Hands-on X.25 Networks

Objectives Prerequisites Who should attend Course Outline Hands-on Sessions

NE-1.0

What you will learn...

This course will enable you to learn about designing, installing and supporting X.25 networks. You will discover its key applications and how X.25 provides a connection to a public data network. You will learn how to interpret frames and packets using a data analyser - a skill you must have to troubleshoot and maintain X.25 networks. You will understand what errors mean and learn to troubleshoot and correct them quickly and effectively. Most importantly you will learn to break down call request packets - a common source of problems.

Prerequisites

You need to have a basic understanding of data communications and RS-232 to gain the most from this course. Otherwise we suggest you attend our Hands-on Networking for Rookies course as a prerequisite.

Who should attend

By attending this course you will directly receive in a hands-on manner all the information you will need about X.25 networks. You might have a job title such as: Systems Administrator, Technical Support Manager, Network Engineer, DP Manager, Communications Engineer, Network Manager, LAN Administrator, Analyst/Programmer or Installation Engineer.

Course Outline

Overview of packet switched networks

  • What is packet switching
  • Packet switched philosophy
  • Packet switched components
  • X.25 as a standard
  • The OSI seven-layer model
  • Other related protocols

X.25 architecture overview

  • The physical layer specifications
  • Character and bit-oriented protocols
  • Bisynchronous, High-level Data Link Control (HDLC) and Synchronous Data Link Control (SDLC) framing
  • ITU-T X.25 standards LAP, LAP-B
  • Link layer recommendations
  • Connectionless protocols
  • Network layer operation

X.25 at the OSI physical layer

  • Physical layer recommendations
  • Implementation of X.21 and X.21bis
  • V.24 standard under X.21bis
  • Functional, electrical and physical characteristics
  • V.35 standard
  • X.21 standard and its scope
  • Similarities to V.11

X.25 at the OSI data link layer

  • Framing structures
  • Flags and idle states
  • Bit stuffing or ones insertion
  • Addressing conventions
  • Frame types, information, supervisor and unnumbered
  • Link layer procedural phases
  • Frame decoding and checking
  • Frame sequencing
  • Link flow control and timers

X.25 at the OSI network layer

  • Packet procedures and phases
  • Identifying packet types
  • Call establishment
  • Virtual circuit structures
  • Packet negotiations
  • Flow control procedures
  • Reset, restart and diagnostic packets
  • Error identification and diagnostic codes
  • Facilities parameters

Packet Assembler/Disassembler (PAD)

  • X.28 functions
  • ITU-T recommendations X.1, X.2, X.3
  • PAD features and function
  • ITU-T recommendation for X.29

X.75 multi-link procedure

  • Trunks interconnections in the Public Data Networks (PDNs)
  • Multi-Link Protocols (MLPs)
  • X.75 packet types, call request and network utilities

Austpac – public X.25 networks

  • Austpac network structure
  • Connectivity options
  • Price and tariff issues

Private networks

  • Private network similarities to public service options
  • Features and benefits
  • Major players
  • Future directions and market longevity

X.25 and LAN internetworking

  • Internetworking using X.25
  • WAN transport of LAN protocols
  • TCP/IP protocol co-existence
  • TCP/IP address mapping
  • Network design and configuration issues

X.25 and frame relay

  • Frame relay overview
  • Frame relay physical and data link layer operations
  • Frame relay standards
  • Frame relay data link frame structure
  • Service comparison of X.25 and frame relay

Hands-on Sessions

Physical layer and standards

In this first session you will build a network that will allow packet switching to take place. You will interpret the physical layer of the OSI protocol suite ensuring that your network meets the required standards.

Data link layer

Interacting with the instructor on the OSI data link layer, you will establish an X.25 trunk operation and then monitor it. You will observe the PAD and packet switching operation on your network. All aspects of the link will be analysed including the start-up procedure, sequencing, acknowledgements and retransmissions.

Network layer and monitoring conversations

This interactive session investigates the information you receive at the network layer to include the packet level subset. During this session you will monitor the conversation between the PAD and packet switch. You will decipher the packet level conversation, monitor and interpret every aspect of a call request packet, call clearing data packets and the associated acknowledgements. All the monitoring and checking will be done on your network using data scopes. You will verify address fields, facilities and call data fields.

Decoding messages

You will supervise an X.25 packet level conversation at the user data level between the PAD and the packet switch. Using information gained from the ITU-T X.29 recommendations, you will analyse and decode messages involved in the PAD environment.

Diagnosing

In a real life situation, you will correctly diagnose packet switching failures across the three OSI levels – the physical, data link and network layers. Faults will be initiated by the instructor to ensure that you obtain the most from these practical exercises. You will carry out final tests on your network to ensure that it is fully functional.