Thinking About the Site Report January 2004 doc.: IEEE 802.11-04/xxxx March 2004 Thinking About the Site Report Bernard Aboba Microsoft bernarda@microsoft.com Dan Harkins Trapeze Networks Areg Alimian Communication Machinery Corporation aalimian@cmc.com Marty Lefkowitz OTCS Consulting Bernard Aboba Microsoft Areg Alimian CMC, Bernard Aboba Microsoft

Outline What is a site report? Query and response semantics January 2004 doc.: IEEE 802.11-04/xxxx March 2004 Outline What is a site report? Query and response semantics Why the site report matters to handoff Issues with the site report Summary Bernard Aboba Microsoft Areg Alimian CMC, Bernard Aboba Microsoft

March 2004 What Is A Site Report? A report on relating to WLAN-enabled stations within a site Possible questions What stations have transmitted in the past – and on what channels What stations are transmitting now – and on what channels Characteristics of the stations Location and transmit power Capabilities Authenticated vs. rogues Connectivity – to what prefixes do they offer access? Why is this important? To regain control over radio spectrum usage. To inventory WLAN capable devices. To provide information to stations wishing to better utilize the network. Information != control; the site report creates no obligation to act. Bernard Aboba Microsoft

Query and Response Semantics March 2004 Query and Response Semantics Query and response semantics are very important Querying station may have differing objectives and goals Diagnostics: May wish to gather data on problems it is experiencing Optimization: May wish to optimize its own performance Inventory: May wish to inventory and map the network In dense deployments, the entire site report may be quite long Querying station may only need a subset of the entire report May only care about stations “on this floor” in a given direction May only care about stations “authenticated by the responder” May only care about stations matching a set of capabilities Bernard Aboba Microsoft

Handoff Scenario Channel 11 Channel 6 c v D AP B STA AP A c ~ 10-20 ft March 2004 Handoff Scenario Latency Contributors 802.11 scan 802.1X authentication 4-way handshake Movement detection Address assignment Duplicate detection IKE renegotiation MIP signalling TCP adjustment period Channel 11 Channel 6 c v D AP B STA AP A c ~ 10-20 ft D ~ 100-300 ft Bernard Aboba Microsoft

Why the Site Report Matters to Handoff March 2004 Why the Site Report Matters to Handoff Site Report enables stations to optimize scan behavior No need to scan on channels/technologies with no potential APs No need for admin to configure stations for optimal scan behavior Saves power, reduces handoff time, decreases radio spectrum pollution Site Report enables stations to identity a potential candidate list prior to entering the coverage overlap area Relevant dimension changed from “c” to “D” Coverage overlap can be decreased, reducing interference issues Site report increases maximum potential station velocity Consequence of changing length metric from “c” to “D” Site Report enables stations to decrease total handoff time Bernard Aboba Microsoft

802.11 Handoff Problem Space Rate Scan + Pre-auth via Old AP B DT March 2004 802.11 Handoff Problem Space Rate Scan + Pre-auth via Old AP 4-way hand., no 802.1X Pre-Auth + Site Report 3-way hand., no 802.1X B DT Association not possible Scan + Radio tuning c DTPA D DTPA D DTFH D DTReassoc Stationary Pedestrian Vehicular High Speed Station Velocity Bernard Aboba Microsoft

Issues with the “Site Report” March 2004 Issues with the “Site Report” “Site report” may or may not be useful in formulating a “candidate list” Depends on the query semantics A list of all APs, or APs meeting criteria to be valid roaming candidates? Site Report Response uses mgmt action frames which are not secured in the current specification. Even if the STA has the BSSID of the AP to pre-authenticate to, it needs to be within the AP’s coverage area to reassociate. Without targeted queries, site report may not narrow the roaming candidates “Site Report” may contain unsuitable roaming candidates SNR is necessary to choose between roaming candidates Using a “site report” as a “candidate list report” may cause the station to pre-authenticate to more APs, increasing load. Bernard Aboba Microsoft

Issues (cont’d) Duplication of the “site report” in other protocols March 2004 Issues (cont’d) Duplication of the “site report” in other protocols Tempting to duplicate the functionality in other protocols, if support is not sufficiently comprehensive Better to have one way to satisfy all “site report” needs, rather than multiple standard ways Vendor extensions OK to “add value” but… Basic elements of the response need to be interoperable Semantics of the response cannot be vendor-specific, only data Bernard Aboba Microsoft

Summary The site report matters. March 2004 Summary The site report matters. In Diagnostics. In Inventory. In performance optimization. Defining the semantics of queries and responses is important. Getting a single facility rather than multiple ones should be a goal. Removing critical functionality does not decrease workload or speed up completion, if you have to implement something multiple times. Bernard Aboba Microsoft

March 2004 Feedback? Bernard Aboba Microsoft