Manual
86
Comrex codecs (and many other brands) have a set of protocols that allow easy IP connecons between units. In general,
when connecng between Comrex hardware, it’s best to use these proprietary modes to take the most advantage of the
features of the product.
However, many users are concerned about geng “locked in” to a certain codec brand. Because of this, an internaonal
commiee was formed by the European Broadcast Union called N/ACIP to hammer out a common protocol to
interconnect codec brands. This commiee resulted in the establishment of EBU 3326, a technical document which
determined standards for codec compability.
EBU 3326 by and large establishes a set of features each codec should support, and then leaves most of the heavy liing
to other, previously agreed upon standards like SIP (IETF RFC 3261). Topics not yet covered by EBU 3326 include things
like carrying ancillary data and contact closures from end-to-end, codec remote control and monitoring, and complex
NAT traversal, which at this point are sll le to the individual manufacturer’s discreon. This is why it’s best to sck to a
single codec vendor and their proprietary protocols.
The Tech 3326 document denes several mandatory encoding algorithms, and the transport layer that could be used
on them for compability. However, the most complex part of the standard was the decision on how to arrange Session
Inializaon, which is the handshake that takes place at the start of an IP codec call. The most commonly used protocol
for this is called Session Inializaon Protocol, or SIP. This is used extensively by VoIP phones and therefore was a logical
choice. SIP carries the advantage of making NX compable with a range of other non-broadcast products, like VoIP
hardware, soware, and even mobile phone apps.
NX does not fully comply with EBU 3326, as it does not feature the mandatory MPEG Layer II codec. Aside from this, NX
has been tested to be compable with several other manufacturers’ devices using encoders supported by both products.
When using mode (this is how the user interface describes EBU 3326), ancillary data, contact
closures, Switchboard TS, Mul-streaming, and Mulcasng are not supported. Outgoing call proles built with the EBU
3326/SIP channel may lack some advanced opons, and cannot be set for dierent encoders in each direcon (i.e. EBU
3326/SIP calls are always symmetrical).
A funcon of placing a SIP-style call is the ability to register with a SIP server. This is a server that exists somewhere on
the network, usually maintained by a service provider. Several free servers exist that can oer registraon like
.
NX allows EBU 3326/SIP calls to be placed or received with or without registraon on a SIP server. If registraon is not
enabled, connecons are made directly to the compable device by dialing its IP address, just like in mode.