PPP:

1. PPP stands for Point-To-Point Protocol.
2. It is Data Link Protocol.
3. This protocol is widely used to connect home computers to the server of an Internet Service Provider.
4. PPP is used to control and manage the data transfer.
5. PPP provides Error Detection.
6. It defines how two devices can authenticate each other.

7. It defines link control protocol (LCP) for:

   a. Establishing the link between two devices.

   b. Maintaining this established link.

   c. Configuring this link.

   d. Terminating this link after the transfer.

PPP Frame Format:

The frame format of PPP resembles HDLC frame. Its various fields are:

I) Flag field:

a. PPP Frame always begin & end with the standard HDLC Flag.

b. Flag byte is 01111110. (1 byte).

II) Address field:

a. This field is of 1 byte and is always 11111111.

b. This address is the broadcast address.

c. All 1’s in the address field indicates that all stations are to accept the frame.

III) Control field:

a. This field is also of 1 byte.

b. This field uses the format of the U-frame (unnumbered) in HDLC.

c. The value is always 00000011 to show that the frame does not contain any sequence numbers.

d. There is no flow control or error control.

IV) Protocol field:

a. This field specifies the kind of packet in the data field i.e. what is being carried in data field. b. The data field can contain the user data or other information.

V) Data field:

a. Its length is variable.

b. If the length is not negotiated using LCP during line set up, a default length of 1500 bytes is used.

c. It carries user data or other information.

VI) FCS field:

a. FCS stands for Frame Check Sequence.

b. It is either of 2 bytes or 4 bytes.

c. It contains the checksum.