14.2 Circuit & Packet Switching
A Level · 18 questions found
What this topic covers
Section titled “What this topic covers”- Circuit switching: benefits, drawbacks and applicable situations
- Packet switching: benefits, drawbacks and applicable situations
- Role of a router in packet switching
- How packet switching passes messages across a network/internet
Past paper questions
Section titled “Past paper questions”(a) Identify one benefit of circuit switching and one benefit of packet switching. 2 marks
Circuit switching
Packet switching
(b) Identify two differences between circuit switching and packet switching. 2 marks
1
2
Show mark scheme
4(a) [2 marks]
One mark for a benefit of circuit switching ( Max 1 ) MP1 Once the connection is made, it is available until the end of the transmission (suitable for long continuous transmission) MP2 The dedicated path ensures a steady rate of data transmission, once connection has been made (because the whole bandwidth is available) MP3 The dedicated path ensures data is less likely to be lost. MP4 No intermediate delays once the circuit is established, enables real time transmission MP5 No additional time/delay to reorder needed because data arrives in the order it was sent / data sent as a continuous stream One mark for a benefit of packet switching ( Max 1 ) MP6 No need to tie up a communication line // path available to multiple users // bandwidth can be shared by multiple users MP7 Possible to overcome failed / faulty / busy lines by re-routing packets MP8 Individual packets can be resent if lost/damaged MP9 Users only charged for the duration of connectivity MP10 High rate of data transmission possible MP11 Always uses digital networks so data is transmitted directly to the destination MP12 Good security because all packets can take different routes // A more secure method because all packets can take different routes
4(b) [2 marks]
One mark per difference ( Max 2 ) MP1 Circuit switching requires a dedicated line to be connected before the data transfer takes place, in packet switching, data transfer commences directly/ straight away MP2 In circuit switching, each data unit knows the entire path address, but in packet switching, each data unit only knows the final address (routers decide intermediate paths) MP3 Circuit switching uses the whole bandwidth of the transmission path, but packet switching shares it with other users // circuit switching uses a constant high bandwidth. Packet switching has variable bandwidth MP4 In circuit switching each data unit follows the same route, but in packet switching, packets can follow any route MP5 In circuit switching data arrives in the correct order but in packet switching it has to be reordered MP6 Data remains intact / a continuous stream in circuit switching but is segmented in packet switching MP7 Lost data in circuit switching requires the whole transmission to be resent resent in packet switching MP8 Circuit switching doesn’t suffer data loss but packets can be lost in packet switching.
Describe how packet switching is used to pass messages across a network. Do not include checking for completeness and resending packets in your answer. 4 marks
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3 [4 marks]
One mark per mark point ( Max 4 ) MP1 the message is divided into small chunks called packets MP2 each packet is given a header with important data including source and destination IP addresses MP3 each packet is sent independently // packets can be sent through different routes MP4 packets are sent through the optimum route // packets can be re- routed if a route is unavailable MP5 packets are reassembled at the destination into the whole message
(a) The Application Layer and Transport Layer are two layers of the TCP/IP protocol suite. 5 marks
Describe the purpose of the Application Layer and the purpose of the Transport Layer.
Purpose of Application Layer
Purpose of Transport Layer
(b) Describe packet switching as a method of transmitting messages across the internet. 4 marks
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3(a) [5 marks]
One mark per mark point ( Max 5 ) One mark per mark point for purpose of Application Layer ( Max 3 ) MP1 To provide services / interface with the user // access to applications, for example login, file transfer, network file access, email, etc MP2 To provide mechanisms for securing communication e.g. encryption/authentication MP3 To define/provide protocols used to allow the exchange of data/communication // to contain programs that exchange data MP4 Error detection and recovery mechanisms to handle application specific errors One mark per mark point for purpose of Transport Layer ( Max 3 ) MP5 To provide logical communication between applications running on different hosts // To ensure that data is delivered to the correct application process on the destination machine MP6 To ensure error-free, end-to-end delivery of data between a source and a destination, in sequence // to provide error recovery techniques such as error detection codes and automatic repeat request MP7 To break data into segments when sent and to reconstruct when received // To reassemble segments at destination MP8 To regulate network connections // to provide flow control mechanisms to prevent data loss.
3(b) [4 marks]
One mark per mark point ( Max 4 ) MP1 Data are broken into equal sized packets MP2 Data packets have headers containing information such as the IP addresses of the sender and receiver MP3 Each packet of data is sent independently to the destination // Packets don’t necessarily follow the same route MP4 Each packet is sent via the most optimum path available MP5 Packets don’t necessarily arrive in the order they were sent // Packets are reconstructed at the destination in the correct order MP6 Missing / damaged packets are re-sent
Circuit switching may be used as a method of data transmission.
State two benefits and two drawbacks of circuit switching.
Benefit 1
Benefit 2
Drawback 1
Drawback 2 4 marks
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4 [4 marks]
One mark for each benefit ( Max 2 ) MP1 Suitable for long continuous transmission once the connection is made, it is available until the end of the transmission MP2 No time lost in resending/rearranging packets as no loss of packets or out of order packets MP3 Steady/high rate of transmission because the whole of the bandwidth is available MP4 Data loss unlikely as all data follows the same path One mark for each drawback ( Max 2 ) MP5 Delays due to dedicated connection required to be set up/established before transmission can begin MP6 The dedicated connection cannot be used to transmit any other data MP7 System resources may be underutilised/inefficient/not very flexible because the bandwidth can’t be shared/high bandwidth is required // Bandwidth may be wasted // May send empty frames // the circuit is always there whether or not used MP8 There are no alternative routes if there is a failure or fault on the line MP9 Reduced security due to use of single path MP10 Scalability is difficult
(a) The Internet layer and Link layer are two layers of the TCP/IP protocol suite. 5 marks
Describe the purpose of the Internet layer and the purpose of the Link layer.
Purpose of Internet layer
Purpose of Link layer
(b) Describe the function of a router in packet switching. 4 marks
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4(a) [5 marks]
One mark per mark point ( Max 5 ) One mark per mark point for purpose of Internet Layer ( Max 3 ) MP1 To identify the intended network and host. MP2 To add header containing IP addresses. // To address packets with their source and destination IP Addresses. MP3 To prepare packets for delivery by formatting them into datagrams. MP4 To route datagrams through the optimum route over a network. One mark per mark point for purpose of Link Layer ( Max 3 ) MP5 To prepare the next hop by managing the link between two directly connected devices. // To identify and move traffic across local segments. MP6 To format datagrams into frames for transmission. MP7 To identify network protocols in the packet header. // To ensure correct network protocols MP8 To deliver frames to the receiving network. // To receive frames from the sending network. // To map IP addresses to MAC physical addresses. MP9 To provide error checking/error correction/recovery/reconstruction MP10 including resend requests.
4(b) [4 marks]
One mark for each correct marking point (Max 4 ) MP1 The router reads the IP address of the destination from the packet header. MP2 A router uses a routing table to find information … MP3 … about e.g., available hops / netmask / gateway used / adjacent routers / the status of the routers along the route. MP4 The router determines the next hop / optimum route. // The router sends the packet on its next hop. MP5 The router manages the hop counter // The hop counter is reduced by 1 every time the packet passes a router.
(a) Describe circuit switching as a method of data transmission. 3 marks
(b) State one benefit and one drawback of circuit switching as a method of data transmission. 2 marks
Benefit
Drawback
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3(a) [3 marks]
One mark per mark point ( Max 3 ) MP1 A dedicated circuit / channel is required MP2 The circuit is established before the transmission begins MP3 The circuit lasts for the whole of the transmission // The circuit is closed at the end of the transmission MP4 Data travels in a continuous stream along the same route MP5 Transmission is usually bidirectional.
3(b) [2 marks]
One mark for a benefit ( Max 1 ) MP1 No need for data to be reassembled // data / frames arrive in the same order in which they were sent MP2 Suitable for real time transmission // fast data transfer rate MP3 The whole of the bandwidth is available One mark for a drawback ( Max 1 ) MP4 No other transmission can use the same circuit when it is in use // Bandwidth can be wasted as it cannot be used by other messages MP5 Not secure // Can be intercepted as all data travelling along the same route MP6 If there is a problem with the route the transmission ends // No other route is available without first doing the setup MP7 The circuit is always there whether or not it’s being used MP8 Can take time to set up before transmission starts.
(a) Describe how packet switching is used to transmit messages across a network. 3 marks
(b) State two benefits and two drawbacks of packet switching as a method of transmitting messages across a network. 4 marks
Benefit 1
Benefit 2
Drawback 1
Drawback 2
Show mark scheme
1(a) [3 marks]
One mark per mark point ( Max 3 ) MP1 The data to be transmitted is divided into equal sized packets MP2 A packet header is attached to each packet containing key information MP3 … such as source/destination IP addresses, packet number, etc MP4 Packets are transmitted independently MP5 … and may travel though different routes/paths to the destination MP6 Routes are determined using a routing table//Packets take the optimum route depending on congestion MP7 The packets usually arrive out of order MP8 The packets are reassembled in the correct order at the destination // The packets are re-ordered using the sequence number/the header MP9 If packets are missing/corrupted a re-transmission request is sent / packets are re-sent.
1(b) [4 marks]
One mark for each benefit ( Max 2 ) MP1 Packets are more likely to arrive because they can be re-routed if a problem occurs with one of the routes//Packets are more likely to arrive because if a packet is lost, it can be re-transmitted MP2 Bandwidth can be shared allowing packets from different messages to share the same path MP3 Considered secure as the packets generally travel via different routes MP4 High data transmission rate is possible One mark for each drawback ( Max 2 ) MP5 Time delay because packets need to be re-ordered/reassembled at the destination//Time delay caused by missing packets needing to be re-sent//Time delay because it has to share the bandwidth of the circuit / channel with other packets MP6 Requires a complex algorithm to function MP7 Needs lots of RAM to handle large amounts of data.
(a) Describe circuit switching as a method of data transmission. 3 marks
(b) State one benefit and one drawback of circuit switching as a method of data transmission. 2 marks
Benefit
Drawback
Show mark scheme
3(a) [3 marks]
One mark per mark point ( Max 3 ) MP1 A dedicated circuit / channel is required MP2 The circuit is established before the transmission begins MP3 The circuit lasts for the whole of the transmission // The circuit is closed at the end of the transmission MP4 Data travels in a continuous stream along the same route MP5 Transmission is usually bidirectional.
3(b) [2 marks]
One mark for a benefit ( Max 1 ) MP1 No need for data to be reassembled // data / frames arrive in the same order in which they were sent MP2 Suitable for real time transmission // fast data transfer rate MP3 The whole of the bandwidth is available One mark for a drawback ( Max 1 ) MP4 No other transmission can use the same circuit when it is in use // Bandwidth can be wasted as it cannot be used by other messages MP5 Not secure // Can be intercepted as all data travelling along the same route MP6 If there is a problem with the route the transmission ends // No other route is available without first doing the setup MP7 The circuit is always there whether or not it’s being used MP8 Can take time to set up before transmission starts.
(a) State, with a reason, where it would be appropriate to use circuit switching. 2 marks
(b) Give two benefits and two drawbacks of circuit switching. 4 marks
Benefit 1
Benefit 2
Drawback 1
Drawback 2
Show mark scheme
5(a) [4 marks]
One mark per mark point ( Max 2 ) Circuit switching is used where a dedicated path needs to be sustained throughout the call / communication // where the whole bandwidth is required // where a real time communication is used. A typical application is standard voice communications / video streaming / private data networks
5(b) [3 marks]
One mark per benefit ( Max 2 ) MP1 Whole of bandwidth is available MP2 Dedicated communication channel increases the quality of transmission MP3 Data is transmitted with a fixed data rate MP4 No waiting time at switches MP5 Suitable for long continuous communication MP6 Fast method of data transfer MP7 Data arrives in the same order as it was sent MP8 Data can’t get lost MP9 Data all follows the same path / route MP10 Better for real-time MP11 Simple method of data transfer. One mark per drawback ( Max 2 ) MP1 A dedicated connection makes it impossible to transmit other data even if the channel is free MP2 Not very flexible MP3 No alternative route in case of failure MP4 The time required to establish the physical link between the two stations can be too long MP5 The need to establish a dedicated path for each connection can have cost implications MP6 Dedicated channels require the whole bandwidth / bandwidth can’t be shared
(a) State two examples of where it would be appropriate to use packet switching. 2 marks
(b) Give four differences between circuit switching and packet switching. 4 marks
1
2
3
4
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7(a) [4 marks]
One mark per mark point ( Max 2 ) MP1 Packet switching is most commonly used on data networks such as the internet to send large data files that don’t need to be live streamed MP2 Packet switching is used when it is necessary to be able to overcome failed/faulty lines by rerouting. MP3 Packet switching is used when it is necessary for the communication to be more secure. MP4 Packet switching is used for high volume data transmission. MP5 Packet switching is used when it isn’t necessary to use all the bandwidth. MP6 Specific examples e.g. email, text messages, documents, VOIP etc. (up to two marks).
7(b) [2 marks]
One mark per mark point ( Max 4 ) MP1 Circuit switching uses a dedicated channel to make communication, whereas packet switching forms data into packets to transmit over a digital network. MP2 The dedicated path for circuit switching must be established before the transfer of data can commence, which is not the case with packet switching (as it doesn’t require a dedicated path). MP3 Data in packet switching is split into packets, in circuit switching the message remains intact. MP4 All of the transmission in circuit switching follows the same path whereas different packets in packet switching can take different routes. MP5 The message is received in the same order in which it is sent with circuit switching, but with packet switching, the packets can be received out of order (for assembly at the destination). MP6 Circuit switching is implemented at the physical layer while packet switching is implemented at the network layer. MP7 Circuit switching uses the whole bandwidth of the channel used, packet switching can share bandwidth. MP8 Circuit switching communication ends with an error but packet switching allows packets to be re-sent. MP9 Circuit switching is a simpler process than packet switching.
(a) State, with a reason, where it would be appropriate to use circuit switching. 2 marks
(b) Give two benefits and two drawbacks of circuit switching. 4 marks
Benefit 1
Benefit 2
Drawback 1
Drawback 2
Show mark scheme
5(a) [4 marks]
One mark per mark point ( Max 2 ) Circuit switching is used where a dedicated path needs to be sustained throughout the call / communication // where the whole bandwidth is required // where a real time communication is used. A typical application is standard voice communications / video streaming / private data networks
5(b) [3 marks]
One mark per benefit ( Max 2 ) MP1 Whole of bandwidth is available MP2 Dedicated communication channel increases the quality of transmission MP3 Data is transmitted with a fixed data rate MP4 No waiting time at switches MP5 Suitable for long continuous communication MP6 Fast method of data transfer MP7 Data arrives in the same order as it was sent MP8 Data can’t get lost MP9 Data all follows the same path / route MP10 Better for real-time MP11 Simple method of data transfer. One mark per drawback ( Max 2 ) MP1 A dedicated connection makes it impossible to transmit other data even if the channel is free MP2 Not very flexible MP3 No alternative route in case of failure MP4 The time required to establish the physical link between the two stations can be too long MP5 The need to establish a dedicated path for each connection can have cost implications MP6 Dedicated channels require the whole bandwidth / bandwidth can’t be shared
Data can be sent over networks using either circuit switching or packet switching.
Describe both methods of data transmission. Include a different advantage and disadvantage for each method.
Circuit switching
Advantage
Disadvantage
Packet switching
Advantage
Disadvantage 8 marks
Show mark scheme
3 [8 marks]
Circuit switching max four marks two from a dedicated circuit circuit is established before transmission starts // circuit is released after transmission ends data is transferred using the whole bandwidth all data is transferred over the same route from Advantage – data /frames arrive in order and do not need to be reassembled Disadvantage – nobody else can use the same circuit even if it is idle //less secure as only one route used Packet switching max four marks two from data is split into packets each packet is given its own route the routing for a packet depends on the congestion packets may not arrive in the order sent from Advantage – packets can be rerouted if there are problems// more secure as harder to intercept messages Disadvantage – time taken to reassemble packets at the destination
Data can be sent over networks using either circuit switching or packet switching.
Describe both methods of data transmission. Include a different advantage and disadvantage for each method.
Circuit switching
Advantage
Disadvantage
Packet switching
Advantage
Disadvantage 8 marks
Show mark scheme
3 [8 marks]
Circuit switching max four marks two from a dedicated circuit circuit is established before transmission starts // circuit is released after transmission ends data is transferred using the whole bandwidth all data is transferred over the same route from Advantage – data /frames arrive in order and do not need to be reassembled Disadvantage – nobody else can use the same circuit even if it is idle //less secure as only one route used Packet switching max four marks two from data is split into packets each packet is given its own route the routing for a packet depends on the congestion packets may not arrive in the order sent from Advantage – packets can be rerouted if there are problems// more secure as harder to intercept messages Disadvantage – time taken to reassemble packets at the destination
(a) Explain how packet switching is used to transfer messages across the internet. 5 marks
(b) Outline the function of a router in packet switching. 3 marks
Show mark scheme
6(a) [5 marks]
One mark for each correct marking point (Max 5) A large message is divided up into a group of smaller chunks of the same • size called packets The packet has a header and a payload • The header contains a source IP address, destination IP address (and • sequence number) Each packet is dispatched independently • … and may travel along different routes / paths • The packets may arrive out of order • … and are reassembled into the original message at the destination • If packets are missing / corrupted a re-transmission request is sent. •
6(b) [3 marks]
One mark for each correct marking point (Max 3) The router examines the packet’s header • It reads the IP address of the destination (from the packet header) • A router has access to a routing table • …containing information about, e.g., available hops / netmask / gateway • used … and the status of the routes along the route • … the router decides on the next hop / best route • … and sends the packet on its next hop. •
(a) Explain how packet switching is used to transfer messages across the internet. 5 marks
(b) Outline the function of a router in packet switching. 3 marks
Show mark scheme
6(a) [5 marks]
One mark for each correct marking point (Max 5) A large message is divided up into a group of smaller chunks of the same • size called packets The packet has a header and a payload • The header contains a source IP address, destination IP address (and • sequence number) Each packet is dispatched independently • … and may travel along different routes / paths • The packets may arrive out of order • … and are reassembled into the original message at the destination • If packets are missing / corrupted a re-transmission request is sent. •
6(b) [3 marks]
One mark for each correct marking point (Max 3) The router examines the packet’s header • It reads the IP address of the destination (from the packet header) • A router has access to a routing table • …containing information about, e.g., available hops / netmask / gateway • used … and the status of the routes along the route • … the router decides on the next hop / best route • … and sends the packet on its next hop. •
Give two benefits and two drawbacks of packet switching.
Benefit 1
Benefit 2
Drawback 1
Drawback 2 4 marks
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6 [4 marks]
One mark for each correct benefit (Max 2) Accuracy – Ensures accurate delivery of the message • Completeness – Missing packets can be easily detected and a re-send • request sent so the message arrives complete Resilience – if a network changes the router can detect this and send • the data another way to ensure it arrives Path also available to other users // Doesn’t use whole bandwidth // • allows simultaneous use of channel by multiple users Better security as packets hashed and sent by different routes. • One mark for each correct drawback (Max 2) Time delays to correct errors // Network problems may introduce errors • in packets Requires complex protocols for delivery • Unsuitable for real time transmission applications •
Give two benefits and two drawbacks of packet switching.
Benefit 1
Benefit 2
Drawback 1
Drawback 2 4 marks
Show mark scheme
6 [4 marks]
One mark for each correct benefit (Max 2) Accuracy – Ensures accurate delivery of the message • Completeness – Missing packets can be easily detected and a re-send • request sent so the message arrives complete Resilience – if a network changes the router can detect this and send • the data another way to ensure it arrives Path also available to other users // Doesn’t use whole bandwidth // • allows simultaneous use of channel by multiple users Better security as packets hashed and sent by different routes. • One mark for each correct drawback (Max 2) Time delays to correct errors // Network problems may introduce errors • in packets Requires complex protocols for delivery • Unsuitable for real time transmission applications •
Give two benefits and two drawbacks of packet switching.
Benefit 1
Benefit 2
Drawback 1
Drawback 2 4 marks
Show mark scheme
6 [4 marks]
One mark for each correct benefit (Max 2) Accuracy – Ensures accurate delivery of the message • Completeness – Missing packets can be easily detected and a re-send • request sent so the message arrives complete Resilience – if a network changes the router can detect this and send • the data another way to ensure it arrives Path also available to other users // Doesn’t use whole bandwidth // • allows simultaneous use of channel by multiple users Better security as packets hashed and sent by different routes. • One mark for each correct drawback (Max 2) Time delays to correct errors // Network problems may introduce errors • in packets Requires complex protocols for delivery • Unsuitable for real time transmission applications •