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TDC 461: Basic Telecommunications

TDC 461: Basic Telecommunications. DePaul University 17 April, 2001 LoriLee M. Sadler. Agenda. Key Systems PBX Centrex Traffic Engineering Voice Processing. Does Everyone Talk on the Phone at Once?. Lines vs. Trunks Why not business lines for large business? How to share? PBX

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TDC 461: Basic Telecommunications

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  1. TDC 461: Basic Telecommunications DePaul University 17 April, 2001 LoriLee M. Sadler

  2. Agenda • Key Systems • PBX • Centrex • Traffic Engineering • Voice Processing

  3. Does Everyone Talk on the Phone at Once? • Lines vs. Trunks • Why not business lines for large business? • How to share? • PBX • Key Telephone systems

  4. Key Telephone Systems • Key System Unit (KSU) ties many multi-line sets into a set of C.O. lines. (generally assume 3 station sets to 1 business line) • User selects outside line by pressing corresponding line button on key set.

  5. Typical Key System Features • Call Transfer • Call Hold • Conference Calling • Consultation Hold • Put one party on hold while talking to another • Speed dialing • Intercom calling between key sets • Speakerphones / Hands-free calling • Automatic Call Information Recording

  6. A Call using a Key SystemFrank calls Sam in New York • Frank picks up phone, hits LINE #2 button • Key system connects set to C.O. line #2 • Frank hears dial tone from the C.O. • Frank dials 1-212-894-6622.

  7. A Call using a Key SystemFrank calls Sam in New York • C.O. routes call to New York, rings Sam’s phone. Sam answers phone. • Frank and Sam talk for a while

  8. A Call using a Key SystemFrank calls Sam in New York • Frank decides to consult with Jane • Frank hits HOLD button - Key System puts current call to Sam on hold. • Frank hits INTERCOM button and dials Jane’s set number

  9. A Call using a Key SystemFrank calls Sam in New York • Jane hears a special intercom ring • Jane and Frank talk

  10. A Call using a Key SystemFrank calls Sam in New York • Frank hits LINE #2 button again and now talks with Sam again.

  11. A Call into a Key SystemJoe calls Frank • Joe picks up phone, dials number associated with LINE #2 of Frank’s Key System

  12. A Call into a Key SystemJoe calls Frank • C.O. rings LINE #2 connected to KSU • KSU sends ringing signal out to all phones programmed for access to LINE #2

  13. A Call into a Key SystemJoe calls Frank • Frank answers phone and talks to Joe

  14. Private Branch Exchange (PBX) • PBX is a true intelligent switching system. • Provides local switching between station sets or access to C.O. Users dial access code (like ‘9’) to get C.O. service. • Provides advanced intelligent features to users. • Costs approximately $750-$1000 per station set

  15. PBX FeaturesNot available on Key Systems • Private Dialing Plans • 4-digit, special prefixes for WATS, FX, etc. • Automatic Route Selection • PBX collects dialed digits and intelligently decides how to route this call for lowest cost • Over FX line • Over WATS trunk • Over DOD trunk

  16. PBX FeaturesNot available on Key Systems • Voice Mail • Automatic Call Distribution (ACD) • Routes incoming calls (usually INWATS) to the best station set and location • Voice Response Unit (VRU) • Provides recorded messages and responds to touch-tone requests from callers

  17. PBX FeaturesNot available on Key Systems • Class-of-Service • Authentication Codes • Data Services

  18. A Call using a PBXFrank calls Sam in New York • Frank picks up the phone and gets dial tone from the PBX. • Frank dials 9-1-212-894-6622. • PBX consults routing tables, determines that this call should go over the FX trunk to New York

  19. A Call using a PBXFrank calls Sam in New York • PBX sends dialed number over FX trunk, dropping area code (sends “894-6622”). • Call to New York is completed. Frank and Sam talk.

  20. A Call into a PBXJoe calls Frank • Joe picks up phone. • Dials Frank’s public number • 1-312-362-6587 • C.O. chooses trunk to PBX (could choose ANY trunk).

  21. A Call into a PBXJoe calls Frank • C.O. sends OFF-HOOK signal to PBX over the trunk • PBX sends WINK-BACK signal to C.O. • C.O. sends last 4 digits - “6587” (this is a DID trunk).

  22. A Call into a PBXJoe calls Frank • PBX looks into its station address table and determines that “6587” corresponds to Frank’s station set. • PBX rings Frank’s station set.

  23. A Call into a PBXJoe calls Frank • Frank picks up telephone handset. • PBX sends ANSWER signal back to C.O. indicating that the call has been answered • Frank and Joe talk

  24. PBX Trunk Signaling • 1-way trunks: A call can only be initiated from one end (incoming or outgoing). • 2-way trunks: A call can be initiated from either end of the trunk (PBX or C.O.)

  25. PBX Trunk Signaling • Trunk signaling for PBX trunks: • Loop start : Like subscriber loop. • Ground start : Either side can ground a wire to initiate a call. Better control than loop start. • E&M : Separate wire pair used for signaling.

  26. PBX Trunk Types • CO Trunk (1-way outgoing) • Standard switched service. • WATS (1-way outgoing) • Switched service to limited geographic area. • INWATS (1-way incoming) • Trunk for incoming 800 number calls.

  27. PBX Trunk Types • DID (Direct Inward Dial) Trunk • 1-way incoming trunk • CO sends dialed number after call connect so PBX can automatically ring station. • DOD (Direct Outward Dial) Trunk • 1-way outgoing trunk • PBX repeats dialed number to C.O.

  28. Least Cost Routing • => • Rationale • How to get it:

  29. Centrex • Centrex is a service that imitates all PBX features at the C.O. • Private dial plans, special features, etc. are all available at a cost from your local telco.

  30. Centrex AdvantagesCompared with PBX system:

  31. Centrex DisadvantagesCompared with PBX system: • Customer has less direct control • Centrex may be more expensive if most calls are internal (between phones on PBX)

  32. Voice Processing • Automated Attendant • Automated Call Distribution • Voice Mail/Messaging • Interactive Voice Response

  33. Inputs • DTMF • Voice

  34. Automated Attendant • Enables technology to handle repeated requests for same information • Examples • Daytime, weekend, and evening dialogs

  35. Automatic Call Distributor • Purpose • When to use • How it works • What it does

  36. Configuration • Standalone— • As a peripheral • Centrex

  37. Benefits

  38. Messaging • Generally referred to as voice mail • Provides message taking and retrieval services • Broadcast • Many new voicemail systems have similar functions as e-mail: Mailing groups, message forwarding, message reply, etc.

  39. Configuration • Standalone system • PBX Integration • Vendors • Provisioning (trunking) • Storage Capacity

  40. Benefits of Messaging Systems

  41. Interactive Voice Response • Also known as Voice Response Unit (VRU) • Applications • PIN • Other peripheral combinations

  42. Benefits of IVR

  43. How much bandwidth do you need?

  44. Traffic Engineering • The process of modeling call traffic patterns in order to provide facilities and infrastructure to meet call demands. • Goal is to serve the maximum number of callers at a single point in time (generally a 1 hour period)

  45. Metrics • Busy hour • Overbuild

  46. Collecting Data • Telephone bills • 800/888 inbound calls. • Telephone bills for all outgoing calls.

  47. Other Data Sources • Call processing time: • Traffic reports from PBXs, ACDs, and voice mail systems • Busy study:

  48. Tools for Analysis • Erlang B: Developed in early 1900s. Assumes that some alternative to a busy signal is available, even if alternative is more expensive. Effective at calculating call completion and attempts on DOD. No queuing. • Extended Erlang B: No alternate route assumption. No queuing. • Poisson: Assumes even load over a group of circuits. Not very sensitive

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