Subject: Re: [MOBILE-IP] handover

From: James Kempf <[email-masked]>
Date: Tue, 25 Apr 2000 11:19:32 -0700

Being able to set up network resources before handover actually occurs
is crucal for mobile telephony applications. In the current cellular system,
the network element handling the connection gathers radio signal
quality from potential future handoff-ees, and uses this information
to determine whether handoff should occur and to which network element
it should occur, for interdomain "hard" handoff. A similar
mechanism, with parameterization for different wireless link technologies,
would be very useful when replacing the current network protocols with
mobile IP. If properly designed, it may even help facilitate handoff
between cellular telephony networks and wireless LANS.

Beacons are not a good solution in telephony applications,
because they take up radio bandwidth, and they require the mobile node
to make the decision about whether to hand off, rather than the network. This
has a couple of disadvantages. Network elements such as FAs often have more
information on topology and can therefore use that to corrolate with
signal strength information to make a smarter decision about where and
when to handoff. Furthermore, it does not allow the network time to set up. An
example is QoS. If the FA handling the connection can decide when to handoff and
to which new FA, then the new FA has time to set up QoS before telling the
mobile to handoff, considerably reducing handoff time. In addition, if
the new FA can't handle the mobile because QoS resources are not
available, it also gives the old FA time to try another FA that has
available resources.

                        jak

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From: "Charles E. Perkins" <[email-masked]>
Date: Tue, 25 Apr 2000 12:41:11 -0700

Hello Jim,

I can agree with almost everything you say, but for the following:

> to make the decision about whether to hand off, rather than the network.

Everything else in your note can remain true and might be easier
to implement if beacons are available on a timely basis.  If beacons
are not available, perhaps there wouldn't be any signal on which to
base a measurement!  If a mobile node has to solicit a beacon, then
there is the danger that many mobile nodes will do solicitations
at the same time, causing collisions and so on.

Anyway, my main point is that there are tradeoffs that have
to be considered.  Probably for some cellular designs, beacons
are better than for others.

Regards,
Charlie P.

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From: Vincent Magret <[email-masked]>
Date: Tue, 25 Apr 2000 15:19:09 -0500

My view on this is that if we want to handle real time traffic, we need to
have "eager cell switching" and thus we need to have some "help" from the
underlying layer. My understanding of GSM is that they have implemented a
"make before break" mechanism, which allows to create a circuit toward the new
base station before breaking the old one. the problem with wireless LAN (i.e.
802.11) is that the standard only defines the radio interface and not the
entire wireless network as done for the cellular networks, so there is no
reason why a manufacturer should bother about unspecified features.

Finally:

1. May be the group could put down some requirements so that network designers
and driver writers could use
or
2. Perhaps, this should not take place in the IETF.

Best regards,

Vincent Magret.

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From: Phil Neumiller <[email-masked]>
Date: Tue, 25 Apr 2000 15:34:35 -0500

> and driver writers could use

Good idea.  Here are a couple thoughts:

1).  Don't forget PANs!  Personal area networks are coming.  These are going have
     lots of handovers, probably more-so than any other network considered thus far
     by mobile IP.  When the world is full of Internet appliances (link local
     addresses may very well apply) we will have many more potential handovers. It
     is true that a large percentage (?) of these handovers will be link layer,
     i.e. not crossing subnets, but I venture to guess that things being carried on
     pedestrians and in cars, etc will handover alot.

2).  Let's be sure that we can upgrade the concept of a handover in a few qualified
     ways.  What Mobile-IP has now, i.e. as in RFC2002 is what I would refer to as
     a "lazy data handover" (terminology police please come and get me!).  I could
     envision a variety of "abstract" handover types:

     A). VOIP handover required sustained QoS at some nominal level.
     B). Normal data handover no QoS requirements.
     C). Data handover with AAA requirements, etc.
     ...

> 2. Perhaps, this should not take place in the IETF.

Since we are talking about Mobile-IP where would be a better place?

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From: "Tom K. Weckström" <[email-masked]>
Date: Wed, 26 Apr 2000 19:43:37 +0300

> to make the decision about whether to hand off, rather than the network.

I disagree on this point. In telecom infrastructures administered by
few big companies, the nkowledge about network topology may be a very
useful thing for network initiated handoffs.

I assume that in the future mobile ip world, there are so many
networks offering access to the network that it is impossible to
administer theri knowledge about each others topology to assist
network initiated handoffs.

Furthermore, I really like the idea of MN being able to decide about
the handoff. It brings some freedom to the MN, and doesn't add
complexity to the network, which makes the network faster/more robust.

--
        Tom Weckström           Dynamics group
                                Helsinki University of Technology
                                [email-masked]

http://www.cs.hut.fi/Research/Dynamics/