Operation Manual; 4 Operation; Signal Path- Page 34

Operation Manual

DBC Network Bridge

page 34

4 Operation

4.7.7 CobraNet: Explanation

In the 

Signal Path

 window, Cinema Surround form, is a 

DBC Network 

Channel Assign 

button which opens the 

CobraNet Output 

window 

(described on the next page). If you need to understand how CobraNet 
works, please read the following section.

CobraNet is a technology developed by Peak Audio, Inc. that allows real 
time digital audio to be distributed over standard Fast (100Mb) Ethernet 
hardware. CobraNet allows the DBC Network Bridge to not only have ana-
log or digital inputs, but also to provide 8 digital Inputs and 8 digital Out-
puts from a CobraNet network.These additional Inputs and Outputs allow 
enhanced routing and processing capabilities, including the passing of 
audio channels to other DBC Network Bridges to create larger mixing and 
processing structures.

Transmission of digital audio via CobraNet is accomplished through 'Bun-
dles' and 'Slots'. Bundles are Ethernet packets that contain up to eight dig-
ital audio channels, called 'Slots'. Each digital audio channel is assigned a 
position (1-8) within the Bundle, hence the name Slot. The Bundle is then 
assigned a unique number that indicates how it will be transmitted on the
CobraNet network. A receiver merely needs to select the Bundle number to 
receive the audio.

Bundles can be either multicast or unicast. Multicast bundles are sent to all 
CobraNet network devices, while unicast bundles are sent to one, and only 
one, CobraNet network device. Through the use of Fast Ethernet switches, 
unicast transmission of bundles can greatly increase the number of bun-
dles that can be present on a CobraNet network since the bundles only go 
to the device that is addressed. Since each device can send and receive 
four bundles (i.e. up to 32 channels), great flexibility is allowed in the
routing of audio over the network. Assignment of bundles as multicast or 
unicast is done through the assignment of the bundle number. Bundles 
with numbers 1-255 are always multicast, while bundles 256-65,279 are 
designated as unicast. Bundle assignments need to be unique, with only 
one CobraNet transmitter allowed per bundle.

The coordination, i.e. clock master, of the CobraNet network is the function 
of the 'Conductor'. The ‘Conductor Priority’ is set in each device and 
decides which unit will be the Conductor. If the Conductor is removed from 
the CobraNet network for any reason, the remaining devices decide who 
becomes the Conductor based on a numerical hierarchy, i.e. priority 
‘0’=never and ‘255’=always.The PS-8810 is set as ‘32’ as a default.

The Conductor is responsible for ensuring that all devices on the CobraNet 
network transmit their bundles in a coordinated way. The Conductor recog-
nizes each device on the network and assigns a transmission position for 
each bundle of each device.

In addition the Conductor sends master clock to each device to ensure that 
all audio is synchronous. Like a conductor of an orchestra, the Conductor 
signals the beginning of a synchronous transmission cycle, and then each 
device sends its bundle(s) in lock step. This occurs 750 times a second, 
with each audio channel having 64 samples of 48KHz audio. Each audio 
channel can be sent as 16, 20, or 24 bit samples. if 24bit audio is used 
then a bundle will be reduced to 7 channels. There is a fixed latency of
5.33ms.

CobraNet networks utilize Fast (100Mb) Ethernet hardware and can use 
either repeater hubs or switches. A repeater hub is a device that takes the 
data that comes into each port, and sends it back out on all ports except the 
port it came in on. As a result, only multicast bundles can be used in 
repeater hub networks and these need to be limited to 8 bundles per net-
work.

On the other hand, switches are much more efficient, in that they examine 
the destination address of each packet of data received on each port, then 
switch that data to the particular recipient of that packet. Unicast bundles 
exploit this feature to minimize the audio traffic on the CobraNet network. 
The result is that an almost limitless number of unicast bundles can be on 
a switched CobraNet network. Multicast bundles are allowed on a switched
network, but they must be used with care.

Peak recommends that not more than four multicast bundles be used in a 
switched CobraNet network. Peak also advise not to mix ordinary computer 
data on a repeater hub network, as this could result in dropout in the audio. 
In switched CobraNet networks, coexistence of CobraNet audio and ordi-
nary computer data is possible, because there are no collisions with the 
audio.

If there are only two DBC Network Bridge units involved in a CobraNet net-
work these can be connected using CAT 5 crossover cables.

More information:
www.peakaudio.com
www.iqaudiosystems.com

CobraNet is a registered trademark of Peak Audio, Inc.