Networking: Chapter 8 (Data Transmission) Flashcards
What is Asynchronous Data Transmission?
Asynchronous Data transmission is when each byte of data is sent individually with its accompanying start and stop bits.
What is Synchronous Data Transmission?
Synchronous Data transmission is when packets of data are sent with its accompanying start frame, which tell the receiving station that a packet is coming.
What are 2 types of error checking in data transmission?
- Parity Check
* Cyclic Redundancy Check (CRC)
What is a Parity Check?
A Parity Check is a way of checking for errors in data that has been transferred between systems
How does a Parity Check work? (4)
- A bit in each byte of data is set aside as the parity bit
- In even parity this bit is set to 1 or 0 to ensure an even number of 1s
- In odd parity this bit is set to 1 or 0 to ensure an odd number of 1s
- If even parity is used and arrives to its destination with an odd number of 1s an error is registered, and vice verse
What is a Cyclic Redundancy Check (CRC)?
A Cyclic Redundancy Check is a way of checking for errors in data before it leaves the source system
How does a Cyclic Redundancy Check work? (3)
- It divides binary data in the packet by a 16 bit or a 32 bit number and produces a remainder, which is sent along with the data
- When it reaches the receiving system the same calculation is carried out
- The results of these calculations must be the same, and if they aren’t then there has been an error
What is Transmission Control Protocol/Internet Protocol (TCP/IP)?
It is a protocol which establishes a communication between nodes on a network before sending data and then routes packets of data to these nodes.
What is Carrier Sense Multiple Access/Collision Detection (CSMA/CD)?
It is a protocol which is used to control which node on a network can transmit at any one time on a baseband network
Why is CSMA/CD needed? (2)
- Baseband networks only allow one device to transmit at any one time
- If more than one device transmits data at one time a collision will occur, and the more collisions there are the slower the transmission rate across the network
How does CSMA/CD work? (3)
- When a node wants to transmit data on the network, the Carrier Sense finds out if another data transfer is taking place and if not then the node will transmit.
- Multiple Access means that more than one node can begin to transmit on the network at the same time.
- If 2 nodes do transmit at the same time, Collision Detection makes the two transmissions wait a random amount of time before trying to re transmit so there isn’t another collision
What is circuit switching?
When a fixed connection path is established between two points on a network and lasts as long as it takes to transmit all the data being sent. It is used in dialup and ISDN connections
What is packet switching?
When data messages between two points on a network are divided into packets and each individual packet can take a different path through a network instead of a fixed path. The packets are reassembled at their destination. It is used in Internet data transmission
What is an advantage of circuit switching?
Once the connection is set up, data can be transmitted directly and steadily to its destination, which is suitable for thing such as transmitting audio/video files
What is a disadvantage of circuit switching?
Circuit switched connections take time to establish, which is unsuitable for things such as connecting to web servers
What is an advantage of packet switching?
Since packets take different routes it utilises the whole network instead of clogging up one route so congestion is avoided
What is a disadvantage of packet switching?
Messages at the receiving end will need to be constructed since the packets of data take different routes at different times
What is a Dialup connection? What speed does it operate at? Where would it be used?
- It is an Internet connection that uses modem and telephone lines to transmit data.
- It operates at 56 kbps
- It would be used for light home use
What is a Cable modem connection? What speed does it operate at? Where would it be used?
- It is an analogue modem that sends and recieves data through a coaxial cable television network instead of telephone lines, and does not require dialling.
- It operates at 36Mbps downstream and 2 to 10Mbps upstream
- It would be used in residential areas
What is a Leased line connection? What speed does it operate at? Where would it be used?
- It is a permanent, dedicated connection from one point to another to allow high speed, always on connection channels
- It operates at 1.54 Mbps
- It would be used for large businesses
What is an ISDN connection? What speed does it operate at? Where would it be used?
- It is a digital transmission service which uses telephone lines, but cuts out analogue to digital conversions out of the modems.
- It operates at a rate of 2 x 64Kbps transmission channels and 1 x 16Kbps for control information
- It would be used for small businesses
What is an ADSL connection? What speed does it operate at? Where would it be used?
- It uses ordinary phone lines to provide broadband access, and provides high transfer rates, but customers must be within 5500m of the exchange
- It operates at 9Mbps downstream and 1.5Mbps upstream
- It would be used for tele-working
What is a Network Interface Card (NIC)?
It is a device that connect a node to a network, and is identified by a unique MAC address.
Why is a Network Interface Card used? (4)
- Data Conversion (From binary to whatever type of signalling is used on the network)
- Buffering (Storing the data during data conversion)
- Packaging data into frames (Adding headers to packets of data for error checking)
- Auto-sensing (Sensing the highest speed supported by network hubs and switches)
What is a MAC address?
It is a unique 6 byte number used to identify a node to a network, stored in the ROM of a NIC.
Why is a MAC address used? (2)
- To receive only intended data for a specific NIC
* Routers use MAC addresses to build routing tables
What does TCP do?
- It breaks down data into packets
- It adds a header containing a sequence number
- It reassembles the packets of data when it reaches the destination
What does IP do?
- It adds its own header to the packets containing address information
- It routes packets of data to the correct addresses
What is a disadvantage of using CSMA/CD?
Time is taken to check if line is free, which reduces network performance
Why is Synchronous Transmission better than Asynchronous Transmission?
The data transfer rate is quicker as a start and stop frame is only needed for each packet with synchronous, whereas a start and stop bit is needed for each byte with asynchronous transmission
What are Cyclic Redundancy checks more effective than Parity checks?
Parity check will not pick up if two bits are flipped, whereas a Cyclic Redundancy Check can detect this type of error
Why would error checking reduce network performance? (2)
- Calculations carried out at each end of transmission
* Extra data is sent (eg. parity bits)
State 2 ways in which CSMA/CD increases transmission time
- If collisions occur, random amounts of time are taken for re transmissions to occur
- Before transmission, time is taken to see if the line is free
