Browse Prior Art Database

E911 in WLANs

IP.com Disclosure Number: IPCOM000020186D
Original Publication Date: 2003-Oct-30
Included in the Prior Art Database: 2003-Oct-30
Document File: 2 page(s) / 589K

Publishing Venue

Motorola

Related People

James E. Womack: AUTHOR [+2]

Abstract

There is clearly a need, and probably an eventual regulatory demand, for a subscriber unit on a voice capable WLAN to be able to initiate E911 calls and have the call be handled with the utmost priority. Methods provided with implementations of 802.1Q and 802.11e may provide enhanced performance through the use of priority markings; however, they will still compete for bandwidth with the rest of the traffic mix. The approach here is to enhance 802.1Q and 802.11e mechanisms by providing E911 calls with their own Access Category that gets mapped to a particular VLAN ID. Once assigned to a unique VLAN, the local administrator has several ways to configure the system that ensures the call can be moved through the network quickly and reliably.

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E911 in WLANs

By James E. Womack and Niranjan Segal

Motorola, Inc.

iDEN Systems Division

ABSTRACT

There is clearly a need, and probably an eventual regulatory demand, for a subscriber unit on a voice capable WLAN to be able to initiate E911 calls and have the call be handled with the utmost priority. Methods provided with implementations of 802.1Q and 802.11e may provide enhanced performance through the use of priority markings; however, they will still compete for bandwidth with the rest of the traffic mix. The approach here is to enhance 802.1Q and 802.11e mechanisms by providing E911 calls with their own Access Category that gets mapped to a particular VLAN ID. Once assigned to a unique VLAN, the local administrator has several ways to configure the system that ensures the call can be moved through the network quickly and reliably.

PROBLEM

It is common for LAN administrators to use virtual LANs (VLANs) as a way to differentiate between different types of users (we will call them groups). This way each group can be switched/routed in the manner they feel most appropriate. For instance, a LAN administrator can create a group for Engineering, Finance, etc. of which each group is treated in a different manner. Each group is defined in the LAN by its VLAN ID as specified by 802.1Q [1].

Also, clearly provided in 802.1Q documentation, there is a way to provide, within each VLAN ID, a higher priority for certain types of data (e.g. voice) and lower priority for others (e.g. ordinary data). Further the 802.11e [2] draft specification provides different Access Categories (ACs) for the purposes of prioritization.

The problem to be resolved is that subscriber units (SUs) in a wireless LAN cannot choose their VLAN ID. They may choose an AC and they may choose a VLAN priority. The idea presented here is a way of allowing the mapping of AC to the VLAN IDs. These VLANs can then be treated as separate flows and routed in ways as determined best by the LAN administrator.

SOLUTION

The solution described here requires that

o        Systems that offer E911 service employ 802.11e QoS functionality that provides differentiated service based on AC, and

o        E911 calls have exclusive use of the highest priority AC.

One of the more common ways to ensure high-priority QoS and ready access to the WLAN is to over provision. We do not propose that here. Neither do we propose that a portion of continuous bandwidth be reserved for the subscriber unit (SU) while it is associated with the AP for use in initiating E911 calls. It would be bandwidth inefficient to waste airtime in the off chance that an E911 would be initiated. Ensuring that E911 call can get through can be achieved simply by giving priority to the E911 during the 802.11 contention period, something that will be available in systems that support QoS.

When the SU is ready to make the E911 call, it will seize the channel at the next contention period. Because it has been assigned exclusive use of the highest AC, it will ...