36 PlanningFor example, if a data device does seize the medium, it can send a1500-byte frame at the lowest data rate (if it is far away from the AP), andfurther delay voice frames. In addition, several data devices contending forthe medium can each, in turn, send large frames before the voice devicegained access to the medium.Without a way to give preferential transmission opportunities to voicedevices, supporting voice applications is a tremendous challenge on 802.11WLANs. SpectraLink Voice Priority (SVP) has evolved into a de factostandard for Quality of Service (QoS) and serves as a model to illustrate thefunctions that a successful QoS mechanism can implement.The 802.11e standard ultimately resolves QoS issues, but the delays in thestandard create a number of additional implementation-specific challenges.Wi-Fi Multimedia (WMM) is a step toward full 802.11e compliance for voiceand multimedia, but it is not a solution. Because it is a step, QoS featureevolution must progress towards better and more solid standards-basedQoS capabilities.WMM refines 802.11 to give statistical preference to certain classes overother classes. It is fully backward-compatible to legacy non-WMM devices,which function just like WMM best-effort class devices.DHCP server planningThe handset IP-related parameters can be configured manually or througha DHCP server (RFC 1541 and RFC 1533). Any DHCP server can be used,but it must support the following capabilities.• Provide Client IP address• DHCP Option 1—Subnet Mask• DHCP Option 3—Default Gateway• DHCP Option 60—Class Identifier. The wireless handsets use the ClassIdentifier of Nortel-221x-A or Nortel-61xx-A. The DHCP server can usethe string in the Class Identifier to uniquely identify a wireless handset.• DHCP Option 66. This can be used to specify the address of the TFTPServer. If this option is not configured, the wireless handset looks at theNext server Boot server (siaddr) Option for the address of the TFTPServer* Vendor Specific Option 43, 128, 144, 157, 191, or 251. Onlyone of these options is required. The DHCP server encodes the Server1 information using the same format as the IP Phone 2004. If the Server2 information is also present in the option, it is ignored.• DHCP Option 151. This option contains the IP address of the WLAN IPTelephony Manager 2245. If Option 151 is not configured, the wirelessNortel Communication Server 1000WLAN IP Telephony Installation and CommissioningNN43001-504 01.02 StandardRelease 5.0 15 June 2007Copyright © 2004-2007, Nortel Networks.
