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Hello, Some comments below to Eric’s mail. BR, Reijo From: owner-stds-802-21@listserv.ieee.org
[mailto:owner-stds-802-21@listserv.ieee.org] On
Behalf Of NJEDJOU Eric RD-RESA-REN 3.12 Handover Policy It is said "Terminal Initiated
Network assisted handofffs should be given preference since the
mobile terminal has knowledge of all the networks an applications
running on the device". I do not agree here
as it can also be argued that Network Initiated terminal assisted mode
brings the possibility for the nework to select the best available
access network for the terminal according to link
utilization and Access Point load information it has and which the
terminal doesn't.
Just letting the terminal have the final decision could then result in
handovers to access network where the user will experience severe service
degradation because it had ignored such information. Comment: This does not necessarily have to
be so that the terminal is not aware of the situation at the AP and vice versa.
Let us assume that we can agree upon a characteristic that would describe the
situation at the STA and AP and which could be used as one information source
for handover invocations. (This characteristic would optimally be common for
all access technologies.) Then if that characteristic is agreed upon, it should
be quite simple effort to build a management protocol to transfer this
information between the AP and STA when needed, for example during the
operation at certain intervals (which has to be studied very carefully so that
the throughput of the links are not sacrificed) and what maybe is more focused
on what Eric is concerned above – in an early phase of the negotiation
procedure where the STA is establishing connection to the AP. An example of
such a management protocol approach can be seen also in the ITU-T Q.714 SCCP –
and in some other places. Also the characteristics of the radio
links have a very dynamic behavior, especially if the STA is in movement –
and also different access technologies have different capabilities to support
the terminal mobility (velocity), these issues must be carefully studied. Also
we should keep in mind that what we today see as a terminal might in the future
be itself a mesh network consisting of a plurality of devices connected with
WPAN (eg 802.15.3/4, Bluetooth, zigbee etc) and some of these devices have
capabilities to communicate with certain access networks and some with other
access networks and some with none. An example of such a network would be the
case where we have removed all the cables we have in our home entertainment
gadgets and replaced them with WPAN – and also added the communication
devices into the same WPAN. This situation is closer than one might think, and
the handover mechanisms should be flexible enough to handle this kind of
situations also. The 802.21 will exist quite many years once it is created. What I try to explain is that it is not so
simple to say that the NW initiated terminal assisted HO is superior to
terminal initiated NW assisted HO – there is quite many things to be
considered here. I agree with Eric that at the requirement
document it might not be an optimal situation to give priorities to different
approaches, maybe it would be better to wait until the detailed technical
investigations of the different approaches have been performed, and thus more
information is available of the pros/cons of the approaches, and then decide
upon the preferences of them. We are not in that position today. Therefore i will suggest just evocating different possible initiationt/assistance
handover modes within the requirements Document without mentioning preference
on any of them. This preference should rather be let at the
discretion of the hanfover policy function that can reside either on the terminal
or the network. |