1. 21-07-831-00-0000 IEEE 802.21 MEDIA INDEPENDENT HANDOVER DCN: 21-07-0831-00-0000 Title: IE prioritization for query response size limit support Date Submitted: January 16, 2007 Presented at IEEE 802.21 session in London, UK Authors or Source(s): Angelo Centonza, Eleanor Hepworth Abstract: This presentation focuses on providing a solution for efficient formatting of query response messages sent via response size limited lower layer transport protocols

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3. 21-07-831-00-0000 Background In the use of MIH within 802.11 networks the query request and query response messages need being transported by means of the Generic Advertisement Service. The limit on the GAS frame size could affect the amount of information exchanged via MIHF during the network discovery process. The integrity of this information could also be affected in case the original MIHF messages are truncated due to lack of space in the GAS frame. Such frame size limitation is likely to affect the MIHF query response messages, which contain large numbers of instances of the information found in the information server (IS) requested by the MS via MIHF query messages. The above could happen for any underlying transport means other than GAS.

4. 21-07-831-00-0000 Problem At present, the IEEE802.21 standard does not provide a full query-language agnostic tool for adapting the MIHF messages to the size limit imposed by the underlying transport protocol. This means that MIHF messages could be much larger than the transport frame used, therefore resulting in truncation. Also, this means that the information encapsulated in such frames are not chosen according to their importance, but only according to how they are arranged in the IS and truncated by the transport protocol. There is the need of a mechanism that allows for efficient filtering of IEs and IEs instances, allowing query response messages within frame size limits. Such tool shall be query language agnostic so to allow the MIHF to format responses not exceeding limit sizes under the use of any type of query language

5. 21-07-831-00-0000 Suggestions Provide priority levels to the information elements required in query messages from the MIHF in the MS to the MIHF in the IS Enabling the MIHF in the IS to check the maximum transport protocol (GAS in the case of 802.11 networks) frame size in order to understand if the query response message derived by the MIHF in the IS is larger than the maximum GAS frame size Enabling the MIHF in the IS to filter out low priority information as well as instances of the information found in the database in order to reduce the MIHF query response message to the maximum GAS frame size Enabling the MIHF in the MS to send a new query message in case the information filtered out by the MIHF in the IS are considered to be essential Setting a limit for the number of consecutive query messages sent by the MIHF at the MS as the consequence of filtering performed

6. 21-07-831-00-0000 Example Scenario 1/3 The MIHF at the MS sends a query message to the IS in order to discover the following parameters for each network available in the MS hot spot: SSPN (up to 253 bytes) SSID (variable assumed 32 Bytes) ESSID (up to 253 bytes) QoS Capability (28 bytes) Service Provider ID (up to 253 bytes) The group of information listed above is available in the IS database in five instances The MIHF in the IS will be able to retrieve the maximum GAS frame via information exchange with the GAS protocol and to adapt the MIH query response message in an iterative way so to fit it into the maximum GAS frame size.

7. 21-07-831-00-0000 Example Scenario 2/3 To do so priority levels are assigned to the IEs requested If Max Frame is smaller than the whole response size, the MIHF will formulate a new response not including priority 6 IEs. This process can be iterated until the response size is less or equal than the Max Frame value or until the priority threshold is reached. 4139 Bytes

8. 21-07-831-00-0000 Example Scenario 3/3 SSPN, SSID and ESSID might be considered to be essential peaces of information for network discovery purposes. Therefore, the priority threshold is chosen so to include these IEs If the priority threshold is reached during the filtering process and if the MIHF query response is still larger than Max Frame then the MIHF will start filtering out instances of the whole set of information required until the instance threshold is reached If the information received by the MIHF at the MS is considered to be insufficient for the process of network selection a new query message will be submitted to the IS requesting the information filtered out from the previous response. The query messages derived as a consequence of the query response size reduction shall be limited in number, i.e. a maximum number of derived queries shall be fixed. Such number will be probably enforced by the underlying transport protocol (GAS in 802.11)

9. 21-07-831-00-0000 Conclusions A method for prioritising IEs requested in query messages and for formulating query responses within size limits imposed by the underlying transport protocol is presented The two main advantages gained by adopting the described solution are: Enabling information element prioritisation in the MIH query message so to enable query response size reduction and to prevent unwanted truncation or discarding of important information Fixing thresholds to avoid filtering out of information essential for network selection as well as to avoid large number of following queries to be sent to the IS

10. 21-07-831-00-0000 STRAW POLL Move to have authors to draft normative text for potential inclusion into 802.21 draft. Yes =, No =, Abstain =