lecture7:POINT-TO-POINT PROTOCOL

POINT-TO-POINT PROTOCOL
Although HDLC is a general protocol that can be used for both point-to-point and multi-point configurations, one of the most common protocols for point-to-point access is the Point-to-Point Protocol (PPP). Today, millions of Internet users who need to connect their home computers to the server of an Internet service provider use PPP. The majority of these users have a traditional modem; they are connected to the Internet through a telephone line, which provides the services of the physical layer. But to control and manage the transfer of data, there is a need for a point-to-point protocol at the data link layer. PPP is by far the most common.

PPP provides several services:
• PPP defines the format of the frame to be exchanged between devices.
• PPP defines how two devices can negotiate the establishment of the link and the exchange of data.
• PPP defines how network layer data are encapsulated in the data link frame.
• PPP defines how two devices can authenticate each other.
• PPP provides multiple network layer services supporting a variety of network layer protocols.
• PPP provides connections over multiple links.
• PPP provides network address configuration. This is particularly useful when a home user needs a temporary network address to connect to the Internet.

On the other hand, to keep PPP simple, several services are missing:
• PPP does not provide flow control. A sender can send several frames one after another with no concern about overwhelming the receiver.
• PPP has a very simple mechanism for error control. Lack of error control and sequence numbering may cause a packet to be received out of order.
• PPP does not provide a sophisticated addressing mechanism to handle frames in a multipoint configuration.