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HDLC&

PPP

Ch 11- 12

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Chapter 11.5

High-level Data Link Control

HDLC

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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.

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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