What is point-to-point protocol?

The point-to-point protocol is referred to as PPP. It is the protocol for point-to-point access that is most frequently used. The PPP protocol will be utilized if the user wants to access the internet from their house.

It belongs to the data link layerlayer 2 of the OSI model of the OSIOpen Systems Interconnection model and is a data connection layer protocol. It transports data via serial links to encapsulate network layer protocols and all available payload data. Synchronous links like ISDN Integrated Services Digital Networkand asynchronous links like dial-up are compatible with the PPP protocol. It is mainly utilized for inter-device communication.

Services PPP offers

PPP is a very useful protocol in networking. The services it provides are listed below.

• It establishes the frame format used during transmission.

• It outlines the procedure for creating links. The PPP protocol handles "how this link establishes" whenever a user creates a connection to a server.

• It outlines the data exchange procedure, including the rate at which data will be sent.

• The encapsulation is the PPP protocol's key component. It specifies how information in the payload and network layer is contained in the data link frame.

• It outlines how the two devices will authenticate one another. The PPP protocol determines the authentication between the two devices, handshaking, and how the password will be sent between the two devices.

Services PPP doesn't offer

With all these functionalities provided, there are a few services that PPP doesn't provide. These include:

• There is no flow control mechanism in this protocol since this protocol allows the sender to send any number of frames to the recipient sequentially without even considering overloading the receiver.

• This protocol does not include any addressing mechanisms in the multipoint setup to handle the frames.

• The PPP protocol offers a relatively straightforward error control technique. The errors are found via the CRCcyclic redundancy check field. A corrupted frame is silently discarded if there is one.

PPP protocol frame format

The data link layer protocol PPP directly links two network nodes. PPP frames follow a particular format. A PPP frame's basic structure is as follows:

1. Flag: PPP frames contain a flag byte at the start and end, represented by the binary sequence 01111110 (0x7E in hexadecimal).

2. Address: Network layer addressing uses the address field, a single byte. For broadcast, it is commonly set to the binary value 11111111 (0xFF in hexadecimal).

3. Control: A single byte is utilized as the control field, which is used for flow control and other control operations. Most PPP implementations set it to the binary sequence 00000011 (0x03 in hexadecimal).

4. Protocol: The protocol field is two bytes long and contains information about the protocol that the PPP packet is encasing. The type of data being transferred is indicated. Typical values are IPv6 (0x0057) and Internet Protocol (IP), which have the value 0x0021.

5. Information: The actual data being communicated is contained in the information field. The encapsulating protocol and the network conditions can affect how long it is.

6. Frame check sequence: A two-byte cyclic redundancy check (CRC) called frame check sequence is used to detect errors in data. It is determined using the full frame’s data, excluding the flag bytes.

Transition phases of PPP protocol

When starting and ending a PPP session, the point-to-point protocol features multiple distinct transition stages. These phases consist of:

Link establishment phase

• Dead phase: This is the initial condition in which no link has been established.

• Link establishment phase: Once the connection has been made, both ends engage in packet exchanges using the Link Control Protocol (LCP) to discuss configuration options and parameters.

• Authentication phase: If necessary, endpoint identities are confirmed using Password Authentication Protocol (PAP) or Challenge Handshake Authentication Protocol (CHAP).

• Network-layer protocol phase: Following successful authentication, the endpoints discuss and decide on the network-layer protocols, such as IP or IPv6, that will be utilized.

Link quality monitoring phase

To keep track of the link’s quality during this phase, LCP packets are periodically exchanged. The link may be renegotiated or canceled if any problems are found.

Network-layer protocol configuration phase

The relevant Network Control Protocols (NCPs) are used to configure the network-layer parameters, such as IP addresses, DNS servers, compression ratios, and other choices after the network-layer protocol has been chosen.

Network-specific parameter configuration and administration are made possible by NCPs at the network layer. They offer a way to negotiate and build the conditions to guarantee proper communication between network elements.

Network protocols, such as the Point-to-Point Protocol (PPP) and the Internet Protocol Control Protocol (IPCP) for Internet Protocol (IP) networks, are used to implement NCPs. For instance, the Link Control Protocol (LCP) is in charge of setting up and configuring the link when establishing a connection over a PPP-based network, while IPCP is in charge of negotiating IP addresses and other associated parameters.

Data transfer phase

Data can be sent between the endpoints after the link and network-layer protocol have been created and configured. The network-layer packets are enclosed in PPP frames and transmitted via the link.

Link termination phase

The link termination phase includes the termination of all sorts of links. It can either be a request or acknowledgment.

• Termination request phase: The link can be terminated anytime by sending a termination request packet from either endpoint. Termination may have occurred due to a timeout, network problem, or user request.

• Termination acknowledgment phase: The other endpoint recognizes the termination by sending a termination acknowledgment packet after receiving the termination request.

• Link dead phase: Once the termination is accepted, the link is considered dead, making it unable to transport data further.

The standard PPP procedure includes these phases, but different implementations may have modifications or additional phases based on the particular requirements and extensions used.

Conclusion

The Point-to-Point Protocol (PPP) is a popular protocol for point-to-point access that makes it easier for people to connect to the internet from their homes. It handles payload encapsulation, device authentication, link formation, and data exchange. However, PPP has restrictions on flow control, multipoint addressing, and error correction. Although it is essential for connection establishment, it is important to consider its particular limits when considering networking requirements.