Liang,
Thanks for the good discussion. Please see
comments below.
Regards,
Ulises
From: Liang Chen
[mailto:leo.liang.chen@gmail.com]
Sent: Tuesday, November 08, 2005
9:52 PM
To: Olvera-Hernandez, Ulises
Cc: STDS-802-21@listserv.ieee.org;
Rahman, Akbar
Subject: Re: [802.21] Questions on
the network detection
Plese check my in-line reply.
On 11/9/05, Olvera-Hernandez,
Ulises <Ulises.Olvera-Hernandez@interdigital.com>
wrote:
Dear Liang Chen,
The model described in Section 6.3 is founded on some
assumptions (such continuous network topology update, either manual or
automatic) and it addresses 802.21 Information Service only. The use case that
you described below is supported in principle, although the initial AP
discovery procedure might relay on 802.21 Event Service and Command service and
on certain degree of scanning.
I feel the network topology update is a big problem, because 802.11 AP
can not locate itself in the existing network topology map with the reference
of other networks unless the 802.11 AP installs other radio to collect the
topology information.
[UO] The AP is discovered by the STA(s)
that attempts to associate to it. If the STA is 802.21 capable this information
can be sent to the MIIS over the existing radio connection. Note that this
would only be required the first time the STA discovers the new AP.
An 802.21-capable STA will detect the presence of newly
deployed APs.and it might trigger events leading to the selection of the new
network.
If 802.21 STA could detect the newly deployed AP before handover, the
network topology information is not necessary.
[UO] Only the initial
discovery is required. Once the network topology map is updated, relevant information
might be delivered over the current connection (e.g., a cellular network). The
benefit becomes apparent when the population of STAs attempting to access the
AP increases (e.g., enterprise environment) . This definitely adds value, in
particular considering this specific use case that we are discussion where the
AP has no 802.21 functionality and it is completely oblivious to its
surroundings.
However, it might introduce another problem if we want to support the
make-before-break handover.
[UO] Could you please
elaborate on the problem you see?
Does 802.21 has any proposal for the problem?
[UO] 802.21 does not
address handover policies. Therefore whether a handover is executed using MBB
or BBM is up to the application controlling the handover. 802.21 simply provides
services that allow both modes of operation.
Depending on operator policies and mobility application
controlling HO, the STA might use 802.21 these events to trigger a HO toward
the 802 network. As new APs are "discovered" the Media Independent
Information Service (MIIS) can be updated using 802.21 messages. Note that the
text in section 6.3 emphasizes this by stating that "the MIIS list of
access networks that are supported by MIIIS may also evolve"
Central to the development of 802.21 specification is the
fact that 802.21 does not define handover policies. The 802.21 specification
supports both methods but it does not explicitly favor anyone in particular.
Network operators might choose to define these policies and exert a tight
control on their subsidized terminal equipment. User on the other hand might
want be given full access to the network of their choice and pay for this.
Kind regards,
Ulises
802.21/D00.01
draft describes an mechanism for the vertical handover decision in Sec.
6.3. With the help of networking location information boardcast in
any medium supported by 802.21, STA could aware the surrounding networks before
handover. However, I guess there are some problems in the real scenarios.
1. Due to
the cheap deployment cost of 802.11 AP, users may want to deploy the
802.11 hot-spot in their office or home independently and without the
notification to the WWAN operators. When a user moves to their
home/office from outsides, how user's STA know there is a 802.21
supporting WiFi AP from the location information boardcast by WWAN.
2. How
STA locates itself in the wireless networks map? GPS may not work in-door
and increase the cost.
Moreover,
I am a little confused on the different benefits of network-initiated and
MN-initiated handover mentioned in Set. 5.2.
--
============================
Sincerely yours,
Liang
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