Basic of computer Network 9：Network Hardware (DCE+DTE) + Transmission Media (Guide and Unguided)

DTE

DTE stand for Data Terminal Equipment, it is the devices allow user to sending and receiving data information which is set at source point and the end point of the data communication system. It allows user input and output data for system. It includes User device and Server.

User Device

The user device that include Laptop, PC, Phone, Game Console, Printer, Scanner, etc.
Laptop and PC are the devices that consist with different components, such as motherboard, CPU, RAM and so on. They allow user to input the data through keyboard and mouse, output the data on the screen that they need.
Phone and Game console are the portable device that allows user to control characters to perform what they want on gaming, it will be output from the screen. It is more use for entertainment, spare user’s free time. Phone also can be used for communication with others, search information and so on.
Generally, what I see is, Scanner and Printer are emerged in to one device which can reduce the space, but they also can be separate devices. Scanner is an input device that allow user to scan image, text, photos and other paper documents into computer. Printer is an output device that allows user to print out what they want from computer or other devices.

Network Interface Card (NIC)

It also known as Network Card, Network Adaptor.
A NIC is an adapter that installed in a computer and provides a network connection point. Its job is to break the data down into appropriately sized packets and send them to the network. Each NIC is designed for a specific type of network, such as Ethernet, token ring, FDDI, ARCNET, and others. A NIC provides a connection point for cable, such as coaxial, twisted pair, or fibre optic. The NIC of a wireless LAN usually has an antenna to communicate with the base station.
The kernel of the network adapter is the data link-layer controller, which is usually a chip that realizes a single specific purpose of many services in data link layer, such as framing, link access, flow control, error detection, etc.

Server

Technically, Server also is a DTE, which allows user to access data from their local machine to server. Server is a kind of high-performance computer, as the node of the network, it is storing and processing 80% of the network data and information, so it is also known as the soul of the network.
It can be separate as internal and external. Internal server is in the Local Area Network, didn’t through port mapping that external network cannot access it. It only can be accessed by private users within the private internal network. External server is the server can be accessed by both, private and public, for example, an organisation set a server in their company about gaming, other user can access it form their home machines, and the employees of the company also can access the data from the same server that is the external server.
Server provides the different services for different purpose, such as File service, Application Service, Telecommunication service and Directory service.

DCE

It is the generic terms of switching equipment, transmission equipment and terminal equipment that are used in data communication system. It is telecommunication equipment which composed of hardware and software system that use wired, wireless electromagnetic or optical to send, receive or transmit binary data. It includes Multiport Repeater, Switch, Router, Transmission Media, etc.
Repeater
It is a Layer 1 device that works in Physical Layer with RJ 45 plugs, which is the centre of all nodes on the LAN.
During the transmission, the signal will become weaker and around with noise (such as light, radio interference, etc.) that would make the signal too weak to be decoded. So, we need the repeater which can remove unwanted noise and boost up the signal, when the signal leaves repeater, it will be full powered and without any signal around.
With the development of technology, it become less common with modern network.

Multiport repeater
Multiport repeater also called hub, it is a network hardware device works at first layer of the OSI model “Physical layer”. It likes the transmission media such as the network card and cable, belong to the basic equipment in LAN and use CSMA/CD to access and control data transmission. Each port of repeater simply sends and receives bits, receive 1 and retransmit 1, receive 0 and retransmit 0, without any change or error correction. It uses the form of a broadcast to transmits information.
It is the centre of all nodes in LAN, it can amplify the signal and support long distance communication. It also can remove unwanted noise for the data and boosts signal power. When data arrive at any ports, the multi-port repeater would clean the unwanted noise and get full power to retransmit on other port.
The length of LAN interconnection is limited, for example, in a 10M Ethernet only allows 4 or 5 repeaters on the transmission path. It can be connected with the same and different transmission media, such as, one side connect to coaxial cable, and another side connect to twisted pair with RJ 45 plug.

Switch
It is a computer network device that can exchange messages. It has more ports that can connect more computers and increase potential network bandwidth. It looks like hub.
Most of network switch works at layer 2 (Data Link) that capable of address learning and message exchange in the form of store-and forward. It uses MAC (Media Access Control) address, hardware address, to forward data. While the network switch works at layer 3 (Network Layer), use Global IP address, to process and forward data.
For example, there are two sites, A and B, using IP protocol communicate through the layer 3 switch. When site A starts sending message, it will compare its IP Address with the site B IP address to determine whether site B is in the same LAN with itself. If site B and site A are in the same LAN, the message will be retransmit at layer 2 switch. If they are not in the same LAN, site A need send APR (Address Resolution) packet to Layer 3 switch. When site A send ARP request to Layer 3 Switch, if the Layer 3 switch has known the MAC address of site B in the previous communication process, it will reply it to site A. Otherwise, the layer 3 switch will broadcast an ARP request to site B through routing information. When Layer 3 switch get reply form Site B about its MAC address, it will save the address and reply to site A. Then, they can communicate.
The function of switch, one side connects computers, servers, network printers, and other terminal devices; another side connects with other network devices, like switches, wireless access points, router and so on to build a LAN and realise the communication between all devices.
Switch is quicker than Hub, because of the hub doesn’t know what destination is and use broadcast which means send to all connection ports. It also can use unicast which means one to one, and multi-cast which means one to selected devices.

Router
It is the device connect between LAN and WAN, it can select and set the route automatically according to the channel conditions and choose the best path to send the signal in order. The main job of router is send out message say “I am here” to the devices in every 30 seconds and give its IP address.
It works at layer 3, network layer, used to connect multiple logically separated networks which mean as single network or subnet. When data is transferred from one subnet to another through router that shows is has the function of jugging the network address and selecting the IP path, like a traffic police. It can establish flexible connection in multi-network interconnection environment. It can connect various subnets by using completely different data packets and media access method, but it only can accepts information from the source station or other router.
One function of router is to connect different networks, and the other is to select the route of information transmission. Choosing an unobstructed and fast short cut can greatly improve the communicating speed, reduce the communication load of the network system, save the resources of the network system and improve the unimpeded rate of the network system.
Routers are divided into local routers and remote routers. Local routers are used network transmission media to connect, such as optical fibers, coaxial cables, and twisted pairs. Remote routers are used remote transmission media and require corresponding devices to connect, such as telephone lines with a modem, wireless need through a wireless receiver or transmitter.

Modem
Modem as known as Modulator and Demodulator. The main job of Modem is converting the digital signal into analogue signal (Modulator) at the sending end and convert the analogue signal into digital signal (Demodulator) at the receiving end.
Normally, a modem has three sockets, one for power, one for phone line, and one for network cable (usually is RJ-45 Interface). Unless the modem has some router’s functions which will have more socket for computers.
There are two types of electronic signals: analogue signal (used by telephone line) and digital signal (used by computers transmit). So, when we want to connect computer to the internet over the phone line which need modem as the interpreter to translate these two signals, so that they can read and understand it.
The protocol used by modem include Modulation Protocol, Error Control Protocols, Data Compression Protocols and File Transfer Protocol.
Bridge
A Bridge is an early two-port, layer 2 network device used to connect different segments of a network. The two ports of the bridge have an independent switching channel, instead of sharing a backbone, the collision domain can be isolated. Bridges perform better than hubs, where all ports share the same backbone. Later, the bridge was replaced by a Switch that had more ports and could also isolate conflict domains.
The bridge works at the data link layer, connecting two LANs and forwarding frames based on the MAC address, which can be viewed as a low-level router.
The most common way to extend a LAN is to use a bridge. The simplest bridge has two ports. More complex Bridges can have more ports. Each port of the bridge is connected to a segment of the network. When the PC1 in segment 1 want to communicate with PC3 in segment 2, the data packet will travel through the bridge (that will check its MAC address table to find out the destination belong to which segment), then the data packet will only broadcast on segment 2 rather than whole LAN which will reduce the traffic.

Transmission Media (Guide and Unguided)

Transmission media is the carrier of transmitting information. Commonly, it is divided into wired (guide) and wireless (unguided). Different transmission media have different characteristics which would affect the quality and speed of data communication in the internet.
Wired transmission media is the physical connection between two communication devices, it can help user to transfer data from one side to other which is guided. The wired transmission media mainly consists of twisted pair (Shielded and unshielded), coaxial cable and optical fibre.
Twisted Pair
As the name implies, a twisted pair cable literally means two or more separate insulated wires wound together with RJ 45 connector, so that they are parallel to each other. Twisted pair wires have the property of eliminating interference. Therefore, because cables reduce the impact of electromagnetic interference on electronic signals, they are suitable for short-range data and voice infrastructure. It is also more flexible and easier to install than coaxial cables.

Two types of twisted pair cables are used: shielded and unshielded. The shielded twisted pair (STP) has a thin wire mesh around the wire to protect the transmission. Unshielded twisted pair (UTP) does not.

The latter is the more common of the two types, used in Ethernet installations and often in residential and enterprise applications. Shielded cables are used in telephone networks as well as in network and data communications to reduce external interference and crosstalk and are designed to aid grounding. Of the two types of cables, UTP cables are cheaper than STP cables and require less maintenance because they do not rely on external shielding. Although UTP can transmit data as quickly as STP cables, they are more prone to noise than STP cables.

Twisted pair cables are the most cost-effective choice among coaxial cables and fibre optics, but they also have lower bandwidth and higher attenuation, meaning that the farther away they are, the lower their performance. They also wear out easily and must be maintained regularly. It is best to use twisted pair cables wherever there is no strong electromagnetic interference.

Coaxial Cable
A coaxial cable has an internal conductor surrounded by an insulating layer and surrounded by a conductive shield. The central conductor carries electrical signals. The shielding design of the cable allows data to be transmitted quickly through the copper core without interference from environmental factors.
Coaxial cable assemblies are easy to install and very durable. Because coaxial cable performs best over short distances, it is ideal for home installations and average capacity data transmission networks. Signal loss is a disadvantage when coaxial cable is used over long distances, and signal leakage tends to occur at the inlet or outlet, at the contact point between the male and female connectors. The signal will be affected when the weather is bad.

Fibre Optic
Fibre optic cable is different from coaxial cable and twisted pair cable. First, its core is optical fibres rather than copper, and data is transmitted by light rather than electrical or electronic signals. The transmission rate is 26,000 times faster than twist pair and the distance is longer. The fibre is insulated in a protective plastic outer layer or in a plastic coating within the pipe. Optical fibres are also flexible and can be tied to cables, which makes them useful for long-distance communications because light travels through them with very little attenuation compared to copper cables.

The fibre is connected by single mode or multiple mode. The former allows only one mode of light to travel through the core at a time, resulting in higher bandwidth. The effect is to reduce the number of light reflections, which reduces attenuation and allows data to be transmitted more quickly. The core diameter of multi-mode connection is larger, which can transmit multiple modes of light at the same time.
The amount of light reflected through the core increases as it travels that allow more data to pass through. But it does lead to high dispersion, which means the lower the bandwidth, the greater the attenuation, the worse the signal quality, the lower the signal quality. Multimode connections are ideal for LAN, security systems and other fibre optic networks for high-speed communications over short distances.
Fibre-optic cabling is the most expensive of the three. Fibre optics are fragile and can easily be cut or damaged during installation or construction. This also means it is not as flexible as copper, which can break if it is bent or twisted too much or at the wrong Angle. Finally, data transmission over longer distances requires optical signals to be amplified by components such as EDFA to be added to the network which increase the cost. Despite these drawbacks, fibre optic cabling is more efficient and has higher transmission capacity if it is within your budget.
Optic Fibre has various connectors, such as ST, SC, etc. There is bayonet fixed after the ST head is inserted and rotated for half turn, the disadvantage is it can be snap easily; SC connector can plug directly, and easy to use, the disadvantage is that is easy to fall out.
MT-RJ: it is a square optical fibre connector with integrated transceiver. It has double fibre in one end and can be used for sending and receiving data both.

Radio
Radio is the technology of signal that can communicate by using radio waves which can travel in free space, include air and vacuum. The shorter and the higher the wavelength and frequency of a radio wave, the more information can be transmitted within the same time.
Radio waves travel in free space is omnidirectional that can be direct, reflect, refract, scatter and so on which is depend on various objects in actual propagation environment. It is use for Wireless data networks (Wi-Fi), various mobile communication, radio broadcasts, Bluetooth and so on. Mobile only occupies several frequency bands which just under 1GHz. Each computer would use antenna to access the radio waves/signal to reach communication purpose. The size of antenna would decide the range of the signal.

Radio waves range in frequency from 300GHz to 3kHz, but it is also defined any wave of 1GHz or more than 3GHz as microwave. Like other electromagnetic waves, Radio waves travel at the speed of light. Radio waves in different wave bands have different propagation characteristics.
The lower the frequency is, the smaller propagation loss is and the further the coverage distance is, also the stronger the diffraction capability is. However, the frequency resources of the low frequency band and the system capacity is limited. Therefore, the low frequency band of radio waves are mainly use in broadcasting, television and other system.
The high frequency band resource is rich, and the system capacity is big. But the higher the frequency, the greater the propagation loss, the closer the coverage distance and the weaker the diffraction ability. In addition, the higher the frequency, the more technically difficult it is and increase the cost of the system correspond.

Bluetooth
Bluetooth is a short-range wireless communication technology that allows electronic devices to connect to each other via Bluetooth, eliminating the need for traditional wires. Through a wireless receiver on the chip, Bluetooth-enabled electronics can communicate with each other within the distances of 10 meters, transmitting at speeds of up to 1 Megabyte per second. In the past, infrared interface transmission technology requires electronic devices within sight distance, but now with Bluetooth technology, such trouble can be avoided.
The standard Bluetooth is IEEE802.15, which operates in a 2.4ghz band with a bandwidth of 1Mb/s.

Wi-Fi
Wi-Fi (Wireless Fidelity) is a wireless network communication technology based on the IEEE 802.11 series standard, which allows user to connect their device into network without any cabling and sockets. It also creates portable network centre (Hot spots) that people can carry it and access to internet in anywhere. It is the same with Bluetooth, connecting to the Internet via radio waves and it is a short-range wireless technology used in offices, homes and school.
With the development of the technology, there are more and more devices in the home need to connect to network, such as phone, computer, floor sweeper robots, air conditioner and so on, the wi-fi standards of the past gradually begin to fail to accommodate so many devices, and the speed starts to decline accordingly. So, IEEE has introduced a new Wi-Fi 6 standard that can better handle a large number of devices on a network at once.
Wi-fi 6 is essentially the 802.11ax, an updated version of 802.11ac.
But the IEEE has given it a more memorable name, calling it the sixth generation of wi-fi technology. Previous generations, such as 802.11ac/n, were also renamed wi-fi 5/4.
It’s like upgrading a mobile network – 2G, 3G, 4G, 5G. The bigger the number, the faster and better the performance. In the future, we do not need to study the meaning of the letter n/ac/ax when choosing a router, we just need to compare the number size.

Microwave
Microwave usually comes from Direct Current (DC) or 50Hz Alternate Current (AC) through semiconductor or vacuum devices.
Microwave refers to the electromagnetic wave whose frequency is from 300MHz to 300GHz. It is short for a finite band in radio waves, that is electromagnetic wave with wavelength is between 1m (excluding 1m) and 1mm.
Microwave have higher frequency than radio waves and are often referred to as “ultra-high frequency electromagnetic waves”. The basic properties of microwaves are usually characterized by penetration, reflection and absorption. For glass, plastic, and porcelain, microwaves pass almost through without being absorbed. For things like water and food it absorbs microwaves and heats itself and for things like metals, it reflects microwaves.

Satellite
It can be natural object or human made devices that can orbit a planet and moves periodically.
Human made satellites are 36000km away from the ground are used for communication, Meteorology, Resources, Reconnaissance, Navigation and so on.
Communication satellite is the space part of satellite communication system. A geostationary communications satellite can cover about 40% of the earth’s surface that enable communicate with each other on any ground, sea or air communications station at the same times. There are three geostationary communication satellite that can provided global communication except for parts of the poles.
The transmission of satellite needs a clear sight without any obstruction between satellite and a space station on the earth. The signal needs to travel in straight lines, but no limit of ground based wireless transmission.
Satellite use microwave to transmit signal to any place on the Earth which means it can provide the high-quality communication in remote area. People can use satellite to access the internet at the maximum download speeds of 1000Gbit/s and maximum upload speeds of 1000 Mbit/s, but the average of download rate and upload rate only got 1Mbit/s and 256kbit/s.

InfraRed (IrDA)
The sun’s rays can be roughly divided into visible and invisible light. Visible light refracts violet, indigo, blue, green, yellow, orange and red light through a prism. The light on the outside of red light, which is the part of the spectrum whose wavelength ranges from 0.76 to 400 microns, that is called infrared. That was discovered by British scientist Herschel in 1800. It is also known as infrared thermal radiation and has a strong thermal effect.
Infrared is an electromagnetic wave whose wavelength is between microwave and visible light. Its wavelength is between 1mm and 760 nanometres (nm), which is longer than that of red light.
Infrared networks can be used in environments such as classrooms, or in small, closed areas. For information security people, infrared network may be a good choice, because it cannot transmit through the walls, people located outside the building will not be able to directly intercept the infrared signal distributed in the building. It also means infrared transmission is highly susceptible to walls.
On the other hand, it is a low-cost form of wireless transmission. It use line of sight technology to transmits data in a straight Line like a laser Line, If there are no obstacles in the way of transmission, the transmission of data can be said to be quite fast and efficient, because infrared is a kind of light, so it travels at the speed of light.
Because infrared light cannot penetrate walls or large objects, so the data sending and receiving ends must be aimed at each other (that is, they can see each other) to communicate, that make it not suitable for mobile communication, and it is vulnerable to the interference of rain, snow or fog.

Laser
The theoretical basis of the laser originated from the great physicist Einstein, who in 1917 proposed a new set of technical theory “light and matter interaction”. This theory is said in the atoms that make up the material, have a different number of particles (electrons) distribution on different level, on the high level of particles by a photon excitation, the energy level jump (transition) from high to low level, at this time will radiate this light is the same and stimulate the nature of light, and in a certain state, can appear a weak light inspired a strong light. This is called “stimulated radiation amplification,” or laser.
Since lasers are equivalent to light, they can be modulated like radio waves to transmit information.
Because laser is equivalent to light, so it can be modulated like radio waves to transmit information. Optical fibre communication is the combination of laser and optical fibre.
Laser is high brightness, which meaning it can concentrate a lot of energy in a small space and a very short period of time. So, people can use laser to cut all kinds of material.
In medicine, lasers can be used as light knives to cut through the skin, and it also can be used for myopia.

Reference： Computer Hope, NIC, 09/03/2019, available from https://www.computerhope.com/jargon/n/nic.htm [01/03/2020] Computer Hope, Server, 06/30/2019, available from https://www.computerhope.com/jargon/s/server.htm [01/30/2020] Computer Hope, Printer, 06/07/2019, available from https://www.computerhope.com/jargon/p/printer.htm [01/30/2020] JavaTPoint, Guided Media, available from https://www.javatpoint.com/guided-transmission-media [01/30/2020] JavaTPoint, Unguided Transmission, available from https://www.javatpoint.com/unguided-transmission-media [01/30/2020]