Interfacing with Dante and CobraNet Digital Audio Systems
Introduction
Purpose
This document will define the settings and setup needed to properly interface Digital Audio Systems that supports Dante™ by Audinate or CobraNet® by Cirrus Logic with the Tellabs OLT.
Document Number
ENG-010594
Applies To
The Tellabs OLT running software SR30.1 and above.
The Tellabs ONT 140C/W, ONT 180C
The Tellabs Panorama PON EMS running SR30.1 and above.
Digital Audio Equipment
Dante and CobraNet are two different protocol suites that are employed in digital audio equipment that are commonly for distributing audio over ethernet packet networks in large venues. They both require time synchronization for proper operation. They also are very heavy users of multicast for almost all its messaging and streams. This allows all the nodes to stay in sync and audio output to be timewise synchronized.
This document defines how to configure the Tellabs equipment to optimize the Dante or CobraNet Equipment for maximum Scalability and reliable operation.
Key Optimizations Checklist
The following section summarizes the key configurations needed for proper Dante/CobraNet operation on Tellabs GPON:
- Segregation to its own VLAN
- Use of CBR1 (CBRrt) with > 16 Mbps of Bandwidth
- Disable ONT Discovery on PONs with Digital Audio Active
- Change PTP responses to Unicast on Dante
- Primary and Secondary timing sources should be above the OLT.
- Manage CBR bandwidth based on network needs
- Mark digital audio traffic with high priorities
Multicast In OLAN
OLAN systems are optimized for downstream IP multicast (Network Interface to ONT UNI direction). Multicast is less efficient when sent in the upstream direction. Within the PON where multicast is sourced, copies must be sent to ONT UNIs on that PON that are on the Dante VLAN. Many of the optimizations stated below attempt to minimize individual copies of multicast packets that need to be sent within a PON when a source is sending multicast upstream. These optimizations work for Dante due to the fact Dante uses IP multicasting. However, for CobraNet systems, multicasting is not performed using IP and as a result, the OLAN IP multicasting optimizations will not be utilized.
Segregation to Its Own VLAN
It is required that audio equipment be segregated into its own VLANs. If both Dante and CobraNet are used, they must both be on separate VLANs. This minimizes wasted bandwidth by sending multicast packets to ONT UNI ports that are not involved in digital audio protocols. This also isolates the digital audio system to its own network, which is good security practice.
Use of CBR1 (CBRrt) Class of Service
Dante
The Dante protocol makes heavy use of the PTP (Precision Time Protocol) packet-based timing scheme. This protocol has fairly tight timing requirements, and it is necessary to use the CBRrt Class of service to get real-time jitter and delay performance needed by Dante. All Dante ports should be configured with a Service Profile like the one shown below.
CobraNet
Like Dante, the CobraNet protocol makes heavy use of a timing protocol with tight timing constraints. Again, the use of the CBRrt Class of service is necessary to achieve the jitter and delay performance required for CobraNet. All CobraNet ports should be configured with a Service Profile like the one shown below.
The following settings are required within the service profile for Dante:
- Service Type: Bridged N:N
- IGMP Proxy:
- Dante: Check to enable IGMP proxy. This optimizes multicast performance for IP protocols.
- CobraNet: Do not enable IGMP proxy because CobraNet does not use IP multicast.
- Class of Service: CBR1 (CBRrt), CBR Real Time minimizes upstream delay and jitter.
- Upstream Sustained Rate: 16128 or higher, ensures PTP packets are never delayed.
- 802.1P Marking Mode: Static
- Marked 802.1P Priority: 7, this ensures Dante traffic gets priority over other traffic.
Remain Aware of CBR Impact to PON Bandwidth
To ensure proper operation of PTP due to jitter on the upstream CBR1 CoS is required. This also has implications on the upstream GPON bandwidth of the link. The number of digital audio devices on the PON restricts the bandwidth available to other applications.
Disable ONT Discovery on Dante/CobraNet PONs
The OLT periodically polls for new ONTs. This leaves a "quiet" window where no devices other than new ONTs can transmit. This puts a gap in transmission which can jitter the Dante or CobraNet clocks.
The OLT MUST be deployed with ONT discovery disabled on Dante/CobraNet-enabled PONs. This profile should only be placed onto the PON after all the ONTs have been discovered. This profile should only be placed onto PONs with Dante or CobraNet equipment on them.
The user can assign the profile via the Ports->PON Tab. Multiple PONs can be assigned by selecting the desired ports and using Profile and Admin State to do assignment of the profiles.
If the user needs to add new ONTs to Dante/CobraNet PONs, apply a profile with Discover Unexpected ONTs checked as shown below.
Dante Unicast Delay Requests
The Dante Devices should be configured to Use Unicast Delay Requests. This will change the Delay Request/Delay Responses of PTP to Unicast messages. This will minimize the number of multicast messages replicated on PONs. This is configured by clicking on a device in the menus, then going to the Clocking Option group and changing the Unicast Delay Requests setting to Enabled.
Timing Source Above the OLT
Dante
The Dante devices need to elect a device as timing source. This can be influenced by the configuration of the Timing Master. Placing the timing source above the OLT (or perhaps placing the timing source for OLT A’s Dante devices on OLT B) ensures that the PTP has the minimum jitter/delay and minimizes the replicated Multicast within the system. It is recommended that the timing source for Devices on an OLT always be above that OLT.
CobraNet
The CobraNet Conductor provides the nominal clock source to the network. For best performance, the CobraNet Conductor, which is often the system controller, should be placed above the OLT. This ensures minimum jitter/delay under normal operation. In the event of a Conductor failure, the CobraNet system will still operate with another device assuming the backup Conductor role.