RE: [802.21] Limit response message length
Dear All,
We thought about this issue within Tgu and came up with some
ideas/suggestions on how to manage size limit from a MIH prospective.
What Cheng Hong says is correct: we cannot assume that the length limit
imposed by the access network can be controlled.
Also, this limit should not be assumed to be fixed: it may vary
according to the type of access network, the way the access network is
implemented and/or the type of network environment, e.g. highly/scarcely
populated areas.
On the basis of the above a mechanism shall be in place within MIH that
allows for discovery of the access network size limit (GAS size limit in
the case of 802.11). As proposed by Dave Stephenson, the length limit
for GAS Query Responses could be part of the Advertisement Protocol IE
and would apply to the GAS Query Response. The latter is due to the
assumption that query messages are relatively small in size and are
unlikely to exceed size limits.
Therefore, MIH should be capable to acquire such size limit from GAS (in
the case of 802.11) and apply such limit to the response size. As far
as I understand, this should be in line with what Yoshi was proposing.
On the other size, Qiaobing raised another very good point. What do we
do if the response is still larger than the maximum size limit allowed
by the access network? It is not clear that issuing an error message is
the most efficient solution as the STA would probably generate a new
query once a response error is received. In fact, a STA keeping on
querying the IS due to "exceeded response size limit" errors would
probably have a worst effect than the IS sending an over large response.
The solution we would like to propose for this problem is to prioritise
the IE requested by the MIHF in the STA so that if the ensemble of IEs
to be sent by the IS as a response exceeds the access network response
size limit, the IS can formulate a shorter response by filtering out the
IEs with lower priority. If the IEs filtered out by the IS are
essential for the STA a new query can be generated in order to retrieve
these extra information.
Such prioritisation could be achieved for example by adding a priority
field for each IE in the MIH query message or it could be deduced by the
order IEs are listed in the query message.
By prioritising the IEs requested and by allowing the IS to adapt the
response to the maximum size made available by the access network the
STA can at least receive the most important information needed rather
than having its query cancelled. This could help limiting the number of
successive queries and the traffic load generated by MIH.
Kind Regards,
Angelo
-----Original Message-----
From: Cheng Hong [mailto:Hong.Cheng@SG.PANASONIC.COM]
Sent: 18 December 2006 05:16
To: STDS-802-21@listserv.ieee.org
Subject: Re: [802.21] Limit response message length
Hi Yoshi, and all,
Regarding the message length issue, I have a few points of clarification
and comments:
- Firstly, the access network (e.g. 802.11), not the IS Server, has a
length limit on info transported using L2 mechanism. Generally, we
cannot assume this limit can be controlled/prior-known by the MIH IS
Server. In order to prepare the response properly, the IS Server should
be made aware of this length limit (either through STA or access network
directly). Dave Stephenson presented something regarding this point
during Tgu joint session in Dallas.
- Secondly, whether the above limit applies depends on which mechanism
is used, rather than which state the STA is in. For example, Tgu GAS
mechanism is designed to support unauthenticated STA (at state 1).
However, it does not preclude a State 3 STA using it. But, if a STA is
using data plane transport or L3 transport, the limit would not apply,
since it will be treated as data traffic by the access network.
- As for the length limit from the STA (as in your proposal), it is
purely a MIH protocol issue. It may provide the IS Server length limit
info from STA point of view. However, it does not directly solve the
(above mentioned) access network length limit problem. As pointed out by
Michael, one possible way is to allow network to piggyback the access
network length limit to the message you proposed. Another possibility is
for the STA to obtain the length limit info from broadcast/beacon of the
network, and reflect that in the info element you proposed. I think all
the above require some changes to the access network functions, and
therefore, we might want to talk to Tgu regarding the proposed
changes/requirements.
Cheers
Cheng Hong
> -----Original Message-----
> From: stds-802-21@ieee.org [mailto:stds-802-21@ieee.org] On Behalf Of
> Yoshihiro Ohba
> Sent: Saturday, December 16, 2006 7:21 AM
> To: Qiaobing Xie
> Cc: STDS-802-21@listserv.ieee.org
> Subject: Re: [802.21] Limit response message length
>
> Hi Qiaobing,
>
> On Fri, Dec 15, 2006 at 03:16:18PM -0600, Qiaobing Xie wrote:
> > Yoshi/Michael,
> >
> > A few thoughts on this:
> >
> > 1. The network (I guess this means the IS server) may want
> to impose
> > different size limit depending on the mobile is in
> unauthenticated or
> > authenticated state. Should there be a way the IS server can know
> > about this?
>
> This is a good point. I believe that the IS server does not have to
> know the mobile's authentication state. There are three cases.
>
> Case 1: IS queries originated by State 1 station. Since State
> 1 station cannot directly communicate with IS server, AP acts as a
> proxy MIH IS client on behalf of the station. In this case, the
> source address of MIH_Get_Information Request message will be the MAC
> address of the AP. The AP should set the per-query MTU needed for
> State 1 queries.
>
> Case 2: IS queries originated by State 3 station. State 3 station can
> directly communicate with IS server. In this case, the source address
> of MIH_Get_Information Request message will be the MAC address of the
> station. The station may set whatever per-query MTU it wants.
>
> Case 3: IS queries originated by AP. AP may want to generate queries
> on behalf of itself for many reasons. In this case, the source
> address of MIH_Get_Information Request message will be the MAC address
> of the AP. The AP can may whatever per-query MTU it wants.
>
> The IS server cannot distinguish Case 1 and Case 3, but it does not
> really have to distinguish the two cases if we expect the AP to set
> per-query MTU differently in Case 1 and Case 3.
>
> For all cases, the IS server can impose its own limit less than that
> is specified by the IS client.
>
> >
> > 2. The actual size limit of a query/response exchange will
> be the the
> > lesser of the mobile's self-imposed limit and network imposed limit.
>
> Yes.
>
> >
> > 3. What should be the consequence if the response is over
> the lesser
> > of the mobile limit and network imposed limit? Probably we
> simply fail
> > the query with some error code.
>
> Yes, the IS server should return a response with an error indication
> in this case.
>
> Regards,
> Yoshihiro Ohba
>
>
> >
> > regards,
> > -Qiaobing
> >
> > Michael.G.Williams@NOKIA.COM wrote:
> > >Yoshi,
> > >
> > >Sounds good. Ideally we want a way for the mobile in one
> packet to
> > >query and the network in one response packet give the
> response back,
> > >esp. in unauth state where fast scanning or high mobility
> are issues,
> > >yes? Is piggybacking the details of limit request or
> enforcement onto
> > >that exchange possible?
> > >
> > >Michael
> > >
> > >-----Original Message-----
> > >From: ext Yoshihiro Ohba [mailto:yohba@tari.toshiba.com]
> > >Sent: Friday, December 15, 2006 10:02 AM
> > >To: Williams Michael.G (Nokia-ES/MtView)
> > >Cc: STDS-802-21@listserv.ieee.org
> > >Subject: Re: [802.21] Limit response message length
> > >
> > >Yes, the network can always impose its own limit if the
> maximum size
> > >specified by the mobile is still too big.
> > >
> > >Yoshihiro Ohba
> > >
> > >On Fri, Dec 15, 2006 at 11:16:10AM -0600,
> > >Michael.G.Williams@NOKIA.COM
> > >wrote:
> > >>HI Yoshi,
> > >>
> > >>That approach could work, as long as the network would
> also need to
> > >>be
> > >
> > >>able to impose/enforce the limit if the mobile's request
> is too big,
> > >>right? That was Tgu's concern I think.
> > >>
> > >>Best Regards,
> > >>Michael
> > >>
> > >>-----Original Message-----
> > >>From: ext Yoshihiro Ohba [mailto:yohba@tari.toshiba.com]
> > >>Sent: Thursday, December 14, 2006 8:50 PM
> > >>To: Williams Michael.G (Nokia-ES/MtView)
> > >>Cc: yohba@tari.toshiba.com; STDS-802-21@LISTSERV.IEEE.ORG
> > >>Subject: Re: Limit response message length
> > >>
> > >>Hi Michael,
> > >>
> > >>What I am trying to do is to add a new parameter in
> > >>MIH_Get_Information.request/indication primitives, which
> is used for
> > >>specifying the maximum size of InfoQueryParameter to be
> returned in
> > >>the corresponding confirm/response primitives, and a new TLV to
> > >>carry the parameter in MIH_Get_Information Request message. This
> > >>allows the
> > >
> > >>querier to specify a different MTU for each query so that
> a smaller
> > >>size can be specified for queries performed in State 1 of 802.11.
> > >>
> > >>We could also define error handling for errors relating
> to message
> > >>size, if needed.
> > >>
> > >>Regards,
> > >>Yoshihiro Ohba
> > >>
> > >>On Thu, Dec 14, 2006 at 06:03:56PM -0600,
> > >>Michael.G.Williams@nokia.com
> > >>wrote:
> > >>>Yoshi,
> > >>>
> > >>>Thanks for tracking this. If possible, could we email a
> bit about
> > >>>it
> > >
> > >>>as it was something .11u was concerned about too.
> > >>>
> > >>>This value could be something configurable by the
> network operator
> > >>>or mobile node provisioner. It could vary from operator to
> > >>>operator,
> > >
> > >>>and possibly vary under other circumstances such as
> authorized vs.
> > >>>unauthorized use of the network, or even query to query.
> > >>>
> > >>>So if the solution here can be something that is discovered, or
> > >>>handled via error cases (i.e. the limit is provided in
> response to
> > >>>an attempt to exceed it) that might provide the
> flexibility and the
> > >>>constraints needed.
> > >>>
> > >>>Best Regards,
> > >>>Michael
> > >>>
> > >>>
> > >>>
> > >>>-----Original Message-----
> > >>>From: ext Yoshihiro Ohba [mailto:yohba@tari.toshiba.com]
> > >>>Sent: Thursday, December 14, 2006 12:06 PM
> > >>>To: Williams Michael.G (Nokia-ES/MtView)
> > >>>Cc: STDS-802-21@LISTSERV.IEEE.ORG
> > >>>Subject: Re: [802.21] Conference call tomorrow Dec 14th
> 9AM Eastern
> > >>>Time US
> > >>>
> > >>>In today's telconf, I forgot to mention that I am working on:
> > >>>
> > >>>> 1.1.4. Limiting Response Message Length: Need a
> > >>>>mechanism to limit the response length of a query.
> > >>>>
> > >>>Regards,
> > >>>Yoshihiro Ohba
> > >>>
> > >>>
> > >
> >
>