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If one of the nodes starts the communication then the connection goes into the established phase. In this phase, the link is not being used.No active carrier is there at the physical layer and the line is simply quiet. The PPP protocol has to go through various phases and these are shown in the diagram given below The escape byte is 011111101 which means whenever the flag-like pattern appears in the data then the extra byte is stuffed that mainly tells the receiver that the next byte is not a flag. It means that the flag in the PPP is a byte and it is needed to be escaped wherever it appears in the data section of the frame. Byte Stuffing in PPPĪs we have told you that the major difference between PPP and HDLC is that PPP is a byte-oriented protocol. It is simply a 2-byte or 4-byte standard CRC(Cyclic redundancy check). This can also be negotiated between the endpoints of communication. The maximum length of this field is 1500 bytes. This field carries the data from the network layer. It can either be user information or other information. This field defines what is being carried in the data field. The two parties can negotiate and can omit this byte. We have already told you that PPP does not provide any flow control and also error control is limited to error detection. The value of this field is also a constant value of 11000000. The value of this field in PPP protocol is constant and it is set to 11111111 which is a broadcast address. But there is a difference too and that is PPP is a byte-oriented protocol whereas the HDLC is a bit-oriented protocol. It is important to note that this pattern is the same as the flag pattern used in HDLC. The PPP frame mainly starts and ends with a 1-byte flag field that has the bit pattern: 01111110. Let us discuss each field of the PPP frame format one by one: 1.
![ppp frame flag ppp frame flag](https://www.rfwireless-world.com/images/PPP-Packet-Structure.jpg)
Given below figure shows the format of the PPP Frame: In the PPP protocol, the framing is done using the byte-oriented technique. In case if there is a corrupted frame then it is discarded silently. There is a CRC field that detects the errors. The PPP protocol provides a very simple mechanism for error control. This protocol does not provide any mechanism for addressing in order to handle the frames in the multipoint configuration. Because when using this protocol the sender can send any number of frames to the receiver one after the other without even thinking about overwhelming the receiver. This protocol does not provide a flow control mechanism. Some services that are not offered by the PPP protocol are as follows: This protocol also provides connection over multiple links. This protocol provides multiple services of the network layer and also supports various network-layer protocols. The PPP protocol defines how the two devices can negotiate the establishment of the link and then can exchange the data. This protocol also defines how the data of the network layer are encapsulated in the data link frame. PPP protocol also defines the format of the frames that are to be exchanged between the devices. This protocol defines how two devices can authenticate with each other. The Point-To-Point protocol mainly provides connections over multiple links. The PPP protocol is mainly used to establish a direct connection between two nodes. PPP(Point-To-Point) protocol is a protocol used in the data link layer. In this tutorial, we will be covering another protocol of the data link layer that is Point-To-Point Protocol. Difference between OSI and TCP/IP Model.TCP/IP REFERENCE MODELCOMPUTER NETWORKS.
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