easy to increase the size of network by adding new components, without disturbing existing architecture.
Flexible: Hybrid Network can be designed according to the requirements of the organization and by optimizing the available resources. Special care can be given to nodes where traffic is high as well as where chances of fault are high.
Effective: Hybrid topology is the combination of two or more topologies, so we can design it in such a way that strengths of constituent topologies are maximized while there weaknesses are neutralized. For example we saw Ring Topology has good data reliability (achieved by use of tokens) and Star topology has high tolerance capability (as each node is not directly connected to other but through central device), so these two can be used effectively in hybrid star-ring topology.
Disadvantages of Hybrid Topology
Complexity of Design: One of the biggest drawback of hybrid topology is its design. Its not easy to design this type of architecture and its a tough job for designers. Configuration and installation process needs to be very efficient.
Costly Hub: The hubs used to connect two distinct networks, are very expensive. These hubs are different from usual hubs as they need to be intelligent enough to work with different architectures and should be function even if a part of network is down.
Costly Infrastructure: As hybrid architectures are usually larger in scale, they require a lot of cables, cooling systems, sophisticate network devices, etc.