# Computing - Communication > Source: https://ollybritton.com/notes/a-level/computing/topics/communication/ · Updated: 2021-01-28 · Tags: computing, networking ### See Also: - [Computing - Networking](https://ollybritton.com/notes/a-level/computing/topics/networking/) ### Serial vs Parallel ##### What is serial data transmission?? Where bits are sent one after another along the same data line. ##### How can you do two-way communication using serial data transmission if you only had one wire?? You would need two wires. ##### What's an example of a serial data cable?? USB ##### How are serial cables sometimes deceptive in their ability to do two-way communication?? The multiple data lines are sheathed together so it only looks like one line. ##### What is parallel data transmission?? Several bits are sent simultaneously along seperate data lines. ##### How can you do two-way communication using parallel data transmission?? You would need twice the number of wires. ##### What's an example of a parallel data cable?? A cable connected to a printer. ##### In one word, what is the main issue with parallel data transmission?? Skew. ##### In parallel data transmission, what is skew?? Where bits travel at slightly different speeds along each line. ##### Why is skew an issue in parallel data transmission?? All the bits will arrive at slightly different times. ##### ![PHOTO SKEW](skew.png) What phenonemon does this photo show?? Skew. ##### When does skew get worse?? When the cables are longer. ##### What is crosstalk?? Electromagnetic interferences between two parallel data lines or wires. ##### When does crosstalk get worse?? When the speed of transmission increases. ##### When can you use parallel data trasmission?? Over very short distances. ##### What's the maximum distance you can use parallel data transmission over?? About $2m$. ##### When can you use serial data transmission?? Over very long distances. ##### Why is serial transmission more reliable than parallel transmission?? You don't get skew or crosstalk issues. ##### What is smaller and cheaper: serial cables or parallel cables?? Serial cables. ### Asynchronous vs Synchronous ##### What is synchronous data transmission?? Where all data transfers are timed to coincide with an internal clock pulse. ##### ![PHOTO SYNCHRONOUS TRANSMISSION](synchronous-transmission.png) Is this synchronous or asynchronous data transmission?? Synchronous. ##### What is asynchronous data transmission?? Where each byte is sent separately the moment it is available instead of waiting for a clock signal. ##### In asynchronous data transmission, what is each byte preceeded with?? A start bit. ##### In asynchronous data transmission, what is each byte preprended with?? A stop bit or a stop period. ##### ![PHOTO ASYCHRONOUS TRANSMISSION](asynchronous-transmission.png) Is this synchronous or asynchronous data transmission?? Asynchronous. ##### In asynchronous data transmission, how are the bits verified?? Using parity bits. ##### Why is synchronous data transmission sometimes considered slow?? Because you have to wait for the clock. ##### Why is asynchronous data transmission sometimes considered slow?? Because you have to send additional stop and start bits. ##### Does a keyboard or mouse use synchronous or asynchronous data transmission?? Asynchronous. ### Latency ##### What is latency?? The time delay between the moment the first byte or packet of a communication starts and when it is received at its destination. ### Speed of Transmission ##### What is bit rate? In [Computing - Networking](https://ollybritton.com/notes/a-level/computing/topics/networking/) ##### What is baseband?? Where you have a high and low voltage which represents a $1$ and $0$. ##### ![PHOTO BASEBAND EXAMPLE](baseband-example.png) What method of transmission does this show?? Baseband. ##### In baseband, what is the speed of signal change directly proportional to?? The bit rate. ##### What is baud rate?? The rate at which the signal in a communications channel changes state. ##### If in baseband transmission, if the baud rate is $1,000,000$ signal changes per second, what is the bit rate?? $1,000,000$ bits per second. ##### What's the relationship between bit rate and baud rate?? They are the same. ##### What is broadband?? Where multiple signals are sent as variations on the wave. ##### ![PHOTO BROADBAND EXAMPLE](broadband-example.png) What method of transmission does this show?? Broadband. ##### If you have 4 different voltages on a carrier wave, how many bits can you send with each signal change?? $$ 2 $$ ##### ![PHOTO BROADBAND EXAMPLE](broadband-example.png) What's the relationship between bit rate and baud rate here?? Baud rate is twice the bit rate. ##### What is the formula for bit rate in terms of baud rate?? $$ \text{baud rate} \times \test{number of bits per signal} $$ ##### If a signal changes at a million times a second and $8$ bits are encoded on each signal, what is the bit rate?? $$ 8,000,000 $$ ##### If a signal changes at a million times a second and $8$ bits are encoded on each signal, what is the baud rate?? $$ 1,000,000 $$ ##### What does even parity mean?? Add a $1$ or a $0$ to make the total number of $1$s an even number. ##### What does odd parity mean?? Add a $1$ or a $0$ to make the total number of $0$s an odd number. ##### What is a stop bit equal to?? $$ 1 $$ ##### What is a start bit equal to?? $$ 0 $$ ##### What's different about stop and start bits to how you would expect?? They go the other way around, stop bits come first, followed by a start bit. ### 2021-02-02 ##### ![PHOTO PEER TO PEER](peer-to-peer.png) How would you describe this network?? A peer-to-peer network. ##### What is a server?? A computer that provides services or resources required by any of the clients. ##### What is a client?? A computer which requests serivces or resources provided by the server. ##### In networking, what is a terminal?? Clients of a central server. ##### What are some examples of specialised servers?? * Web server * Print server * Mail server * File server * Database server ##### Why are peer-to-peer networks not as secure?? Because if one machine is a weak link then the whole network is insecure. ##### What kind of organisation would a peer-to-peer network be useful for?? Small companies with fewer computers. ##### Which is cheaper: client-server networks or peer-to-peer networks?? Peer-to-peer networks. ##### Which is more restrictive/secure: client-server networks or peer-to-peer networks?? Client-server networks. ##### How could you describe each node of a peer-to-peer network in terms of a client-server architechture?? Each node can act as both a client and a server. ##### What is the main use of peer-to-peer networks?? File-sharing. ##### Why are peer-to-peer networks used for pirating?? They are hard to shut down. --- Olly Britton — https://ollybritton.com. Machine-readable index: https://ollybritton.com/llms.txt