SIP Protocol UDP, TCP and TLS

By default, VoIP calls forwarded over AVOXI's network have been done so through a UDP (User Datagram Protocol) connection. This is the industry standard and the connection type most commonly recommended for VoIP users. However - due to personal preference, familiarity, local restrictions, or business need – some customers would like to have calls forwarded using a TCP (Transmission Control Protocol).  So, what's the difference? 


  • Point A establishes a connection with Point B
  • Point A sends a data packet to Point B
  • Point B receives the data packet, it sends a confirmation to Point A
  • Point A receives confirmation of delivery and delivers the next packet of data
  • If Point A does not receive confirmation from Point B, it resends the packet of data again
  • Repeat from Step 2

This connection type ensures every packet of data is delivered in the order it is sent, regardless of how much time it takes.


  • Point A establishes a connection with Point B
  • Point A sends a data packet to Point B
  • Point A immediately sends the next data packet
  • Point B receives the audio packets from Point A in whatever order they come in. A small percentage of data packets may be lost along the way.

This connection type means some data packets may be lost, but the majority will be delivered as fast as possible. UDP is the more commonly used method for VoIP calls because it is a faster delivery method than TCP. When a packet is lost in UDP connections, it leads to a negligible lag in the audio – but this lag is normally unnoticeable or negligible. Though TCP ensures all the audio packets are delivered in the order they are sent, the additional time it takes to confirm the delivery of every single packet of data may lead to pauses in audio during calls.

TLS V1.2

We support TLS version 1.2 or greater and this only applies to our AVOXI Genius platform and is not compatible with AVOXI Core.  TLS, or transport layer security, protocol is the top and most powerful layer responsible for securing SIP voice and media messages. This protocol uses cryptographic encryption to provide end-to-end security. TLS is best for encryption, authentication, data integrity, and secure SIP trunking in general.  Establishing a TLS connection authenticates both transport endpoints but does not authenticate the SIP messages flowing through the link.

What is AVOXI doing differently? 

AVOXI now allows for TLS/SRTP and TCP connections to be selected as your default connection type when forwarding calls. By default, your VoIP calls will still be forwarded using a UDP connection. If you would like to have your forwarding settings changed to use a TLS/SRTP or TCP connection, please contact an AVOXI representative at

For more information view our informative guide to Secure SIP Protocols: UDP vs. TCP vs. TLS

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