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CobraNet is a combination of software, hardware and network protocol which allows distribution of many channels of real-time, high quality digital audio over an Ethernet network. CobraNet is supported for repeater and switched Ethernet variants. On repeater networks, CobraNet eliminates collisions and allows full bandwidth utilization of the network. CobraNet uses standard Ethernet packets and network infrastructure (controllers, hubs, repeaters, switches, cabling, etc.).
Cirrus Logic is not an equipment manufacturer or re-seller, so please contact the manufacturer directly for product information. Many audio product manufactures have licensed CobraNet from Cirrus and a listing of these manufacturers can be found on the CobraNet Community page of our web site.
If you are a manufacturer, you may wish to consider licensing CobraNet from Cirrus.
CobraNet delivers audio in standard Ethernet packets over 100Mbit Fast Ethernet. Switches, hubs, media converters and other gear that operate in compliance with the IEEE 802.3u specification for Fast Ethernet, will work with CobraNet. CobraNet does not support 10Mbit Ethernet varieties (10BASE-T, Coaxial) due to their limited bandwidth.
For more information on Ethernet, check out the Ethernet Overview document or these WWW Links.
Fast Ethernet distance limitations apply to CobraNet installations: 100 meters over CAT-5 copper cable. 2 kilometers over multimode fiber. Proprietary Fast Ethernet via single mode fiber solutions can reach even further.
256 samples (5-1/3 milliseconds [thousands of a second]) of delay is incurred by the buffering of audio data into Ethernet packets in CobraNet transmitters and receivers. Additional delay is incurred in analog to digital conversion, digital to analog conversion and sample rate conversion. These additional delays are usually on the order of dozens of samples.
Data on an Ethernet network travels at the speed of light. The time for data to traverse a 2 kilometer network is several microseconds (millionths of a second). This delay is inconsequential in light of the delays enumerated above. Therefore, the audio delay is considered constant from any input to any output anywhere on the network.
It is completely synchronous for channels coming from the same CobraNet connection and 10us for channels coming from different connections to same switch. Devices connected to different switches may be experiencing different forwarding delays and will have a clock skew proportionate to that.
No. RealAudio has a latency of 3 to 10 seconds which is almost 1000 times the delay of CobraNet. RealAudio uses lossy compression of audio signals to reduce bandwidth requirements. CobraNet uses no compression; it is a transparent audio transmission system.
No. CobraNet provides a transparent, digital transmission link over Ethernet. Unlike most “real-time” internet audio transmission systems (see “Is CobraNet like RealAudio?” above), CobraNet introduces no digital distortion or audio artifacts. Used to transmit 20 bit audio, CobraNet is capable of 122.16 dB dynamic range (signal to noise ratio), and 0.000078% distortion at full level. Used to transmit 24 bit audio, the performance increases to 146.24 dB dynamic range (signal to noise ratio), and 0.0000049% distortion at full level. Frequency response is +0dB, -0dB, 0hz to 24Khz at either bit resolution. Note that these specifications are well beyond those achievable by current A/D and D/A technology. Thus the audio performance is limited only by the quality of the A/D and D/A converters used.
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. Gigabit links provide even greater channel capacity. Because the overall bandwidth of a switched network scales with the size of the network (more bandwidth is added as the network grows), bandwidth does not limit to the number of channels that can be supported network-wide. For additional information, read the white paper Bundle Assignments in CobraNet Systems. Also see “How many actively transmitting devices can exist on a CobraNet network at a time?” below.
A repeater network supports up to 64 channels of 48KHz, 20-bit audio transmitted onto the network in bundles of 8 audio channels. More channels can be accommodated on a network carrying 16-bit audio, fewer on a network carrying 24-bit audio.
All of these terms have been used to refer to the basic CobraNet audio transmission unit. This concept has recently been re-christened as bundle. The other terms (“network channel,” “CobraNet channel,” etc.) have been deprecated.
A bundle can carry multiple audio channels. A “bundle number” is what you dial in on the front of your unit to set up routing between two devices. There are two ranges bundles: multicast bundles are numbered 0-255 and unicast bundles are numbered 256-65279.
In general, CobraNet and networking terminology is described on our Glossary of Terms page.
Yes. As long as you’re using a switched network, traffic from other network devices such as PCs can coexist on the same network with CobraNet devices.
Networks constructed of the older repeater hubs must follow more stringent design rules. Refer to the Network Design area of this web site for additional information.
CobraNet has been demonstrated to work over at least one wireless Ethernet system, Tsunami from Proxim Wireless Networks. Infrared transmission systems from several manufacturers are believed to work as well since these are essentially simple fiber optic systems without the fiber! We have recently done some experimentation with 802.11b WiFi wireless Ethernet. Even under best case laboratory conditions we found this technology did not provide adequate bandwidth for most CobraNet applications. Additionally network performance was not stable enough to meet the real time requirements of CobraNet.
We have seen applications which naturally desire a large network with components wired in series as in a ring topology (i.e., stadiums, theme parks, etc.). We suggest you download a free copy of our CobraCAD design software and verify CobraNet compliance of any network design. CobraCAD checks for excessive switch hops, bandwidth bottlenecks and other problems.
The first deployment of CobraNet was in the background music system of Disney’s Animal Kingdom in 1997. Since then, thousands of CobraNet installations have been deployed in facilities that include churches, government hearing rooms, stadiums, convention centers and even live touring shows.
For information on some of the latest featured CobraNet installations, visit the CobraNet Installations section of the website.
CobraNet allows audio interoperability through a standard communications protocol. CobraNet compliant devices are based on a common hardware reference design from Cirrus Logic. Cirrus also supplies the firmware that implements the communications protocol. Audio can be delivered between CobraNet devices from different manufacturers.
Cirrus Logic has set up the CobraNet Manufacturers Consortium (CobraMC) through which the CobraNet standard is maintained. Membership is restricted to representatives of CobraNet licensed manufacturers.
The currently shipping version of CobraNet represents a network capable of carrying 16, 20 and 24 bit resolution audio channels at a 48kHz sample rate. The number of audio channels in a bundle is also selectable (up to a maximum of 8 depending upon the selected resolution). All enhancements to the reference design are done in a backwards compatible manner whenever possible.
CobraNet provides a common transport for control protocols. Because CobraNet is Ethernet, multiple protocols may be carried on the medium without seeing or interfering with one another.
Any bandwidth not consumed by audio data is available for control messaging.
Both IEEE-1394 and CobraNet can provide reliable delivery of time sensitive data for audio applications. CobraNet is based on well understood, well deployed, reliable Ethernet LAN technology. IEEE-1394 is an entirely new desktop network designed primarily for consumer applications.
A key benefit of IEEE-1394 claimed by its supporters is that it delivers excellent performance (bandwidth) per dollar. Fast Ethernet has become a commodity technology and now offers comparable, if not superior, affordability.
IEEE-1394 has some serious limitations in scalability that make it unsuitable as a media networking technology for professional facilities. It has a distance limitation of 4.5 meters between devices and is bandwidth limited to 400Mbit network wide. In its operation, it is comparable to an Ethernet repeater network and does not enjoy the bandwidth scalability (unlimited channel capacity) of networks employing switching.
Real-time audio and video share the same basic network performance requirements. At the network layer, CobraNet is more than an audio network. CobraNet provides reliable delivery of time sensitive data over Ethernet. Cirrus Logic is currently concentrating on CobraNet deployment within our area of expertise - audio. Cirrus is eager to license the basic technology into applications outside audio distribution.
There are independent technologies for transmission of video over Ethernet (VBrick, PictureTel, etc.). On a switched network with sufficient bandwidth, these products can be made to coexist with CobraNet.
The CobraNet network is synchronized to a single CobraNet device on the network known as the conductor. The conductor generates a timebase from a crystal oscillator or receives it from an external clock source. Based on this timebase, the conductor regularly broadcasts beat packets onto the network. Other devices on the network lock onto the arrival time of this packet and regenerate the clock locally.
If the conductor fails, another CobraNet device will assume the duties of the conductor. The changeover is accomplished within milliseconds. CobraNet is unable to deliver audio data in the absence of a conductor.
The error in clock delivery is ±1/4 sample period (about 5µs at 48KHz sample rate). This error is in the form of a clock “wander”. Due to careful control of the clock corrections, cycle-to-cycle clock variation (jitter) is maintained at less than 1ns.
CobraNet packets are standard Ethernet packets. CobraNet uses a registered logical link layer protocol (protocol identifier 0x8819). These link layer packets pass easily through hubs, media converters, bridges and switches. Due to performance considerations, CobraNet does not use the TCP/IP audio transport.
The CobraNet protocol includes three basic packet types. The beat packet is transmitted with a multicast address (01:60:2B:FF:FF:00) from the conductor at a regular interval (750 packets per second). Audio data packets from other CobraNet devices on the network follow the beat packet. Audio data packets may be multicast (one-to-many) or unicast (one-to-one) addressed. Reservation packets are transmitted with a multicast address (01:60:2B:FF:FF:01) approximately once per second. Reservation packets control bundle allocation and allow the status of CobraNet devices to be monitored.
The general problem is that of multicast traffic on the network. Multicast data comes out of all switch ports. If you get more than 10Mbit of multicast traffic on your network you’ll saturate any 10Mbit port and those ports will start indiscriminately dropping packets — some of the dropped packets will be the multicast traffic that you don’t care about, but some will be the control traffic that you care oh-so-much about.
Solutions to this problem are addressed in a publicly available white paper written by Ray Rayburn.
There are two limitations on the number of transmitting devices. First there is network bandwidth; you cannot exceed the capabilities of the network. Once the network is fully utilized, you can’t add additional transmitters. This is mainly an issue on a repeater network where 100Mbit of bandwidth is shared network wide. On a switched network there is essentially no limit due to bandwidth considerations as long as unicast bundles are used for audio transport. A second limitation is encountered in the capacity of the conductor and its ability to represent permission for many active transmitters in a maximum length 1500 byte beat packet. The answer to this depends on the number of bundles each device is transmitting. If each device is transmitting one bundle, there may be up to 184 transmitters active simultaneously, producing a total of 184 active bundles. If each device is transmitting a full 4 bundles, only 105 transmitters could be active, though theses would be producing a total of 421 active bundles. The eventual introduction of private bundles will erase this limitation.
There is no limit to this because any number of receivers may listen to a multicast bundle without using additional network, transmitter or conductor resources.
0 to 8 audio channels may be stuffed into a bundle. Since each bundle represents an Ethernet packet transmitted once per isochronous cycle, the total amount of data transmitted per isochronous cycle cannot exceed the 1500 byte Ethernet payload limit. You can make a rough determination as to whether you are exceeding this limit by adding up the number of bits you’re trying to send in each bundle. 8 audio channels/bundle x 64 samples/isochronous cycle x 20 bits/sample = 10,240 bits = 1280 bytes. When you go to 24 bits/sample you get 12,288 bits or 1536 bytes which is in violation of the 1500 byte limit.
The RAVE is based on an earlier version of the CobraNet interface circuitry. As such it is not capable of full-duplex operation. This in no way presents an interoperability issue. It is not necessary to worry about full-duplex or half-duplex as modern Ethernet equipment figures this out automatically through a process known as auto-negotiation. The only thing you need to worry about is that if there’s an option on any of the network gear (via dip switch or console connection or what-have-you) for disabling or over-riding auto-negotiation, make sure it is enabled.
