CobraNet network design

Definitions

Ethernet

Network standard of communication for Local Area Networks (LAN). There are several types of Ethernet for both speed (10Mbps, 100Mps, 1Gbps) or physical medium (Twisted pair, Fiber, Coaxial).

CobraNet network

CobraNet is a combination of hardware, software and protocol which distributes many channels of digital audio over fast Ethernet. CobraNet uses standard Ethernet packets and network infrastructure.

CobraNet interface

All Biamp products carry the CM1 CobraNet interface, a module allowing buffering of audio into Ethernet packets (CobraNet output) and vice versa, Ethernet packets to digital audio signals (CobraNet input).

Bundle

Refers to the basic CobraNet audio transmission unit. A bundle typically carries 8 audio channels. The AudiaFlex DSP platform supports flexible bundles ranging from 1 to 8 channels.

Unicast bundle

Supports a one to one (1 source and 1 destination) routing of audio on the network. Unicast bundle numbers range from 256 to 61439.

Multicast bundle

Supports a one-to-many (1 source but multiple destinations) routing of audio to the network. Multicast addressing consumes network bandwidth and usage. It is recommended that you do not have more than 4 multicast bundles on a switched network. Multicast bundle numbers range from 1 to 255.

Network latencies

Three deterministic network latencies, resulting from the buffering of Audio into Ethernet packets, are available for setup on a CobraNet network: 5-1/3, 2-2/3 and 1-1/3 ms.

Auto-negotiation

Process during which one device tells another device if it is capable of Full/Half duplex and determines connection rate (10/100/1Gbps). CobraNet interfaces and many network devices undergo this process.

CobraNet conductor

The interface supplying the master clock. There is only one conductor per network, the conductor is the device which has the highest conductor priority. Multiple devices may share conductor priority level (a value defined between 1 and 255) but only one device will elected as the conductor. In situations where a network has been oversaturated with CobraNet data it is possible for multiple Conductor instances to appear, causing jitter, crackle, and noise issues. Conductors can be identified in CobraNet Discovery "Disco" software and in Wireshark using the display filter "eth.dst == 01:60:2b:ff:ff:00".

CobraNet in numbers

CobraNet interface channel count:

32x32 I/O channels are available at 5-1/3ms and 2-2/3ms latency.

A total of 32 channels (e.g.32x0, 16x16, 24x8...) are available at 1-1/3ms latency when using fixed 8-channel bundles.

CobraNet network channel count:

64x64 channels (for total of 128 channels) over a single 100Mbit link.

Greater channel capacities are possible over a Gigabit link.

Cable run distance limitations: 100m for CAT5/6 or 2km for multimode fiber

Sample rate: 48kHz

Resolution: 20 bits

Conductor priority: Biamp Audia = 48; Biamp Tesira = 245; Biamp EXPI, EXPO, Vocia = 32

Latency: Audia and Tesira CobraNet latency is user defined, fixed at 1.33ms, 2.66ms, or 5.33ms. Vocia is always 5.33ms.

System design guidelines

When designing CobraNet networks, remember the following simple requirements:

Provide a dedicated switched network infrastructure for CobraNet. It will prevent possible network dropouts or failure triggered by other Ethernet data. The network must be operating, at a minimum, over industry standard Fast Ethernet (100BaseTX/FX).

Use quality switches only (from proven manufacturers). Hub based repeater networks limit performance and the minimal cost difference between a switch and a hub does not justify using hubs anymore.

Installation guidelines

Network performance

Poor quality of the cable plant, EMI and RFI susceptibility, and pull force or bend radius are all factors that could degrade network performances. Pay attention to these factors to improve the quality of your CobraNet network and prevent data packet loss.

Device to device connections

Audia family CobraNet ports do not support auto-MDIX. If two Audia family CobraNet endpoints (AudiaFlex, EXPI, EXPO, etc.) are connected directly to one another it requires the use of a crossover Cat-5 cable. If a switch is placed between the devices straight-through Cat-5 cables should be used.

Tesira SCM-1 cards do support Auto-MDIX and can be connected directly to an Audia device CobraNet port with a straight-through cable. The Tesira port will auto-detect the need to cross-over and do so.

Basic block

Besides gain, mute, and phase settings, the dialog box of a typical CobraNet I/O includes bundle type (Unicast/Multicast), bundle number and an enable toggle button. Latency setting needs to be configured for the system in the Equipment Table. (The default latency can be set in Tools > Options > Compile).

EXPI / EXPO

If connecting EXPI/EXPO units to an AudiaFlex frame, remember to manually specify the latency settings and bundle number with the scroll wheel on the front panel of each EXPI/EXPO unit. Remember to double check the bundle assignment.

Flexible bundles and network latency

Although flexible bundles allows the reduction of the size of a typical CobraNet bundle (8 channels), there are also limitations.

The following table (also available in the System Network Consideration of the Help file) summarizes limitations of the CobraNet interface and their corresponding network latencies when using flexible bundles. Note for example that the interface will only be able to send and receive 16 x 1 channel bundles as a maximum.

Implicit vs explicit CobraNet bundles

Two types of CobraNet bundles may be used by the DSP platform:

• Explicit links: CobraNet bundles manually set by the designer when using the CobraNet input/output block.
• Implicit links: CobraNet bundles automatically configured by the compiler during compilation. They typically appear as a blue dotted line on your design and do not require any bundle assignment. Implicit CobraNet links use unicast private bundles that are not accessible to users or any CobraNet enabled product. They are a key advantage of the AudiaFlex platform; allowing one-page, multi-unit system design without the hassle of setting up manual links.

Compiling process and CobraNet information

Once compilation is successful, useful information becomes available to the designer.

• Implicit CobraNet links are displayed in the configuration design file with a blue dotted line.
• Latency settings are shown in Tools > Layout Compile Results... or immediately after compiling the system. It's good practice to confirm that you have the expected settings. Latency settings are changed in the Equipment Table.

• The CobraNet Link info (Tools > Options > Compile > “Display CobraNet Info”) of the Layout Compile Results indicates the total number of transmitted (TX) and received (RX) channels on a per unit basis. This allows one to quickly evaluate the resources and limitations of the current CobraNet configuration.

Managed switches

Basic network switches suffer from a number of issues:

• Single point of failure, e.g. if one link becomes faulty, the network may be partitioned
• No management solution available for network flooding
• Bandwidth choke points when excessive data traffic is forced down a single link

To combat these issues, the following tools have been implemented in managed switches:

• Spanning Tree Protocol (STP) maintains the active links of the network as a tree while allowing physical loops for redundancy. If available, enable STP to prevent loops from occurring on the network and allow the STP algorithm to figure out a new route in case of link failure.
• Virtual LAN (VLAN) are logically independent networks that allow the designer to segment a network without physically re-arranging it. They may be used with CobraNet networks to allocate dedicated bandwidth requirements on a shared network. Setting up a VLAN requires advance networking skills that a designer will need to learn prior installation.
• Trunking (also called link aggregation) allows two or more parallel links between switches to behave as a single link. The most typical application is to increase bandwidth performance.

Redundant networks

Network redundancy is nothing out of the ordinary for the IT industry. It has already been addressed with the introduction of proven network topologies, monitoring tools or built-in features for switches (as listed above). CobraNet interfaces on AudiaFlex products also include a redundant (secondary) network link to allow automatic switch over in case of a link failure.

The following block diagram illustrates the typical CobraNet network for redundant systems. (Note that redundant links have dedicated switches and Spanning Tree Protocol is required to enable the link between switches to work properly.)

Error:1002 CM1 WDOG

This is the most common error seen on the front panel of an EXPI or EXPO on a CobraNet system. It means that the host processor has seen the CM-1 module crash.

Most likely this error is caused by a network that has been flooded with an excess of broadcast traffic which has crashed the device. This is also referred to as a "broadcast storm". A broadcast storm can be caused by a hard-wired loop inadvertently created somewhere in the network.

• If you disconnect the unit from the CobraNet network, reboot it, and the error persists (while disconnected from the network), then you have a hardware failure.  
• If you disconnect the unit from the CobraNet network, reboot it, and the error is gone, but then reappears when re-connected to the CobraNet network you are suffering from the broadcast storm scenario.

In the event you have a broadcast storm and it is the result of too much network traffic, you will need to analyze the network traffic and potentially segregate the traffic to reduce it to allowable levels.

One channel of CobraNet data uses approximately 1.5625Mbps for 20-bit 48kHz audio.

32 channels x 1.5625Mbps = 50Mbps

32+32 channels x 1.5625Mbps = 100Mbps

Because switches are full-duplex devices, up to 64 channels of 48KHz, 20-bit audio can be sent over a single 100Mbit link in each direction. This means 128 audio channels over a single CAT5 cable.

Additional troubleshooting for CobraNet can be found at Cirrus Logic's Troubleshooting page.

http://www.cobranet.info/support/installation/troubleshooting#loop_network

http://www.cobranet.info/support/design/switched_networks#spanningTree