--- "@context": https://schema.org "@type": TechArticle "@id": https://www.twilio.com/docs/sip-trunking/sending-sip-to-twilio-best-practices#article headline: Sending SIP to Twilio - Best Practices description: Ensure efficient SIP integration with Twilio by balancing traffic and preventing overload. Discover best practices for optimal call processing. url: https://www.twilio.com/docs/sip-trunking/sending-sip-to-twilio-best-practices inLanguage: en dateModified: 2026-07-21T11:17:13.000Z author: "@type": Organization name: Twilio Developer Education Team publisher: "@type": Organization name: Twilio --- # Sending SIP to Twilio - Best Practices To ensure that calls sent from a customer's SIP infrastructure to Twilio Elastic SIP Trunking are processed correctly, follow these guidelines: * Traffic should be evenly load balanced across Twilio infrastructure IP addresses. * Traffic should not exceed **30 CPS** sent from a single customer IP to a single Twilio IP. This is to avoid network-level constraints and anti-abuse mechanisms. If your traffic might exceed this rate consider adding more IPs that you are sending traffic from or load balance to multiple Twilio edge locations. ## Elastic SIP Trunk Your Elastic SIP trunk has a unique domain name, such as `mytrunk.pstn.twilio.com`; this is referred to in your Twilio Console as your Termination SIP URI. The request URI (specifically the host part) must contain this domain name so that Twilio can identify your traffic. When targeting your traffic to a specific [Twilio Edge Location][twilio-edge-locations], you have two main approaches: ### Using a localized SIP URI Your Twilio SIP domain comes in a localized version, `mytrunk.pstn.[edge].twilio.com`, for example `mytrunk.pstn.ashburn.twilio.com`. Using this domain is simple but may be less flexible since the same name is used for identifying your trunk as well as controlling where traffic is routed. Specifically there may be limitations on how your server is able to load balance traffic across Twilio IPs. All Twilio customer SIP domains resolve to the same A DNS record, which means customers share the same Twilio SIP endpoints. These A records provide all IPs in random order, but it is up to your SIP server to load balance across all of them. This behavior will vary by vendor and In many cases only the first IP is used which would not produce the expected load balancing. ### Using your SIP URI and an Outbound Proxy or Route Header A more reliable approach for predictable load balancing is to configure your SIP server with both your personalized domain name and an "Outbound Proxy" or Route header set to one of Twilio's generic localized edge domain names. These domains offer NAPTR and SRV records (see [RFC 3263][rfc-3263]). The DNS names for these records are `pstn.[edge].twilio.com`, for example `pstn.ashburn.twilio.com`. These records resolve to the same IPs as the personal localized SIP Trunk domain name, but supported SIP servers can query the SRV record for additional load balancing information. To be able to use this option, your SIP server still has to use your personal trunk domain name in the Request URI. You can do this by specifying the generic localized DNS as the "Outbound Proxy" in your configuration. The exact name might vary and might include configuring a Route header or similar. Consult your vendor's manual for details. Example configuration: * Request Domain: `mytrunk.pstn.twilio.com` * Outbound Proxy/Route: `pstn.ashburn.twilio.com` ## Example DNS Records The following examples are DNS queries for the A record of the localized domain as well as the NAPTR and SRV of the proxy domain. Examples are from US East, Ashburn. ```console title="Query A, SRV, and NAPTR records for the Ashburn edge" dig +short mytrunk.pstn.ashburn.twilio.com 54.172.60.0 54.172.60.1 54.172.60.3 54.172.60.2 dig +short SRV _sip._udp.pstn.ashburn.twilio.com 10 10 5060 public-sip0.ashburn.twilio.com. 10 10 5060 public-sip1.ashburn.twilio.com. 10 10 5060 public-sip2.ashburn.twilio.com. 10 10 5060 public-sip3.ashburn.twilio.com. dig +short NAPTR pstn.ashburn.twilio.com 10 10 "S" "SIP+D2U" "" _sip._udp.pstn.ashburn.twilio.com. 20 10 "S" "SIPS+D2T" "" _sips._tcp.pstn.ashburn.twilio.com. 20 10 "S" "SIP+D2T" "" _sip._tcp.pstn.ashburn.twilio.com. ``` [twilio-edge-locations]: https://www.twilio.com/docs/global-infrastructure/edge-locations [rfc-3263]: https://datatracker.ietf.org/doc/html/rfc3263