Secure Reliable Transport (SRT) is a legacy protocol for low-latency, reliable transport over the Internet based on a file transfer protocol called UDP Data Transfer (UDT). Since its development SRT has been placed in the public domain and it includes the following primary features:
- Two methods for packet loss recovery:
o Retransmission of lost packets (ARQ).
o Reconstruction of lost packets using Forward Error Correction (FEC) techniques.
- Optional Pre-Shared Key encryption, using AES, with key sizes of 128, 192 and 256-bit.
- Uses a single UDP port per flow.
- Roles of sender/receiver are independent of client/server.
- Support for “rendezvous mode”, where, in some very limited situations, devices can connect over the Internet without previous firewall configuration (firewall-dependent).
- Configuration can be negotiated between endpoints.
SRT is known to have lower packet recovery performance than more modern protocols (such as RIST), and is missing important features such as multi-link bonding, seamless switching, multicast support, and authentication.
Cobalt has added full SRT support to the 9992-ENC and 9992-DEC devices, and is planning support for the 9990-DEC. SRT licenses are available as options (one per card) for both the 9992-ENC and 9992-DEC. The devices also support RIST Simple and Main Profile with optional RIST licenses (one per card); SRT is provided for backward compatibility with legacy devices still using the protocol.