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. “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 of 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 also 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 television 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 “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.