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Telecoms Networks

Telecoms Networks. Mohamed Mokdad HES – Biel/Bienne. Agenda. OSI Model Networks modelling Connection types Interfaces SS#7 Transfer Message Part User Parts Standards. OSI Layers dynamics. 7. 7. 6. 6. 5. 5. 4. 4. 3. 3. 2. 2. 1. 1. Transport network. Signalling network.

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Telecoms Networks

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  1. Telecoms Networks Mohamed Mokdad HES – Biel/Bienne

  2. Agenda • OSI Model • Networks modelling • Connection types • Interfaces • SS#7 • Transfer Message Part • User Parts • Standards

  3. OSI Layers dynamics 7 7 6 6 5 5 4 4 3 3 2 2 1 1

  4. Transport network

  5. Signalling network

  6. A real SS#7 network

  7. Management network

  8. Network Overlaying

  9. The networks Access Edge Core

  10. Current architectures CS Core (POTS, ISDN) Fixnet PS Core (IPSS IP Based) Telephony Gateway Wireline Access xDSL PS Core (ATM) Mobile Wireless Access Telephony Gateway Wi-Fi Cellular Access GSM Core GSM-GPRS-UMTS

  11. Networks modelling • 1 component = 1 objet • Switch • Access Point • Router • 1 objet = Σ fonctions • 1 Dialog protocole with the object • MIB & SNMP

  12. ISDN Interfaces TE1 NT2 NT1 TE2 TA R S T S/T

  13. GSM Interfaces MT0 BS/MSC TE1 MT1 BS/MSC TE2 TA MT1 BS/MSC TE2 MT2 BS/MSC R S Um

  14. Circuit/Packet Switched? • Circuit switching • 1 circuit dedicated to a connection • Connection must exist before data transfer • Connection oriented • Paquet switching • 1 paquet can follow any connection • Connection doesn’t exist before data transfer • Connectionless

  15. Interconnexion • PTS (Provider of Telecom Services) • What is it? • Interconnexion • Transport • Signaling • Billing • TDM & IP voice services interconnection • Présentation and discussion

  16. SS#7 example = CCBS ?

  17. SS#7 Architecture - STP examines the destination of messages it receives, consult a routing table, and send the messages via Cross Links - C links.

  18. SS#7 Architecture - SEP End point in the SS#7 in the same way that a telephone is an end point in the PSTN. This is located in the local switch and is addressed by the Signalling Point Code. These are linked via Access Links - A links.

  19. SS#7 Architecture – B&D Links Bridge Links - B links - connect 2 STPs in a redundant way and at the same hiercharchy level.

  20. SS#7 Architecture – D Links

  21. SS#7 Architecture – E Links Extended links - E links – can be connected for redundancy and reliability reasons to another pairs of STPs.

  22. SS#7 Architecture – F Links SEP can be providing services to another SEP (data, special processing, data concentration, etc.). Connection is made via Fully AssociatedLinks – F Links.

  23. SS#7 - The Userparts Possible Future extentions.

  24. Mapping OSI-SS#7

  25. The Layered Model • Different networks can share common resources.e.g. “transport mechanism” for signalling • New specific user partse.g. MAP integration afterwards • Easier protocol conversions and encapsulation in different networks, e.g. not just SS#7, but genrally speaking

  26. SS#7 - Userparts OMAP: Operations, Maintenance and Administration Part ASE: Application Service Element TUP: Telephone User Part DUP: Data User Part TCAP: Transaction Capabilities Application Part ISUP: ISDN User Part SCCP: Signalling Connection Control Part MTP: Message Transfer Part

  27. OSI-Primitives

  28. OSI-Primitives - 2

  29. Message Transfer Part MTP level 2 simply monitors and reports to the layer above. It assembles the outgoing messages into packets known as signalling units. MTP level 1 considers the links, the control of clocking, and all of the physical considerations of sending messages over wires. Electrical Design Engineers job. No interest for software designers

  30. MTP level 2 Messages # of bits > Up to 279 bytes packet size Lock on “flag” pattern: 0111110 - zeros at both ends & 1s in the middle. Bit stuffing could be necessary

  31. Bit Stuffing

  32. Byte Stuffing

  33. MTP level 2 Messages Backward Sequence Number (BSN). Backward Indicator Bit (BIB) Forward Sequence Number (FSN) Forward Indicator Bit (FIB) Length Indicator (LI)

  34. MTP 2 - Transmission

  35. MTP 2 – Basic Error Correction

  36. Basic Error Correction • When the packet is received at the transmitting side the difference in the FIB and the BIB trigger a series of actions: • Transmission is stopped. • Messages beginning with FSN #19 are retransmitted in sequence. • Messages which were in the buffer before FSN #19 are deleted. • Transmission begins again

  37. MTP 2 - Frames

  38. SS#7 – MTP level 3 Signalling Network Management (SNM) Signalling Message Handling (SMH) Major part of the job of Level 3 is to control traffic on the traffic resources over which it has control, e.g. congestion, redirection, changeover, changeback

  39. Signalling Network Management • Force Rerouting • Controlled Rerouting • Changeover • Changeback • MTP Restart

  40. Signalling Message Handling

  41. Userparts • SCCP: Signalling Connection Control Part • Sequence control and delivery • ISUP: ISDN User Part • Digital networks • TUP: Telephone Users Part • Analog telephony • DUP: Data Users Part • Data

  42. Architecture

  43. Stack & message coding

  44. ISUP Example

  45. SS#7 - Call Setup • IAM: Initial Address Message • ACM: Address Complete Message - Switch can alert • Off Hook: ANM: ANswer Message - All switches connect the path • Busy: The caller can release - REL - the call setup

  46. SS#7 – Call Release REL – Release - and – RLC – Release Complete

  47. SS#7 - Simple Call Setup

  48. RingBack Tones

  49. SS#7 - More complete Figure

  50. SS#7- IAM Fields

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