A communication protocol is a standard set of rules used to ensure that different network devices, possibly using different technologies, can send and receive data properly. The rules formally defined by a communication protocol include message formats, authentication methods, error detection and correction methods, how data is split up into packets, and how data packets are sent and received. 

The Open Systems Interconnection (OSI) model The OSI Model provides a framework for data to be transferred between networked computers. The model works even if different data formats or different types of networks are communicating. The core of this standard is the OSI Reference Model, a set of seven layers that define the different stages that data must go through to travel from one device to another over a network. The OSI model was developed by the International Standards Organisation (ISO) as guidelines for developing standards. If a manufacturer’s products obey these standards it will mean ease of connection to a device from another manufacturer. The OSI model is based on seven layers as shown below: 

Any hardware that meets the OSI standard will be able to communicate with any other hardware that also meets the standard; the same applies to software that meets the OSI standard – again, it will be able to communicate with any other hardware or software that also meets the standard. 

Consumers are given a wider choice since hardware/ software from any manufacturer will work together and as OSI is independent of country, it doesn’t matter where the hardware/software is made.

 OSI is not dependent on the operating system used and the protocols for OSI are defined at each stage. Other benefits include error handling in each layer and the different layers can operate automatically. 

Notice that the top three layers have been grouped together and are called the ‘Application Set’ and the bottom four layers are called the ‘Transport set’. The ‘Application Set’ is mainly concerned with controlling how the various applications currently running are making use of the network. For example, you could be running ‘Internet Explorer’ to view web pages and at the same time be writing a report in ‘Word’ that is stored on the C2K file server. Both are making use of the network in different ways. 

The ‘Transport Set’ is only concerned with passing information through the network – it does not care whether the information comes from the Internet Explorer application or the Word application currently running on the machine. Each layer can only ‘talk’ to the one above it and below it e.g. The ‘Network’ layer can only pass information to the ‘Transport’ layer above it and the ‘Data Link’ layer below it. Passing information from one layer to another is done in a standard way. This means that if company ‘A’ has written some software for the ‘Transport’ layer – and company ‘B’ has written some software for the ‘Network’ layer – then they are guaranteed to be able talk to each other. 

This is the top layer of the OSI model. The application layer is only concerned with presenting information in a human friendly way. 

The OSI model is relevant to all kinds of devices, that use inbuilt computer processors, including mobile phones, iPods etc. The Application Layer receives its information from the ‘Presentation’ layer just below it. 

This layer shares information with the Application layer above it and the Session layer beneath it. 

Converting information This layer is not concerned with ‘presenting’ information to a person, but rather ‘presenting’ information to the various electronic devices in the correct format. For example, it will send video information in the right format to the VDU or the correct audio information to the sound card. Data Encryption Another useful task for this layer is to implement encryption. For example, say the Application layer is running a shopping application and you have just pressed the ‘Buy’ button. The job of the Presentation layer is to scramble the credit card number you have supplied so that only the store itself can read the number. Note that the Presentation layer on the shop computer will be responsible for ‘unscrambling’ the data back into the correct credit card number (decryption). The presentation layer will encrypt \ decrypt information if required. Data Compression The presentation layer may compress \ decompress information 

The session layer shares information with the Presentation layer above it and the transport layer beneath it. 

In the world of networking, a session begins when an application wants to make a connection to a remote server (WAN). The session layer opens a temporary ‘channel’ between the two to allow for communication. You can have more than one session running at the same time. 

The transport layer shares information with the Session layer above it and the Network layer beneath it: 

It will divide the information into convenient sized packets – these packets will then be sent on different routes to their destination. The packets may arrive in a different order to which they were sent. The packets are then reassembled at the destination point into the order in which they were sent. This layer can also check for errors. 

The Network layer shares information with the Transport layer above it and the Data Link layer beneath it. 

The Network layer is the “traffic policeman” of the OSI model as it works out the best route for the packets to use. Every packet that the Transport layer has created needs to be sent to the correct machine across the network. Every computer has a unique address (IP address) allowing the network layer to add the correct address to each packet. It also reads the addresses of incoming packets to a computer and if they are destined for that computer then it allows them through. Packets not addressed are blocked (principle of network ‘firewall’). 

The Data Link layer shares information with the Network layer above it and the Physical layer beneath it 

Data is broken down by the higher layers into ‘packets’. Each packet needs to be broken up into the most basic form of data i.e. data ‘bits’. A ‘bit’ has two values – a ‘high’ or a ‘low’. (high is a 1 bit and a low is a 0 bit). Each packet is converted into a series of bits. This is the job of the data link layer. It converts the outgoing packets into the correct series of bits. It also converts incoming bits back into complete packets. Bits can be corrupted as they travel along the network i.e. a bit can be flipped into the wrong state so a ‘high’ bit may become a ‘low’ bit and vice versa. The data link layer will attempt to spot these reversals and fix them. 

The Physical layer shares information with the Data Link layer above it. 

Bits and bytes have to be converted into a physical effect so that they can be transmitted. There are various methods of transmitting information - for example a pulse of light can be used to represent a data bit, fibre optic cables are then used to provide a path in the network. A radio signal can be used, indeed, ‘Wi-Fi’ networks have become ubiquitous. Electrical signals can be used, which are carried along copper wires. There are millions of Ethernet networks using this method. It is the job of the Physical layer to convert the abstract ‘data bit’ inside the computer into a physical effect of some kind. 

The TCP/IP is a set of protocols defining how information is split into packets, and how data packets are sent and received at the correct destination. 

The TCP layer supports the transfer of files between computer systems and controls security/permission issues. It handles different character sets, end of line conventions, etc. The TCP layer also splits data into packets and allocates an address to each packet. 

The IP layer is responsible for transferring packets of data from node to node (a node is a device on a network), by forwarding each packet using its address. It is responsible for verifying the correct delivery of data and detecting errors or lost data 

Ethernet is a network protocol that controls how data is transmitted over a LAN. Technically it is referred to as the IEEE 802.3 protocol. Ethernet defines not only the networking protocol but also the physical plugs and sockets used. It defines the hardware, as well as how data is handled. Ethernet implements the Physical and Transport layers of the OSI 7 Layer Model. 

Carrier Sense Multiple Access with Collision Detection (CSMA/CD) CSMA/CD is a set of rules determining how network devices respond to a collision which occurs when two devices attempt to use a data channel simultaneously. Ethernet networks use CSMA/CD to physically monitor the traffic on the line between different computers on the network. If no transmission is taking place at the time, the a computer can start transmitting data. If two computers attempt to transmit simultaneously, this causes a collision, which is detected by all participating stations; after a random time interval the computers that collided attempt to transmit again. If another collision occurs, the time intervals from which the random waiting time is selected are increased. 

Token passing uses a token, a special series of bits, to give a device permission to transmit over the network. Only the device which has the token can put data into the network. When its transmission is complete, the device passes the token along to the next device in the topology. Protocols determine how long a device may keep the token, how long it can transmit for and how to generate a new token if no token is currently in circulation. 

Wi-Fi (Wireless Fidelity) is a communications protocol, through which devices can communicate with each other without using any cabling. A wireless transmitter is required; this device receives information from the internet via the broadband connection. This transmitter converts this information into radio waves and emits it, effectively creating a small, local area around itself, within which devices can receive these radio signals provided they are fitted with the appropriate wireless adapter. This area is often termed a Wireless Local Area Network, or WLAN for short. 

The radio signals are not very strong, which is why the Wi-Fi signal does not travel very far; it will travel far enough to cover the average home and to the street directly outside, for example, but not much further. When you send information back to the internet – by clicking on a link or sending an email, for example – the process works in reverse; your device sends information via a radio signal to the wireless transmitter, which converts the signal and communicates it back via the broadband connection. For a device such as a phone or computer to be able to pick up Wi-Fi signals, it needs to have the relevant technology incorporated within it, or have a wireless adapter fitted. Many devices, such as smartphones and tablets, come ready to accept Wi-Fi signals straight out of the box, whilst others, such as some PCs, will require buying a separate wireless card or adapter, which often comes in the form of a small device which plugs into the USB port of your PC or laptop. 

This device is known as a broadband “dongle” and can easily be bought on the high street. In summary, Wi-Fi enables two or more devices to connect (wirelessly) for data sharing. A computer with a Wi-Fi network card can connect wirelessly to a wireless router over a limited distance (60m/90m). A Wi-Fi network can either be “open” (anyone can use them) or “closed” (a password is needed). An area with wireless access is called a wireless hotspot. 

A Bluetooth device uses radio waves to connect to other devices. A Bluetooth device contains a tiny chip with a Bluetooth radio and software to enable it to connect with other such devices. When two Bluetooth devices want to communicate with each other, they need to pair. Bluetooth is a short-range radio technology (or wireless technology) aimed at simplifying communications among enabled devices with a range of up to 10m (Class 3) or up to 100m (Class 1). It also aims to simplify data synchronization between devices. 

Voice over IP (VoIP) technology allows telephone calls to be made over digital computer networks including the Internet. VoIP converts analogue voice signals into digital data packets and supports real-time, two-way transmission of conversations using Internet Protocol (IP). Essentially, VoIP is a method of using the internet to make voice telephone calls. Digitised speech is just data and can be sent over the internet as with any other data; with the widespread installation of broadband connections, it is possible for this data to be transmitted fast enough to allow twoway conversations. With appropriate software, e.g. Skype, a user can talk with any other user connected to the internet. 

Radio-Frequency Identification (RFID) involves the use of radio waves to read and capture information stored on a tag attached to an object. A tag can be read from up to several feet away and does not need to be within direct line-of-sight of the reader to be tracked. The RFID tag contains data programmed into a small computer chip and this tag is activated by radio waves emitted from an RFID reader. The tag sends the data stored in its memory back to the reader. The range can be anything from centimetres to metres. RFID can be used in active systems whereby the chip has its own power supply; or in passive systems whereby the chip is activated by the reader’s power. 

There are many advantages regarding the use of RFID, when comparing their use in the retail industry, for example. For example, there is no line of sight requirement and RFID tags can be read from a greater distance (as opposed to the traditional laser and barcode scanner), even in harsh environments. The information stored in a barcode is fixed and cannot be changed whereas RFID tags can be dynamically updated. Human intervention is usually required in order to scan a barcode whereas data from an RFID tag can be read without the need for someone to properly align the tag with the equipment that reads the data. Barcodes must be visible on the outside of a product’s packaging whereas RFID tags can be placed inside either the packaging or the product itself. Finally, more data can be stored in an RFID tag than on a barcode and RFID tags have both read/write capability, whereas barcodes are read only and cannot be reused.