Handbook for Sound Engineers

1504 Chapter 39

manufacturer for specifications on the specific cable
used in your installation.

39.11.17.5 Cable Testing

All network cable infrastructure, both copper and fiber,
should be tested prior to use, and after any suspected
damage. The tester used should certify the performance
of the link as meeting the Cat5, Cat5e, Cat6, or what-
ever performance level you thought you had bought.
Inexpensive Cat5 testers are often just continuity
checkers and are worse than useless since they can
provide a false sense of security that the cabling is fine
when in fact it may be horrible.
A tester that can correctly certify a link as meeting
all of the Cat5 specifications will cost thousands of
dollars, and testers capable of certifying to higher levels
are more expensive.
While there are dedicated fiber testers, many of the
quality Cat5 testers can accept fiber testing modules.

39.12 CobraNet®

CobraNet® is a technology developed by Peak Audio a
division of Cirrus Logic, Inc., for distributing real-time,
uncompressed, digital audio over Ethernet networks.
The basic technology has applications far beyond audio
distribution, including video and other real-time signal
distribution.
CobraNet® includes specialized Ethernet interface
hardware, a communications protocol that allows
isochronous operation over Ethernet, and firmware
running on the interface that implements the protocol. It
can operate on either a switched network or a dedicated
repeater network.
To the basic Ethernet capabilities, CobraNet® adds
transportation of isochronous data, sample clock gener-
ation and distribution, and control and monitoring
functions.
The CobraNet® interface performs synchronous to
isochronous and isochronous to synchronous
conversions as well as the data formatting required for
transporting real time digital audio over the network.
A CobraNet® interface provides conversion from
synchronous to isochronous and back, and formats the
data to meet Ethernet requirements. This allows it to
provide real-time digital audio across the network.
As shown in Fig. 39-54, CobraNet® can transport
audio data, and carry and use control information as
well as allowing normal Ethernet traffic over the same
network connection. Simple Network Management
Protocol (SNMP) can be used for control and moni-

toring. In most cases normal Ethernet traffic and

CobraNet® traffic can share the same physical network.

39.12.1 CobraNet® Terminology

CobraNet® Interface.

The hardware or hardware design with associated firm-

ware provided by Peak Audio to CobraNet® licensees

and affiliates.

CobraNet® Device. A product that contains at least

one CobraNet® interface.

Conductor. The particular CobraNet® interface

selected to provide the master clock and transmission

arbitration for the network. The other CobraNet® inter-

faces in the network function as performers.

Audio Channel. A 48 kHz sampled digital audio signal

of 16, 20 or 24 bit depth.

Bundle. The smallest unit for routing audio across the

network. Each bundle is transmitted as a single Ethernet

packet every isochronous cycle, and can carry from zero

to eight audio channels. Each bundle is numbered in the

range from 1 to 65,535. A given bundle can only be

transmitted by a single CobraNet® interface. There are

two basic types of bundles.

Multicast Bundle. Bundles 1 through 255 are multi-

cast bundles and are sent using the multicast MAC

destination address. If a transmitter is set to a multicast

bundle number it will always transmit regardless of

whether a receiver is set to the same bundle number.

Multiple receivers can all pick up a multicast bundle.

Unicast Bundle. Bundles 256 through 65,279 are

unicast bundles and are sent using the specific MAC

destination address of the receiver set to the same

bundle number. Only a single receiver can receive each

Figure 39-54. CobraNet“Data Services showing the

different types of data flowing through the Ethernet

network.

Ethernet

Control data

Isochronous data

(audio)

Unegulated

traffic

Clock