Subject: Re: [MOBILE-IP] Fast Handoff Issues

From: James Kempf <[email-masked]>
Date: Mon, 24 Jul 2000 14:34:37 -0700

Hi Pete,

Actually, I was talking about interdomain, single technology
hard (break before make) handoff.

The case is the following. Suppose in today's network you have
two RANs (wCDMA, cdma2000, EDGE) whose only connection is through an MSC.
Now, replace the MSC with an IP core network. The only way you can do hard
handoff is if there is some RAN specific information
that goes through the IP core. Otherwise, the old RAN can't
learn the radio quality seen by the new, and the new can't learn
the channel parameters.

The IS-41 HandoffMeasurementRequest and FacDir messages accomplish
this in today's core networks. For interdomain hard handoff to
work in all IP networks, there would need to be some kind of
replacement.

I agree that, for the intertechnology handoff to work, the mobile
node may need to get involved.

                jak

>Hi, James,
>
>James Kempf <[email-masked]> (JK) writes:
>
>>> I know some of the considerations I've raised are really link-specific
>>> issues, but their impact on the fast handoff mechanism should be
>>> considered.  It may turn out that fast handoff is best addressed in
>>> the appropriate link-layer groups (3GPPs, IEEE) and not the IETF.
>
>JK> Well, there's an issue you've not included:
>
>JK> - There needs to be some radio-link independent way to transfer radio
>JK> quality measurements and radio link context information between the two FAs
>JK> at L3.
>
>I'm not so sure that there is a need for this.  Just for information,
>here's how it works in CDMA today: the BSC, based on pre-provisioned
>information, tells the MN to watch the pilot strengths of a number of
>neighbor BSCs in a "candidate set."  When some of these measurements
>exceed a threshold for a given duration, the MN reports that fact to
>the BSC.  The BSC then decides whether to initiate a hard or soft
>handoff.  Soft handoff is uninteresting here because it does not
>involve a change in the MN's L3 point of attachment.  In hard handoff,
>a message is sent to the candidate BSC asking if it has the radio
>resources (and other resources) necessary to accept the handoff.  If
>so, the handoff is requested and the MN is told on which channels
>to re-tune.
>
>To me, this process only makes sense if both BSCs are of the same
>technology.  It is theoretically possible for BSCs of different
>technologies to run the message flow above, but at each step, the
>information must be translated from one system's representation to
>another, and the measurements might even be so totally different in
>shape that this is not possible.
>
>If you do have two different technologies, such as 802.11 and
>cdma2000, then it should be up to the MN to decide when it wants to
>hand off.  I do not think we can expect the cdma2000 BSC to get
>involved in asking for power measurements from WaveLAN.  The MN
>supports both technologies (and there is probably a different pricing
>model involved for the two services) so it is in the unique best
>position to make a decision.  Also, a fast handoff can be completed
>simply by bringing up the WaveLAN before shutting down the cdma2000
>link - both interfaces are physically present on the MN so this should
>be doable.  No interaction between the two networks is required.
>
>JK> As I mentioned in my response to Karim, the mobile IP working
>JK> group may not be the place to work this out if the taboo on L2 is
>JK> so strong, but it *will* have to be worked out somewhere,
>JK> regardless of the ultimate fast handoff scheme we adopt, if mobile
>JK> IP interdomain handoff is to work with CDMA and TDMA.
>
>I guess I was really talking about inter-domain, single technology
>handoffs, because it seems to me that the inter-domain, different
>technology handoff problem has a simple solution (let the MN decide).
>So maybe "proactive FA" only makes sense in the case of homogeneous
>radio transmission technology, but I think it can be of great benefit
>there, assuming we can solve the "PPP re-establishment" problem.  The
>way I think of the proactive FA solution is that there is always an
>unshown flow of information between the BSCs attached to each leaf FA
>to exchange information and decide whether the handoff should take
>place.  It seems to me this flow of information should be left
>unspoken in the IETF and defined elsewhere (i.e., in the 3GPPs).
>
>-Pete
>

---

From: Pete McCann <[email-masked]>
Date: Tue, 25 Jul 2000 11:39:31 -0500

Hi, James,

JK> Actually, I was talking about interdomain, single technology
JK> hard (break before make) handoff.

Ok - when you said "radio link independent" I thought you meant
supporting handoff between heterogeneous technologies.

If you are only worried about the homogeneous case, then yes, this
signaling should eventually be done over IP - but is the IETF the
right place to standardize such signaling?  It seems like a link-layer
specific problem that should be solved in the 3GPP's.

-Pete