1. Advanced Computer Networking Graduate Course from Electrical Engineering School
A. Beheshti
Communication Group
Iran University of Science and Technology
Chapter 5 Link Layer
Text Book:
Computer Networking: A Top Down Approach 6th edition Jim Kurose, Keith Ross Addison-Wesley March 2012
All material copyright
J.F Kurose and K.W. Ross, All Rights Reserved
Link Layer

2. Point to Point link protocols
High level Data link control (HDLC)
History
IBM: SDLC (synchronous data link control)
ANSI: ADCP (advanced data communication control prcedure)
ISO: HDLC
CCITT: adopted as a part of X25 link access procedure (LAP)
then modified to LAPB
specification
Bit oriented
Bit stuffing for data transparency

3. Point to Point link protocols
High level Data link control (HDLC)
Frame format
information
supervisory
unnumbered
Elec. Eng. Dept. , IUST

4. Point to Point link protocols
High level Data link control (HDLC)
Frame format
information
supervisory
unnumbered
TYPE0: RECEIVE READY (Next)
TYPE1: Negative Acknowledge (Next)
TYPE2: RECEIVE NOT READY (before Next) stop the sender
TYPE3: SLECTIVE REJECT (retransmission of Next)
32 frame types for control purpose or data in different protocols
Elec. Eng. Dept. , IUST

5. Point to Point link protocols
Data link layer in Internet
Connecting user to internet (host to internet)
Connecting different LANs by routers (router to router)
Both of these connections are point to point
Point to point protocol
Elec. Eng. Dept. , IUST

6. Point to Point link protocols
Point to point protocol (PPP)
It is defined in RFC1661 standard and modified in RFC1662, RFC1663
Error correction
support multiple protocols
Allows IP address negotiated during connection time
Permits authentication
Elec. Eng. Dept. , IUST

7. Point to Point link protocols
Main features of PPP
Framing method defines start and end of frame without ambiguity
A link control protocol (LCP) that allow
bringing up the lines
Test the line
Negotiate options
Bringing the lines down when not needed anymore
A method to negotiate network layer options independent of network layer (NCP)
Elec. Eng. Dept. , IUST

8. Point to Point link protocols
PPP frame for unnumbered format
It is byte oriented
It use HDLC flag with byte stuffing
It is mostly used as unnumbered
Numbered frame is also defined in RFC1663 for wireless noisy channels
LCP can negotiate to omit the address and control fields
LCP,NCP,IP,IPX,APPLE Talk
Negotiable with LCP (1500 Default)
Elec. Eng. Dept. , IUST

9. Point to Point link protocols
Simplified diagram for bringing line up and down
Elec. Eng. Dept. , IUST

10. Point to Point link protocols
LCP frame types
Initiator
Responder
Elec. Eng. Dept. , IUST

11. Point to Point link protocols
NCP
It depends on the network layer protocols
For each protocol list of negotiable options are defined
For IP dynamic IP address assignment is important
Elec. Eng. Dept. , IUST