xlab1 project: SBC requirements

A Session Border Controller as a gateway between back-end vPBX servers and ITSP is needed in the scope of xlab1 project, with the following functionality:

  1. Called and Caller ID normalization:
    • Various SIP trunk providers require different number formats (national, e.164, or some special format)
    • Different customers vPBX’es may require national number formats for different countries
  2. Codec normalization: SIP providers are typically limiting the choice of codecs, and customer vPBX’es may require to support a bigger variety of codecs.
  3. Security: SIP trunk providers may require authorization, and SBC should perform it, screening the global route selection and authorization from back-end systems.
  4. Admission control: ITSP trunk overload should be avoided
  5. Where possible, public VoIP should be used for route selection (enum).
  6. For incoming calls, caller’s name should be looked up if possible (Switzerland).

The following workflow for number normalization is proposed for inbound calls from PSTN:

  1. Trunk-specific procedure translates the Caller and Called ID into e.164 form
  2. Called ID is looked up in internal routing database
  3. Once the internal destination SIP server is selected, the Caller and Called ID are translated into the form required by the destination (typically, national format for a specific country).

For outbound calls originated from back-end servers,

  1. A special SIP attribute, e.g. X-Dialplan-Country is looked up for a country code (“CH”, “DE”, “FR”, …). If found, the Caller and Called ID are translated from national plan into e.164
  2. If the country code is not found, the Caller and Called ID are treated as e.164 numbers
  3. Called ID is looked up in internal routing database. If found, proceed as in the inbound call procedure
  4. Called ID is looked up in public ENUM database(s). If found, send an unauthenticated SIP call with e.164 numbers in To and From fields
  5. Called ID is looked up in the local LCR database. If found and if the trunk is not overloaded, the call is sent to a specific SIP trunk. The Called and Caller ID are translated by a trunk-specific procedure to the format expected by ITSP.
  6. A last-resort ITSP trunk is selected if no other trunks are found.

References:

  1. ETSI TS 184 011: Requirements and usage of E.164 numbers in NGN and NGCN
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