Protocols & Layers exam questions

17 Edexcel GCSE Computer Science (1CP2) exam-style questions on Protocols & Layers (4.1 Networks), 32 marks in all. Answer them on paper or print them, then open the mark schemes and example answers to see how each is marked.

1Multiple choice1 mark

A user sends an email from a laptop to a mail server.

Identify the protocol used to send the email.

[1 mark]

AFTP
BHTTP
CSMTP
DTCP

Mark scheme

C SMTP (1)
The only correct answer is C. The correct answer is SMTP.
A is not correct because FTP is used to upload and download files
B is not correct because HTTP is used to request web pages
D is not correct because TCP is a transport-layer protocol that splits data into packets and reassembles them

Example answers and how they were marked

Full marks1/1

C SMTP

Why: Selected the correct email sending protocol (1).

No marks0/1

A FTP

Why: FTP is a file transfer protocol, not an email sending protocol, so no mark is awarded (0).

No marks0/1

B HTTP

Why: HTTP is used for requesting web pages, not for sending email, so no mark is awarded (0).

2Multiple choice1 mark

A user reads email on a laptop. The emails are downloaded to the laptop and removed from the mail server.

Identify the email protocol being used.

[1 mark]

AFTP
BIMAP
CPOP3
DSMTP

Mark scheme

C POP3 (1)
The only correct answer is C. The correct answer is POP3.
A is not correct because FTP is used to transfer files.
B is not correct because IMAP keeps emails on the server.
D is not correct because SMTP is used to send outgoing email between mail servers.

Example answers and how they were marked

Full marks1/1

C POP3

Why: POP3 downloads emails and removes them from the server (1).

No marks0/1

B IMAP

Why: IMAP keeps emails on the server, so it does not match the scenario where emails are removed from the server (0).

No marks0/1

D SMTP

Why: SMTP is used to send outgoing email, not to retrieve email (0).

3Multiple choice1 mark

The TCP/IP model is made up of four layers.

Identify the layer that is responsible for routing packets.

[1 mark]

AApplication
BInternet
CLink
DTransport

Mark scheme

B Internet (1)
The only correct answer is B. The correct answer is Internet.
A is not correct because the application layer creates data for applications such as web browsers and does not route packets
C is not correct because the link layer sends data over physical hardware using MAC addresses and does not route packets
D is not correct because the transport layer sets up the connection between two computers and reassembles the packets

Example answers and how they were marked

Full marks1/1

B Internet

Why: The internet layer is responsible for routing packets (1).

No marks0/1

A Application

Why: The application layer creates data for applications such as web browsers and does not route packets (0).

No marks0/1

C Link

Why: Confuses the link layer with the internet layer: the link layer sends data over physical hardware using MAC addresses and does not route packets (0).

4Multiple choice1 mark

Data is sent over a network using the TCP/IP model.

Identify the protocol that reassembles the packets at the destination.

[1 mark]

AFTP
BHTTP
CIP
DTCP

Mark scheme

D TCP (1)
The only correct answer is D. The correct answer is TCP.
A is not correct because FTP is used to transfer files
B is not correct because HTTP is used to request web pages
C is not correct because IP routes packets but does not reassemble them

Example answers and how they were marked

Full marks1/1

D TCP

Why: TCP reassembles the packets at the destination (1).

No marks0/1

C IP

Why: IP routes packets but does not reassemble them (0).

No marks0/1

B HTTP

Why: HTTP is used to request web pages, not to reassemble packets (0).

5Short recall1 mark

Data is transmitted over networks using the TCP/IP model.

Name the layer of the TCP/IP model in which routers operate.

[1 mark]

Mark scheme

Award one mark for:

Internet (layer) (1)

Accept IP layer / Internet Protocol layer.

Do not accept Network layer (this is the name used in the OSI model, not the TCP/IP model).

Do not accept Transport layer, Application layer or Link layer.

Example answers and how they were marked

Full marks1/1

Internet layer

Why: Names the internet layer, where routers operate.

No marks0/1

Transport layer

Why: Near-miss layer; routers operate in the internet layer, not the transport layer, so no mark.

No marks0/1

Link layer, because routers use MAC addresses

Why: Confuses the link layer with the internet layer; routers route packets using IP addresses at the internet layer, and the link layer is named in the do-not-accept line.

6Short recall1 mark

TCP is a protocol in the transport layer of the TCP/IP model.

State one role of TCP when data is transmitted over a network.

[1 mark]

Mark scheme

Award one mark for any of the following up to a maximum of one mark:

Breaks messages/data into packets (1)
Reassembles packets (at the destination) (1)
Detects errors (1)
Resends lost/missing packets/requests retransmission of lost packets (1)
Creates/establishes a connection between two computers/hosts/sets up a connection before data is sent (1)

Do not accept routing packets or using IP addresses, which is the role of IP.

Do not accept encrypting data or providing security.

Do not accept vague answers such as 'transmits data' or 'sends data' without saying how TCP does this.

Example answers and how they were marked

Full marks1/1

It splits data into packets.

Why: States that TCP breaks data into packets.

No marks0/1

It routes packets between IP addresses.

Why: Near-miss: routing packets is the role of IP, not TCP.

No marks0/1

It encrypts data so it is secure.

Why: Encryption is not a role of TCP, so no creditworthy point.

7Short recall2 marks

Computers on a network communicate with each other.

Define the term protocol.

[2 marks]

Mark scheme

Award one mark for any of the following up to a maximum of two marks:

A set of rules/standards (1)
Agreed by devices/computers (1)
For how data is transmitted/sent (1)
Between devices/computers (on a network) (1)
So that devices can interpret/understand each other's data (1)

Allow 'communication' only where the candidate makes clear that data is being sent or exchanged, e.g. 'rules for the communication of data'.

Do not accept 'a set of rules for communication' on its own, with no reference to data being transmitted/sent.

Do not accept a program/software/device, e.g. 'software that connects devices to a network'.

Do not accept 'a set of instructions' or 'a method of connecting devices to a network'.

Example answers and how they were marked

Full marks2/2

A set of rules that says how data is sent between devices on a network.

Why: Set of rules/standards (1) and how data is transmitted/sent (1); the reference to devices on a network does not add a third mark as the maximum is two.

Some marks1/2

A set of rules for computers.

Why: Set of rules/standards (1), but nothing about data being transmitted/sent between devices.

No marks0/2

Software that connects devices to a network.

Why: Describes a program, not a set of rules; no creditworthy point and covered by the 'Do not accept' line for software.

8Short recall2 marks

Emails are stored on a mail server.

State two email protocols that can be used to retrieve email.

[2 marks]

Mark scheme

Award one mark for any of the following up to a maximum of two marks:

POP3 / Post Office Protocol version 3 (1)
IMAP / Internet Message Access Protocol (1)

Allow POP.

Allow IMAP4.

Do not accept SMTP, as it is used to send email.

Example answers and how they were marked

Full marks2/2

POP3 and IMAP

Why: POP3 (1) and IMAP (1).

Some marks1/2

POP3 and SMTP

Why: POP3 credited (1); SMTP is used to send email, so not credited.

No marks0/2

SMTP

Why: SMTP is used to send email, not retrieve it; no creditworthy point.

9Describe2 marks

A school network connects computers made by different manufacturers.

Describe why network protocols are needed on this network.

[2 marks]

Mark scheme

Award up to two marks for a linked description such as:

Protocols are rules/standards for communication (1) so that devices can exchange data (1)
Devices must use the same protocol (1) so that they can understand the format/order of the data (1)
Protocols set how data is sent and received (1) so that the receiving device can interpret it correctly (1)

Do not accept a bare definition such as 'a protocol is a set of rules' without a link to communication/exchanging data.

Do not accept answers that only name a protocol (e.g. TCP/IP, HTTP) without describing why protocols are needed.

Do not accept responses that describe hardware such as routers or cables as protocols.

For both marks, the development must explain why the rules/standard are needed.

Do not award two marks for two statements that make the same point.

Example answers and how they were marked

Full marks2/2

Protocols are rules for communication, so devices can exchange data.

Why: Linked point: rules/standards for communication (1) and exchange of data (1).

Some marks1/2

Protocols are rules for communication.

Why: Gives the first mark for rules/standards for communication (1), but does not develop why they are needed.

No marks0/2

A protocol is a cable used to connect devices.

Why: Misconception: a cable is hardware, not a protocol; covered by the do-not-accept guidance for describing hardware as protocols.

10Describe2 marks

Ethernet is a network protocol. A school uses Ethernet to connect the computers in its IT room.

Describe the role of Ethernet in a network.

[2 marks]

Mark scheme

Award up to two marks for a linked description such as:

A standard/set of rules for connecting (two or more) devices using cables (1) to transmit/send data over a network/LAN (1)
Defines how data is sent as electrical/light signals (1) along copper/fibre optic cable (1)
Gives a device a wired connection to a switch/network (1) so it can send and receive data (1)
Allows devices without Wi-Fi to join a network (1) by connecting them with a cable (1)

Allow cable/wired for the first mark.

Do not accept responses about wireless/radio connections; these relate to Wi-Fi.

Do not accept 'Ethernet is a cable/a type of cable' with no reference to rules or connecting devices to send data.

Do not accept responses describing TCP/IP or IP addressing; these are different protocols.

Do not award credit for naming Ethernet only.

Example answers and how they were marked

Full marks2/2

Ethernet is a standard for connecting devices with cables so they can send data over a network.

Why: Linked point: standard for connecting devices with cables (1) developed to sending data over a network (1).

Some marks1/2

Ethernet is used to connect devices with cables.

Why: Gives the cabled connection point (1), but does not develop it to data transmission.

No marks0/2

Ethernet is a wireless protocol used by phones.

Why: Misconception: Ethernet is wired, not wireless; no creditworthy point, and wireless responses are in the do-not-accept line.

11Describe2 marks

The TCP/IP model has four layers.

Describe how the transport layer handles data transmission.

[2 marks]

Mark scheme

Award up to two marks for a linked description such as:

Splits the data into packets (1) and gives each packet a number (1)
Sets up a connection between the two hosts before sending (1) so that the receiver is ready to accept the data (1)
Detects lost packets using acknowledgements/sequence numbers (1) so that they can be resent (1)
The receiving transport layer reassembles the packets (1) into the original order using the packet numbers (1)

Do not accept generic statements such as 'it sends the data' / 'it transmits the data', as these repeat the question.

Do not accept responses about routing packets or IP addressing; these relate to the internet layer.

Do not accept responses about converting data into signals; these relate to the link layer.

Do not accept responses about ports or encryption.

Example answers and how they were marked

Full marks2/2

The data is broken up into packets and each one is given a number, so that at the other end they can be put back together in the right order.

Why: Linked point: data split into packets (1) and numbered so the receiver can reassemble them in order (1).

Some marks1/2

It splits the data into packets.

Why: Gives the splitting point (1), but no linked development.

No marks0/2

It routes packets using IP addresses.

Why: Misconception: routing and IP addressing belong to the internet layer, which the mark scheme says is not accepted here.

12Describe2 marks

Network protocols are used to transmit data over a network.

Describe the purpose of the application layer.

[2 marks]

Mark scheme

Award up to two marks for a linked description such as:

Provides the protocols used by applications (1) so a web browser can use HTTP/HTTPS or an email client can use SMTP/IMAP (1)
Prepares/creates the data produced by the application (1) and passes it down to the transport layer (1)
Selects the correct protocol for the application being used (1) so the receiving application can understand the data (1)

Do not accept responses about routing packets/IP addresses; these relate to the internet layer.

Do not accept naming a protocol without describing the purpose of the application layer.

Do not accept generic statements that the layer 'sends data' or 'connects to the network' without a linked development.

Example answers and how they were marked

Full marks2/2

It provides the protocols that applications use, so a web browser can use HTTP/HTTPS and an email client can use SMTP.

Why: Linked point: provides protocols used by applications (1) and gives linked protocol examples for a browser/email client (1).

Some marks1/2

It selects the correct protocol for the application being used.

Why: Gives the point that the layer selects the correct protocol (1), but does not link it to why this is needed or what it allows.

No marks0/2

It routes packets to the correct IP address.

Why: Misconception: routing packets and IP addresses belong to the internet layer, which the mark scheme says is not accepted.

13Explain2 marks

Two computers exchange data over a network.

Explain why network protocols are needed for the two computers to communicate.

[2 marks]

Mark scheme

Award up to two marks for a linked explanation such as:

Devices (can) understand/interpret the data they receive (1) because they follow the same set of rules for communication (1)
Data is sent in an agreed format/structure (1) so the receiving device can interpret/understand it correctly (1)
Devices (can) connect/communicate successfully (1) because they agree how the data is transmitted, such as the type of signal used (1)
Errors (can) be detected/handled (1) because both devices follow the same rules for checking the data (1)

For both marks, the expansion must follow/associate with the statement.

Do not accept 'so devices can talk/communicate with each other' or 'so they can understand each other' without saying they follow the same rules/agreed format.

Do not accept an answer that only states protocols are a set of rules, without saying what this allows (e.g. the data can be understood/interpreted).

Do not accept a faster connection/speed as a reason why protocols are needed.

Do not accept naming a protocol (e.g. TCP/IP, HTTP, Wi-Fi) without an explanation of why it is needed.

Do not accept a description of what a protocol does (e.g. 'TCP splits data into packets') without saying why this is needed.

Example answers and how they were marked

Full marks2/2

Devices can understand the data they receive (1) because they follow the same set of rules for communication (1).

Why: Linked point (1) and reason (1): following the same rules is what lets the devices understand the data.

Some marks1/2

Data is sent in an agreed format (1).

Why: Point (1) identified, but no linked reason saying what the agreed format achieves.

No marks0/2

Protocols are needed so the connection is faster (0) because more data can be sent at once.

Why: Speed is not a reason protocols are needed, so there is no creditworthy point or linked reason.

14Explain2 marks

A bank's website can use HTTP or HTTPS.

Explain one benefit to a customer of the bank's website using HTTPS.

[2 marks]

Mark scheme

Award up to two marks for a linked explanation such as:

Data is encrypted/scrambled (1) so it cannot be read/understood if it is intercepted (1)
The customer's bank/personal details are kept secure/private (1) because the data is encrypted/scrambled during transmission (1)
The customer's login details/password cannot be read by an eavesdropper (1) because HTTPS encrypts/scrambles the data sent to and from the web server (1)

For both marks, the expansion must follow/associate with the statement.

Allow 'scrambled' as an alternative to 'encrypted'.

Do not accept 'it is more secure/safe' or 'the data is secure' on its own, without saying how it is made secure (e.g. encryption/scrambling).

Do not accept faster loading/speed, or claims that HTTPS stops viruses or always proves the website is genuine.

Example answers and how they were marked

Full marks2/2

The data is encrypted (1) so anyone intercepting it cannot read the customer's bank details (1).

Why: Linked point (1) and reason (1): encryption means intercepted data cannot be read.

Some marks1/2

The data is encrypted (1) so the website is secure.

Why: Point (1) for encryption, but 'secure' on its own is a near-miss that the mark scheme does not credit as the linked reason; it must say why, e.g. that intercepted data cannot be read.

No marks0/2

HTTPS is faster than HTTP (0) so the customer can log in more quickly.

Why: Speed is not a benefit of HTTPS and is named in a 'Do not accept' line, so no creditworthy point is given.

15Explain2 marks

Email protocols are used when an email is sent and received.

Explain the role of SMTP when an email is sent.

[2 marks]

Mark scheme

Award up to two marks for a linked explanation such as:

Sends outgoing email from the client to the mail server (1) so it can be forwarded/relayed to the recipient's mail server (1)
Transfers email between mail servers (1) so it reaches the destination server (1)
Pushes/sends the email message (1) because it handles outgoing mail while POP3/IMAP handle incoming mail (1)

For both marks, the expansion must follow/associate with the statement.

Do not accept receiving/downloading email or storing email on the server, which is POP3/IMAP.

Example answers and how they were marked

Full marks2/2

SMTP sends the email from the sender's computer to the mail server (1) so it can be forwarded on to the recipient's mail server (1).

Why: Linked point (1) and reason (1): sends to the mail server so it can be forwarded.

Some marks1/2

SMTP is used to send emails (1).

Why: Role (1) identified, but no linked reason or expansion of what sending involves.

No marks0/2

SMTP downloads the email to the recipient's device (0) so they can read it.

Why: Downloading email is the role of POP3/IMAP, not SMTP, so no credit is given.

16Explain2 marks

The TCP/IP model has four layers.

Explain one function of the transport layer when a file is sent over a network.

[2 marks]

Mark scheme

Award up to two marks for a linked explanation such as:

Splits the data/file into packets (1) so each packet can be sent separately across the network (1)
Adds a packet/sequence number to each packet (1) so the packets can be put back into the correct order at the destination (1)
Detects lost/missing packets (1) so they can be requested/resent (1)
Creates a connection between the two computers/hosts (1) before the file is sent (1)

For both marks, the expansion must follow/associate with the statement.

Allow 'segments' for 'packets' (TCP divides the data into segments, which become packets at the internet layer).

Do not accept 'sends the data/file' on its own without saying what the transport layer does to the data.

Do not accept naming TCP or a port number on its own without expansion.

Do not accept routing/addressing packets using IP addresses, which is the internet layer.

Example answers and how they were marked

Full marks2/2

The transport layer splits the data into packets (1) so each packet can be sent separately across the network (1).

Why: Linked point (1) and reason (1): splitting into packets lets each one be sent separately.

Some marks1/2

It splits the data into packets (1).

Why: Point (1) identified, but no linked reason given, so only the first mark is awarded.

No marks0/2

It routes the packets using IP addresses (0) so they reach the right destination.

Why: Routing using IP addresses is the internet layer, not the transport layer, so no credit is given.

17Discuss6 marks

A veterinary practice has desktop computers connected by cables, staff laptops that connect wirelessly, and a file server that stores large X-ray images. Staff also use a web-based booking system.

Discuss the network protocols the practice should use and why protocols are needed.

Your answer should include:

why network protocols are needed
Ethernet and Wi-Fi
TCP/IP, FTP and HTTP/HTTPS

[6 marks]

Mark scheme

Indicative content

Why network protocols are needed

A protocol is a set of rules that governs how devices communicate on a network.
Protocols are needed so that the desktop computers, laptops and file server can understand the format of the data being sent, even when the devices are made by different manufacturers.
Protocols set out how data is formatted, addressed, transmitted and received, and how errors are detected, so that the large X-ray images are not corrupted.
Without agreed protocols the devices could not interpret each other's data, so the laptops could not use the file server or the booking system.
TCP/IP is the protocol suite used to send the data across the practice's network; TCP splits the data into packets, checks that they arrive and resends any that are lost, while IP routes each packet to the correct address.

Ethernet and Wi-Fi

Ethernet is a wired protocol, so it suits the desktop computers and the file server, which stay in one place and are connected by cables.
Ethernet gives a reliable, consistent connection, which is useful when large X-ray images are sent to and from the file server.
Wi-Fi is a wireless protocol that uses radio waves, so staff can use the laptops anywhere in the practice without a cable.
Wi-Fi may be affected by walls and interference, so Ethernet is the better choice for the file server.
Using both protocols means the fixed desktop computers have a stable wired connection while the laptops stay mobile.

TCP/IP, FTP and HTTP/HTTPS

FTP is used to transfer files, so it can upload and download the X-ray images to and from the file server.
HTTP is used to request and receive web pages, so staff can view the booking system in a browser.
HTTPS is the secure version of HTTP and encrypts the data, which protects login details and patient details on the booking system.
The practice should use HTTPS for the booking system because data sent over the internet could otherwise be intercepted.
TCP/IP is needed so that the laptops can reach the file server and the booking system, as IP addresses identify the source and destination of each packet.

Levels

Level 0 (0 marks): No rewardable content.
Level 1 (1–2 marks): Basic, independent points are made, showing elements of understanding of key concepts/principles of computer science. (AO1) The discussion will contain basic information with little linkage between points made or application to the context. (AO2)
Level 2 (3–4 marks): Demonstrates adequate understanding of key concepts/principles of computer science. (AO1) The discussion shows some linkages and lines of reasoning with some structure and application to the context. (AO2)
Level 3 (5–6 marks): Demonstrates comprehensive understanding of key concepts/principles of computer science to support the discussion being presented. (AO1) The discussion is well developed, with sustained lines of reasoning that are coherent and logically structured, and which clearly apply to the context. (AO2)

Do not accept POP3, SMTP or IMAP as protocols for transferring files or for accessing the booking system.

Level 3 responses are likely to explain the need for protocols and to apply more than one named protocol to the practice's devices.

Example answers and how they were marked

Full marks6/6

The practice needs protocols because they are the rules that decide how data is formatted, sent and received, so that devices from different manufacturers can understand each other. For the fixed desktop computers and the file server, Ethernet is the best choice because it uses cables and gives a reliable, consistent connection for the large X-ray images, even though those devices cannot be moved. Staff laptops should use Wi-Fi because they connect by radio waves and can be carried around the practice, although walls and other devices can interfere with the signal, so Wi-Fi is not the best choice for the file server. To move X-ray images to and from the file server, FTP is used because it transfers files. To open the web-based booking system, HTTP or HTTPS is used; HTTPS is better because it encrypts login details and patient information so they cannot be intercepted. All of this data is carried by TCP/IP, with TCP splitting it into packets and checking they arrive, and IP routing the packets to the correct address.

Why: Level 3: explains the need for protocols (1 heading), applies Ethernet and Wi-Fi to fixed and mobile devices with reasons, and develops FTP, HTTP/HTTPS and TCP/IP with sustained reasoning applied to the practice.

Some marks2/6

Protocols are a set of rules for how data is sent across a network. Ethernet uses cables, so it is used for the desktop computers. Wi-Fi is wireless, so the laptops can connect without cables. FTP transfers files and HTTP is used for web pages. HTTPS is more secure than HTTP.

Why: Level 1: a basic definition of a protocol plus Ethernet and Wi-Fi named with brief context, and FTP, HTTP and HTTPS named, but the points are independent with little development, no link to the X-ray images or booking system and no TCP/IP, so Level 1 top range (2 marks).

Some marks1/6

Protocols are rules for how data is sent, but they are not needed if all the computers use the same software. The practice should use POP3 to transfer the X-ray images and SMTP to open the booking system.

Why: 1 mark for the basic definition of a protocol. The claim that protocols are not needed is wrong, and POP3 and SMTP are email protocols, which the mark scheme says are not accepted for file transfer or accessing the booking system, so no further credit.

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