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Ref: https://www.3cx.com/docs/centurylink-business-sip-trunk/
I received some Pre-installation info from Level3/CenturyLink regarding setting up a new SIP trunk service. They have some "Key Considerations" for configuring the service and I wanted to make sure what I'm reading from 3CX is still current and correct.
Here's a excerpt from Level3:
Level 3 SIP Trunking Interconnect:
1. Level 3 will only send E. 164 formatted number in INVITEs sent to your equipment. Ex: +13035551212
2. Your equipment must send 10, 11 or E. 164 formatted digits to Level 3. Seven digit dial plans are unsupported.
3. Level 3 requires that your equipment be provisioned to always use the RTP IP Address provided in the SDP messages for
each call. NATs are unsupported.
4. Level 3 uses the IP Port range 5000-28998 for RTP (even numbers) and RTCP (odd numbers) when using public access and
6000-38000 when using VPN access. If you use a firewall, you will need to allow these ranges as appropriate. Non– SIP
aware NATs are unsupported.
5. Level 3 will always send RTP to the address indicated in SDP we receive. RFC 1918 private IPs are only supported when using
VPN transport. NATs are unsupported.
6. Private IPs in SIP headers are only supported with IP-VPN transport.
7. Level 3 recommends a Diversion Header on all forwarded calls that includes the original called number in compliance with
rfc5806. Various problems may occur if Diversion is not included when forwarding calls.
8. The SIP REFER method is unsupported.
9. Level 3 does not send SIP OPTIONS. If SIP OPTIONS are sent to Level 3, we will respond with a 405 Method Not Allowed.
10. Registration is unsupported.
11. Digest authentication is unsupported.
12. A maximum of six sockets are supported with SIP/TCP. Socket reuse is required.
I received some Pre-installation info from Level3/CenturyLink regarding setting up a new SIP trunk service. They have some "Key Considerations" for configuring the service and I wanted to make sure what I'm reading from 3CX is still current and correct.
Here's a excerpt from Level3:
Level 3 SIP Trunking Interconnect:
1. Level 3 will only send E. 164 formatted number in INVITEs sent to your equipment. Ex: +13035551212
2. Your equipment must send 10, 11 or E. 164 formatted digits to Level 3. Seven digit dial plans are unsupported.
3. Level 3 requires that your equipment be provisioned to always use the RTP IP Address provided in the SDP messages for
each call. NATs are unsupported.
4. Level 3 uses the IP Port range 5000-28998 for RTP (even numbers) and RTCP (odd numbers) when using public access and
6000-38000 when using VPN access. If you use a firewall, you will need to allow these ranges as appropriate. Non– SIP
aware NATs are unsupported.
5. Level 3 will always send RTP to the address indicated in SDP we receive. RFC 1918 private IPs are only supported when using
VPN transport. NATs are unsupported.
6. Private IPs in SIP headers are only supported with IP-VPN transport.
7. Level 3 recommends a Diversion Header on all forwarded calls that includes the original called number in compliance with
rfc5806. Various problems may occur if Diversion is not included when forwarding calls.
8. The SIP REFER method is unsupported.
9. Level 3 does not send SIP OPTIONS. If SIP OPTIONS are sent to Level 3, we will respond with a 405 Method Not Allowed.
10. Registration is unsupported.
11. Digest authentication is unsupported.
12. A maximum of six sockets are supported with SIP/TCP. Socket reuse is required.