Basics of SIP over UDP, TCP, & TLS

Sip Over UDP, TCP, & TLS (The Transport Layer’s)

Are your SIP calls transmitted securely? To find out, check how your calls are being transported. There are three common protocols used in SIP: UDP, TCP, and TLS. Each protocol has a use-case, which don’t always include security as a priority. Let’s take a deeper look at the differences between these three SIP protocols.  

User Datagram Protocol (UDP)

UDP, or user datagram protocol, is the default layer for VoIP applications because of its excellent delivery speeds. This protocol provides only the essentials needed to transport voice and media messages, rapidly and efficiently moving these packets between hosts. UDP is good for speed and efficiency. 

How Does UDP Work? 

  1. Gathers data, adding unique header information to the packet. Data consists of origination and termination ports, packet length, and checksum. 
  2. UDP packets (datagrams) are condensed into IP packets and moved to their destination.

Transport Control Protocol (TCP)

TCP, or transport control protocol, provides users with reliable voice and messaging delivery across the Internet. This protocol is responsible for delivering the packets in a specific order, regardless of how long it takes. TCP is great for reliable packet delivery. 

How Does TCP Work? 

Configuring TCP uses a three-way handshake between the client and a server. It’s composed of three messages that enable endpoints to synchronize (SYN) and acknowledge (ACK) each connection property, including port addresses.

  1. The client selects a sequence number (SYN).
  2. The server selects its own sequence number and acknowledges the clients’ sequence number (SYN/ACK).
  3. The client acknowledges the server’s number (ACK).

Transport Layer Security (TLS)

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. 

How Does TLS Work? 

Like TCP, TLS begins with a handshake:

  1. The protocol initiates parties to negotiate a shared encrypted key code between the client and server.
  2. It permits both endpoints to authenticate themselves and verify who they say they are.
  3. With its own framing mechanism, the protocol inscribes each message with an authentication code to ensure message integrity and authenticity.