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LEARNING OBJECTIVES

  • Understand what layers in a network are.

  • Understand why packet switching is important.

SUCCESS CRITERIA

Success Criteria:

  • Know how data packets are broken down and transported across a network.

1.5  Network topologies, protocols and layers

Learners should have studied the following:

  • star and mesh network topologies

  • WiFi:

    • frequency and channels

    • encryption 

  • ethernet

  • the uses of IP addressing, MAC addressing, and protocols including:

    • TCP/IP (Transmission Control Protocol/Internet Protocol​

    • HTTP (Hyper Text Transfer Protocol)

    • HTTPS (Hyper Text Transfer Protocol Secure)

    • FTP ( File Transfer Protocol

    • POP ( Post Office Protocol)

    • IMAP (Internet Message Access Protocol)

    • SMTP (Simple Mail Transfer Protocol)

  • LO4 the concept of layers

  • packet switching

KEYWORDS

Layering - Rules organised into a distinct order in which they need to be applied.

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Interoperable - The ability of different systems and software applications to communicate, exchange data, and use the information that has been exchanged.

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Encapsulation - Enclosing the data inside another data structure to form a single component.

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De-encapsulation - Removing the data from inside an encapsulated item.

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Packet - A unit of data that is transmitted across a network.

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Packet switching - The process of sending data packets across a network.

key points

  • In order for different devices to communicate they need to establish common rules or protocols.

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  • Protocols are layered so that each can be developed independently.

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  • Layering has several advantages:

  1. reduced complexity

  2. standardised interface

  3. facilitates modular development

  4. a range of developers can contribute to the system

  5. development is faster

HOME LEARNING

Answer the following questions in Word and print once completed:

  1. What is ethernet?

  2. Explain how a cyclic redundancy check helps to ensure that data sent on a network is not corrupted.

  3. Explain the concept of packet switching and how it differs from circuit switching.

  4. State four items that are commonly found in a data packet.​

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Stretch and Challenge:

  1. Explain what is meant by half-duplex data transmission.

Networks - LESSON 8

The concepts of layers and packet switching

STARTER​

In pairs using the Caesar cipher wheels on your tables decipher the message. Plain text is on the bigger circle and the smaller circle has the cipher text. 

 

You have to work out the shift yourself. Achievement points for the first person to crack it.

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                      AI EVI PIEVRMRK EFSYX PECIVW ERH TEGOIXS XSHEC

Click on the link to access the worksheet for this task.

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A protocol is normally separated into different layers. The layers in a protocol are responsible for different parts of the process. The process is broken down into layers to make it less complex. The main things that need to be considered when using a network to communicate data are: What is being communicated? Who is the data being sent to? How will the data get there? 

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Layering is not confined to computer science but can also be used in cars as many of them are built using interchangeable parts, with the same components being used on various makes and models.

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In computer programming, layering is the organisation of a program into separate functional components that interact in some sequential and hierarchical way. Each layer will often have an interface only to the layer above it and the layer below it. This means the layers can be individually sourced and merged into a functional system.

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Communication programs are examples of layered applications. One example of a layered protocol is TCP/IP.  The TCP/IP protocol is used to define how data is transferred through a network, for example over the internet or over a private network.

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The TCP/IP stack shown below is a complete set of protocols covering the movement of data across a network. These rules include how data should be formatted, addressed, routed and received.

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When data is sent, each layer encapsulates the data and adds information around the data to identify features that will be required to unpick the original data once received.

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Click on the following link to learn more about encapsulation and de-encapsulation.

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http://www.omnisecu.com/tcpip/tcpip-encapsulation-decapsulation.php

lo4- the concepts of layers

lo4-Packet Switching

Watch the video first:

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On TCP/IP networks, data is divided up into packets. These packets are created by software, not by hardware as in the case of frames. These packets are then encapsulated into frames for sending.

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Packets normally contain three elements/parts:

  1. A header -  this contains the sender's IP address, the receiver's IP address, the packet number, the length of the packet and the protocol.

  2. The payload -  this is the data itself.

  3. The trailer - this contains the end-of-packet marker and error checking.

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The protocol is needed in order to determine what sort of data is being sent such as email, video, or a web page.

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The packet number is needed because the data is usually split into many packets that may get sent by different routes. The packet number allows the receiving computer to reconstruct the whole message in the correct order.

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The payload is the actual data that is being sent. Sometimes, in order to make sure that all packets have the correct number of bytes, it might be padded with dummy information.

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The trailer contains a small number of bytes that indicate that the packet has come to an end. It also contains some error-checking data, which is normally used by a mechanism called the cyclic redundancy check or CRC, which is an error-checking process used in many networks. 

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When data has been divided into packets, it can be sent across a network. This act of sending the packets is called switching. There are two ways in which packets can be sent across a network: these are packet switching and circuit switching.

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A packet-switched network is an example of connection-less mode communication. In other words, there is no single fixed connection between the sender and receiver of the message. The packets are sent to a router, which forwards them on to the next router.

 

The pathway is decided according to a table of nearby routers that it has built up and uses a routing algorithm to select the best path.

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As all the packets do not need to follow the same route if a problem occurs with a connection on a network, each packet can take a different route. When all the packets have arrived they are reassembled.

taSK 1

You will now be completing an activity to show you how packet switching works.

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Teachers note: Communication_Networking_Handout 

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