RAVENNA

showstack / protocols / ravenna

Also called RAVENNA/AES67.

ALC NetworX's audio-over-IP technology built on RTP media streams, PTPv2 clocking, DNS-SD discovery and RTSP connection management. It is common in broadcast infrastructure and Merging Technologies recording systems, and it carries AES67 as a subset.

Audio transportProprietary, documentedALC NetworX GmbHReported

Stewarded by ALC NetworX GmbH, merged into Lawo in January 2024.

Media Large, continuous, on time and in order

Continuous streams that are large enough to be sized properly, and that must arrive in order and on time.

What kills it. Anything that starves the link — usually a management transfer nobody scheduled — and jitter that outruns the receive buffer.

The four flows, and why the model is worth having →

Ports

tcp/8080 HTTP configuration interface
Assignable, with 8080 as the documented default. RTP, RTCP and RTSP ports are all assignable too; RTCP is always the RTP port plus one.

Multicast

RTP streams can be unicast or multicast and the addresses are assigned by the implementation, not reserved by the specification. PTP uses the well-known 224.0.1.129 to 224.0.1.132 and 224.0.0.107 groups.

What it carries

Sample rates: 44.1 kHz, 48 kHz, 88.2 kHz, 96 kHz, 176.4 kHz, 192 kHz, 352.8 kHz, 384 kHz
Audio bit depth: 16-bit, 24-bit, 32-bit
Audio encoding: Linear PCM, L16 and L24, over RTP

Audio: The high rates are the point of RAVENNA and the reason it is not interchangeable with AES67. Anything above 48 kHz, or a packet time other than 1 ms, is outside the subset an AES67-only receiver accepts.

What goes wrong

RAVENNA is a superset of AES67. Two RAVENNA devices can agree on sample rates above 48 kHz or packet times other than 1 ms that an AES67-only receiver cannot accept, so interop needs the stream forced into the subset.

Discovery is DNS-SD, with mDNS only as the fallback where there is no DNS server. A plant running unicast DNS-SD and a device expecting mDNS will not see each other even though both are working correctly.

Connection management is RTSP plus SDP, not SAP. Many AES67 devices only listen for SAP announcements on 9875, which is why converter tools exist to translate between the two.

PTP is IEEE 1588-2008 and RAVENNA supports Default, AES67 and SMPTE ST 2059-2 profiles. Domain number and profile must match across the whole plant, and mismatches present as slow drift rather than as a clean fault.

ALC NetworX recommend static IP addressing and explicitly warn off DHCP. A DHCP lease change mid-show pulls the stream addresses out from under receivers that were told about them in an SDP.

Recommended DSCP is CS6 for PTP event messages and EF or AF41 for RTP, and RAVENNA traffic normally has to outrank VoIP on shared corporate infrastructure. On a default switch config it will not.

What speaks RAVENNA (2)

Product	Direction	Notes
DirectOut PRODIGY.MP DirectOut	bidirectional	Via module.
Luminex GigaCore 16Xt Luminex Network Intelligence	bidirectional	Transported, listed alongside AES67.

Open source implementations

ALSA RAVENNA/AES67 driver — C
aes67-linux-daemon — C++, GPL-3.0-or-later

Typical use

Broadcast studio and OB truck audio infrastructure
Merging Technologies Pyramix and Horus/Hapi recording systems
High channel count and high sample rate studio links
Feeding and receiving AES67 streams from other vendors' networks

Sources

RAVENNA Operating Principles — Draft 1.0 — ALC NetworX primary
RAVENNA Network Requirements V1.4 — ALC NetworX primary
ALC NetworX (introduced at IBC 2010, merged with Lawo January 2024) — RAVENNA Network primary
RAVENNA and AES67 white paper — ALC NetworX primary

Understand the mechanism

Show networks Numbers that stand for signals

Something wrong, or missing?

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