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Point-to-Point Protocol

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Presentation on theme: "Point-to-Point Protocol"— Presentation transcript:

1 Point-to-Point Protocol
More on PPP Point-to-Point Protocol

2 Data Link Layer Process
Internet layer process passes EACH IP packet to the data link layer process for delivery over the data link Internet Layer Process IP Packet Data Link Layer Process

3 PPP Point-to-Point Protocol
Popular data link layer protocol for dial-in connections Supported by Microsoft Windows Between data link layer processes on user PC and first router Not between user PC and the destination host PPP DLL Process DLL Process User PC First Router

4 PPP Negotiation Phase Before exchanging data frames, the two sides
Negotiate conditions of PPP operation Also negotiate how specific protocols will be handled, such as IP Not limited to IP PPP DLL Process DLL Process User PC First Router

5 PPP Data Frames Header Information field (IP packet or other information) Trailer with Frame Check Sequence field Error detection but not correction If an error is found, PPP frame is discarded Trailer Information Field Header IP Packet

6 PPP Flag Fields (1 Octet Each) Always contain: 10000001
Designates start of frame and end of frame No length field necessary Flag Addr Ctrl Prot Info CRC Flag

7 PPP Address Field (1 Octet)
PPP was designed to allow several devices at each end For modem-modem communication, only one device at each end Has fixed value: Flag Addr Ctrl Prot Info CRC Flag

8 PPP Control Field (1 Octet)
PPP was designed to allow control information Not used in PPP; included because PPP is based on an older protocol that used this field In PPP, the control field contains the fixed value Flag Addr Ctrl Prot Info CRC Flag

9 PPP Protocol Field (2 Octets)
Identifies the contents of the information field There are values for IP, IPX, other internet layer protocols that may be carried in the information field There are values for supervisory messages Flag Addr Ctrl Prot Info CRC Flag

10 PPP Cyclical Redundancy Check (2 Octets)
For error-checking information Allows receiver to detect a PPP frame with a transmission error Receiver discards such frames; error detection but not reliability (no error correction) Flag Addr Ctrl Prot Info CRC Flag

11 Physical Layer Process
Data link layer process passes EACH data link layer frame to the physical layer process for delivery to the next computer (router or host) Data Link Layer Process DL Frame Physical Layer Process

12 Physical Layer Process
Physical layer process does not create a protocol data unit Sends one bit at a time over the data link connecting the sending computer to the next computer It is the data link layer process that organizes these bits into frames over the data link Physical Layer Process Physical Layer Process 10110

13 Reliability Only TCP is Reliable or Needs to Be
Corrects errors, gives application programs clean data Corrects errors that occur a the transport layer or lower layers because only correctly received TCP segments are acknowledged


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