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Re: [STDS-802-16] SPAM-LOW: Re: [STDS-802-16] [HO] Usage of "network assisted HO supported flag"




How about the descriptive language for the message:
6.3.2.3.55 HO Indication (MOB_HO-IND) message
 
An MS shall transmit a MOB_HO-IND message for final indication that it is about to perform a HO.
Note that the requirement for the MS to transmit HO-IND does not specify correlation with a MOB_BSHO-REQ or MOB_BSHO-RSP, only that the HO-IND message be transmitted, if it can be. If you look at all of the other MAC management messages in 802.16, when paired as REQ & RSP, the RSP always has language that says 'this message shall be sent in response to the xxx-REQ message'. HO-IND does not have such language.
 
There are a lot of reasons for the decision that was made, not the least of which is the likely unavailability of time to conduct HO-REQ and HO-RSP activity during high mobility. But the network works much better if it at least gets an HO-IND with the Target BS ID that an MS intends to handover to. Unpredictive handover (and that is a WiMAX term coined by Alvarion, not an IEEE term; it is called drop handover in 802.16) does not even require HO-IND to be successful, though it may not be well optimized. That was intended when we authored this mechanic in 802.16 as well; graceful recovery from marginalized link performance.
 
There is a lot of language in 6.3.22.2.2 HO decision and initiation that talks about how HO-IND may be used as a response to a BSHO-RSP. There is even some language that says, in certain circumstances, HO-IND should be sent. But we had to be very careful. We could not create some unreasonable rule saying that MS absolutely had to send HO-IND in order to conduct handover because in mobility, especially at time of intent to handover, the channel may become so marginalized that transmittal of HO-IND became impossible. So it is best to think of HO-IND as something the MS should send, if it has the opportunity.
 
We wrote some complicated language in the beginning of the section ('The HO may proceed with a notification...' and the following paragraph) to try and avoid a race condition for MOB_MSHO-REQ/MOB_BSHO-REQ/MOB_BSHO-RSP/MOB_HO-IND. But in any instance it is problematic to attribute an HO-IND to a specific BSHO-RSP. So we made HO-IND both a general response, not to any specific message, and an unsolicited transmittal whereby the MS could signal its will not based on any specific message. For instance, MS can cancel a contemplated handover by sending HO-IND with the Action Code for Cancel without worrying to which instance of any BSHO-RSP it may refer. It cancels ALL contemplated handovers. Same thing with rejection. HO-IND with the Action Code for Reject rejects ALL contemplated handovers.
 
The only time an MS absolutely MUST send HO-IND is when the MS is seeking to cancel a previously announced (via HO-IND with Action Code for Serving BS Release) handover prior to expiration of Resource Retain Timer at the Serving BS. But of course this is not in response to any HO-REQ/RSP action. This is an unsolicited transmission to permit the MS to regain Normal Operation with its Serving BS when aborting a handover attempt.
 
Well, you get the idea.
 
Thanks,
Phillip Barber
Chief Scientist
Broadband Wireless Solutions
Huawei Technologies Co., LTD.
----- Original Message -----
Sent: Wednesday, June 28, 2006 12:44 AM
Subject: SPAM-LOW: Re: [STDS-802-16] [HO] Usage of "network assisted HO supported flag"


Hello,

Going through the specification of 802.16 one does not get a picture that MOB_HO-IND is an asynchronous message.

In my understanding MOB_HO-IND is sent by MS only as a response to previously received MOB_BSHO-REQ
or MOB_BSHO-RSP message from serving BS.

Ofcourse in the uncontrolled or un-predictive HO as per NWG Stage 2 document, the MS can send MOB_HO-IND
asynchronously to serving BS after HO.

Please let me know what sections to refer in the 802.16 specification to understand your point of view that MOB_HO-IND
is sent by MS all by itself without previously received HO messages..

Thanks,
Project Lead

Communication and Embedded Systems,

Larsen &Toubro Infotech,

Bangalore,INDIA





"Phillip Barber" <pbarber@broadbandmobiletech.com>

06/28/2006 09:23 AM

To
"Malini Raghavendra" <Malini.Raghavendra@LNTINFOTECH.COM>, <STDS-802-16@listserv.ieee.org>
cc
Subject
Re: [STDS-802-16] [HO] Usage of "network assisted HO supported flag"





Actually, no timer for BS wait on HO-IND was intended. HO-IND is not actually a response to a specific message (MOB_BSHO-REQ or RSP). You get a race condition if you make HO-IND a response to a message. You have to look at the relationship between MOB_MSHO-REQ, MOB_BSHO-REQ, and MOB_BSHO-RSP carefully and you will see it. Note that the language in the standard says that MS will send HO-IND to signal handover, not as a response to a specific message. So BS cannot start a timer because HO-IND is always 'unexpected'.
 
Thanks,
Phillip Barber
Chief Scientist
Broadband Wireless Solutions
Huawei Technologies Co., LTD.

----- Original Message -----
From: Malini Raghavendra
To: STDS-802-16@listserv.ieee.org
Sent: Tuesday, June 27, 2006 10:25 PM
Subject: Re: [STDS-802-16] [HO] Usage of "network assisted HO supported flag"


Hello Mr Lee,

Your perception of Network Assisted HO is now same as mine.


For the issue of Serving BS releasing the resources when Serving BS does not get MOB_HO-IND,
it can be done in following 3 ways.


The referenced sections are in 802.16e D12 Specification.


case 1: Referring to section 6.3.22.2.5 Termination with the serving BS


Regardless of Resource retain timer, the serving BS shall remove MAC context and MAC PDUs associated with the MS

upon reception of a backbone message from the target BS
indicating MS Network Attachment at target BS.


Case 2 when BS detects MS drop, refer section 6.3.22.2.6 Drops During HO

A drop is defined as the situation where an MS has stopped communication with its serving BS (either in the

downlink, or in the uplink) before the normal HO sequence outlined in Cell Selection and Termination with

the serving BS has been completed.


When the serving BS has detected a drop, it shall react as if a MOB_HO-IND message has been received

with HO_IND_type indicating serving BS release.



Case 3 when BS does not get indication from target BS of successful HO, Refer 11.7.12.1 System Resource_Retain_Time


The Resource_Retain_Time is the duration for MSS’s connection information that will be retained in Serving

BS. BS shall start Resource_Retain_Time timer at MSS notification of pending HO attempt through

MOB_HO-IND or by detecting an MSS drop. The unit of this value is 100msec.


So even when there is a drop the resource retain timer wll be used by BS to retain resource for a possible MS

coming back to Serving BS for resumption of connection.


Another point to note, MSS has T29 and T42 timers which aid MSS is handling MOB_HO-IND retransmissions,


A similar timer support is not given at BS[Not in 16e D12 atleast,], so that BS can wait for a specific time to receive MOB_HO-IND

after sending MOB_BSHO-REQ/MOB_BSHO-RSP.


This should have been defined by standards committee as it is a common support provided for any message based protocol handling.


Thanks,
Project Lead

Communication and Embedded Systems,

Larsen &Toubro Infotech,

Bangalore,INDIA



"Chi-Chen Lee" <jjlee@itri.org.tw>
Sent by: chichen.lee@gmail.com

06/27/2006 08:26 PM


To
"Malini Raghavendra" <Malini.Raghavendra@lntinfotech.com>, STDS-802-16@listserv.ieee.org
cc
Subject
Re: [STDS-802-16] [HO] Usage of "network assisted HO supported flag"







Hi Malini,

I like to correct my perception about the usage of Network Assisted HO supported flag. I think the only difference between Network Assisted HO supported flag is set to "1" or "0" is that if the flag is set to "1", MS can send a MOB_HO-IND without specifying a target BS ID and just using 0x000000 as target BS ID. In contrast, if the flag is set to "0", MS must specify the target BS ID in MOB_HO-IND.
Thus, the last issue is that, in the case of "uncontrolled HO" you mentioned, if serving BS not receives MOB_HO-IND, therefore, resource retain timer will not be started. How can MS decide that it can send MOB_HO-IND with cancel in some abnormal cases such as drop or failed to handover to target BS? Or in this case, the MS should not assume the serving BS will retain the resource allocated to the MS.

thanks,



On 6/27/06, Malini Raghavendra <
Malini.Raghavendra@lntinfotech.com> wrote:

Hello Mr Lee,


Here is my view on the Network Assisted HO Flag going through the specification.


The Network Assisted Flag in
MOB_BSHO-REQ and MOB_BSHO-RSP messages indicates to MS
of serving BS support in specifying the candidate BSs for Handoff .


In this scenario there are 3 cases.

Case 1: When MS decides to handoff with recommended BSs of
MOB_BSHO-REQ or MOB_BSHO-RSP,
as per section 6.3.2.3.55 of IEEE 802.16e-2005 MS may choose to send MOB_HO-IND as a n acknowledgment
with Target BS set to 0x00000000 which indicates the serving BS of MS deciding to handoff.

In which case BS may release its resources allocated for that particular MS without waiting for resource retain timer to expire.

Case 2: When MS decides to handoff but does not send MOB_HO-IND, it is like uncontrolled HO specified in NWG stage 2,
and BS shall retain its resources till the resource retain timer expiry.

Case 3. When MS does not want to handoff, it may choose to send MOB_HO-IND with reject/cancel.

Hence i think the network assisted flag is necessary to be included in the message and signifies a specific behavior in HO.

Let me know if there is any difference in opinion.

Thanks,


Malini Raghavendra

Project Lead

Communication and Embedded Systems,

Larsen &Toubro Infotech,

Bangalore,INDIA


Chi-Chen Lee <jjlee@ITRI.ORG.TW>

06/27/2006 11:28 AM
Please respond to
Chi-Chen Lee <
jjlee@ITRI.ORG.TW>


To
STDS-802-16@listserv.ieee.org
cc
Subject
[STDS-802-16] [HO] Usage of "network assisted HO supported flag"









Hi,

I have one question about the usage of Network Assisted HO supported flag in MOB_BSHO-REQ message and MOB_BSHO-RSP message. In my understanding, if Network Assisted HO supported flag is set to "1" in MOB_BSHO-REQ or MOB_BSHO-RSP message, MS may perform a handover to any BS among the recommended BSs without MOB_HO-IND. However, according to section 6.3.2.3.55 of IEEE 802.16e-2005, an MS "shall" transmit a MOB_HO-IND message for final indication that it is about to perform a HO. It seems that there is conflict between the usage of MOB_HO-IND and the usage of Network Assisted HO supported flag.

There are two possibilities of the above issue:

(1) An MS shall transmit a MOB_HO-IND message for final indication even though the Network Assisted HO supported flag is set to "1", i.e. MS behavior has no difference between Network Assisted HO supported flag is set to 0 and 1. In this case, why we still need Network Assisted HO supported flag? What does it mean to MS?

(2) An MS may perform a handover to any BS among the recommended BSs without MOB_HO-IND. Note that in this case, the MS MAY send MOB_HO-IND with target BS ID = "0x00000000" as an acknowledgement to the MOB_BSHO-REQ message but may not send MOB_HO-IND during actual HO. However, this case incurs another issue: if there is no MOB_HO-IND before MS starts HO, how does the Resource retain timer work in this case? Without Resource retain timer, how can the MS decide that it can cancel HO except in the drop case?

I appreciate any comments and discussion on this issue.

thanks,


==========================================
Chi-Chen Lee
Design Engineer
Wireless System Technology Div.,
SoC Technology Center(STC),
Industrial Technology Research Institute
Tel: +886-3-5914579
Fax: +886-3-5829733
E-mail:
jjlee@itri.org.tw
http://www.stc.itri.org.tw/

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--
Cheers,


==========================================
Chi-Chen Lee
Design Engineer
Wireless System Technology Div.,
SoC Technology Center(STC),
Industrial Technology Research Institute
Tel: +886-3-5914579
Fax: +886-3-5829733
E-mail:
jjlee@itri.org.tw
http://www.stc.itri.org.tw/
==========================================
______________________________________________________________________

______________________________________________________________________


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