Qualification:
Cambridge Advanced Nationals in Computing (AAQ)
Certificate:
Computing: Application Development (H029 / H129)
Unit:
F161: Developing Application Software
3.2 - Protocols
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Protocols
TCP/IP Stack
You need to know the role and uses of specific common protocols (FTP, HTTP, POP, SMTP, SNMP, TCP, UDP, ICMP, IP).
You also need to understand the structure, content and use of the 4-layer TCP/IP stack.
What You Need to Know
Common Protocols
A protocol is a set of rules that determines how data is communicated between devices over a network.
FTP
FTP (File Transfer Protocol) is used to transfer files between computers over a network, typically between a client and a server.
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It is used when uploading or downloading files from a server, such as transferring website files to a web server.
HTTP
HTTP (HyperText Transfer Protocol) is used to request and transfer webpages and other web content between a web browser and a web server.
It is used when accessing websites or when web-based applications communicate with servers. However, HTTPS is the secure, encrypted version commonly used today.
POP
POP (Post Office Protocol) is used by an email client to retrieve emails from a mail server, traditionally storing them on the user's device.
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It is used when emails need to be downloaded from a mail server for access through an email application, particularly where local or offline access is required.
SMTP
SMTP (Simple Mail Transfer Protocol) is used to send and transfer email messages between email clients and mail servers and between mail servers.
It is required when a user sends an email, including transferring that email between mail servers on its way to the recipient.
SNMP
SNMP (Simple Network Management Protocol) allows network administrators and management software to monitor and manage devices on a network to collect information about their status.
It is used to monitor devices such as routers, switches, servers and printers, for example checking whether a network device is operating correctly.
TCP
TCP (Transmission Control Protocol) provides reliable and ordered delivery of data packets between devices. It checks that packets arrive correctly and retransmits missing packets when necessary.
It is used when accuracy and reliability are more important than speed, such as transferring files, loading webpages and sending emails.
UDP
UDP (User Datagram Protocol) sends data quickly, although without checking that every piece has arrived or is in the correct order, reducing delays.
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It is used when speed is more important than perfect delivery, such as live video/audio, online gaming and voice calls.
ICMP
ICMP (Internet Control Message Protocol) is used to send network status, diagnostic and error messages between network devices.
It is required when diagnosing network problems and checking whether another device can be reached, such as when using the ping command.
IP
IP (Internet Protocol) addresses and routes data packets across networks by using IP addresses to uniquely identify devices.
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It is used when data needs to be sent between devices across networks, with IP helping packets travel from the source towards the correct destination using an appropriate route.
TCP/IP Stack
The TCP/IP stack is a four-layer model that describes how data is prepared, transmitted across networks and received by applications.
When sending data, it travels down through the layers. When receiving data, it travels up through the layers. Different protocols are used at specific layers of the model.
Application Layer
This is the top layer, where network applications and services interact with the network. It includes protocols such as HTTP, FTP, SMTP, POP and SNMP. It determines how applications communicate and exchange specific types of data across a network.
Example: A web browser uses HTTP to request content from a web server.
Transport Layer
This layer is responsible for transporting data between devices and includes TCP and UDP. It determines how data should be delivered, including whether reliability (using TCP) or speed (using UDP) is more important.
Example: TCP can ensure that a downloaded file arrives completely and in the correct order, while UDP can prioritise speed during an online game.
Internet Layer
This layer is responsible for addressing and routing packets between networks and includes protocols such as IP and ICMP. It ensures packets can travel towards the correct destination using IP addresses.
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Example: IP is used to route packets across the internet to the destination device.
Network Access Layer
This is the lowest layer, concerned with how data is physically transmitted across the network using technologies such as Ethernet (a wired connection) and WiFi. It handles communication between a device and the network it is directly connected to.
Example: A laptop could transmit data wirelessly to a local router using WiFi.
Questo's Questions
3.2 - Protocols:
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1. What is a network protocol, and why do you think protocols are needed when devices communicate? ​[2]
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2. State the role of FTP, HTTP, POP, SMTP and SNMP and give an example of when each would be used. ​[2 each]
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3. State the role of TCP, UDP, ICMP and IP and give an example of when each would be used. ​[2 each]
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4. Describe the structure and purpose of each of the four layers of the TCP/IP stack. ​[2 each]
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5. Explain how different protocols and layers of the TCP/IP stack can work together to transfer data across a network, such as sending an email on a wired connection. ​ [4]
Online games use UDP because receiving data quickly is often more important than receiving every single packet. A tiny amount of missing data may be preferable to the game pausing while it waits for it to be resent.
Did You Know?
