Open Systems and Data Link Protocols November 7, 2002

Open Systems and Data Link Protocols

November 7, 2002

Announcements• Short Test or Long Quiz: November 21

– Will cover Chapters 14, 15 and 16.

• Homework– Chapter 14: 3, 4, 6, 12, 22, 26 (hand in next

week)– Chapter 15: 4, 5, 6, 7, 16, 17, 26, 27, 40 (hand

in November 21)– Read Chapter 16 (pages 475-502) Internet-

ATM. It will not be discussed in class but the quiz bonus test will come from it.

Class Objectives

• Open Systems– Why do we need open standards?– Seven-layer OSI model

• Data Link Protocols– The past: BISYNC– The present: HDLC

Before Open Standards

• Getting two systems to communicate between them was a major effort.

• Once you purchased a system you were “stuck” with it for years for both hardware and software:– IBM– Digital– Unisys

With Open Systems

• System interoperability becomes much easier.

• Allows the combination of different hardware and software “solutions”.

• Results:– Lower costs due to increased competition– Faster implementation (alternate sources)– Easier system maintenance and troubleshooting

FIGURE 14-1 Seven-layer OSI model.

Warren HiokiTelecommunications, Fourth Edition

Copyright ©2001 by Prentice-Hall, Inc.Upper Saddle River, New Jersey 07458

All rights reserved.

OSI Layers

1. Physical: Concerned with the transmission of unstructured bit stream over physical medium; deals with the mechanical, electrical, functional, and procedural characteristics to access the physical medium.

2. Data Link: Provides for the reliable transfer of information across the physical link; sends blocks of data (frames) with the necessary synchronization, error control, and flow control.

OSI Layers (cont.)

3. Network: Provides upper layers with independence from the data transmission and switching technologies used to connect systems; responsible for establishing, maintaining, and terminating connections.

4.Transport: Provides reliable, transparent transfer of data between points; provides end-to-end error recovery and flow control.

OSI Layers

5. Session: Provides the control structure for communications between applications; establishes, manages, and terminates connections (sessions) between cooperating applications.

6. Presentation: Provides independence to the application processes from differences in data representation (syntax).

7. Application: Provides access to the OSI environment for users and also provides distributed information services.

FIGURE 14-2 (a) Computers connected point-to-point; (b) computer connected to several terminals in a multipoint (or multidrop) configuration.




BISYNC

• Developed by IBM in 1964

• Byte or character oriented protocol

• Geared toward mainframe-terminal relationship

• Half-Duplex operation

• Use has been in decline due to better protocols

FIGURE 14-3 BISYNC message block format.







FIGURE 14-4 BISYNC transparent text mode format.




FIGURE 14-5 BISYNC point-to-point line control sequence.




FIGURE 14-6 An error condition encountered causes the receiving station to request a retransmission.




FIGURE 14-7 Acknowledgment, ACK, lost en route to the transmitting station.




FIGURE 14-8 Host computer poll and selecting a device for transmitting data in a multipoint setup.




FIGURE 14-10 Circuit switching network.




FIGURE 14-11 Message switching network.




FIGURE 14-12 Packet switching network.




High-Level Data Link Control

• Bit-oriented protocol

• Used throughout the world

• Implemented in X.25 packet switching networks

• Full-duplex operation

• Flexible– Point-to-point and multi-point links– Primary-secondary and peer-to-peer interaction.– Works with long distance (e.g. satellite) as well

as short distance links.

FIGURE 14-13 HDLC frame format.




FIGURE 14-14 HDLC framing pattern and bit order of transmission.




FIGURE 14-15 Extending the HDLC ADDRESS BYTE field.




FIGURE 14-16 Format of CONTROL BYTE for information transfer, supervisory, and unnumbered HDLC frames.




FIGURE 14-18 HDLC supervisory frame structure.




FIGURE 14-19 HDLC unnumbered frame structure.




FIGURE 14-20 Zero-bit insertion range.




FIGURE 14-21 HDLC zero-bit insertion, bit-stuffing technique.




FIGURE 14-22 HDLC frame sequencing.




Documents

Open Systems and Data Link Protocols November 7, 2002