When one device wants to send data to another device, a SEL frame is sent first. Before sending data, the primary device creates and transmits a select (SEL) frame, which includes the address of the secondary device. Select function is used, when primary device wants to send something to secondary device.

The checksum field is the 16 bit one's complement sum of all 16 bit words in the header and text. If a segment contains an odd number of header and text octets to be checksummed, the last octet is padded on the right with zeros to form a 16 bit word for checksum purposes. The source port and destination port also have 16 bits.

The sending system handles each group independently, relaying it to the link whenever ready, without regard to a timer.

It deals with the electrical and mechanical specifications of the interface and transmission medium.

It finds the change from the previous sample.

Here the bit stream is combined into larger frames that may contain multiple bytes.

It supports two B-channels with 64 kbps each, and a 16 kbps D-channel for control information.

If two frames are transmitted simultaneously. They overlap in time and the resulting signal is distorted or garbled. This event or situation is called a collision.

If some data bits are in error, then checksum will be wrong and the error will be detected.

Pad truncates the current frame, when a transceiver detects a collision, which means that the stray bits and pieces of frames appear on the cable all the time.

The level of the voltage determines the value of the bit.

Here, the positive voltage defines bit 1 and the zero voltage defines bit 0 and the signal does not return to zero at the middle of the bit.

It is a simple error detection method used with character oriented protocols.

It is a technique for detecting errors in digital data, but not for making corrections when errors are detected.