Subject: [MOBILE-IP] Some comments on draft-kempf-cdma-appl-00.txt

From: Vincent Magret <[email-masked]>
Date: Thu, 4 May 2000 11:15:27 -0500

Hello,

In the section 4 you state: "Taking mobile IP as an example, using
mobile IP in the RAN would require that a mobile IP foreign agent (FA)
be present at each base station", I think this argument is little bit
too extreme, in the sense that the closet you locate the FA to the
mobile node, the less efficient will be the protocol. Further more with
the macro diversity scheme defined in CDMA the concept can not be
applied. At least it would gave a better impact if the draft used the
case of locating the FA in the RNC would be discussed. My feeling is the
argumentation tend to take the case that makes the use of Mobile IP
obviously not suitable.

My understanding of macro diversity (and I'm not a radio expert) is that
the splitting realized at the RNC is made so that the information
conveyed via a base station is slightly different to the one sent to
another base station. As you said the mobile node needs to compute some
sophisticated mathematics to get the original information sent.

Best regards,

Vincent.

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From: Pete McCann <[email-masked]>
Date: Thu, 4 May 2000 11:56:27 -0500

Vincent Magret <[email-masked]> (VM) writes:

VM> Hello,
VM> In the section 4 you state: "Taking mobile IP as an example, using
VM> mobile IP in the RAN would require that a mobile IP foreign agent (FA)
VM> be present at each base station", I think this argument is little bit
VM> too extreme, in the sense that the closet you locate the FA to the
VM> mobile node, the less efficient will be the protocol. Further more with
VM> the macro diversity scheme defined in CDMA the concept can not be
VM> applied. At least it would gave a better impact if the draft used the
VM> case of locating the FA in the RNC would be discussed. My feeling is the
VM> argumentation tend to take the case that makes the use of Mobile IP
VM> obviously not suitable.

You are correct - the proper location for a Mobile IP FA is at the RNC
or behind it, NOT at every BTS.  That is what the draft tries to argue.

VM> My understanding of macro diversity (and I'm not a radio expert) is that
VM> the splitting realized at the RNC is made so that the information
VM> conveyed via a base station is slightly different to the one sent to
VM> another base station. As you said the mobile node needs to compute some
VM> sophisticated mathematics to get the original information sent.

I think the frames sent to each BTS are identical, and this is
necessary to achieve the proper effect when the multiple signals are
received by the MN.  However, they are sent with unequal power which
is an aspect not covered by the draft - RNCs typically perform very
tight-loop power control on the signals sent by each BTS.  This is
another aspect that would be difficult to recapture with end-to-end
IP signaling.

-Pete

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From: Andras Veres <[email-masked]>
Date: Thu, 4 May 2000 13:24:15 -0500

Pete,

> another aspect that would be difficult to recapture with end-to-end

What do you mean by 'end-to-end'? It is a message between the
control unit (typically in the RNC) and the BTS or MH. In this
respect it IS e2e, as it involves two (possibly IP layer) nodes.

Andras

--
Andras Veres

http://comet.ctr.columbia.edu/~veres
Columbia University
Dept. of Electrical Engineering mc 4712
500 West 120th Street, H1
New York, NY 10027

Office phone:   (212) 854-3117
Office fax:     (212) 932-9421

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From: Gerald Maguire <[email-masked]>
Date: Thu, 4 May 2000 19:22:42 +0200

Power control is a link layer issue -- not an IP layer issue. Although
at one point some students here looked at doing the power control via
SNMP packets running over IP. I believe that there was a doctoral
dissertation under Prof. Jens Zander which showed what the bandwidth
necessary for doing the power control is -- however, I don't recall
the details exactly.

Note that the combining does not have to happen at any particular
stage in the radio (i.e., you can do it at many different points --
ranging from the very front where it gets called "smart antennas" to
longer after the chips have been converted into bits, but before the
packet is passed up to the transport layer).

Note that since you can't tell the difference between a reflection and
a copy sent by another base station unless the copies set by
basestations were different. But if they were different, then you
would have to do the combining later in the processing. Hence they are
idential to allow the combining at a very early stage.

Chip

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From: Pete McCann <[email-masked]>
Date: Thu, 4 May 2000 13:20:29 -0500

Andras Veres <[email-masked]> (AV) writes:

AV> Pete,
>> another aspect that would be difficult to recapture with end-to-end

AV> What do you mean by 'end-to-end'? It is a message between the
AV> control unit (typically in the RNC) and the BTS or MH. In this
AV> respect it IS e2e, as it involves two (possibly IP layer) nodes.

What I meant by "end-to-end" was an IP stack on an MT communicating
with another IP stack somewhere in the network to convey power control
information.  As Chip correctly pointed out, power control is a link
layer issue, not an IP layer issue.  We should not use end-to-end
IP packets to do power control.

-Pete

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From: veres <[email-masked]>
Date: Thu, 4 May 2000 14:52:22 +0200

Pete,

> IP packets to do power control.

If you consider the RAN to be L2, then it is a L2 issue. If, on the other
hand,
RAN is a L3 network, which means that there are several L3 routers between
the
BTS and the RNC, then signaling between the two nodes is to be done on L3.

In my view the major problem with current RAN is that it tries to reinvent

a networking layer on - what it calls - L2, i.e., L2/L1 radio frames are
routed
in the RAN network (consisting of hundreds of nodes!) - which requires
fundamentally L3 funcions e.g., routing protocols.
And do not forget, that on top of this we still need IP with its own
solution
for routing etc.,  even in the current WCDMA solutions, for all data and
management traffic.

Now, IF on top of this pile, we want to place MIP to interwork with all of
this,
well, where do we end up? Who will be able to manage it? I am not sure
operators
would be happy...

Andras

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From: Behcet Sarikaya <[email-masked]>
Date: Mon, 8 May 2000 13:54:14 +0900

IMHO this draft has several serious (typing) mistakes and when corrected

it is easy to understand and appreciate its conclusion, in short this
draft is not a bombshell
trying to invalidate Mobile IP in cellular networks.

The typos are:
1. base station should be replaced by base transceiver station or BTS
everywhere.
2. RAN should probably be replaced by base station controller or BSC in
most places.
3. that soft handoff is an application layer mechanism should be
replaced by L2 mechanism in at least two places.

Basically BTS is a link layer entity and Jak has a nice picture of it in
Fig.3 of SC-AllIP-20000217-015.

With the above corrections this draft is a nice contribution and makes
its point quite well. I think the largest impact
is with host route based approaches, it is in those drafts that there is
a claim on soft handoff.

--behcet

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From: campbell <[email-masked]>
Date: Mon, 8 May 2000 02:50:57 -0400

> is with host route based approaches, it is in those drafts that there is

Cellular IP supports, what we call, semisoft handoff.