Hands On X.25

4 Day Course
Code PDN057

This course has been superseded by the MPLS Transport Networks, VPNs & Control Plane course.


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Data Communication Fundamentals (6 topics)

  • Synchronous data transmission
  • The need for a protocol reference model
  • Open systems interconnection
  • Data networks in the OSI model
  • Connection-oriented and connectionless
  • communication

Introduction to Packet Switching (3 topics)

  • Types of traffic and the efficient use of capacity
  • Alternative approaches - frame relay, ISDN, leased lines
  • Applications of packet switching

What is X.25? (4 topics)

  • The relationship between X.25 and OSI
  • Components of the X.25 standard
  • Versions of the X.25 standard
  • User model of X.25

Addressing Schemes for X.25 Networks (3 topics)

  • E.163 and F.69 for telecommunications
  • X.121 for data networks including X.25
  • National and international networks

The Physical Layer - X.21 and X.21bis (4 topics)

  • The connectors and the pin functions
  • Modes of interface operation - leased circuit, direct
  • circuit and addressed call
  • X.21bis as an alternative approach

The Data Link Layer - HDLC (7 topics)

  • High level data link control - LAP and LAP B
  • Transparency and bit insertion
  • Sequencing and flow control
  • Error detection and correction
  • The extended mode of operation
  • Types of frame and their uses
  • The Poll/Final bit and its uses

The Packet Layer and the X.25 Protocol (7 topics)

  • OSI primitives for packet switching
  • Types of control and data packet
  • Call control procedures and negotiation of options
  • Datagrams and virtual circuits
  • Interrupts, resets and restarts
  • Logical channels and logical channel groups
  • The end-to-end properties of X.25

The OSI Transport Layer and X.25 (5 topics)

  • Services provided by the transport layer
  • Classes of transport protocol
  • Multiplexing and error recovery
  • Network types and the place of X.25
  • The use of X.25 to support the transport layer

X.25 and the ISDN (5 topics)

  • Introduction to the ISDN
  • ISDN interfaces and their control
  • The use of X.25 to provide the ISDN packet-
  • mode service
  • Addressing considerations

Packet Assemblers/Dissassemblers (PADs) (7 topics)

  • X.3, X.28 and X.29 - the 'Triple-X' standards
  • Use of the X.25 'Q' bit
  • PAD operation and parameters
  • PAD profiles
  • The X.28 recommendation
  • PAD command and service signals
  • Editing as a PAD function

The X.29 Protocol for PAD control (4 topics)

  • PAD messages for parameter control
  • Break, clear and reselection messages
  • Error messages
  • Reverse PADs and their application

Network Internal Operation (4 topics)

  • Routing and relaying in the X.25 network
  • Addressing and internetworking
  • Packet switch configuration
  • Linking public and private networks

Interworking with Other Networks (9 topics)

  • The structure of the ISDN
  • Interworking X.25 and the ISDN
  • Maximum and minimum integration scenarios
  • X.31 Case A and Case B
  • PSTN integration - the X.32 recommendation
  • User identification methods
  • Interconnecting X.25 networks using X.75
  • Interworking with SNA
  • The place of X.25 in SNA networks

Packet Network Management and Design (8 topics)

  • Network management principles
  • Measurement and monitoring
  • Control of the network
  • Network routing strategies
  • Service levels and response times
  • The use of network modelling techniques to
  • establish performance levels
  • Simulation methods compared with modelling

Security for X.25 Networks (5 topics)

  • Security requirements: threats and counter-measures
  • Security standards: X.509, ISO 7498/2
  • Physical and technical approaches to security
  • Encryption, public keys and digital signatures
  • Key certification

Modern Developments in Packet Switching (5 topics)

  • Frame relay as a simplified data interface
  • Frame relay networks
  • Fast packet switching, otherwise known as cell
  • relay or ATM
  • The transition to broadband communications

Further Uses of X.25 (4 topics)

  • Private X.25 networks
  • International usage of X.25
  • Connecting independent X.25 networks
  • Connecting LANs with X.25

X.25 Compared with Frame Relay (4 topics)

  • Fundamentals of frame relay
  • Committed Information Rate (CIR)
  • Infrastructure requirements
  • Situations to avoid

X.25 Compared with Leased Lines (4 topics)

  • Impact of ISDN
  • Interoperability challenges
  • Benefits and limitations

The Economics of X.25 (5 topics)

  • Advantages and disadvantages of X.25
  • Typical public data network services
  • Private vs. public networks
  • X.25 tariff variations
  • User- vs. server-provided PADs


Delegates should have a basic understanding of data communications concepts and terminology.

What Our Customers Say

The training was delivered with a high level of expertise and excellence. Instructor was highly knowledgeable.”

Technical Trainer, Aviat Networks

Overall the course was really good, the trainer really understood the material and was very approachable.”

Customer Training Manager, Aviat Networks

Excellent course, informative and well-paced.”

CSE, Cisco

Course was very well outlined. Topics were great and bridged many gaps.”

System Engineer, Cable & Wireless

An excellent intro to video encoding & MPEG transport streams - I would definitely recommend it.”

Broadcast Engineer, Cisco

Definitely an excellent intro. Left me interested in learning more.”

Broadcast Engineer, Eircom

Excellent training course with real examples and practical classroom demonstrations.”

Transport Designer, Orange

Instructor knowledge and experience was excellent.”

Solutions Engineer, Akamai

Excellent course, very clear and well organised. Course content delivery was very good.”

Assistant Engineer, Dhiraagu

Very informative and appropriate.”

Network Support Technician, BT

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