Hardware Addressing and its Types

                           Hardware Addressing:

We need to devise technique for delivering message through LAN medium to single, specific destination computer. Sending computer uses a hardware address to identify the intended destination of a frame. The sending computer also identifies type of data carried in the frame.

Specifying a Destination:

The data sent across a shared network reaches all attached stations - for all LAN topologies. Interface hardware detects delivery of frame and extracts frame from medium. But most applications want data to be delivered to one specific application on another computer but not all computers.

Hardware Addressing:

Most network technologies have a hardware-addressing scheme that identifies stations on the network. Each station is assigned a numeric hardware address or physical address. Sender also includes hardware address in each transmitted frame. In this way only station identified in frame receives copy of frame. Most LAN technologies include sender's hardware address in frame too.

LAN Interface:

LAN interface handles all details of frame transmission and reception which are given as follows:

• It adds hardware addresses, error detection codes, etc. to outgoing frames.
• It may use DMA to copy frame data directly from main memory.
• It obeys access rules (e.g., CSMA/CD) when transmitting.
• It checks error detection codes on incoming frames.
• It may use DMA to copy data directly into main memory.
• It checks destination address on incoming frames.
• The frames not addressed to the local computer are ignored and don't affect the local computer in any way.

Format of Hardware Address:

It consists of a numeric value and its size is selected for specific network
technology. The length of the format is one to six bytes.

Assigning Hardware Address:

The hardware address must be unique on a LAN. There are three types of address forms:

• Static
• Configurable
• Dynamic

Static:
The hardware manufacturer assigns permanent physical address to each network interface and manufacturer must ensure that every interface has a unique address.
Configurable:
The address can be set by the end user either manually e.g. switches or jumpers on the interface or electronically (e.g. through software). The system administrators must coordinate to avoid the conflict.

Dynamic:
The interface automatically assigns physical address each time it is powered up. This automatic scheme must be reliable to prevent conflicts.
Broadcasting:
Some applications want to broadcast messages to all stations on the LAN. For this purpose shared communication channel can make broadcast efficient in such a way that message is delivered to all stations. A special broadcast address is used to identify broadcast message, which are captured by all stations.

Written By: Asad Hussain