Inbound calling integration guide


Derrick Tanzini


Bandwidth has multiple geographically redundant signaling proxy facilities in the United States. Here are the specifications and details as to what you should expect:

SBC (Session Border Controller) IP information

Bandwidth employs mated pairs of SBCs for signaling redundancy. For Inbound Calling services, please ensure that both IP addresses are configured for inbound traffic in the event that one SBC is offline. Your implementation specialist will provide these during the onboarding kick-­off call or via the welcome email. 

SIP (Session Initiation Protocol)

Bandwidth SIP signaling protocol is designed for RFC3261. If any other method is used, calls will fail to set up.

Allowed ports for media/audio

If your PBX is protected by a firewall, you'll need to verify the manufacturer compliance to ensure the firewall can act as either a SIP ALG or a Back-­to-­Back User Agent (B2BUA). The following ports are required to allow for full 2-­way audio:

  • UDP port 5060 – must be opened to support SIP signaling.
  • UDP ports 1024-­64,000 – must be opened either statically or dynamically (ALG) to allow for audio path.
  • Bandwidth uses multiple IP addresses to allow media from its gateways.


The following attributes are allowed within Bandwidth SIP trunks:

  • DTMF
  • Dial Plans
  • Codecs
  • Signaling Protocol
  • IP Protocol
  • Media Anchoring

Supported DTMF

Bandwidth supports both in-­band and out-­of-­band DTMF outlined in RFC2833.

Dial plans

Bandwidth supports E.164 for inbound calling only. This is an internationally recognized standard characterized by a "+" followed by the country code and the phone number. For example:

Local and Long Distance: +19192971000

International: +4402074942020

IP protocols

Bandwidth requires that all SIP and audio be delivered via UDP, in packets no larger than 1350 bytes. TCP isn't supported. 

Supported codecs

Codec list choices:

  • G711ulaw, G729a, ILBC (will default to ptime 30)
  • G711ulaw, G729a (will default to ptime 20)

Call concurrency limits

Please open a ticket with your Bandwidth Support Team to determine what the appropriate call concurrency limits are. If you reach your call concurrency limit, you'll receive a 503 – Service Unavailable or 486 – Busy Here Signal message.

Supported caller ID / privacy types

  • FROM field – default option for caller ID name, number and rating.
  • RPID (Remote Party ID) – secondary option
  • P-­Asserted ID – supported option
  • Privacy Headers – supported option 

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