Rane NM 84, Operator'S Manual

Manual-12

Network Examples

There are two ways to transmit CobraNet audio across a

network. An example for each transmission method follows.

The application dictates which of the two methods to use.

Some applications may require both methods simultaneously.

Multicast Network example [a.k.a. broadcast] requir-

ing simpler repeater hubs

One way to transmit audio over the network is to allow all

of a device’s audio channels to be transmitted to all devices.

This is called multicast in network lingo and can be thought of

using the more familiar term: broadcast. Thus, when you

transmit audio using one of the Multicast Bundles (Bundles 1

through 255), the audio is broadcast to every device on the

network.

This broadcasting of all channels everywhere is required

for applications such as paging when emergency audio must

be delivered to every node. When users at each node need

independent access to all available audio channels, use

Multicast Bundles. If your application is a large music

complex with many audio channels and all the audio channels

are required in all rooms or nodes, use a multicast network by

selecting Multicast Bundles 1-255 for audio transmission.

One advantage when using Multicast Bundles is that an

unlimited number of receivers (CobraNet devices) are allowed

for a single transmission with no additional network band-

width being consumed. This is just like radio broadcasts: one

transmitter, unlimited receivers.

Another advantage is the lower cost and complexity

network that is required to implement the audio system using

Multicast Bundles which are implemented utilizing simple

Ethernet repeater hubs, which are quite inexpensive. This

makes this Multicast application and system a “Networking

101” example – inexpensive and easily implemented.

The disadvantages of Multicast Bundles include the loss of

bandwidth network-wide, since every device and every

network cable contains the same quantity of data. All

multicast data takes up the same amount of bandwidth

throughout the entire network. Another thing to be cautious of

is that multicast CobraNet data will swamp any 10 megabit

(10Base-T) data ports on the network.

Modern computers with 100 Mbit PCI Ethernet interfaces

(100Base-T) are quite capable of ignoring this multicast traffic

until their network connection becomes saturated. However, if

the computer is connected to the network via

10 Mbit Ethernet, that link will easily saturate. In any case, it

is not CobraNet which suffers under these conditions, it is the

computers.

The final disadvantage using multicast transmission is the

inability to reliably share computer network data and

CobraNet data on the same network. This is not to say that it

is impossible, it indeed works. However, the problem is that

the network bandwidth required by the computer data is ever-

changing and not controlled or monitored by the CobraNet

devices. Thus, when the computer data suddenly and unpre-

dictably requires more bandwidth than is available, the entire

network bogs down creating computer data collisions which

slow down the computer network, and simultaneously creates

audio dropouts, pops or ticks. Not fun, or necessary.

Oftentimes however, computer data must be shared on the

network or not all audio channels are required at every node.

This is where unicast networking comes in.

Unicast Network example [a.k.a. point-to-point]

using more flexible switches

A second way to send audio over the network uses a

different scheme called unicast – or point-to-point. You must

use unicast when you require only certain locations on the

network to receive certain channels. For example, in a

campus-sized church complex, it may be useful to send all

channels from the live band mics to the front of house (FOH)

mixer, monitor mix location and to the recording studio. But

the left-center-right (LCR) audio feed to the overflow building

across the street only needs three channels. The stereo FM

broadcast room only needs a stereo mix and the video truck

which is used only every other week may require all channels.

In the above case, it is not required, overly complex, and

most importantly, expensive to send all channels to all

locations. Thus, a unicast (point-to-point) network to feed the

mic channels from the stage to the four required locations –

FOH, monitor, recording studio and video truck – is required.

Therefore, using Bundles starting at 256 or above, sends the

audio over Unicast Bundles which forces the use of network

switches (not repeater hubs) which support unicast data.

For the LCR and stereo FM broadcast feeds, you could use

hard-wired cable runs which may be less expensive. Or, use a

single CAT 5 cable, three CobraNet devices and a couple of

dedicated repeater hubs and utilize a single Multicast Bundle

(1 through 255) to transmit all 5 audio channels to both the

remote LCR and FM locations from the front of the house.

Now let’s make things fun and assume, since this church

pays no taxes, that their infinite budget (so common these

days) requires an audio system in the church’s on-site hotel

and gymnasium. Oh, how fun.

The church’s hotel, gymnasium and attached convention

center requires a dozen stereo channels of background music

as well as 4 paging audio feeds. Additionally, the LCR and

stereo feeds from the church are fed into the gymnasium and

convention center for more overflow on Christmas, Easter and

when Father Guido Sarducci is in town.

Including the 12 stereo background feeds on the network,

allows the church complex access to these background music

sources for intermissions and open houses.

I think you can see where this is going. By using a

combination of multicast and unicast networking, you can

easily use CobraNet technology to efficiently distribute many

audio channels to and from many locations and save consider-

able money on cable, conduit, labor and the re-configuration

time needed to accommodate the wide variety of audio

distribution needs in large and small facilities.

CobraNet network designs must not exceed 32 Multicast

Bundles per VLAN. A VLAN (virtual LAN) is an advanced,

“Networking 401” term associated with managed switches

used on only the most advanced systems. Managed switches

allow point-to-point virtual LANs to be defined by the

network designer.