Communication Technologies Essay

In this assignment I am going to describes different types of communication devices. For example Switches, Routers, etc. Then I am going to explain the principles of signal theory. After this I will look at difference methods of electronic communication and transmission used. Communication Devices Switches – These are mainly used for local area networks (LAN). The reason behind this is that they can be used to bridge a lot of computers together. They do look like hubs but they can vary in speed. They are more intelligent due to the fact that they can send out packets from a set port. There is advantage of using a network switch, they can be used with an Ethernet cable or a fibre optic cable and they still will work perfectly fine. When connecting a router or a server in an LAN or WAN network it is slightly easier because you would just need one cable which would mostly need to a fibre optic cable, so you can get the maximum rate of transfer speed. Routers – They are mainly used for connecting one network to another. They are meant for handling information and forwarding to another network connected to the router. You can either connect using wireless or a cable. Normally an Ethernet cable is used to connect the computer networks. Hubs – Also known as a concentrator or a multiport repeater. Used in a star or a hierarchical network setup to connect the station or the cable segments. There are two main types of hubs: passive & active. Active takes the incoming traffic, amplifies the signal and then forwards it all the ports. In a passive hub it simply divides the incoming traffic and forwards it. A hub can be used to manage and allow individual port configuration and traffic. Hubs operate on the physical layer of the OSI model and they are protocol transparent. This means that they do have the ability to set upper layer protocols such as IP, IPX or a MAC addresses. Hubs just extend them do not control the broadcast or collision domains. Bridges – Used to increase the performance of a network by dividing it into separate collision domains. Even though they are more intelligent than hubs due to the fact that they operate at the Data Link layer of the OSI model, they still are not able to control the upper layer protocols. On a separate segment they store the MAC addressing table of all nodes. Basically it takes the incoming frames and checks the destined MAC address and lookups it up against the store MAC addressing table and decides what to do. If the frame is comes from the same port as the destined port than it simply discards the frame. If the destined location is not known than it will be flooded throughout the outgoing ports and segments. Repeaters -One of the less complex hardware of the networking world, because it basically runs at the physical layer of an OSI model, so it is not aware of the frame formats and upper layer protocols. Repeater basically is used to expand a LAN network over large distance regenerating a signal. When using a repeater remember the 5-4-3 rule which means that a maximum distance between two hosts on the same network is 5. Use only maximum of 4 repeaters in a network and only 3 segments can be populated. Gateways – Very intelligent devices, they work at the Transport Layer protocol. This is higher than the Upper Layer protocol. This means that can manage and control IP, IPX and MAC addressing. They allow IPX/SPX clients to IP/TCP uplink network to connect to the internet. A gateway in simple terms is like a post office. All the information is sent to it and then as a post office knows the number of houses in the area in the same way a gateway would know all the ports and direct it there. Cell Phones – It is a piece of device which is used by a lot of people. It is a portable version and more advanced version of a normal home phone. It lets you voice calling, text messaging, the some other advanced phones even allow video calling and internet browsing. Cell phone is a full duplex device therefore you can connect it to your computer and use it as a modem even though it would be very slow. The newer released phones are somewhere near capable of the proper modem speeds. DCE & DTE devices – Data Communication Equipment (DCE) is basically equipment which allows communication with a Data Terminal Equipment (DTE). In another words DTE ends the communication line and a DCE provides the path of communication. An example of an DCE is an modem and a computer is a DTE. Fax Machine – A device which allows you to send paper copies using PSTN lines to other people. It can also be used to send memos and other information as well. It uses the phone line to transmit the data that is sent. A fax machine has a sensor to read the data and the end of it. It will encode the black and white that it picks on the paper and moves it to the receiving end. It will compress the data before transmitting it. As soon as it receives the data it decodes and decompresses the data so it can arrange it in the way that it scanned it from the original document. There are a lot of things in a fax machine that allow it to do its function. It consists of a source projecting a light beam, a rotating cylinder and a photo electric cell. It also has paper feed like a printer. E-Mail – Email also which is the short form for electronic mail. You can use e-mail to stay in contact with your friend/family even colleagues. It does it by finding out the person you want to email he’s email address and then you will send him an email and click send and then that person will receive it. Signal Theory When talking about signal theory data is represented by digital format which is dependent on binary or base 2 principles. Analogue and digital frequencies are used for transmitting signals along a medium link. Analogue records the waveform as they are. Digital on the other hand turns the analogue signals normally to sets of number. Analogue signals can have varying amplitude and frequency. Amplitude analyzes the loudness of the signal and Frequency determines the pitch of the signal. â€Å"Pitch† mostly used to refer to low and high notes. If the frequency is lowered than you get a low note and if the opposite is applied than you get a high note. Bit is a binary digit which represents value of 0 which is normally off and 1 which is normally on. Bit can also be referred to as a electrical pulse which is generated by the inner clock in the control unit or data register. Bit can also be used for digital electronics which is another system that uses digital signals. Manipulation o f a bit within the memory of a computer can be kept in a steady level on a storage device as a magnetic tape or disc. Byte which is made up of 8 bits is a unit measurement used for information stored on a computer. Synchronous & Asynchronous Communication To sum up synchronous communication it is when interaction with data takes place it is done in real time. On the other hand asynchronous or delayed communication is when any data which is archived or stored and accessed later. It is important to choose the most effective delivery mode because it directly impacts the level of interaction that is going to take place. Synchronous It does not use start or stop bits but instead it synchronizes the transmission speed with receiving and sending end of transmission using the clock signals specifically built for each of the components. After this constant streams of data are transmitted between two sources. Because no start or stop bits are involved data transmission is faster, but more problems occur because if latency takes into effect then the synchronization clock will be out of timing therefore the receiving node will get the wrong timings that have been acknowledged in the protocol sending and receiving data. If this happens then data can be corrupted, missing or even wrong message. There are ways around this which take time. You could use check digits and re-synchronize the clocks so that you can verify that the transmission has been successful and has not been interrupted. Advantages of using synchronous transmission are that lower overhead and more data can be transmitted and data transmission rates are al so faster. The drawbacks of using synchronous transmission is obviously more prone to problems, it is more expensive and more complex. Asynchronous Opposite to synchronous it uses start and stop bits to mark the start and end of a transmission, this means that 8 bit ASCII characters would be transmitted using 10 bits because the use of start and stop bits. For example (1)10111111(0) the bracketed out one and zero at the start and end mark the start and end of a transmission. This tells the receiving either the first character is transmitting or finished transmitting. This method of transmission is normally used when data is sent occasionally as opposed to in solid stream. Benefits of using asynchronous data is that it works out cheaper because timing is not that important and it is also simple because both end do not require synchronization. Drawback are that if a large amount of data is to be transmitted it would take a long time this is because a lot of bits are only for control uses they do not contain any useful information. Bandwidth is used to define how much volume a medium can transmit. Basically it is the maximum rate at which data can be transmitted across mediums. The more bandwidth a wire can handle the higher transmission rates can be achieved. It can also high transmission rates for multiple users. But there are restrictions in place such as if a user has been transmitting a lot of data between a period of time then a temporary limit will be put on. This is quite common with ISP’s. To stop this happening to you best thing to do is not to download a lot at the same time and also close programs which use the bandwidth continuously. Radio Transmission Radio is a way of transmitting signals using varied tones which convey a message of electromagnetic waves with a frequency. Electromagnetic radiation travels in direction of oscillating electromagnetic fields which go through the air and vacuum of space. Changes in radiated waves such as amplitude, frequency or phase allow information to be carried systematically. If the radio waves pass through electrical conductors the oscillating fields induce an alternating current in the conductor. This could be detected and changed into sound or any other type of signal which is able to carry information. Every radio system has a inbuilt transmitter this is the source which allows electrical energy that produces a alternating current of a desired frequency of oscillation. The inbuilt transmitter also has a system which changes some properties of the energy produced to impress a signal on it. This change could be as simple as turning the signal on or off. Change could be more complex such as alternating more subtle properties such as amplitude, frequency, phase or combination of all three properties. The modulated electrical energy is sent via the transmitter to an antenna. Antenna changes the alternating current electromagnetic waves; this allows the waves to transmit in the air. There are drawbacks of using radio. First is attenuation can happen, this basically means the longer the wave has travelling to get to its destination the more weaker it gets. Most obvious example of this would be someone listening to FM radio in the midlands; the further he goes away from the midlands the more signal gets weaker. Microwave An electromagnetic based wave which has a range or wavelength of up to 30 GHz. Currently microwaves are getting more popular due to advancing technologies. Microwave offers high bandwidth at low cost. Most common problem with microwave transmission is reflection. Microwaves are common used for radar which pickup planes and helicopters flying in the air. Microwaves will hit the plane or helicopter and reflect back and gets calculated giving the position of the flying object. Waves are reflected due to a barrier which stops the wave from going further so it hits the barrier and reflects back. Reflection affects the signal if the reflection is not good then the reflection won’t happen therefore a dead or a blank signal will be received. To minimize the effect try staying close the satellite. Wireless protocols such as Bluetooth use microwaves to transmit. Satellite Satellite is a orbiting piece of hardware which has been left floating in the air from big companies like Microsoft, satellite can be used for communication. There are also other types of satellites which are used for spying or used for online maps such as Google maps, Microsoft live maps or another services. Satellites provide high bandwidth solutions. Satellite is categorized as a WAN because it uses high speed & long distance communication technology which allows them to connect to computers. Attenuation also affects satellite connection due to the same reason. If a satellite is not in the required position and starts transmitting signal it will not reach television so they might not work properly or correctly. Satellite dish has to be in the same direction as the satellite. Satellite signals reach television using a transmission antenna which is located at an uplink facility. The facility has an uplink satellite dish which would be around 9-12 meters in diameter. The bigger the diameter of the satellite the more accurate signals and better signal strength from the satellite is received. The satellite dish would be pointed towards the satellite and the uplinked signal is received by the transponder at a certain frequency. This frequency is normally C-band (4-8 GHz) or KU-band (12-18 GHz). The transponder then retransmits the signal back to the earth. NTSC, PAL or SECAM are three broadcast standards used through out the world. NTSC is normally used in the US, Canada, Japan, Mexico, Philippines, South Korea and other countries. PAL which stands for Phase Alternating Line is an colour encoding system which is used by over 120 countries in the world. In a few years time most of the countries will stop using PAL and either change to DVB-T SECAM It is sequential colour with memory is the analogue colour television system. SECAM was Europe’s first colour t elevision standard and France currently uses it. The analogue signals for the three broadcasting types are transmitted via a satellite link scramble or unscramble. The analogue signal is a frequency modulated and transformed for a FM to something called baseband. The baseband fuses the audio and video sub carrier. The audio sub is further demodulated to provide a raw audio signal. Digital TV’s that transmit via satellites are normally based on open standards such as MPEG and DVB-S. MPEG which stands for Moving Pictures Experts Group is a compressed format which code moving pictures and associated audio information. There is also MPEG 2 which is a digital television signal which is broadcasted via terrestrial cable and direct broadcast satellite TV systems. DVB-S which stands for Digital Video Broadcasting is a standard for satellite TV’s which forward error coding and modulation. It is used by every single satellite that serves a continent. Standards Organizations There are difference types of standard organizations. These are the various types of standard organizations TIA/EIA, RS-232, IEEE, ISO, OSI and Manchester Encoding. ISO/OSI – International Standards Organization’s Open System Interconnect (ISO/OSI) is the standard model for networking protocols and distributed applications. ISO/OSI defines seven network layers. 1. Physical 2. Data Link 3. Network 4. Transport 5. Session 6. Presentation 7. Application I will be only be explaining in-depth the first network layer: Physical. This layer defines what cable or physical medium to be used. There are lots of different types of cable thinnet, thicknet, TPC, UTP. All of these mediums are functionally the same. The major difference between the various cables is the cost, convenience, installation and maintenance. Converters from one media to another operate at this level. TIA/EIA – Telecommunications Industry Association & Electronics Industries Alliance (TIA/EIA), state the standards which should be used laying cables in a building or a campus. TIA/EIA describes how a hierarchical topology should be laid out. A system where a main cross connect system is used and connected using a star topology using a backbone cabling through a intermediate or a horizontal cross connect. This type of cabling or similar is also used for laying out telecommunication cables. The backbone cabling method will be used to connect the entrance facilities to the main cross connect. In areas such as office a horizontal cross connect for the consolidation of the horizontal cabling, which extends into a star topology. Maximum stated horizontal cable distance should anywhere between 70M-90M. This applies to TTP (Twisted Pair Cable), but the fibre optic horizontal cabling has a set limit of 90M. IEEE – Institute of Electrical and Electronics Engineers allows the development of â€Å"Electro Technology† which in other words applies to electricity applied to technology. Societies like the IEEE Computer Society are subsidiaries of the IEEE itself. This standards organization also publishes journals. Devices such as digital camera need set amount of bandwidth speed so it uses a IEEE plug. Any device that uses the IEEE standard uses a twisted pair cable. Signalling Standards NRZ- It stands for Non Return to Zero. It is a binary code normally used for slow speed synchronous and asynchronous transmission interfaces. Ones is represented as a small voltage and zero is negative voltages. They are transmitted by either by set or constant DC voltages. It also uses additional synchronisation so it dose not lose any bits in the process. NRZ-L – Non Return to Zero Level is similar to NRZ, but it not a binary code. Same as NRZ one is represented as small voltage, but zero is also represented as a small voltage but it is not as big voltage as one, Therefore it allows more data to be send without a lot of signal change. NRZ-M – Non Return to Zero Mark again similar to NRZ, but one is actually represented by a change in physical state and zero is represented as change in physical state. This basically means that there is no voltage when there is no change in physical state. RS-232 – This standard applies to serial data transfer such as the 9 pin serial connecters which are commonly used on a computer motherboard. The data is sent in as time series of bits. Synchronous & Asynchronous is both supported by this standard. This standard and states the number of control circuits that can be or need to be used to connect the DCE & DTE terminal with one another. Data and control circuits which are signalled from a DTE connected to a DCE or vice versa will always flow and operate in one direction this is called half duplex. Only full duplex allows data to be sent and received in both directions at the same time. Manchester Encoding – Data bits which are represented by transitions from a logical state another is called Manchester encoding. This is a digital type encoding. In this encoding the signal is self clocking because the length of every data bit is set by default. Depending on the transition direction the state of the bit can be analyzed. In Manchester encoding the signal synchronizes itself. This is an advantage because this will decrease the error rate and optimize the reliability. But on the other hand it is also a disadvantage because the amount of bits sent in the original signal when transmitted has be twice the amount of bits from the original signal. Differential Manchester – Also known as Conditioned Diphase (CDP). It is a encoding method which uses data and clock signal as fused to create a self-synchronizing data steam. Similar to Manchester encoding it uses present or absent transitions to represent logical value. TTL – Transistor Transistor Logic is a binary code which either uses high voltages between 2.2V and 5V to represent one and no voltages between 0V and 0.8V to represent a zero Name Specification Maximum Length/Speed Advantages Disadvantages Cat.5 Cable RJ45 Connector. Made from Copper, PVC, Plastic Length:100 M Speed:100 Mbit/s Cheapest type of cable, Mostly unshielded & more prone to electrical noise. Cat.6 Cable RJ45 Connector. Made from Copper, PVC, Plastic Length:100 M Speed: 10 Gbit/s Very fast transmission. Unshielded & more expensive than Cat.5 Cat.7 Cable RJ45 Connector. Made from Copper, PVC, Plastic Length:100 M Speed:100 Gbit/s Extremely fast and less interference Incredibly expensive and mostly likely be manufactured till 2013 Bluetooth Mostly Copper for the circuitry, Plastic for casing. Length: 100 M Speed:1 Gbit/s Send from cell phones, do not need wires to connect, Most of the phone are equipped with it Open and other people can access your phone if not protected. Quite slow when sending and receiving on a cell phone. Infrared Receiver, Antenna and Transmitter, Copper & Plastic Length: 40 km Speed: 4 Mbit/s Shorter wave than microwaves, not as harmful. Less interference. Microwaves Antenna & Receiver. Length: 1 M Speed: 300 GHz Good for sending data over longer distances Dangerous, if something that uses microwaves e.g. cell phone for too long. Too much interference Wi-Fi Wi-Fi Signal Transmitter. Length: 95 M Speed: 5 GHz Usable anywhere in the house, can even be used as a hotspot in public places e.g. airports, cafà ¯Ã‚ ¿Ã‚ ½, etc Other people can also access it so many connections can make it slow. Satellite Dish and a satellite in orbit Length: 22,000 Miles Speed: 40 Mbit/s Connection from anywhere in the world. Delay of up to 500 millisecond due to rain or moisture Fibre Optic LED/Laser Connector. Glass, Plastic, PVC. Length: 40,000 Speed: 10 Gbit/s Extremely fast speeds can be achieved without the use of switches, hubs, etc over long distances Simply expensive to buy. Radio Transmitter & Receiver Length: 100 Miles Speed: 300 GHz Available anywhere in the world. Very limited range and gets easily affected by interference. Name Specification Advantages Disadvantages Coaxial Diameter: 6 mm / Resistance: 85.2 km Capacity: 70 km at 1KHz Cheap. 500 meters length. It very reliable Expensive and hard to install Fibre Optic Diameter: 2 microns. Good for transmission over long distance because it is immune to magnetic interference. Electrical interference protected. Stretches up to 3000 meters. No noise is generated Very expensive and over time the sent signal will get weaker because of signal reflecting. UTP/Cat.5 Foiled and uses copper wire. Stretches up to 100 meters. Easy installation and transmission rates reaching up to 1 Gbps. Very open to interferences. STP Foiled and also uses copper wire. Shielded. Length up to 100 meters. Transmission rates between 10-100 Mbps Expensive heavy and big in physical size. Radio Uses antenna to transmit. Signal can be refracted. No wires needed and very long distances capable. Signal gets weaker the more time taken to reach the destination. Security is a problem very open for hackers. LAN This is type of network which covers a small office, home or a school network. A LAN uses either wired Ethernet or wireless RF technology. Using a LAN can be much easier when there is a printer available or sharing a file throughout the network. Updating software is much easier because updating software will automatically update all the other software’s. LAN has much higher transmission rates because it is wired connection rather than wireless. Ethernet and Wi-Fi as most widely used technologies, however many others such as token rings have been used before. This relates to standard IEEE 802.2. This standard allows two connectionless and one connection orientated operational mode: Type 1 which allows frames to be sent to a single destination or multiple destinations on the same network is a connectionless mode. Type 2 is the oriented operational connection mode. In this mode it uses something called sequence numbering which makes sure that when the data is send it gets to the destination in the correct order and not a single frame has been lost. Type 3 which is also a connectionless service, but only support point to point communication. Infrared is related to this service because in computer infrared network it can receive and transmit data either through the side of the device or the rear side of the device. When connections are made using Microsoft Windows Infrared the same method used for LAN connections can be used. Infrared technology has been extended to allow more than two computers to be connected semi permanent networks. The advantage of a LAN is that the same physical communication path can be shared by multiple devices. For example it there is a printer, a computer and the internet connection the LAN will allow connections to the printer and it will also allow connections to the internet. If a software is loaded onto the file server that all the computers on the network can use it. There are quite a few drawbacks of a LAN network. For example security measures need to be taken so that users cannot access unauthorised areas. It is quite hard to setup the network. Skilled technicians are needed to maintain the network. Yet the biggest disadvantage is that if the file server goes down than all the other computers on the network are affected as well. WAN This type of network covers a wider area. It is used over high speed, long distance communications such as computers in two different areas. A WAN can also be shared. For example two occupants in two buildings can share the wireless connection to a third person, or a business or anyone or anything they wish to do so. Data is safe, secure and quick when it is transmitted between two computers. WAN can also be used to connect different types of networks together for example a WAN network connected to a LAN networks. The reason behind this is that it is AppleTalk. It is a cheap LAN architecture which is a standard model built for all Apple Macintosh computers and laser printers. It also supports Apple LocalTalk cabling scheme as well as Ethernet and IBM token ring. AppleTalk can connect to standard computers which do not have AppleTalk. This all relates to FDDI standard which stands for Fibre Distributed Data Interface. It is a backbone of a wide area network. It uses fibre optic cable to transmit data up to supported rate of 100 Mbps. An advantage of a WAN it allows secure and fast transmission between two computers. Data transmission is inexpensive and reliable. Sharing a connection is easy as well because it allows direct connectivity. A WAN also allows sharing of software and resources to other workstations connected on the network. Disadvantage of a WAN network is that the signal strong all the time so anyone trying to hitchhike a connection can use the WAN connection it is not protected. WAN are slow and expensive to set-up. They also need a good firewall to stop intruders using the connection. Networking Mediums Different types of medium are used for different types of topologies. Coaxial Cable It is normally used to connect telecommunication devices which used for broadband connection which use high transmission rates to transfer data. The cable is insulated using a braided shield which is also known as a screen. It protects the cable from electromagnetic interference. It has higher capacity than a standard copper wire. Therefore it allows radio frequencies and television signals to be transmitted. Various types of coaxial cables are available which can be used for thin Ethernet which are used for networking 10Mbps connections lengthening up to 200 meters. There is also thick Ethernet cable is also used for 10Mbps connections but stretching up to 500 meters. Unshielded Twisted Pair (UTP) coaxial cable has been used in the past when building networking using thick or thin Ethernet. Ethernet cables quite expensive but they are still used because they carry more data then a telephone wire and it is less susceptible to interference. Optical Fibre Optical fibre also known as a fibre optic cable uses light to transmit data. Light is made using a laser or LED is sent down a fibre which is thin strand of glass. Fibre optic is about 2 microns in diameter which is 15 times thinner than a single human hair. Optic fibre is not affected by electromagnetic interference. It is cable of higher than data transmission rates, ideal for broadband usage. Fibre optics are manufactured in two different types the single mode and multi mode. The difference between the two is quite obvious single mode uses one beam of light to transmit data to longer distance of around 3 km but the multimode uses multiple beams of light to transmit data but only to shorter distance of 2 km. This allows more data to be sent simultaneously. It is normally used for broadband transmission as mentioned before because it is faster at transmission than any other cable currently available. Fibre optic also has an advantage of long distance transmission because light propa gates through the fibre with little attenuation compared to electric cables. Not many repeaters are needed for long distance. Data travelling using the fibre can reach rates of unto 111 Gbps. Fibre optics also restrict high voltages travelling from end to end of a fibre to another end. It also restricts cross talk and environmental noise between signals transmitting to different cables. UTP (Unshielded Twisted Pair) & STP (Shielded Twisted Pair) UTP and STP both use copper wires which are known to man as one of the oldest types of transmission media methods. STP is insulated with a metallic plastic foil which is all under the plastic sheath. This insulating is expensive to make that’s why it is more expensive than normal cable. Even though STP cable is shielded there is still crosstalk. It cannot be eliminated. Both UTP & STP individual wires are twisted together so it creates there is less crosstalk. Core of each of the type of cable is a very good conductor and easy to work with. Media which can be used with UTP is internet, because it is easy to install, maintain, less expensive and allows higher transmission rates. The media used with STP is also internet, but it is more expensive and difficult to install. The advantage is that there is less interference. It is difficult to install because it has to be grounded at both ends. Improper grounding will result I metallic shielding acting as a antenna and it will pick u p unwanted signals. Due to the cost and difficult to install and maintain it is hardly used in Ethernet networks. It is mainly used in Europe. Crosstalk Crosstalk means that signal that are transmitting in different circuits interfering with each other. Crosstalk happens because unwanted signals interfere with another channel transmitting undesirably. Electrical Noise Noise is when an electrical signal is transmitted across a wire which is not the sent signal by the user, but it is another signal which has been picked up randomly. Twisted pair cables eliminate the interference because they are twisted with each other so they cancel out each other. The thickness and varied insulation of a cable and its capacitance of the wires will cause noise. For example when there is communication on a telephone and either person cannot hear the message clearly this is caused by noise affecting the signal. This is known as crosstalk, as mentioned before crosstalk is when signal is affected by electromagnetic field around a wire. Electric noise cannot be eliminated but can be minimized by taking caution. Keep cables away from electrical equipments and shield the cable weather it is a fibre optic or a STP. Checksum It is a method used for error-checking the received data against a calculated checksum. For example when a data is received by the designated node the checksum error detection method will create a new calculation and check it against the old calculation to check weather the same result it received. This makes sure the data has not been altered in any way when it was transmitting. The checking of the data is called checksum function or checksum algorithm. Cyclic Redundancy Check (CRC) CRC is another type of error-checking technique used in data communication. A CRC character is generated at the end of the transmission. The produced CRC character’s value depends on the hexadecimal value of ones in the data block. The node receiving the transmission makes a similar calculation and compares it to the source node and it the values are different then it asks for retransmission of the data. Frame It is a collection of bits sent over a medium. It contains physical address and control information. It also contains error-detection methods like CRC. The size and role of the frame is all dependent on the type of protocol, which is often used synonymously with packet. When the data is split and if necessary it is sent to Ethernet frame. The size of the Ethernet frame varies between 64 and 1,518 bytes. It uses the IEEE 802.3. It contains address, length, data and error checking utility. The data is passed onto the lower level components corresponding to OSI’s Physical layer. This converts the frames into bit-stream and sends it over the transmission medium. Other network adapters on the Ethernet receive the frame and analyze it for the destination address. If the destination address match of the network adapter, the adapter software simply processes the incoming frame and the passes the data to higher levels of the protocol stack. Packets It is a unit of data sent across networks. When a computer transmits data it will split or divide it into packets when it reaches the defined node it is transformed into the original transmission. Also known as a datagram it contains two parts. The header which acts as a envelope and the other part is the payload which is contents. Any message sent over the size of 1,500 bytes is fragmented into packet for transmission. When packet filter is put into place the header of incoming and outgoing packet is analyzed and decides whether to let them pass or restrict the packet, this is decided based on network rules. Data Transmission Modes & Methods There are three different ways transmission can take place. Data transmits either using simplex, half duplex or full duplex mode. There are two different ways how data is transmitted. Data can be transmitted via serial or via parallel transmission. Simplex Simplex data can only travel in one direction. Television and radio broadcasting are example of simplex. Fibre optic works with simplex mode. Simplex is good for satellite communications. TV signal is the proof that satellite communication is good because the transmission is good and clear. Simplex is rarely used for computer based telecommunications. Half Duplex Half duplex data can travel both ways but only in one direction. Coaxial cable works in half duplex mode. Radio is a example of half duplex because the signal reaches the destination and comes back to the original source. Communication between networks also works at half duplex. If a node is transmitting a message and another node wants to transmit it has to wait till the token ring comes back. Full Duplex In full duplex data can travel in both directions and at the same time. The bandwidth is divided in both directions. UTP/STP mediums work at full duplex. For example Bluetooth is a full duplex because data can be received and sent by both devices. Another example is landline telephone because both end of the phone can speak and listen to each other. Serial Transmission In serial transmission one bit is sent at a time. It is good for communication between several participants. Serial transmission is slow. When the data is sent it is dissembled by the source and reassembled by the receiver. Parallel Transmission Parallel transmission is when every bit is sent simultaneously but using separate wire. Basically when data is parallel channel transmitted for i.e. 8 bits or a byte everything is sent simultaneously therefore it’s faster than serial because serial channel would send the 8 bits or byte one by one. Most common example is communication between a printer and the computer.