UC trunking implementation guide


Derrick Tanzini


Configuring your platform for our service

Bandwidth has multiple geographically redundant signaling proxy facilities in the United States. This section gives guidance as to how to set up your service and what should be expected.

IP Information

Bandwidth employs a mated pair of IP proxies for signaling redundancy. Please ensure that either can be accessed for the purpose of redundancy.

To obtain the specific IPs, please reach out to your Implementation Specialist, if you're currently working with one. If not, please open a support ticket.

  • For Origination (inbound), please ensure that both IP addresses are white listed as signaling could originate from either proxy.
  • For Termination (outbound), please ensure that both IP addresses are configured for outbound traffic in the event that one is offline.

No Registration

Bandwidth doesn't support REGISTRATION. It's required that the customer provide a Public Static IP Address for Bandwidth to send calls to. For the customer to send Bandwidth calls, the user needs to provide the Public Static Address. After a registration method is sent, Bandwidth may return a 200 OK message (but this is not guaranteed).


Bandwidth will only allow signaling via the SIP method encompassing the following RFCs (if any other protocol is sent, calls won't setup). 

Ports to be Opened

Many customers require that their PBX be protected by a firewall. The user needs to check with their firewall manufacturer for compliance. The Firewall must have the ability to 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 to 64,000 – must be opened (ALG) for audio
    • Bandwidth uses multiple IPs to allow media from its gateways.


Bandwidth SIP trunks have certain attributes such as DTMF, Dial Plans, Codecs, Signaling Protocol, and IP Protocol.  


Dual-tone multi-frequency signaling is used for detecting dialed digits over the SIP connection, either outbound or inbound. Bandwidth supports in-band or out-of-band DTMF outlined in RFC 2833.

Dial Plans

Bandwidth supports only E.164 for outbound and inbound calling.


This is the recognized International standard. It's characterized by a “+” followed by a country code (i.e. “1” U.S.) and then the specific phone number. Some phone systems don't have the ability to support this method. A user shouldn't choose this method unless they are sure of their PBX’s compliance. If this method is chosen, then Bandwidth will be ending all calls into the PBX in this format (TO: FROM: RPID: CONTACT:). Bandwidth will also expect that calls are sent back to them in this method.  

  • Example Local & Long Distance: +19192971100  
  • Example International: +4402074942020

IP Protocols

Bandwidth requires that all SIP and Audio be delivered via UDP. TCP won't be accepted or delivered by Bandwidth. The UDP packets must be no larger than 1350 bytes. If a user sends UDP packets bigger than this, a “Message Size Too Big” error will keep the call from completing.

Codecs Supported

Bandwidth supports 2 codecs to date: G.729a and G711mulaw. Inbound calls to Bandwidth CLEC numbers will also support ILBC.


Bandwidth SIP trunks utilize SIP features like; Inbound Caller-ID, Outbound Caller ID, Call Transferring, Conference Calling and Forwarding in very specific ways.

Caller ID In/Out

Bandwidth SIP uses the FROM field to represent the caller ID name and number & call rating. If a Remote-Party ID field (RPID) is included in the SIP INVITE message, the RPID will be used for caller ID and for call rating. The “From” field and the RPID must be in a 10-digit format. Note: P-Asserted-Identity and Privacy headers are also supported.

  • Example <<FROM>>
  • Example <<TO>>
  • Example <<RPID>>

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