HDLC and PPP  protocols are the communication protocol responsible for transmitting information between nodes or points. It deals data in form of frames.

Both HDLC and PPP are the part of data link layer. The major difference between them is, HDLC refers to bit-oriented protocol, whereas, PPP is byte-oriented protocol.

Difference between High-level Data Link Control Protocol and Point-To-Point protocol

High-Level Data Link Control ( HDLC )

HDLC stands for High-level Data Link Control. HDLC is a type of WAN protocol which necessarily performs the encapsulation of data inside the data link layer. This is the type of encapsulation which changes the format of data and information.

Furthermore,it is used to exchange data between nodes. It transmits data in the form of frames over a network.

It allows the use of point to point and multipoint links. It provides two types of transfer modes that is:

• Normal Response Mode (NRM): In this, station’s configuration is unbalanced. NRM involves a primary station that is capable of sending commands and multiple secondary station that can only response.
  • It can be used as point to point that includes one primary station and a secondary station that communicate with each other.
  • Other is, point to multi-point, it involves one primary station and multiple secondary stations that communicate with one other.

•  Asynchronous Balanced Mode (ABM): In this, station’s configuration is balanced. It involves only point to point communication which means single primary station and a secondary station are the part of communication. The main difference is, every station can send and receive data.

Types of frames in HDLC

It generally supports three types of frames:

•  Information frames or I frames
•  Supervisory frames or S frames
• Unnumbered frames or U frames

Frame format of HDLC

It consists 6 types of fields:

• Flag: It used to verify beginning and end of a frame. It serves synchronisation pattern for receiver
• Address: It consists address of the receiving station
• Control: It is used for error control and flow control
• Payload :Contains users data
• FCS: It stands for frame check sequence that is dedicated to error detection

Point to Point Protocol ( PPP )

PPP stands for Point-To-Point protocol. PPP is also a type of WAN protocol, which comes up with loads of advancements over the HDLC protocol. PPP protocol does not need any physical addresses or any tangible wires, only the IP address is sufficient.

It defines format of frames, connection establishment, data exchange process, Authentication process and more. However, it doesn’t support flow control, addressing mechanism and efficient error control

Frame format of PPP:

• Flag: used to verify beginning and end of a frame. It serves synchronisation pattern for receiver
• Address: It consists address of the receiving station. A constant value is used to set the address field which is 11111111 that resembles broadcast address
• Control: A constant value is used to set the field which is 11000000 . Since, flow control is not supported and PPP has very limited error control. Tberefore, it is generally not needed
• Protocol : It decides the data that is going to transmit
• Payload field :Contains users data
• FCS: It stands for frame check sequence that is dedicated to error detection