OCR J277 Mark Scheme

OCR	GCSE (9-1) Computer Science Mark Scheme J277/01: Unit 1.3 Network Protocols

Question	Answer	Marks	Guidance
1	HTTP -> Hypertext Transfer Protocol FTP -> File Transfer Protocol SMTP -> Simple Mail Transfer Protocol IMAP -> Internet Message Access Protocol	4	1 mark per correct line. If multiple lines are drawn from one box, award 0 marks for that specific item.
2a	IMAP / Internet Message Access Protocol	1	Reject: SMTP (Sending only). Reject: POP (Does not sync).
2b	IMAP characteristic: IMAP syncs the email with the server / keeps emails on the server. (1) Comparison with POP: POP downloads and deletes the email from the server (so it would only be on one device). (1)	2	Key Difference: IMAP = Server based (Sync). POP = Local download (Delete).
2c	SMTP / Simple Mail Transfer Protocol	1
3a	FTP / File Transfer Protocol	1
3b	Encryption: HTTPS encrypts the data (HTTP does not). (1) Difference: HTTPS is secure; HTTP is insecure. (1) Context: Essential for a bank to protect passwords/financial data from theft. (1)	3	Examiner's Note: Candidates often just say "HTTPS is secure". This is worth 1 mark. To get full marks, they must mention Encryption and apply it to the Bank context.
4a	Any 2 points: Splits data into packets. Numbers the packets. Reassembles packets at the destination. Checks for errors / missing packets.	2	Focus: TCP handles the data integrity and packets.
4b	Any 2 points: Assigns source and destination IP addresses. Routes the packets across the network/internet. Ensures packets are directed to the correct destination.	2	Focus: IP handles the addressing and routing.
4c	Decomposition: Breaks network communication into manageable pieces (1)... so developers can concentrate on one layer at a time (1). Interoperability: Layers are self-contained / independent (1)... so one layer can be changed without affecting the others (1). Standards: Sets a universal standard (1)... so hardware/software from different manufacturers can work together (1).	4	Examiner's Note: The most common correct answer is "You can change one layer without breaking the others".
5	Any 4 logical points: The Browser (Client) sends a request. The request is sent to the Web Server. HTTP is the protocol (rules) used to define how the request is sent. The Web Server processes the request / locates the file. The Web Server sends the web page data back to the browser. The Browser renders/displays the page.	4	Key Concept: Request and Response. Award marks for correctly using the terms in bold in a logical sequence. Just saying "HTTP gets the website" is too vague; they must describe the Client-Server request/response cycle.