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					           HDLC
             &    Ch 11- 12



            PPP

K. Salah    1
 Chapter 11.5


           High-level Data Link Control

                  HDLC


K. Salah               2
               11.17 HDLC frame

              HDLC supports communication over point-to-
               point and multipoint links.
              I-Frame (Information frame): Used to
               transport user data and control information
              S-frame (Supervisory frame): Used only to
               transport control information.
              U-frame (Unnumbered frame): Reserved for
               system management.




K. Salah                           3
               11.18 HDLC frame types

              I-Frame has sequence and ACK numbers
              S-frame contains the code for Receive Ready, Receive Not
               Ready, Reject, Selective Reject.
              U-frame is used for session management and control
               information




K. Salah                                  4
           11.22 Piggybacking without Error




K. Salah                                 5
           11.23 Piggybacking with Error




K. Salah                                   6
 Chapter 12


           Point-to-Point
              Access:
               PPP

K. Salah         7
               12.1 PPP frame

              Two devices can be connected by a dedicated link or a
               shared link.  point-to-point access.
              Connection to ISP via PPP
                   Format of the frame
                   Negotiate the establishment of the link and the exchange of
                    data
                   How network layer data are encapsulated in the data link
                    frame
                   How two devices can authenticate each other.
                   Flag = 01111110
                   Address = Broadcast
                   Control field = No sequence numbers and so no flow or error
                    control




K. Salah                                    8
               12.2 Transition states




              Establishing: Negotiation of options




K. Salah                                9
               12.3 Protocol stack


              Link Control Protocol
                   Negotiation mechanisms.
                   Establishing or terminating state
              Authentication Protocols
                   Password Authentication Protocol (PAP)
                   Challenge Handshake Authentication
                    Protocol (CHAP)
              Network Control Protocol




K. Salah                              10
               12.5 PAP


              Send user name and password
              Check validity and accept or deny.




K. Salah                        11
           12.6 PAP packets




K. Salah                      12
               12.7 CHAP

              System sends a challenge packet containing
               challenge value, usually a few bytes
              User applies predefined function with challenge
               value, user’s password. The result is sent as
               response.
              System does the same as user and compares the
               result.




K. Salah                              13
           12.8 CHAP packets




K. Salah                       14
               12.9 IPCP packet encapsulated in PPP frame

              Network Control Protocol is a set of control protocols
               to allow the encapsulation of data coming from
               network layer protocols into the PPP frame.
              The set of packets that establish and terminate a
               network layer connection for IP packets is called
               Internetwork Protocol Control Protocol (IPCP).
              Use configure-request to negotiate with the other
               party. Ex., to set the IP addresses and so on.




K. Salah                                     15
           Table 12.3 Code value for IPCP packets

               Code                IPCP Packet


                01       Configure-request

                02       Configure-ack

                03       Configure-nak

                04       Configure-reject

                05       Terminate-request

                06       Terminate-ack

                07       Code-reject


K. Salah                           16
           12.10 An example




K. Salah                      17

				
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