Avaya Communication Server 1000 Installation And Commissioning Manual page 67

Figure 10: Single telephony VLAN implementation
Consolidating VoWLAN handsets into one VLAN (subnet) has a few advantages. First, it allows
the WLAN IP Telephony Manager 2245 design to be greatly simplified. Instead of purchasing
and deploying at least one WLAN IP Telephony Manager 2245 per voice subnet, you can now
install one WLAN IP Telephony Manager 2245 for the single voice subnet. For larger VoWLAN
deployments, more WLAN IP Telephony Manager 2245 units may be required in that single
subnet to support the number of calls; however, fewer WLAN IP Telephony Manager 2245 units
are needed than in an equivalent multisubnet deployment.
A second advantage is that external security measures are easier and less costly to implement.
It is common practice to put a telephony WLAN behind a firewall for security reasons. This is
because security features on handsets, particularly authentication capabilities, tend to lag
behind the industry. So to mitigate risks, you can use a firewall to block all but the ports needed
for IP Telephony. This practice becomes complex and costly when multiplied by a number of
subnets. A more cost-effective alternative to implementing a firewall is to assign private
addresses to the handsets and let the WLAN IP Telephony Manager 2245 network address
translation (NAT) capabilities serve as a form of secure firewall to the telephony LAN (T-
LAN). Of course this is not as secure as using a traditional firewall to secure the T-LAN.
The downside of putting all telephony devices into the same subnet is that broadcasts are
increased. Also, while security is simplified, the importance of implementing adequate security
measures increases because more devices will be impacted in the event of a security breach.
Note:
Avaya does not recommend running the WLAN IP Telephony Manager 2245 behind a
firewall. Any routing device introduces a possibility of delay, and the higher layer routing
tends to introduce longer and less predictable delays. Regularly timed packets are important
in order to assure optimum voice quality, so Avaya recommends putting as little and as
Avaya WLAN IP Telephony Installation and Commissioning
Other network design considerations
November 2010 67