Handbook for Sound Engineers

1506 Chapter 39

39.12.7 Bundle Identification

Audio is carried over CobraNet® networks in bundles.
Bundles may contain from zero to eight audio channels.
Each bundle consists of a stream of packets of one of
three types specified in Fig. 39-56.

39.12.8 Multicast Bundles

In a given network or VLAN there can only be a single
instance of a given multicast bundle number at a time.
The conductor will only allow one CobraNet® trans-
mitter to be active during any isochronous cycle on a
given multicast bundle number.

Multicast bundles are always multicast addressed,
and are always transmitted even if no receiver has
selected that bundle. Since they are multicast, they will
appear on every port of a network or VLAN, even on
switched networks. Therefore, the receiver does not
have to submit a reverse reservation request to the
conductor in order to receive a multicast bundle since
the bundle will always appear at its input.

Caution must be used with multicast bundles and
switched networks so as not to overwhelm the ports
with multicast traffic. It is generally suggested to not
use more than four multicast bundles on a given
switched network or VLAN at the same time.

Multicast bundles can serve as a common denomi-
nator to allow interoperability with CobraNet® devices,

which can only be configured from their front panel

switches.

39.12.9 Unicast Bundles

In a given network or VLAN there can only be a single

instance of a given unicast bundle number at a time. The

conductor will only allow one CobraNet® transmitter to

be active during any isochronous cycle on a given

unicast bundle number.

Unicast bundles may be either unicast or multicast

addressed based on the transmitter’s reception of one or

more reverse reservation requests for its bundle number.

The txUnicastMode variable is used to control the trans-

mitter’s ability to switch to multicast on a unicast

bundle number. The default setting of the txUnicast-

Mode variable disables the ability to transmit multicast

on a unicast bundle number. With the default setting, if

more than one receiver requests a given unicast bundle

number, only the first receiver to get its reverse reserva-

tion request in will get that bundle. With the default

setting, unicast bundles can’t be used for point to multi-

point routing, instead multicast bundles must be used.

Some CobraNet® devices allow the same audio to

be transmitted on more than one bundle at a time. This

can provide an alternative way for a single CobraNet®

device to unicast to as many as four receiving devices at

the same time.

Unicast bundles are only transmitted if a receiver has

requested that bundle. This allows a receiver to select

Hexadecimal

Bundle

Number

Decimal

Bundle

Number

Designation Usage Transmission

Addressing

Transmission Mode

0 0 Null Unused bundle. Disables transmission/

reception when selected.

Never transmitted. Never transmitted.

1–FF 1–255 Multicast Publicly available bundles. Each bundle

is transmitted by a single unit and may

be received by any number of units.

Always multicast. Always transmitted.

100–FEFF 256–65279 Unicast Publicly available bundles. Each bundle

is transmitted by a single unit. If the

default unicast mode setting is used, it

will only be received by a single unit.

Generally unicast, but

may multicast if txU-

nicastMode variable

is so adjusted.

Only transmitted when

at least one receiver is

identified via reverse

reservation.

FF00–FFFF 65280–65535 Private Individual transmitters locally allocate

private bundles. The bundle number is

conditioned on the transmitter's MAC.

There are 256 of these bundles per

transmitter thus the total number of pri-

vate bundles is virtually unlimited.

Generally unicast, but

may multicast if txU-

nicastMode variable

is so adjusted.

Only transmitted when

at least one receiver is

identified via reverse

reservation.

Figure 39-56. CobraNet“ bundle types. The bundle number specifies the type of bundle. There can only be a single trans-
mitter for any given multicast or unicast bundle number at a time on the same network or VLAN. The three bundle types
have different characteristics. Multicast bundles will be routed to every port in a switched network, or to every port in a
VLAN, so use them sparingly. It is generally suggested that no more than four multicast bundles be used at any one time in
a given switched network or VLAN within a switched network.