Wheatstone Corporation WheatNet-IP BLADE3, Техническое руководство, Страница: 346 / 366

WheatNet-IP BLADE 3 / June 2018
page A – 117
A P P E N D I C E S
Using WNIP with AES67
Since AES67 only specifies stream content parameters and does nothing to manage
stream discovery and control, these functions must be managed manually. To put it another
way, since AES67 does not include a standard way for AoIP streams to be identified there
is no way for a device from vendor A to “see” or know about a stream from vendor B. And
if you can’t “see” an available stream, you can’t receive it. The current work around for
this problem is to specifically tell device B that there is a stream from device A available
with such and such parameters that it should start receiving. This is purpose of the SDP
( S ession D escription P rotocol) mentioned in the AES standard. Not only does the standard
specify the parameters in an AES67 stream, it also specifies how those parameters should
be presented. So in fact, the system engineer becomes the audio router by manually telling
which devices should listen to which streams.
This is a bit of work, but easy enough until you realize that because the different
devices can’t “see” each other, it is entirely possible that they may be using address
settings already in use elsewhere.
So the first step in putting together the system is to map out an IP and stream multicast
address plan that assures every stream on every device will have a unique address available
for it.
Multicast addresses are in the form of 239.xxx.yyy.zzz. Each AoIP vendor has their
own way of allocating addresses for each stream. WNIP does it automatically but the
user can change the starting address and range if needed. Axia uses “Livewire Channel
numbers” but can also accept a manually entered address. Dante will let the user specify
the xxx octet of the address but automatically generates the yyy and zzz without any user
control of what it chooses. Other equipment may do this yet differently.
To make your stream multicast address plan you must know all the different devices
that will be in the system and how they allocate multicast stream addresses. Start with
the devices which are least common or least flexible in specifying or changing multicast
addresses and isolate them in an address range well removed for what the majority of
your devices will be. As an example, if you have a WheatNet-IP system with 50 BLADEs
and you want to add two Dante devices to it, you would give the Dante device streams a
multicast address of .192 for the second octet and check what multicast addresses Dante
auto‑assigns. Then have the WheatNet‑IP devices auto‑generate multicast addresses
starting lower (239.192.192.1) or higher (239.192.yyy.zzz+10) to make sure there are no
WNIP streams assigned the same multicast addresses.
It’s important to go through this effort to create a plan first, because as you add AES67
devices to your system you will be doing a lot of hand entry specifying which stream
addresses which device is using to transmit on and which stream address each device is
using to receive. If you go through all this effort only to discover that some other device
is using that same address you’ll only have to start over. Besides, having your multicast
address plan in place will be useful later when you are routing AES67 streams in your
network; you’ll refer to it over and over again.
With a multicast address plan in place lets begin.