Subject: [mobile-ip] [Mobile IP] MN behaviors to uplink data packets during a handoff

From: "Ji Zhang" <[email-masked]>
Date: Wed, 23 Jul 2003 21:37:55 +0100

Hi all,

Could anybody offer me some instructions on the behaviors of a Mobile Node
to
uplink (MN-->FA) data packets during a handoff?

For example,
1. when the MN loses link contact with the old FA (before getting an agent
advertisement), are all uplink data packets stored up at the link layer?
2. when the MN is aware of agent advertisements are missing, at the same
time it sends an agent solicitation, should it stop sending data packets
until
it gets an agent advertisement (or even until the registration is
successful)?

Many thanks,
Jee

---

From: Jay J Lee <[email-masked]>
Date: Wed, 23 Jul 2003 22:59:25 -0400

Hi,

I believe these are all implementation time decisions.

For #1, if you are talking about MIPv4, what is happening within the IP 
layer should not affect the link layer.  If it still has upper layer 
packets to send out it will continue to do so.  The link/MAC layer does not 
and should not know what happens at the other layers other than the packets 
it receives from them.  Although with MIPv6 there are proposals for 
inter-layer communications.

For #2, the OPNET MIPv4 simulation model, for example, keeps sending the 
data packets to the last known agent (HA or FA) on the last known good 
interface whether it is lost or in the process of registration.  This 
decision was made because once you start queueing packets and managing 
them, the implementation becomes expensive considerably in the simulation 
domain as well as for the OSes in the real devices.

Hope this helps, - Jay

---

From: "Jee J.Z." <[email-masked]>
Date: Thu, 24 Jul 2003 17:03:30 +0100

Hi Jay and all,

Thank you very much for your reply.

According to your comments, can I think this way that the disruption to
uplink stream caused by a handoff is largely depending on the link layer
technology and the Mobility Agent (or the administrative domain) behaviors?
That is,

For example, as far as I know, Mobile Nodes in WLAN make sure there is an
Access Point reachable before everytime they send out a frame. In this case,
even if the MN loses contact with any AP for some time, IP packets would not
be lost, instead, they queue up at the link layer and wait for the link data
frame to be sent out. (?)

When the MN is in registration process with a new FA, it sends out data
packets to the new FA as long as it knows the FA's MAC address. Whether to
offer service to the unauthorized MN (at least before the successful
registration reply comes back) depends on the policy the new FA (or the
admistrative domain it belongs to) deploys. If it does not, uplink data
packets are discarded by it during the registration process. If it does
offer service, there could be no uplink data packets lost in WLAN. (?)

However, it is not WLAN, things might be different. (?)

Regards,
Jee

----- Original Message -----
From: "Jay J Lee" <[email-masked]>
To: "Ji Zhang" <[email-masked]>; <[email-masked]>
Sent: Thursday, July 24, 2003 3:59 AM
Subject: Re: [mobile-ip] [Mobile IP] MN behaviors to uplink data packets
during a handoff

---

From: Jay J Lee <[email-masked]>
Date: Sun, 27 Jul 2003 21:02:32 -0400

Hi,

I am not an expert on WLAN behavior but I do not think it should hold 
packets when it looses connectivity with the AP.  The main reason for that 
is that this type of condition is best handled (at least currently) by the 
upper layer (most likely transport layer).

Let's say you have a TCP session going on and you lost connectivity with 
your AP for 10 seconds then reconnects.  If the TCP session was terminated 
then the MAC layer is left with stale data that nobody can process if it 
were queueing packets (for other than the purpose of limited retries). With 
UDP, you most likely want to receive the most current packets transmitted 
rather than the ones transmitted 10 seconds ago (real time video anyone?).

Again, I am strictly talking about real life devices and their 
implementations.  I have seen similar proposals (smarter link layers) in 
several research papers. They were not necessarily related to Mobile IP but 
on improving wireless network performance in general.

Good luck, - Jay

---

From: "Jee J.Z." <[email-masked]>
Date: Mon, 28 Jul 2003 03:07:14 +0100

Hi Jay,

You are quite right. So after several times try and fail, link layer drops
the packet.

Another question is in OPNET MIPv4 model, what do "the last known agent" and
"the last known good interface"  mean? If the MN gets an agent advertisment
from a new FA, while haven't got any adversitments from its old FA recently,
then the new FA immediately becomes the last known agent? If so, at this
time the MN turns to send packets to the new FA without waiting for the
registration reply, and whether these packets from the unauthorized MN would
be served depends on whether the new FA would provide service to them?

Many thanks,
Jee

----- Original Message -----
From: "Jay J Lee" <[email-masked]>
To: "Jee J.Z." <[email-masked]>; <[email-masked]>
Sent: Monday, July 28, 2003 2:02 AM
Subject: Re: [mobile-ip] MN behaviors to uplink data packets during a
handoff

> > > packets to send out it will continue to do so.  The link/MAC layer
does
> >not

---

From: Jay J Lee <[email-masked]>
Date: Sun, 27 Jul 2003 22:42:50 -0400

Hi Jee,

Yes, you described exactly the behavior of the current OPNET model. The 
last known good interface comes into the picture if you have a mobile 
router with multiple roaming interfaces.

- Jay