Subject: Re: [MOBILE-IP] charter update

From: James Kempf <[email-masked]>
Date: Tue, 7 Mar 2000 14:40:36 -0800

Jim,

Thanx for your reply.

>>The example of CDMA networks is somewhat unclear, and seems to lay between
>>these two cases. These networks typically have a requirement for very
>>fast handoff and stringent QoS guarantees because they are primarily voice.
>
>It is true re: fast handoff and QoS but these aspects occur at the physical
>layer. A packet data stream over CDMA would not be subject to either of
>these conditions as they occur below L2. Packet mobility-related handoff
>occurs at IWF (or PDSN) boundaries and only occur at boundaries.
>

I was speaking about packetized voice in the RAN, not strictly packet
data bound for the Internet. What I was trying to describe was a RAN in which
the transmitters are sending a stream of packets back through the RAN to a
controller that selects one for the core network and, conversely, in which a
controller is splitting packets as they come off the core network and sending
multiple streams into the RAN to the transmitters. The packets can be either
AAL2/ATM (as in the release 99 3GPP network) or, hypothetically, IP. I was not
speaking about what happens after the packets go on the air.

>>They
>>also don't obey the subnet model very well, because there can be multiple
>>physical packet streams coming from/going to a mobile node through individual
>>radio access points that logically correspond to a single packet stream
>>outgoing
>>from the mobile node or incoming from the corresponding node.
>
>This statement is not accurate. Now it is true that at the physical layer
>CDMA when a user on a traffic channel is in a soft or softer handoff
>condition (ie. connected to multiple BTSs) that traffic channel frames are
>moving between the mobile and multiple BTSs, BUT these are in fact the same
>frames coming from multiple sites. For voice they are the same voice
>frames, for data they are the same packets. In either case the the CDMA
>physical layer 'merges' them together. In summary this situation should not
>be considered multiple packets coming/going because they are not.
>

My understanding is that a CDMA mobile terminal can be receiving up
to 6 streams at once, and, as you say, uses an L1 algorithm to
combine these streams into a single voice or data packet that the
upper layers see.

But as far as the network is concerned, these multiple streams need to
be generated from a single stream incoming from the core network. Conversely,
the outgoing streams received by the transmitters need to be combined
at the controller into a single stream which the core network sees.

Since the RAN is running a standard, wired L1/L2 (and potentially L3) the
splitting and combining must be done on top of a standard, wired protocol, no?

Similarly, when soft handoff occurs, the RAN must arrange for the
incoming and outgoing streams to follow the mobile. My understanding
is that this is currently done with proprietary RAN protocols that
each individual radio vendor supplies.

>>The multiple streams get combined in the radio access network into a single
>>packet stream or on entrance to the radio access network are generated by
>>splitting the single stream coming from the corresponding node.
>
>Ahh, this is true.
>
>>The mobile IP framework doesn't handle this case very well.
>
>This is where I do not agree. MobileIP has no idea the combining/separating
>has even occured. So mobileIP has no problem with this as soft/softer
>handoff would only occur within a single operators equipment (so a single
>PDSN would be the case for all soft/softer handoff situations).
>

Agreeed, that is the case for packet data generated in user applications
on the mobile terminal that is bound for the Internet. But consider somewhat
lower down, where what's flowing over the wire is not the packets generated
by the user's application on the mobile terminal, but rather shaped
radio packets generated by the controller. These radio
shaped packets are unpacked and transmitted and reassembled at the
mobile terminal by the L1 process you describe above to generate
either packet data or voice packets. Similarly in the opposite direction.

The upshot of this is that the RAN considered as a separate network (i.e.
not as an addressable part of the global Internet) has multiple data
streams that physically get combined at L1 in the mobile terminal
into a single logical data stream. And these multiple streams move as the
mobile terminal moves. The issue I've been trying to present is that
the movement of these multiple streams in the RAN are not well
modelled by the current mobile IP architecture.

>So in summary the CDMA network does NOT introduce additional complexity for
>network layer mobility.
>

I agree if you consider the PDSN (or SGSN and GGSN in GPRS) and
connectivity to the Internet. But if you look at the RAN as a self contained
network, and consider soft handoff for mobility, then I would maintain that it
does introduce more complexity, due to the multiple incoming and
outgoing streams (macrodiversity in the cellular jargon).

                jak

---

From: Jim Willkie <[email-masked]>
Date: Wed, 8 Mar 2000 07:59:51 -0800

>outgoing streams (macrodiversity in the cellular jargon).

James:

A CDMA network handles soft handoff within the RAN, so network components
outside the RAN should not be involved in soft handoff issues. Now an all
IP network in the RAN would introduce some hassles. I would think that this
is a shortcoming of 'all IP' within a RAN and not a complexity of CDMA.
Perhaps people that are on the 'all IP' bandwagon should consider that and
weigh the benefits versus the hassles of 'all IP'.

Jim Willkie