Subject: Re: [MOBILE-IP] Maximum fequency of hand-offs in MIP

From: Shiang-wei Chao <[email-masked]>
Date: Fri, 19 May 2000 12:59:29 +0800

Hi Basavaraj ,

>>     When mobility of MNs is getting high, how much is the maximum
>>frequency of hand-offs that is allowed by MIP?  How much is the
>>proper range of this frequency?
>>Is there any document or simulation result refering to this ?

>The frequency of handoffs depends on cell size, the MNs speed , the MN
>itself, among other factors.
>The Mobile IP spec does not specify any limits for the number of
>handoffs.
>
>-Basavaraj

i agree with you. The frequency of handoffs depends on advertising interval of
FAs, power range of
  FA, MN mobility ... ,etc.

Maybe i should make myself clear.  Is there minimum registration interval in HA
? i mean, if two registration messages
arrive HA in very close time, will there be a time constraint to accpet the
later one? Or this registration frequency
(registration message per sec) has no limitation in spec and only relies on the
computing power/bandwidth of HA?

Thank you in advance

Paul

---

From: Wolfgang Schoenfeld <[email-masked]>
Date: Fri, 19 May 2000 11:12:21 +0200

In addition to previous answers,
let me mention that RFC2002bis specifies

- the maximal frequency by which a mobile node issues registration requests

(in 2.4.2, p. 20):
"However, the mobile node MUST NOT register
more frequently than once per second on average,..."
(in 3.6, p. 33):
"In the absence of link-layer indications, a mobile node
MUST NOT attempt to register more often than once per second."
This sets an upper limit to the handoff frequency.

- the frequency by which a foreign agent forwards requests

(in 3.7.2):"...except in cases where the foreign agent would be
required to send out more than one such denial per second to the same
mobile node."
This means that the foreign agent reacts accordingly,
but does not impose any limits by itself.

- no frequency by which the home agent processes requests

However, if the requests do not suffer from too much jitter,
you may expect that the frequency of requests
handled by the home agent is at most once per second "on average".

Clearly, there is no minimal frequency.
Like everything in the Internet,
requests are handled in a best-effort way.

Wolfgang

--
Wolfgang Schoenfeld, GMD-IPSI,
+49-6151-869-865 (Phone), +49-170-2285450 (Mobile)

---

From: Jiwoong Lee <[email-masked]>
Date: Sun, 21 May 2000 15:23:23 +0900

Thank Schoenfeld for the concise comments.

RFC2002bis: in 3.6 pp.33, 

> MUST NOT attempt to register more often than once per second."

This sentence seems to imply that MN's switching to the new base 
station MAY trigger MN's new registration, with, if any, link-layer 
indication.

How about the Mobile IP test implementations ? Are they supporting
the triggering by a link-layer indication?

Jiwoong Lee

---

From: "Tom K. Weckström" <[email-masked]>
Date: Mon, 22 May 2000 08:13:41 +0300

Hi,

Good points, Wolfgang.

Jiwoong, please check Dynamics - HUT Mobile IP (url in signature).
Dynamics has a 'Monitor' module that provides information from the
IEEE 802.11 link layer to the mobile node to support more intelligent
and more efficient handoffs. There is also an API for the Monitor
module, and the mobile node supports 'handoff policies' that are rules
according to which the handoff decisions are made. The 'iwspy' is used
for the quality infromation. The code is available from Dynamics CVS
repository.

The idea can be extended to any link layer that provides link quality
information. Our wireless network covering parts of the HUT campus
only has IEEE 802.11 WLAN as a link layer, so we do not have
experience about measuring other link layers.

Regards,
        Tom

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

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