Introduction to RAVENNA Technology.

Overview

RAVENNA is a technology for real-time distribution of audio and other media content in IP-based network environments.
Utilizing standardized network protocols and technologies, RAVENNA can operate on existing network infrastructures.
RAVENNA is designed to meet the strict requirements of the pro audio market featuring low latency, full signal transparency and high reliability.
RAVENNA is suitable for deployment in many pro audio market segments including broadcast, live sound, studios, the install market and location music recording.
Possible fields of application include (but are not limited to) in house signal distribution in broadcasting houses, theaters, concert halls and other fixed installations, flexible setups at venues and live events, OB van support, interfacility links across WAN connections and in production &
recording applications.
In short, it represents a new take on the third generation form of audio interconnect, where the first generation of interconnect is analogue point-to point copper, the second generation uses digital codes representing the analogue signal, conveyed point to point over copper or fibre-optic cabling and the third generation also employs digital codes representing the analogue audio but transported as packets over network infrastructure.
RAVENNA is very well suited to areas where complex audio routing / mixing systems are deployed.
For example;
In-house distribution in broadcasting centres and WAN connections to satellite studios, OB vans, where hook up to venues with the same infra-structure becomes simple, in venues themselves for local signal distribution and connection to just such OB vehicles when required.
For live events and concerts it offers highly flexible temporary installation possibilities and in theatres, opera houses and houses of worship it can provide low cost local signal distribution.
Notwithstanding all of the above, RAVENNA is also an excellent candidate for relatively simple point to point interconnects such as computer to audio interface.
However, RAVENNA, leaving aside the other advantages touted, is an open standard based on the ubiquitous IP protocol.
Specifically, protocol levels on or above layer 3 of the OSI reference model.
Since RAVENNA is purely based on layer 3 protocols, it can operate in most existing network environments.
Unlike layer 1 or layer 2 solutions, it does not, in principle, require its own network infrastructure. IP can be therefore be transported on virtually any LAN and is used as the base layer for communication across WAN connections (including the internet).
Although in most cases Ethernet will be deployed as the underlying data link layer, IP is in general infrastructure-agnostic and can be used on virtually any network technology and topology.
All the protocols and mechanisms used in RAVENNA are based on well established and commonly used methods from the IT and audio industries and comply with various standards defined and maintained by the international standards bodies.

Basic Components

A RAVENNA system requires a carefully configured IP network, a master clock device and any number of RAVENNA enabled I/O nodes.
The master clock can be either a dedicated device or any RAVENNA node capable of serving as a grandmaster.
The preferred time domain reference is GPS.
Simple streaming across a network can be achieved without any synchronization at all but in pro audio applications tight synchronization between all devices and streams is absolutely mandatory.
While playback synchronization in most applications requires sample accuracy, one goal for RAVENNA is to provide superior performance by offering phase-accurate synchronization as an option thus rendering separate reference word clock distribution throughout a facility or venue redundant.

Flexibility

The system design approach allows for operation with or without centralized services for configuration / connection management.
ALC NetworX recommends that basic device configuration (e.g. initial settings and setup of audio streams) should be executed via a web interface (http).
However other methods may be used in addition or as an alternative.
Device discovery is accomplished with DNS-SD (via an mDNS or DNS service). In small networks, without DHCP / DNS servers, the zeroconf mechanism - a fully automatic, self-configuring method - is used for auto-IP assignment and service advertisement & discovery.
Streams available on the network are represented by SDP records with extended information (i.e. a clock domain identifier, RTP time stamp association etc.) Clients can connect to streams via RTSP or SDP/http.

Resilience

As you would expect RAVENNA supports redundancy.
Although modern network infrastructures can be configured to guarantee a high level of transport security and reliable 24/7 operation for added security there is the option of full network redundancy.
Each RAVENNA device can include two independent network interfaces which can be connected to independent physical networks.
By duplicating any outgoing stream to both network links, any destination device will receive the full stream data on both network interfaces independently.
If data from one link is corrupted, or one network link fails completely, the uncorrupted data is still present on the other link.
Changeover in the event of the failure of a network link is automatic.

Streaming

Unicast

Unicast (one-to-one) is used in application scenarios such as an individual stream between two devices (e.g. a multi-channel stream between a console and a recorder/DAW).
This uses a point-to-point connection between the sender and receiver.
Since each additional receiver adds its own individual connection network traffic increases with every additional unicast stream.

Multicast

Multicast (one-to-many) streaming is used in scenarios where a single source is to be distributed to many potential recipients (e.g. program stream to journalists' desktops).
At the sending end this only requires one connection per stream.
Network switches are aware which participants (receivers) should receive any particular multicast and forward packets only to registered nodes.
In multicast set-ups the network traffic only increases on the last (closest to receiver node) segment(s) of the network path.

Infrastructure

The network infrastructure must be able to transport IP packets and must support a number of standard operating protocols, e.g. RTP/RTPC for streaming since this is used widely and supports a wide variety of standard payload formats.
Some of these formats are mandatory for all RAVENNA devices, others are optional.
For example this protocol offers the possibility of standard media player applications subscribing to RAVENNA streams.
Synchronization across all nodes is achieved via the IEEE1588-2008 (PTPv2 Precision Time Protocol).
This is another standard protocol which can be used on IP.
PTPv2 provides a means for synchronizing local clocks to a precision as defined in AES-11.
Accurate synchronization can even be achieved across WAN connections when GPS is used as a common time domain.

Quality of Service

For the QoS (Quality of Service) protocol DiffServ has been chosen since it is widely supported by most modern managed switches.
Since other traffic can co-exist with RAVENNA on the same network, RAVENNA traffic must be on the fast track.
RAVENNA packets are assigned a high priority classification to ensure expedited transport across the network, while other packets with lower priority are treated as best-effort traffic.
Even within RAVENNA there are different priorities assigned to different classes of traffic.
Synchronization is assigned the highest priority, immediately followed by any real-time media traffic, while control and configuration traffic will be on a lower priority level.
Any non-RAVENNA traffic would receive the lowest (standard) priority and be treated as best-effort traffic.
Performance and capacity scale with the capabilities of the underlying network architecture.