Nortel Networks Recording Equipment 1 User Manual
Voice over Wireless LAN Solution Guide
v1.0
December 2005
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Page 25
Figure 10: Not recommended VoWLAN design
The VPN feature is not designed for remote connectivity over a WAN back to the corporate
network. This may in some cases work, but it is not supported. The latency, jitter, and packet loss
requirements are sure to be violated when crossing WAN connections.
network. This may in some cases work, but it is not supported. The latency, jitter, and packet loss
requirements are sure to be violated when crossing WAN connections.
If you deploy the VPN feature of the 2212 handset in a mixed network where 2211s and 2210s
are also in use, then the design recommendation becomes a little more complex. If you place a
WTM 2245 in the subnet with the 2210 and 2211 handsets, and place a WTM 2245 in the subnet
with the VPN Router to support the 2212 handsets, then there will be admission control problems
for the telephony WLAN. Each WTM 2245 will count the number of their own devices placing calls
over APs, but not count the number of calls controlled by the other WTM 2245. This creates a
blind spot for each device, and it becomes possible to oversubscribe an AP by up to 2:1! The best
solution to this problem is to have the 2210 and 2211 handsets use the same WTM 2245 as the
2212 (VPN) handsets. This WTM 2245 would be on the other (remote) side of the VPN Router
from the handsets, that is, over a routed hop—see the next section.
are also in use, then the design recommendation becomes a little more complex. If you place a
WTM 2245 in the subnet with the 2210 and 2211 handsets, and place a WTM 2245 in the subnet
with the VPN Router to support the 2212 handsets, then there will be admission control problems
for the telephony WLAN. Each WTM 2245 will count the number of their own devices placing calls
over APs, but not count the number of calls controlled by the other WTM 2245. This creates a
blind spot for each device, and it becomes possible to oversubscribe an AP by up to 2:1! The best
solution to this problem is to have the 2210 and 2211 handsets use the same WTM 2245 as the
2212 (VPN) handsets. This WTM 2245 would be on the other (remote) side of the VPN Router
from the handsets, that is, over a routed hop—see the next section.
2.2.2.8
WTM 2245 placement and engineering rules
Usually the WTM 2245 is placed in the same subnet as WLAN Handsets 221x. This was
previously a rule, but is now just a recommendation. As was discussed in the 2212 VPN section
above, the WTM 2245 sometimes must be placed in a different subnet from the handsets.
However, the rules for delay, jitter, and packet loss still apply.
previously a rule, but is now just a recommendation. As was discussed in the 2212 VPN section
above, the WTM 2245 sometimes must be placed in a different subnet from the handsets.
However, the rules for delay, jitter, and packet loss still apply.
Ethernet connectivity between the WTM 2245 and the call server or other voice endpoint must
never exceed 100 milliseconds (ms) of one-way delay, 30 ms of jitter, and 2 percent packet loss
end to end regardless of the physical properties of the link. Whether or not the WTM 2245 is in
the same subnet with handsets, the link between the WTM 2245 and the handset must be under
100 ms of one-way delay, 1 ms of jitter and under 2 percent packet loss.
never exceed 100 milliseconds (ms) of one-way delay, 30 ms of jitter, and 2 percent packet loss
end to end regardless of the physical properties of the link. Whether or not the WTM 2245 is in
the same subnet with handsets, the link between the WTM 2245 and the handset must be under
100 ms of one-way delay, 1 ms of jitter and under 2 percent packet loss.
For branch offices, you may be tempted to configure the WSS 2350 to be part of the Mobility
Domain and backhaul the telephony devices to the campus telephony VLAN, just like WSS 2300s
are configured in the campus. But because in this configuration the WTM 2245 is across the
WAN from the handsets, this design (shown in Figure 11) is not supported, except when the
above-mentioned requirements for latency, jitter, and packet loss are met. In reality most WAN
links do not meet these requirements. The proper design to support VoWLAN in the branch office
is to deploy a WTM 2245 in the branch to locally support handsets, and to configure the branch
office WSS as a separate Mobility Domain or null Mobility Domain.
Domain and backhaul the telephony devices to the campus telephony VLAN, just like WSS 2300s
are configured in the campus. But because in this configuration the WTM 2245 is across the
WAN from the handsets, this design (shown in Figure 11) is not supported, except when the
above-mentioned requirements for latency, jitter, and packet loss are met. In reality most WAN
links do not meet these requirements. The proper design to support VoWLAN in the branch office
is to deploy a WTM 2245 in the branch to locally support handsets, and to configure the branch
office WSS as a separate Mobility Domain or null Mobility Domain.