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
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
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
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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______________________________________________________________________
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