Motorola TEAM Badge (EWB100), Deployment Manual

Page: 45 / 146

EWB100 Usage and Deployment Guide Rev 1.13
Page 45
At the end of a WTT session, a user will typically hear two beeps. The first is
indicates either the termination of the existing WTT session or the return to home
channel. The second indicates the termination of the Private Reply setup period,
the operation of which is described in the next section.
There is also the option for a user to replay the last received wtt message. It is
described later in this section.
8.2 Protocol Elements
The Walkie Talkie Protocol used on the EWB is compatible with that used in the
Push-to-Talk Express products that run on EWP and MCxx products. This
section describes the relevant details of that protocol.

The voice stream is half duplex and uses packets that are approximately
450 bytes in length. The packets are sent every 200ms. This is different
than most VOIP products that are full duplex and use small packets sent
at short intervals. Thus the packets are tagged with AC 1 when used with
WMM rather than AC 0.

The packets are sent using multicast addresses at both the MAC and IP
layers. The MAC address is :01:40:EF:40:02:02 and the IP address is:
239.192.2.2. Note that the latter is a class D address which is generally
not passed across subnets by routers without explicit configuration of the
routers.

The EWB100 will communicate across subnets, provided the routers
connecting those subnets are configured to pass the class D defined
above. As noted previously, the EWB itself will not generally roam across
subnets. This configuration may be complex so the default
recommendation is to deploy in a single subnet environment.

In the normal flow, the packets are sent by the originating device as
unicast packets to the AP. Such packets are acknowledged by the AP.
They are typically sent at the highest rate supported by the AP, at least on
the first attempt. The EWB will rate scale on subsequent packets and over
the long term to minimize lost packets and subsequent retries. The APs
will rebroadcast such packets following beacons at the DTIM interval.
Such packets are multicast and are not acknowledged by the receivers.

The packet rate is 5pps (every 200ms). Given the low packet rate the load
on the network from even multiple EWB voice sessions is very small.

Different voice channels are identified only by different UDP ports in the
range 5000-5031 (decimal). Channel 1 uses port 5000, Channel 2 uses
port 5001, etc.. The MAC and IP addresses used for the different channels