As the data link layer protocol is used to identify from where the transmission starts and ends, so ISP (Internet Service Provider) use the PPP protocol to provide the dial-up access to the internet.
PPP FRAME FLAG SERIAL
It can be used over many types of physical networks such as serial cable, phone line, trunk line, cellular telephone, fiber optic links such as SONET. It is mainly used for the communication between the two devices. The PPP protocol can be used on synchronous link like ISDN as well as asynchronous link like dial-up. It is used to encapsulate the layer 3 protocols and all the information available in the payload in order to be transmitted across the serial links. It is a data link layer protocol that resides in the layer 2 of the OSI model. Suppose the user wants to access the internet from the home, the PPP protocol will be used. It is the most commonly used protocol for point-to-point access. Its length may vary from one network to another.įCS: It is a 2 byte or 4 bytes frame check sequence for error detection.The PPP stands for Point-to-Point protocol. Payload: This carries the data from the network layer. The address field may be from 1 byte to several bytes.Ĭontrol: It is 1 or 2 bytes containing flow and error control information. The fields of an HDLC frame are:įlag: It is an 8-bit sequence with bit pattern 01111110.Īddress: It contains the address of the receiver. High-level Data Link Control (HDLC) is a group of communication protocols of the data link layer for transmitting data between network points or nodes.
PPP FRAME FLAG CODE
The standard code used is CRC (cyclic redundancy code). The maximum length of the payload field is 1500 bytes.įCS: It is a 2 byte or 4 bytes frame check sequence for error detection. Protocol: 1 or 2 bytes that define the type of data contained in the payload field. The fields of a PPP frame are:įlag: It is of 1 byte that with bit pattern 01111110.Īddress: 1 byte which is set to 11111111 in case of the broadcast.Ĭontrol: 1 byte set to a constant value of 11000000. Point – to – Point Protocol (PPP) is a communication protocol of the data link layer that is used to transmit multiprotocol data between two directly connected (point-to-point) computers. Let us study the frame structure used in two protocols: Point – to – Point Protocol (PPP) and High-level Data Link Control (HDLC). The structure of the data link layer frame may be specialized according to the type of protocol used. Seq: This contains the sequence number of the frame for rearrangement of out – of – sequence frames and sending acknowledgments by the receiver.Īck: This contains the acknowledgment number of some frame, particularly when piggybacking is used. Kind: This field states whether the frame is a data frame or it is used for control functions like error and flow control or link management etc. It is also called a Frame Check Sequence (FCS).įlag: Two flag at the two ends mark the beginning and the end of the frame.Ī frame header contains the destination address, the source address and three control fields kind, seq, and ack serving the following purposes: Trailer: It contains the error detection and error correction bits. Payload field: It contains the message to be delivered. Fields of a Data Link Layer FrameĪ data link layer frame has the following parts:įrame Header: It contains the source and the destination addresses of the frame and the control bytes. At receiver’ end, data link layer picks up signals from hardware and assembles them into frames. If the frame size becomes too large, then the packet may be divided into small sized frames. Data link layer takes the packets from the Network Layer and encapsulates them into frames. A frame is a unit of communication in the data link layer.
0 kommentar(er)
