Communication and internet technologies

6 One mark for each correct benefit (Max 2) 4 • 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 © UCLES 2021 Page 7 of 10

6 One mark for each correct benefit (Max 2) 4 • 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 © UCLES 2021 Page 7 of 10

6 One mark for each correct benefit (Max 2) 4 • 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 © UCLES 2021 Page 7 of 10

6(a) One mark for each correct marking point (Max 5) 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) One mark for each correct marking point (Max 3) 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. © UCLES 2021 Page 6 of 10

6(a) One mark for each correct marking point (Max 5) 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) One mark for each correct marking point (Max 3) 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. © UCLES 2021 Page 6 of 10

3 Circuit switching max four marks 8 Any 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 Two 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 Any 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 Two 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 © UCLES 2022 Page 5 of 11

3(a) Protocol one mark, description one mark, max four 4 Any two from  HTTP(S) (1) for sending and receiving web pages / hypertext documents (1)  FTP (1) for sending and receiving files over a network / between devices (1)  SMTP (1) for sending/uploading emails /push protocol (1)  POP(3) (1) for receiving/downloading emails /pull protocol (1)  IMAP (1) for receiving/downloading emails /pull protocol (1) 3(b) Layer one mark, matching function one mark, max four 4 Any two from  Transport (1) handles packets (1)  Internet (1) handles transmission of data using IP addresses // provides (optimal) route (1)  Network Access (Interface) // (Data) Link // Physical (1) Handles how data is physically sent (1) Question Answer Marks

3 Circuit switching max four marks 8 Any 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 Two 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 Any 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 Two 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 © UCLES 2022 Page 5 of 11

2 One mark for each point (Max 3) 5 MP1 The Transport Layer breaks data into manageable packets / performs segmentation MP2 It sequences the packets // adds data to the packet header // adds a packet header MP3 It sends the packets to the Internet / Network Layer // It receives data from the Application Layer MP4 It controls the flow of packets MP5 It handles packet loss/corruption // Acknowledges receipt of complete error free packets One mark for each point (Max 3) MP6 The Internet Layer identifies the intended network and host MP7 It transmits packets to the (Data) Link / Physical Layer MP8 It routes the packets independently through the optimum route MP9 It addresses packets with their source and destination IP addresses MP10 It then uses an IP address and port number to form a socket. Question Answer Marks

3(a) One mark per point (Max 2) 2 • Protocols set a standard for communication • Protocols enable communication/compatibility between devices from different manufacturers/platforms • If two devices were sending messages to each other but using different protocols, they would not be able to communicate properly 3(b) One mark for each correct answer 2 Application (Layer) Transport Internet/Network (Layer) Link 3(c) One mark per point (Max 2) 2 • used by email clients to retrieve email messages // a pull protocol • from a mail server (over a TCP/IP connection) • keeps the server and client in sync (by not deleting the original email). // allows a copy of the email to be downloaded from the mail server. © UCLES 2022 Page 5 of 16

2 One mark for each point (Max 3) 5 MP1 The Transport Layer breaks data into manageable packets / performs segmentation MP2 It sequences the packets // adds data to the packet header // adds a packet header MP3 It sends the packets to the Internet / Network Layer // It receives data from the Application Layer MP4 It controls the flow of packets MP5 It handles packet loss/corruption // Acknowledges receipt of complete error free packets One mark for each point (Max 3) MP6 The Internet Layer identifies the intended network and host MP7 It transmits packets to the (Data) Link / Physical Layer MP8 It routes the packets independently through the optimum route MP9 It addresses packets with their source and destination IP addresses MP10 It then uses an IP address and port number to form a socket. Question Answer Marks

5(a) One mark per mark point (Max 2) 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) One mark per benefit (Max 2) 4 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 Question Answer Marks

7(a) One mark per mark point (Max 2) 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). © UCLES 2023 Page 7 of 12 7(b) One mark per mark point (Max 4) 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. Question Answer Marks

5(a) One mark per mark point (Max 2) 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) One mark per benefit (Max 2) 4 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 Question Answer Marks

2(a) One mark for each correct line connecting a protocol to its most appropriate 4 description (Max 4). Protocol Use to provide peer-to-peer file sharing HTTP when retrieving email messages from a mail server over a TCP/IP connection BitTorrent when transmitting hypertext documents SMTP to map MAC addresses onto IP addresses IMAP when sending email messages towards the intended destination 2(b) One mark per mark point (Max 2) 2 MP1 To ensure correct network protocols are followed MP2 To enable the upper layers to access the physical medium // enables connection/ communication with the internet / network layer MP3 To be responsible for transporting data within the network/local segments MP4 To format the data into frames for transmission MP5 Maps IP addresses to MAC/Physical addresses. © UCLES 2023 Page 3 of 9

4 One mark for each correct word (Max 3) 3 The protocols in a stack determine the interconnectivity rules for a layered network model such as the TCP/IP model. Question Answer Marks

2(a) One mark for each correct line connecting a protocol to its most appropriate 4 description (Max 4). Protocol Use to provide peer-to-peer file sharing HTTP when retrieving email messages from a mail server over a TCP/IP connection BitTorrent when transmitting hypertext documents SMTP to map MAC addresses onto IP addresses IMAP when sending email messages towards the intended destination 2(b) One mark per mark point (Max 2) 2 MP1 To ensure correct network protocols are followed MP2 To enable the upper layers to access the physical medium // enables connection/ communication with the internet / network layer MP3 To be responsible for transporting data within the network/local segments MP4 To format the data into frames for transmission MP5 Maps IP addresses to MAC/Physical addresses. © UCLES 2023 Page 3 of 9

2(a) Two marks for all protocols in correct position 2 One mark for at least two protocols in correct position Application Transport Internet Link 2(b) One mark per mark point (Max 2) 2 MP1 The transport layer is responsible for delivery of data from the source host to the destination host MP2 It is where data is broken up into packets and sent to the internet layer MP3 Adds the sequence number to the packet header MP4 It establishes end to end contact MP5 It ensures data arrives error free // It retransmits packets if lost. 2(c) One mark for name of protocol and one mark for expansion (Max 2) 2 HTTP(S) – responsible for correct transfer of files / hypertext documents that make up web pages on the world wide web FTP – used when transferring files from a server to a client on a network POP3 – handles the receiving of emails IMAP – handles the receiving of emails SMTP – handles the sending of emails BitTorrent – provides peer-to-peer file sharing © Cambridge University Press & Assessment 2024 Page 5 of 14

2(a) One mark per mark point (Max 2) 2 MP1 Protocols provide a standard set of rules that enables successful data transfer between devices. MP2 Allows communication between devices on different platforms. MP3 Makes communications independent of software and hardware. 2(b) One mark per mark point 2 MP1 Sending - SMTP MP2 Receiving – POP3 // IMAP // Post Office Protocol 3 2(c) One mark per mark point (Max 3) 3 MP1 BitTorrent allows the sharing of files between thousands of users who are connected together over the internet. MP2 It allows more users to share files with each other than would be the case with a peer-to-peer network. MP3 Users share files directly with each other // the users’ computers are acting as peers MP4 … no web server / central device is used // all users are of equal status. © Cambridge University Press & Assessment 2024 Page 4 of 14

2(a) Two marks for all protocols in correct position 2 One mark for at least two protocols in correct position Application Transport Internet Link 2(b) One mark per mark point (Max 2) 2 MP1 The transport layer is responsible for delivery of data from the source host to the destination host MP2 It is where data is broken up into packets and sent to the internet layer MP3 Adds the sequence number to the packet header MP4 It establishes end to end contact MP5 It ensures data arrives error free // It retransmits packets if lost. 2(c) One mark for name of protocol and one mark for expansion (Max 2) 2 HTTP(S) – responsible for correct transfer of files / hypertext documents that make up web pages on the world wide web FTP – used when transferring files from a server to a client on a network POP3 – handles the receiving of emails IMAP – handles the receiving of emails SMTP – handles the sending of emails BitTorrent – provides peer-to-peer file sharing © Cambridge University Press & Assessment 2024 Page 5 of 14

3(a) One mark per mark point (Max 3) 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. © Cambridge University Press & Assessment 2024 Page 5 of 17 3(b) One mark for a benefit (Max 1) 2 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. Question Answer Marks

4 One mark per mark point (Max 4) 4 MP1 Each layer can only accept input from the next higher layer or the next lower layer MP2 There is an interface between the adjacent layers which is the only interaction between layers MP3 Data is added to the headers as the frames/packets pass through the layers MP4 The interactions are carried out by installed software MP5 User interaction takes place at the highest/Application layer of the stack through protocols associated with that layer of the stack MP6 Direct access to hardware takes place at the lowest/Link layer of the stack. © Cambridge University Press & Assessment 2024 Page 6 of 17

11(a) One mark per mark point (Max 4) 4 MP1 Four additional nodes with correct data values MP2 Correct null pointers in all added nodes (6) with no extra null pointers where the arrow points to the next node MP3 Correct arrows to represent pointers joining parent nodes to child nodes MP4 All nodes in correct order and no extra data added to pointers. RootPtr LeftPtr Data RightPtr Red Green Yellow -1 -1 Blue -1 Orange -1 -1 Indigo -1 -1 Violet -1 © Cambridge University Press & Assessment 2024 Page 15 of 17 11(b) One mark per mark point (Max 4) 4 MP1 Correct Red and Green rows MP2 Correct Yellow and Blue rows MP3 Correct Orange, Indigo and Violet rows MP4 Correct FreePtr with blank row 7 RootPt RightPt Index LeftPtr Data r r 0 0 1 Red 2 1 3 Green 4 2 6 Yellow -1 3 -1 Blue -1 4 5 Orange -1 5 -1 Indigo -1 FreePt 6 -1 Violet -1 r 7 7 © Cambridge University Press & Assessment 2024 Page 16 of 17 11(c) One mark for any correct row (Max 4) 4 FUNCTION SearchTree(Item : STRING) RETURNS INTEGER NowPtr  RootPtr WHILE NowPtr <> -1 IF BinTree[NowPtr].Data > Item THEN NowPtr  BinTree[NowPtr].LeftPtr ELSE IF BinTree[NowPtr].Data < Item THEN NowPtr  BinTree[NowPtr].RightPtr ELSE RETURN NowPtr ENDIF ENDIF ENDWHILE RETURN NowPtr ENDFUNCTION © Cambridge University Press & Assessment 2024 Page 17 of 17

1(a) One mark per mark point (Max 3) 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) One mark for each benefit (Max 2) 4 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. © Cambridge University Press & Assessment 2024 Page 4 of 15

5(a) One mark for each correct name (Max 2) 4 One mark for each correct corresponding expansion (Max 2) MP1 HTTP/HTTPS MP2 For sending and receiving / transferring web pages / hypertext MP3 FTP MP4 For sending and receiving files over a network / between devices MP5 POP3 MP6 Pull protocol / for receiving / downloading emails MP7 IMAP MP8 Pull protocol / for receiving / downloading emails MP9 SMTP MP10 Push protocol / for sending / uploading emails MP11 BitTorrent MP12 Peer-to-peer file sharing over a network 5(b) One mark per mark point (Max 3) 3 MP1 The application layer provides access to all the programs that exchange data // Interacts directly with user. MP2 … used by, for example, web browsers, server software. MP3 Communicates/enables data transfer to/from Transport layer // It allows applications to access the services used in other TCP/IP layers. MP4 It defines the protocols that any application uses to allow the exchange of data. © Cambridge University Press & Assessment 2024 Page 7 of 15

11(a) One mark per mark point (Max 4) 4 MP1 Five additional nodes with correct data values MP2 Correct null pointers in all nodes (7) – no extra null pointers where the arrow points to the next node MP3 Correct arrows to represent pointers joining parent nodes to child nodes – must come from the correct left or right pointer not the middle MP4 All nodes in correct order and no additional data in left/right pointer boxes. RootPtr LeftPtr Data RightPtr 25 4 -1 36 -1 1 -1 16 -1 64 -1 -1 9 -1 -1 49 -1 © Cambridge University Press & Assessment 2024 Page 13 of 15 11(b) First eight rows of table (Max 3) 4 Three marks for all eight correct rows Two marks for six or seven correct rows One mark for three, four or five correct rows Last row of table and FreePtr (Max 1) One mark for correct FreePtr with last row of table completely blank RootPt RightP Index LeftPtr Data r tr 0 0 1 25 2 1 3 4 4 2 -1 36 5 3 -1 1 -1 4 6 16 -1 5 7 64 -1 FreePt 6 -1 9 -1 r 8 7 -1 49 -1 8 © Cambridge University Press & Assessment 2024 Page 14 of 15 11(c) One mark for any correct row (Max 4) 4 FUNCTION SearchList(Item : INTEGER) RETURNS INTEGER NullPtr  -1 NowPtr  RootPtr WHILE NowPtr <> NullPtr IF LinkList[NowPtr].Data < Item THEN NowPtr  LinkList[NowPtr].RightPtr ELSE IF LinkList[NowPtr].Data > Item THEN NowPtr  LinkList[NowPtr].LeftPtr ELSE RETURN NowPtr ENDIF ENDIF ENDWHILE RETURN NullPtr ENDFUNCTION © Cambridge University Press & Assessment 2024 Page 15 of 15

3(a) One mark per mark point (Max 3) 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. © Cambridge University Press & Assessment 2024 Page 5 of 17 3(b) One mark for a benefit (Max 1) 2 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. Question Answer Marks

4 One mark per mark point (Max 4) 4 MP1 Each layer can only accept input from the next higher layer or the next lower layer MP2 There is an interface between the adjacent layers which is the only interaction between layers MP3 Data is added to the headers as the frames/packets pass through the layers MP4 The interactions are carried out by installed software MP5 User interaction takes place at the highest/Application layer of the stack through protocols associated with that layer of the stack MP6 Direct access to hardware takes place at the lowest/Link layer of the stack. © Cambridge University Press & Assessment 2024 Page 6 of 17

11(a) One mark per mark point (Max 4) 4 MP1 Four additional nodes with correct data values MP2 Correct null pointers in all added nodes (6) with no extra null pointers where the arrow points to the next node MP3 Correct arrows to represent pointers joining parent nodes to child nodes MP4 All nodes in correct order and no extra data added to pointers. RootPtr LeftPtr Data RightPtr Red Green Yellow -1 -1 Blue -1 Orange -1 -1 Indigo -1 -1 Violet -1 © Cambridge University Press & Assessment 2024 Page 15 of 17 11(b) One mark per mark point (Max 4) 4 MP1 Correct Red and Green rows MP2 Correct Yellow and Blue rows MP3 Correct Orange, Indigo and Violet rows MP4 Correct FreePtr with blank row 7 RootPt RightPt Index LeftPtr Data r r 0 0 1 Red 2 1 3 Green 4 2 6 Yellow -1 3 -1 Blue -1 4 5 Orange -1 5 -1 Indigo -1 FreePt 6 -1 Violet -1 r 7 7 © Cambridge University Press & Assessment 2024 Page 16 of 17 11(c) One mark for any correct row (Max 4) 4 FUNCTION SearchTree(Item : STRING) RETURNS INTEGER NowPtr  RootPtr WHILE NowPtr <> -1 IF BinTree[NowPtr].Data > Item THEN NowPtr  BinTree[NowPtr].LeftPtr ELSE IF BinTree[NowPtr].Data < Item THEN NowPtr  BinTree[NowPtr].RightPtr ELSE RETURN NowPtr ENDIF ENDIF ENDWHILE RETURN NowPtr ENDFUNCTION © Cambridge University Press & Assessment 2024 Page 17 of 17

3(a) One mark per mark point (Max 5) 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) One mark per mark point (Max 4) 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 © Cambridge University Press & Assessment 2025 Page 8 of 15

3(a) Two from 1 • Application Layer • Transport Layer • Internet Layer • Link Layer 3(b) One mark per mark point (Max 4) 4 MP1 The TCP/IP suite can be viewed as layers within a stack MP2 Each layer can only accept input from the next higher or the next lower layer/adjacent layer MP3 The user/sender/computer interfaces with the top layer/application layer to send/receive a message MP4 The message when sent passes from the top layer/application layer to the bottom layer/link layer MP5 The message when received passes from bottom layer/link layer to the top layer/application layer MP6 The link layer interfaces directly with the network and sends/receives the message. © Cambridge University Press & Assessment 2025 Page 5 of 12

4 One mark for each benefit (Max 2) 4 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 Question Answer Marks

4(a) One mark per mark point (Max 5) 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 are/is followed. 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) One mark for each correct marking point (Max 4) 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. © Cambridge University Press & Assessment 2025 Page 9 of 16

3(a) One mark per mark point (Max 2) 2 MP1 Protocols set a standard for communication // Protocols establish a standard set of rules for communication MP2 Protocols enable compatibility between devices from different manufacturers/platforms MP3 Two devices wouldn’t be able to communicate/send messages to each other if they were using different protocols © Cambridge University Press & Assessment 2025 Page 7 of 15 3(b) One mark for a protocol and one mark for a description (Max 4) 4 Example answers: SMTP [1] a protocol used to send emails between mail servers // a protocol used to send emails from a computer to a mail server [1] IMAP [1] allows users to access/read their emails from any device without removing the message from the mail server // synchronises emails on any device [1] 3(c) Two marks for each description mark as 2 x 2 (Max 4) 4 Example answers: Packets checked at receiving end / on arrival [1] … if packets arrive damaged or don’t arrive at all, a re-send request is sent [1] Packets routed through different paths / sent individually [1] … if a route is blocked, the packet is sent through a different route to ensure it arrives [1] If the packet’s hop count is exceeded [1] … the packet will be retired, which can generate a re-send request [1] Question Answer Marks Guidance

3(a) One mark per mark point (Max 2) 2 • HTTP to send and receive / transfer web pages / hypertext / images / videos • IMAP allows users to access/read their emails from any device without removing the message from the mail server // synchronises emails on any device 3(b) One mark per mark point (Max 4) 4 MP1 Files are shared over a peer-to-peer network MP2 A small file, a torrent (descriptor file), is initially created by a peer MP3 The torrent (descriptor file) contains metadata about the file to be shared MP4 The whole file must initially be located on at least one peer MP5 The file is broken into equal sized pieces MP6 Other peers who wish to download the file first obtain the torrent (descriptor file) and connect to a tracker MP7 A tracker acts like a server that holds all the data about all the computers connected to it / the swarm MP8 Each peer downloads parts of the file from other peers until the entire file has been downloaded MP9 As each peer receives a piece of the file, they become a source for that piece of the file MP10 A peer who has a complete file and is sharing it is a seed // Once a peer has completely downloaded the file and made the file available to others in the swarm, they become a seed. © Cambridge University Press & Assessment 2025 Page 8 of 17

4(a) One mark for a benefit of circuit switching (Max 1) 2 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 © Cambridge University Press & Assessment 2025 Page 9 of 17 4(b) One mark per difference (Max 2) 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, but individual packets can be resent in packet switching MP8 Circuit switching doesn’t suffer data loss but packets can be lost in packet switching. Question Answer Marks

3 One mark per mark point (Max 4) 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 © Cambridge University Press & Assessment 2025 Page 7 of 16

4 One mark for a correct protocol and one mark for a correct corresponding 6 description (Max 6) Three from: HTTP/S [1] a protocol/secure protocol used to transfer hypermedia documents / web pages / (data) files between networked devices [1] FTP [1] a protocol to download, upload and transfer files from one location to another on a network [1] POP3 [1] a protocol used to retrieve/receive emails from a mail server to a computer [1] IMAP [1] allows users to access/read their emails from any device without removing the message from the mail server // synchronises emails on any device [1] SMTP [1] a protocol used to send emails between mail servers // a protocol used to send emails from a computer to a mail server [1] BitTorrent [1] a communication protocol used for peer-to-peer file sharing [1] Question Answer Marks Guidance