�鶹Լ��

Any form of communication requires rules. These determine how the communication is actually made and manage key factors like transmission speed, error checking and methods of addressing, for example, how to locate another node on the network. Rules that govern communication are known as protocols. Many types of protocol exist, but the ones that govern addressing are:

• Internet Protocol (IP)adressing
• media access control (MAC) addressing

IP Addressing

When connected to a network each device is given a unique IP address. This address consists of four sets of up to three digits, each with a maximum value of 255, which are separated by dots. An example is:

192.168.0.254

When a node wants to send a message to another node, it uses the recipient node's address as the destination. A switch on the network knows where the node with this address is and routes the message to it accordingly.

IP addresses can be static or dynamic.

A node given a static address always keeps the same address. A node given a dynamic address has a different address assigned to it each time it connects to the network. This method is known as dynamic host configuration protocol (DHCP). Static addressing makes it easy for network managers to know which device is which on a network. However, dynamic addressing allows more devices to connect than there are available addresses. When a device disconnects from the network, its address is freed up for another device to use. When the first device reconnects it is assigned any free address.

This method of addressing using four sets of digits is called IPv4. When IPv4 was devised, the range of addresses allowed was deemed to be enough. However, the huge increase in internet enabled devices has seen IPv4 run out of addresses. A new version, IPv6, which includes six sets of three digits, has been introduced, greatly increasing the number of possible addresses to trillions.

MAC addressing

A MAC address is a unique serial number assigned to each network interface controller (NIC). This allows a network to uniquely identify any device, even when a dynamic IP address is assigned using DHCP, each time the device connects to a network. The device’s IP address changes depending on the network and the MAC address is unique to the device.

A MAC address consists of a string of hexadecimal numbers. An example is:

1A:5B:6H:98:78:35

The MAC address is assigned by the NIC’s manufacturer and cannot be changed. If a device has more than one NIC, for example a wired NIC and a wireless NIC, each NIC will have its own MAC address.

Other protocols

Many other protocols exist. Some of the more common protocols are:

• TCP/IP - Transmission Control Protocol/Internet Protocol - enables communication over the internet.
• HTTP and HTTPS - Hypertext Transfer Protocol - governs communication between a webserver and a client. HTTPS (secure) includes secure encryption to allow transactions to be made over the internet.
• FTP - File Transfer Protocol - governs the transmission of files across a network and the internet.
• SMTP - Simple Mail Transfer Protocol - governs the sending of email over a network to a mail server.
• POP and IMAP - Post Office Protocol and Internet Message Access Protocol - govern retrieving emails from email servers. POP is an older implementation, largely replaced by IMAP.