Subject: Re: [MOBILE-IP] Applicability of IP Mobility to CDMA Soft Handoff

From: Arek Dadej <[email-masked]>
Date: Fri, 5 May 2000 05:06:09 +0930

Andreas,

Please let us not forget that the mobile radio environment is slightly
different from what you are used to in a fixed IP world - a cable from point to
point, with virtually unlimited bandwidth (if one cable is not enough, you can
always add some...). I think in the discussion thus far, the only real voice of
reason has come from Pete. Mobile radio is a very complex beast and, for
efficiency, involves such tricks as the diversity discussed here (and there is
more to come - time/space diversity, smart antennas etc...), most of them
involving coordinated activities of multiple base stations. This clearly
touches the network level, and therefore the mobile radio access cannot be seen
as L1/L2 only. It is, in fact, an infrastructure involving at least layers 1 -
3, ALL of them radio access specific. Why should it be replaced by
radio-ignorant standard Internet protocols? See more below -->

-----Original Message-----
From: Andras Veres
To: [email-masked]
Sent: 5/5/00 3:36 AM
Subject: Re: [MOBILE-IP] Applicability of IP Mobility to CDMA Soft Handoff

All,

I think that draft-kempf-cdma-appl-00.txt assumes a scenario where
all components of a WCMDA network remain the same, only the networking
layer would be replaced by IP.

If this is the case, I am not surprised at all that we run into
serious problems. The reason is that WCDMA was designed based on the
circuit switched model and it follows the principle of
    ** total control for maximum efficiency (TM) **.

******* What else would you expect? The operators pay billions of dollars for a
chunk of scarce radio bandwidth. A very small change in efficiency of using
that bandwidth may mean a swing in the balance between cost of operation and
revenue. Simplicity of equipment and system architecture becomes much less
relevant here - no equipment is as expensive as the chunk of radio spectrum the
operator needs to buy. Besides, with the progress in technology, the cost of
equipment goes down, unlike the cost of radio spectrum which continues to grow.
*******

I think that one thing we can learn from IP is that by eliminating
total control, of course we loose in performance, but we gain a lot
in simplicity and scalability. (And who knows, this loss may
be negligible - just think of the great performance of IEEE 802.11)

******* Is this really a lesson to learn from IP? Maybe one could agree long
years ago, when the Internet was no more than enjoyable toy for a few computer
scientisis, but not now, when we expect it to grow to the level of  IP-centric
solution to all communications needs of general public. If you were right, the
IETF repository would not contain such a huge volume of RFCs and Internet
Drafts as it does now. Clearly, the new role of Internet calls for new
solutions, and these new solutions somehow refuse to be simple. As to the
802.11, it was designed for a different purpose and different "geographical"
scope than cellular networks. Not much of a lesson from 802.11 applies to
cellular environment. ********

I know that radio channels call for more control than usual IP
networks (e.g., Ethernet), but I do beleive that the current
WCDMA and 3G concepts are fundamentally problematic and not
scalable -- requiring terrible protocol stacks (IP over ATM
over UDP over IP over Whatever over AAL2 over ..... :-),
leading to such monsters like RNC.

***** Terrible protocol stacks? Why? If the specifics of mobile radio
environment call for solutions that span across layers 1-3 (or higher), because
diversity schemes neccesary for efficiency reasons involve co-ordinated
activities of a number of geographically distributed entities,  what's wrong
with that? Would you rather replace these radio-specific solutions with
standard Internet? In that case, why not use the same L1 transmission scheme
over the mobile radio channel as, say, in a cable-based 802.3 network? Clearly,
the Radio Access Network is a very specific infrastructure upon which
IP-centric network can be build. And, there is nothing terrible in the way the
protocols are stacked upon each other, if you only have a right "mental tool",
or template, to deal with that. Have you ever heard of STRATIFIED protocol
stacks? You must have heard of looking at the protocol stacks in terms of three
planes (user, control and management). That was the first step to aid
visualisation of protocol stacks that involve multiple protocols at the same
layer level. Te concept of planes simply categorises protocols in the same
stack by their purpose/function. The next step is to recognise that a stack of
protocols spanning across layers 1-3 can be (from above) treated in the same
way as you treat Physical Layer (an infrastructure that can be used to transmit
data from point to point), upon which you can use L2 and L3 protocols of your
choice. You can iterate that trick a number of times. Each time, what ends at
L3 is treated as an infrastructure layer from the layer above. This process of
STRATIFICATION is described in the ITU-T Recommendation I.322. It is a very
slick and useful way of interpreting complex systems, where protocols do not
fall nicely into a typical 7-layer stack. Whenever you see the same level
protocol in more places than one when traversing the stack upwards, you may
need to stratify the stack. Try the stratification concept on your example
above, and it will look VERY SIMPLE. The RAN is a stratum (often made of
multiple strata itself). ******

Cheers
--Arek

James: Do you think that IP is still a non-feasible solution,
if we consider that even the curcuit switched model may be
redesigned based on IP principles?

Regards,
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

---

From: Andras Veres <[email-masked]>
Date: Thu, 4 May 2000 16:19:11 -0500

Arek,

I think there is a slight misunderstanding here. When I claim that RAN
should be built on IP, I do not mean that radio specific optimizations
should be forgotten. These two can coexist easily.

I am targeting the terrestrial access network (RAN). I have seen reports
claiming that only ATM can support the QoS requirements of WCDMA.
Is it true?

I am sure it is not. ATM does not contain any fundamental differences
compared IP regarding QoS. The current UMTS standard is based on an
IP/AAL2/ATM stack, each implementing its own QoS architecture -
and the QoS definitions defined in these layers are highly incompatible.
The end-result?
 - large overhead
 - mapping between service classes lead to unnecessary underutilization
 - complexity

To reply to the isses of the radio channel, it is for sure that it
is the focus: by using smart antennas, soft handoff, and don't forget
softer handoff (which has higher gain than soft handoff) the efficiency
of the scarce radio can be significantly improved.
In many countries the radio network is redesigned every few weeks
(by adjusting antennas etc.) to squeeze the most out of the radio.
On the terrestrial side this means that it has to be reconfigured
much more often than in a fixed IP network, it has to be managed
more frequently, which can only be solved by a simple RAN architecture.

Regards,
Andras
PS: I think we are getting more and more off-topic, so I should stop
now.

--
Andras Veres