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Psdn and ccitt x series

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Psdn and ccitt x series

  1. 1. PSDN and Data Communication Systems Chapter 23 Electronic Communications Sytems , Fifth Editon By: Wayne Tomasi ECE @Saint Louis University, Baguio City 1 Prepared by: Engr. Jeffrey Des B. Binwag
  2. 2. PUBLIC SWITCHED DATA NETWORKS • A switched communications network similar to the public telephone network except that it is designed for transferring data only. • Transports data from source to destination through a network of intermediate switching nodes and transmission links. • COMPONENTS OF PSDN: – END STATIONS – SWITCHING NODES – TRANSMISSION LINKS ECE @Saint Louis University, Baguio City 2
  3. 3. PUBLIC SWITCHED DATA NETWORKS ECE @Saint Louis University, Baguio City 3
  4. 4. VALUE ADDED NETWORK • “Adds value” to the services or facilities provided by a common carrier to provide new types of communication services. • Comprises an organization that leases communications lines from common carriers and adds new types of communications services to those lines. • Examples Value Added Services: – Error Control, Enhanced Connection Reliability, Dynamic Routing, Failure Protection, Logical Multiplexing, and Data Format Conversion ECE @Saint Louis University, Baguio City 4
  5. 5. PSDN SWITCHING TECHNIQUES • CIRCUIT SWITCHING • MESSAGE SWITCHING • PACKET SWITCHING ECE @Saint Louis University, Baguio City 5
  6. 6. PSDN SWITCHING TECHNIQUES • CIRCUIT SWITCHING – The switching technique used for making a standard telephone call – Involves establishing a call, information transfer (in real time), and call disconnection – Blocking occurs due to a limited number of circuits and switching paths • Blocking is the inability to complete a call because there are no facilities or switching paths available between the source and the destination – A circuit switch is transparent to the data ECE @Saint Louis University, Baguio City 6
  7. 7. PSDN SWITCHING TECHNIQUES • MESSAGE SWITCHING – A store-and-forward network where data is not transmitted in real time but rather passes through transactional switches capable of storing data and then transmitting them when it is convenient to do so or when the load on the network has decreased. • Transactional switches can store data or change its format and bit rate, then convert the data back to their original form or an entirely different form at the receive end. – Blocking cannot occur although delay time from message transmission to reception varies from call to call. – Multiplexes data from different sources into a common facility. ECE @Saint Louis University, Baguio City 7
  8. 8. PSDN SWITCHING TECHNIQUES • PACKET SWITCHING – Involves dividing data into smaller segments called packets prior to transmission. – Called a hold-and-forward network because unlike messages in message switching that are stored for a longer period, packets are usually stored (held) for shorter periods. – Hold time is generally quite short and message transfer is near real time. – Require complex and expensive switching arrangements and complicated protocols. ECE @Saint Louis University, Baguio City 8
  9. 9. PSDN SWITCHING TECHNIQUES ECE @Saint Louis University, Baguio City 9
  10. 10. CCITT X.25 USER-TO-NETWORK INTERFACE PROTOCOL • Designated by the CCITT in 1976 as the international standard for packet network access. • Addresses the ISO physical, data-link, and network layers. • PHYSICAL LAYER STANDARDS: – X.21, X.26, X.27 – EIA RS-232, RS-423A, RS-422A • DATA-LINK LAYER STANDARDS: – HDLC (High-Level Data Link Control Protocol) – ANSI 3.66 ADCP (Advanced Data Communications Control Procedures) ECE @Saint Louis University, Baguio City 10
  11. 11. CCITT X.25 USER-TO-NETWORK INTERFACE PROTOCOL • Link Access Procedure Balanced (LAPB) – A subset of HDLC that provides for two-way, full-duplex communications between DTE and DCE at the packet network gateway. • LAPB COMMANDS ECE @Saint Louis University, Baguio City 11
  12. 12. CCITT X.25 USER-TO-NETWORK INTERFACE PROTOCOL • LAPB RESPONSES ECE @Saint Louis University, Baguio City 12
  13. 13. CCITT X.25 USER-TO-NETWORK INTERFACE PROTOCOL X.25 SWITCHING SERVICES PERMANENT VIRTUAL CIRCUIT VIRTUAL CALL DATAGRAM ECE @Saint Louis University, Baguio City 13
  14. 14. CCITT X.25 SWITCHING SERVICES • PERMANENT VIRTUAL CIRCUIT – Logically equivalent to a two-point dedicated private line circuit except slower because no hardwired circuit is provided. – Appropriate switches and circuits must be established through the network to provide interconnection – Identifies the routing between two predetermined network subscribers which will be used for all subsequent messages. ECE @Saint Louis University, Baguio City 14
  15. 15. CCITT X.25 SWITCHING SERVICES • VIRTUAL CALL – Logically equivalent to making a telephone call through the DDD network except no direct end- to-end connection is made. – Temporary virtual connections that use common usage equipment and circuits. – It is a one to many arrangement or point-to- multipoint. ECE @Saint Louis University, Baguio City 15
  16. 16. CCITT X.25 SWITCHING SERVICES • DATAGRAM – Consists of self-contained packets that travel through the network independent of other packets of the same message by whatever means possible. – The network does not acknowledge the packets nor ensure successful transmission. – Reliable only when a message can fit into a single packet. – Called a single-packet-per-segment protocol. ECE @Saint Louis University, Baguio City 16
  17. 17. CCITT X.25 PACKET FORMAT • CALL REQUEST PACKET – Format Identifier – Logical Channel Identifier (LCI) – Packet Type – Calling Address Length – Called Address Length – Called Address – Calling Address – Facilities Length Field – Facilities Field – Protocol Identifier – User Data Field ECE @Saint Louis University, Baguio City 17
  18. 18. CCITT X.25 PACKET FORMAT • DATA TRANSFER PACKET – Similar to a call request packet except for considerably less overhead and a much larger user data field. – Also includes two additional fields namely: • Send Packet Sequence Field • Receive Packet Sequence Field ECE @Saint Louis University, Baguio City 18
  19. 19. ITU-T X SERIES OF RECOMMENDED STANDARDS • X.1-X.39 – Deals with services and facilities, terminals, and interfaces. • X.40-X.199 – Deals with Network architecture, transmission, signaling, switching, maintenance, and administrative arrangements. ECE @Saint Louis University, Baguio City 19
  20. 20. ITU-T X SERIES OF RECOMMENDED STANDARDS End

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