Subject: Re: [MOBILE-IP] Differences between the two MIPv4 handoff approac hes

From: "Hesham Soliman (EPA)" <[email-masked]>
Date: Tue, 28 Nov 2000 08:21:31 +1100

Hello Ajoy,

>         at source or target. Whereas I think, the fast handoff assumes
> that
>         it is possible to register mobile node through old access point
>         which is not possible in most of the current networks. For
> example,
>         in case of 802.11 network, it is not possible to register through
> the
>         old access point as only target AP knows about the handoff before
>         link layer handoff is complete. So we can not assume something
> which is not
>         doable in present network.  <AS>
>
        =>  Are you saying that the MN does not know that it's about to
        do a handoff in 802.11 ? If that's what you're saying then I
disagree.
        The MN would know that handoff is about to take place.
        Also please elaborate on why you say Fast Handoffs doesn't
        work in current systems. What is not doable in a present network ?

        While we're discussing this particular system (802.11) perhaps
        you could explain how the proactive approach would work in 802.11.
        A simple point form will do.

        Regards,
        Hesham

---

From: Ajoy Singh <[email-masked]>
Date: Mon, 27 Nov 2000 16:56:55 -0600

<AS> No, I was not saying that MN does not know about the link layer handoff
in
802.11. I was just saying that the source AP does not know about the
link layer handoff until link layer handoff is complete.
The MN does not have enough time to discover the IP address of
target FA through old AP and perform mobile/IP registration
through old AP with target FA. <AS>

<AS> I think, 802.11 AP can be modified to provide target trigger
required for proactive handoff. Perhaps the target trigger can be initiated
at the reception of some link layer handoff message at target AP. The link
layer
message can be modified or some field of link layer message (e.g., source AP
id) can be used
to deduce the IP address of source FA required at target FA. Please
note we are not assuming that MN should be connected long enough
with source AP to allow sufficient time to perform mobile/IP registration
through old AP. This type of assumption brings lots of RF related
issues which may be too much to change and may adversely affect the
capacity of wireless network.  <AS>

-----Original Message-----
From: IP Routing for Wireless/Mobile Hosts (mobile-ip)
[mailto:[email-masked]]On Behalf Of Hesham
Soliman (EPA)
Sent: Monday, November 27, 2000 3:22 PM
To: [email-masked]
Subject: Re: [MOBILE-IP] Differences between the two MIPv4 handoff
approac hes

        Hello Ajoy,

        Regards,
        Hesham

---

From: Eunsoo Shim <[email-masked]>
Date: Mon, 27 Nov 2000 18:49:32 -0500

Please let me participate in this discussion.
Proactive Handoff requires modifications in link layer messages or system
functionality to convey the IP address of the new FA to the old FA or the
other way around as described in the below.
You might have good solutions to do it for CDMA networks and WLAN.
But I am hearing that people are trying to allow multiple access in
Bluetooth and also hearing about developments of various new wireless link
technologies. People would need to consider Proactive Handoff in their
wireless link design or system design to support fast handoff for IP.
I don't feel comfortable in putting some constraint on link layer
technologies to support mobility support in IP level.
IP is considered to be easy to deploy. I guess one of the reasons is that it
works with almost all the link layer technologies well without reqiring
modifications on lower layers.

Eunsoo

----- Original Message -----
From: "Ajoy Singh" <[email-masked]>
To: <[email-masked]>
Sent: Monday, November 27, 2000 5:56 PM
Subject: Re: [MOBILE-IP] Differences between the two MIPv4 handoff approach
hes

---

From: Pat Calhoun <[email-masked]>
Date: Mon, 27 Nov 2000 15:52:54 -0800

> other way around as described in the below.

Not at all. I am not sure where this came from.

> technologies.
Exactly what we intended

> People would need to consider Proactive Handoff in their

Right, and I would feel uncomfortable with requiring mods to link layers as
well.

PatC

---

From: Eunsoo Shim <[email-masked]>
Date: Mon, 27 Nov 2000 19:24:03 -0500

----- Original Message -----
From: "Pat Calhoun" <[email-masked]>
To: <[email-masked]>
Sent: Monday, November 27, 2000 6:52 PM
Subject: Re: [MOBILE-IP] Differences between the two MIPv4 handoff approach
hes

> Not at all. I am not sure where this came from.

That came from a few things.
One of them is one of Ajoy's messages copied in the below. To stress the
point, I copied it from Hesham's reply to Ajoy's message.
Also I don't know how the IP address of the new FA can be conveyed to the
old FA in the existing wireless networks without any modification in the
link layer messages or the network system and I have not heard any explicit
answer about it after I asked the question in this mailing list.
If you let me know it, I would appreicate it.
----------------------
> at the reception of some link layer handoff message at target AP. The link
        => So for proactive to work we have to modify that link layer.
        Exactly my point.

        Regards,
        Hesham
-----------------------

> Right, and I would feel uncomfortable with requiring mods to link layers
as

I am glad that we are in the same position regarding it. I don't like
arguing about philosophical differences. :-)
Then please let me state my question again:
How would the new FA know the IP address of the old FA?

This is my biggest and probably sole question about Proactive Handoff.
Thanks.

Eunsoo

---

From: Pat Calhoun <[email-masked]>
Date: Mon, 27 Nov 2000 16:30:04 -0800

[...]
> arguing about philosophical differences. :-)

Good, because that's pretty much where this whole thing has ended up...
somewhat reminds me of the current elections :)

> How would the new FA know the IP address of the old FA?

How a Foreign Agent knows the identity of Access Points, Base Stations, or
whatever terminology one wants to use is through configuration. When a network
is deployed, each adjoining cells (or coverate area) are configured, as are
the IP addresses of the Foreign Agents handling those cells.

btw, there is NO difference here between proactive and fast handoff. In both
cases, the old Foreign Agent contacts the new Foreign Agent. This is either
via the Handoff-Request (Proactive), or by issuing an Agent Advertisement on
behalf of the Mobile Node. If one wants to have smooth handoffs (I am using
the term smooth here because fast handoff would incorrectly reference Hesham's
proposal).

> This is my biggest and probably sole question about Proactive Handoff.

I hope I answered it.

PatC

---

From: Ajoy Singh <[email-masked]>
Date: Mon, 27 Nov 2000 18:51:47 -0600

<AS> If AP implements FA functionality then no link layer change is
required to support Proactive handoff. The link layer message carries source
AP ID which can be used
to deduce source FA address.  I think, Pat mentioned that Cisco
AP supports FA functionality. <AS>

-----Original Message-----
From: IP Routing for Wireless/Mobile Hosts (mobile-ip)
[mailto:[email-masked]]On Behalf Of Eunsoo Shim
Sent: Monday, November 27, 2000 6:24 PM
To: [email-masked]
Subject: Re: [MOBILE-IP] Differences between the two MIPv4 handoff
approach hes

----- Original Message -----
From: "Pat Calhoun" <[email-masked]>
To: <[email-masked]>
Sent: Monday, November 27, 2000 6:52 PM
Subject: Re: [MOBILE-IP] Differences between the two MIPv4 handoff approach
hes

        Regards,
        Hesham
-----------------------

Eunsoo

---

From: Eunsoo Shim <[email-masked]>
Date: Mon, 27 Nov 2000 21:17:30 -0500

----- Original Message -----
From: "Ajoy Singh" <[email-masked]>
To: <[email-masked]>
Sent: Monday, November 27, 2000 7:51 PM
Subject: Re: [MOBILE-IP] Differences between the two MIPv4 handoff approach
hes

> AP supports FA functionality. <AS>

[eunsoo]
In CDMA's soft handoff mechanisms, the MN provides id of the new BS in the
link layer message to the old BS.
So if the FA has access all the contents of the link layer messages to the
BS or they are the same entity as you said in the above, the FA would be
able to figure out IP address of the new FA or the old FA from configuration
or other similar mechanisms.
Recently I saw slides showing the all IP approaches in the 3GPP2, which put
BCS and PCF between BS and PDSN. It seems to me they want to put FA at PDSN.
I don't know all the details of the interfaces between each entity and what
information is transferred between them. But it does not look obvious that
the FA has access to all the information each BS gets. Actually you said
there might be need for 'slight' modification in a previous email. I copied
that part from your email in the below.
------------------------
<copied from one of Ajoy's messages>
> -> Even in case of CDMA network, FA is not collocated with radio quipment.
> We all agree that some changes are required at network side to
> get trigger at source/target Foreign agent. For example, in case of CDMA
> 2000, we might
> have to make slight modification to R-P interface to send foreign agent
> address
> from PCF to PDSN. Similarly, we have to make some changes where FA is not
> collocated
> with radio equipment. The exact nature of changes will be dependent upon
> the
> specific technology and should be decided by respective SDOs.
------------------------

If 3GPP2 people put FA on BS, this would disappear again I guess.
Probably it can be argued that this is a matter of network configuration or
implementation.
I wonder whether it is a simple issue for them to change the location of the
FA from the PDSN to the BS.
I hope it is.
Still I have some questions.
How about 3GPP?
I think CDMA will be a dominent wireless link technologies in the near
future since all 3G technologies are based on CDMA and also WLAN is. Due to
its soft handoff capability, the new BS's ID and other similar information
can be retrieved from the old BS.
Can we assume this kind of soft handoff is generally available in the
current or future wireless technologies? Isn't it a special case considering
many kinds of wireless network technologies? Also such capability is not
available with GSM. People say 2G network won't disappear very soon. Do we
exclude GSM or other non-CDMA wireless networks from our handoff design?

I am not sure whether supporting WCDMA, CDMA2000 and WLAN (802.11 probably)
is good enough. Am I bringing in non-practical concerns?

Thanks.

Eunsoo

> Subject: Re: [MOBILE-IP] Differences between the two MIPv4 handoff
approach

---

From: Eunsoo Shim <[email-masked]>
Date: Mon, 27 Nov 2000 21:25:01 -0500

----- Original Message -----
From: "Pat Calhoun" <[email-masked]>
To: <[email-masked]>
Sent: Monday, November 27, 2000 7:30 PM
Subject: Re: [MOBILE-IP] Differences between the two MIPv4 handoff approach
hes

> the IP addresses of the Foreign Agents handling those cells.

[eunsoo]
Probably I did not state my question very well.
What you are saying is that mapping between cells (or AP or BS) and the
correspoding FA's addresses is configured.
I understand this.

My question is how the old FA finds out the IP address of the new FA before
the MN registers itself with the new FA?
1) First of all, it requires the old FA to know where the MN is going. Then
the old FA should be able to retreive the ID of the BS covering the new cell
or area.
2) Last, it should be able to map the information to the IP address of the
new FA.

Without assuming soft handoff in link layer, I wonder how the old FA knows
where the MN is going.
I guess you answered about the second issue, that is, 2) in the above.

Thanks.

Eunsoo

---

From: Pat Calhoun <[email-masked]>
Date: Tue, 28 Nov 2000 07:19:11 -0800

> that part from your email in the below.

You are correct, the FA is in the PSDN, and not in the BSC. However, there are
a couple of things to consider:

1. The PCF runs a protocol known as the R-P protocol. Proactive FA is very
well suited for this purpose. This is similar to the PDSN being a GFA, and the
PCF being an FA. (It is slightly more complicated than this, but it is
sufficient to state that proactive works because the PCF receives the link
layer triggers from the BSC).

2. As the work in OpenRAN continues, it is likely that IP will be introduced
in the RAN. Once this is done, a BSC may be a likely Foreign Agent.

Correct, but proactive is still useful on the PCF.

> FA from the PDSN to the BS.

Not in the short term, but again it isn't necessary.

> Still I have some questions.

I do not have an answer to this question because I concentrate on P2. I have
heard that 3GPP is very reluctant to make use of Mobile IP within their
networks, but have considered using a Foreign Agent at their network boundary.
If they aren't using Mobile IP, then I am not sure that anyone has an answer
to this question.

DISCLAIMER: I don't participate in 3GPP meetings, so things may have changed
in the past months.

> many kinds of wireless network technologies?

I believe that a wireless technology that does not have a proper handoff
mechanism is flawed, so I hope the answer is no (but I am willing to be proven
wrong).

> Also such capability is not

I believe that people with expertise in such networks need to step up to the
plate, and help us in our design. However, we MUST consider the networks that
do NOT provide sufficient time for the mobile to start reacting, and this is
what proactive FA assumes. In networks where the mobile is instructed to
handoff (immediately), proposals that require the mobile to interact with the
network will NOT work. In networks that DO provide time for the mobile to
interact, then proactive FA would work anyways. Right?

> is good enough. Am I bringing in non-practical concerns?

Not at all. My point all along was to get people to being in concrete examples
where things wouldn't work, and no one has yet to do so. I am talking about
examples where the link layer COULD NOT work with proactive FA, not
implementation issues of co-locating an FA with an access point.

Again, the co-authors of the proactive FA I-D are more than willing to work
with any concerns, and tweak the protocol as needed. We welcome comments such
as these, but non-fact based hand-waving is not all that useful (which is NOT
what this e-mail was about, but some other threads certainly fall within that
realm :(

PatC