hdlc & ppp
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K. Salah 1
HDLC&
PPP
Ch 11- 12
K. Salah 2
Chapter 11.5
High-level Data Link Control
HDLC
K. Salah 3
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 4
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
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11.22 Piggybacking without Error
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11.23 Piggybacking with Error
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Chapter 12
Point-to-PointAccess:
PPP
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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
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12.2 Transition states
Establishing: Negotiation of options
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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
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12.5 PAP
Send user name and password Check validity and accept or deny.
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12.6 PAP packets
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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.
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12.8 CHAP packets
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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.
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Table 12.3 Code value for IPCP packetsTable 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
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12.10 An example
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