Mumbai University > Computer Engineering > Sem 5 > Computer Networks

Marks: 10 Marks

Year: Dec 2015

• The Point-to-Point Protocol (PPP) originally emerged as an encapsulation protocol for transporting IP traffic over point-to-point links.
• PPP also established a standard for the assignment and management of IP addresses, asynchronous (start/stop) and bit-oriented synchronous encapsulation, network protocol multiplexing, link configuration, link quality testing, error detection, and option negotiation for such capabilities as network layer address negotiation and data-compression negotiation.
• PPP supports these functions by providing an extensible Link Control Protocol (LCP) and a family of Network Control Protocols (NCPs) to negotiate optional configuration parameters and facilities.

• PPP provides a method for transmitting datagrams over serial point-to-point links, which include the following three components:

  i. A method for encapsulating datagrams over serial links

  ii. An extensible LCP to establish, configure, and test the connection

  iii. A family of NCPs for establishing and configuring different network layer protocols

• The PPP frame format appears in the Figure Shown below:

  Field length,

• The following descriptions summarize the PPP frame fields illustrated in Figure 3.6

  i. Flag - A single byte that indicates the beginning or end of a frame. The flag field consists of the binary sequence 01111110.

  ii. Address - A single byte that contains the binary sequence 11111111, the standard broadcast address. PPP does not assign individual station addresses.

  iii. Control - A single byte that contains the binary sequence 00000011, which calls for transmission of user data in an unsequenced frame. A connectionless link service similar to that of Logical Link Control (LLC) Type 1 is provided.

  iv. Protocol - Two bytes that identify the protocol encapsulated in the information field of the frame. The most up-to-date values of the protocol field are specified in the most recent Assigned Numbers Request For Comments (RFC).

  v. Data - Zero or more bytes that contain the datagram for the protocol specified in the protocol field. The end of the information field is found by locating the closing flag sequence and allowing 2 bytes for the FCS field. The default maximum length of the information field is 1,500 bytes. By prior agreement, consenting PPP implementations can use other values for the maximum information field length.

  vi. Frame check sequence (FCS) - Normally 16 bits (2 bytes). By prior agreement, consenting PPP implementations can use a 32-bit (4-byte) FCS for improved error detection.

  vii. Flag - A single byte that indicates the end of a frame. The flag field consists of the binary sequence 01111110.