Understanding AoIP and Livewire+ AES67

Livewire+ AES67 and AoIP Introduction

Livewire+™ AES67 delivers the core operation of Telos Infinity and other Telos products. It is a complete solution to AoIP and as well as providing low latency audio, it also delivers discovery, metadata, and control messages.

The success of IP (Internet Protocol) in part, is because the datagram and data in the IP packet exists independently of the hardware it is transferred on. This is a break from traditional digital audio systems, such as MADI and AES3, as the audio samples are intrinsically connected to underlying hardware and distribution systems. The sample rates are synchronous and a function of the hardware clocks.

Synchronous distribution systems deliver low-latency real-time audio at the cost of flexibility and complexity. Specialist hardware is required to extract and insert audio samples through complex multiplexing solutions. Exchanging control and metadata is possible, but it is complex and relies on dedicated hardware solutions.

Interoperability can soon become cumbersome due to the amount of hardware required and the physical patching needed to distribute the audio. Point-to-point systems demand advanced planning to predict operational demands years ahead. Often this is unachievable and after a short time after an installation is completed, new hardware and patch-cords soon find their way into a control room to solve problems nobody had thought of in the planning stage.

Broadcast Control

Although it is possible to embed control systems into AES3 using spare data bits available in the protocol, expensive bespoke solutions are required, and the signal often only travels in one direction. Broadcast control systems must be reliable and predictable but single direction control-based networks do not provide this level of dependability.

Device control using simplex data paths compromises reliability as there is no reverse path to tell the controller to resend lost or corrupted data. Even if FEC (Forward Error Correction) strategies are adopted, the redundant data needed in the FEC algorithm slows data-throughput and delays response times. And there is still no reverse path to get status information about connected devices, or just some level of assurance that it has successfully executed the control command.

Although IP only sends data packets in one direction, it often operates to combine a send and receive pair to provide bidirectional data transmission. IEEE-802.3i provides transmit and receive over separated data pairs on a twisted-pair cabling infrastructure. Ports on Ethernet switches and IP routers are designed in this way so transmit and receive data is achieved between devices.

Low Latency

Livewire+™ AES67 combines the audio and control data over a single IP path to keep latency between them low and to reduce the amount of cabling required. Multiple audio inputs and outputs, with their control data, are multiplexed over single IT infrastructure cabling using dedicated Axia switches or IT Ethernet switches.

Consequently, audio systems are greatly simplified, and the amount of cabling required is significantly reduced.

With Livewire+™ AES67 nodes, intercom Panels, IP Routers, and Ethernet switches, audio routing systems can be easily built. PC’s and laptops can be easily integrated into the system as they do not require specialist hardware cards or USB interfaces. A Livewire+™ AES67 driver is installed onto the PC or laptop. The driver conducts all the Livewire+™ AES67 discovery and configuration to make the audio channels appear as inputs and outputs to the Windows operating system. Windows Media and VLC players can be used to monitor the audio.

Discovery

The discovery and configuration part of Livewire+™ AES67 is one of its most important aspects of the whole system and makes installation on an IP network simple and easy to achieve.

Livewire+™ AES67 systems use the terminology of sources and destinations to describe inputs and outputs. A source is an audio input to an intercom Panel. It is also available on the network as an audio stream, in effect a multicast stream, so that other intercom Panels or Livewire+™ AES67 nodes can also receive it.

In this aspect it is worth thinking in terms of multicasts as opposed to traditional broadcast inputs and outputs. A multicast consists of a source and multicast address. The multicast address is similar, but not the same as a destination address and is part of the router configuration.

Multicast Streaming

IP control and data exchange generally works using unicast address, that is, there is a source and destination address representing the sender device and receive device. This model works perfectly well for point to point distribution, such as connecting the director’s intercom microphone to a single camera headset. But it becomes more of a challenge when providing one-to-many mapping.

If the director provides open-talkback, multiple intercom Panels and headsets would need to listen to them. Using unicast, each Group of audio samples in the IP packet would need to be sent to each destination. If ten intercom Panels and headsets were listening to the director, each packet would need to be sent ten times, resulting in the Ethernet switch bandwidth requirements increasing by ten-fold. Clearly this is a very inefficient use of resources.

Multicast overcomes this inefficiency by making the Ethernet switch or IP router repeat packets and send them to the ports, and hence the intercom Panels, that require them. Multicast is a layer-3 protocol and is designed to connect routers to facilitate streaming using the IGMP (Internet Group Management Protocol).

IGMP Provision

Although Livewire+™ AES67 and the Telos Infinity telecoms system works perfectly well on layer-2 Ethernet switches, provision must be made for an IGMP server.

To accommodate IGMP on Ethernet switches, a variation called “IGMP snooping” has emerged in the IT industry. IGMP snooping allows Ethernet switches to monitor the messages between the IGMP server and the connected devices. This implies a need for a separate IGMP server, however, many modern Ethernet switches have the IGMP server built into them. The system integrator must confirm their selection of

Ethernet switches will support IGMP with the “Querier” feature enabled. Telos Alliance xNode

Traditionally, layer-2 switches were much faster than layer-3 routers as the routers relied on software to provide the packet forwarding. However, in recent years the difference between them is becoming blurred and many of the forwarding features of IP routers and switching functions of Ethernet switches have been moved to high-speed hardware specific integrated circuits making them very fast and comparable in speed.

Telos Alliance xSwitch Solution

To make configuration easier, Telos offers the Telos Alliance xSwitch. This is an Ethernet switch that provides plug-and-play connectivity for the Telos Infinity Intercom System. It greatly simplifies configuration and includes multicast with full support for IGMP.

The genius with multicast is that the Ethernet switch only streams packets to the ports that require them resulting in better use of resource and network bandwidth. It’s efficient as it only sends packets to intercom Panels that have opted-in to receive the stream. If no Panels or headsets opt-in to the stream, then the switch does not send the audio packets to any of the ports.

The Ethernet switch must know which ports require copies of the streamed source and this is achieved using IGMP. A source is configured to stream the audio IP packets to one of the 248 million reserved IP multicast addresses. The IGMP compliant Ethernet switch runs the IGMP protocol on its processor, to create an IGMP server, and listens for opt-in request messages from destination devices. Once they are received the Ethernet switch copies the IP packets associated with the source to the port destination and hence intercom Panel. This process is repeated for all connected intercom devices.

As an example, if Graphics, VT, and Vision all want to listen to the open talkback provided by the director Panel microphone, they will push-to-listen the Panel button associated with the directors’ microphone. Doing this sends an IGMP message from the Panel to the IGMP server on the Ethernet switch which in turn acknowledges the request and copies the streamed packets from the port connected to the directors’ Panel, to each of the ports connected to the Panels that have requested the stream.

If VT no longer wants to listen to the director and the director contact key is removed, a message is sent to the IGMP server to cancel the stream. The Ethernet switch then stops copying packets to the port associated with the VT Panel.

Periodically, the IGMP server will send messages to each device receiving streams to ask if they still want to receive them. This helps if a Panel is inadvertently disconnected from the network and cannot send a cancel-stream message.

IP Sources and Destinations (Inputs and Outputs)

Livewire+™ uses concept of sources and destinations to route audio on the network. Physical inputs become sources to the network and advertise this information to the Ethernet switch. Destinations are configured with Livewire+™ Channel number or Multicast IP Address. Once configured destinations will request the stream from the Ethernet switch.

Combining digital audio signals, streaming, and control into one IP stream makes the Telos Infinity IP Intercom system both highly configurable and easy to use. All over a single cable to each Panel.\