RE: [Mip4] RE: Differences between Low Latency Handovers and FMIP v4

[Narayanan Vidya-CVN065 <vidya at motorola.com>]

Maybe I am just missing something important here. Sorry, but I still don't understand. 

Both in the L2LU and L2MT, it seems like LLH is expecting at least the nFA L2 address (if not the IP address) or some nFA identifier - is that true? 

Typically, this information is not available as a result of the AP scan, right? The FA is most likely more than one L2 hop away from the MN. An AP, by default, will not include any information about the nFA in its beacon. 

What am I missing here? 

Thanks,
Vidya

-----Original Message-----
From: Karim El-Malki \(AL/EAB\) [mailto:karim.el-malki at ericsson.com] 
Sent: Tuesday, March 22, 2005 5:13 AM
To: Narayanan Vidya-CVN065; Rajeev Koodli 
Cc: mip4 at ietf.org
Subject: RE: [Mip4] RE: Differences between Low Latency Handovers and FMIPv4


As you can see from the table some triggers provide very
little info (e.g. link up - L2UP). Others provide L2 OR
L3 parameters (e.g. L2-MT). The result of an AP scan to get BSSIDs e.g. above a certain signal strength (SNR) is defined as a trigger in LLH (L2-MT). No L3 parameters involved there. That doesn't need any special change to L2s, like WLAN in this example. So my point is that it is incorrect to say that LLH requires special changes to L2. LLH covers different types of L2s that provide different trigger info. /Karim

-----Original Message-----
From: Narayanan Vidya-CVN065
To: Karim El-Malki (AL/EAB); Rajeev Koodli
Cc: mip4 at ietf.org
Sent: 22/03/2005 02:56
Subject: RE: [Mip4] RE: Differences between Low Latency Handovers and FMIPv4

Karim,
I have a rather stupid question. All the triggers listed in table 1 of LLH list some L3 parameter or another that needs to be present in the trigger. This suggests to me that any kind of L2 trigger that is needed for LLH (Pre-reg or post-reg) requires the presence of the appropriate parameter listed in the "Parameters" row of the table. 

Am I missing something here? 

Vidya

-----Original Message-----
From: mip4-bounces at ietf.org [mailto:mip4-bounces at ietf.org] On Behalf Of Karim El-Malki \(AL/EAB\)
Sent: Monday, March 21, 2005 5:20 PM
To: Rajeev Koodli 
Cc: mip4 at ietf.org
Subject: RE: [Mip4] RE: Differences between Low Latency Handovers and FMIPv4


>>I understand your point that you took FMIPv6 and applied
>>it to v4 to make FMIPv4. But that doesn't make it substantially
>>different from Low Latency. Your spec does use link-layer triggers to 
>>be able to send the RtSolPr. An interface coming up in the MN is used 
>>just the same in Low Latency and is defined as a mobile trigger in Low
>>Latency (L2-LU). PRE-REG involves the MN getting such a
>>mobile trigger and sending a PrRtSol and receiving a
>>PrRtAdv. What's the difference compared to your spec?
>>  
>>
>As I explained below (and also itemized in the List below), the
>essential difference is that LLH requires L2 to provide L3 information 
>(nFA, MN IP addresses, their MAC addresses etc.) via various L2-*T type

>of triggers.
>This is a Big difference for us since we do not wish to change L2 to 
>implement fast handovers. Both FMIPv6 and FMIPv4 work without requiring 
>such changes to L2.

That's not correct.
Let's take the case where the L3 handoff is initiated before
L2 handoff. Taking WLAN for example, in LLH the MN gets info from L2 (e.g. AP scan) and sends a PrRtSol to get a PrRtAdv containing information of the subnet it may move to. I can't see any change required to L2. Where is the difference compared to what you have described? The only difference is that we definied all "handoff hints" as L2 triggers, just as a result of the AP scan is defined as a mobile trigger. The LLH spec doesn't mandate the presence of all trigger types in all cases. It depends on what the L2 has to offer.

>>The messages are even called the same. Nothing special
>>or L2-dependent about this L2 trigger. For example PRE-REG
>>  
>>
>Well, the essential difference is what requirements LLH imposes on L2
>triggers. Table 1 in LLH specifies what information is expected from L2

>triggers including the nFA, MN IP addresses from the various L2-*T
>triggers.

LLH can work with different types of L2 triggers (which is very different from requiring L2 changes) and supports the case you have described in FMIPv4. Table 1 specifies the different types of triggers that LLH can utilise. Note that it includes very simple triggers that work even on WLAN. It is wrong to say that all triggers in Table 1 are required on all L2s for LLH to work.

>>can be applied to WLAN using AP scans. I don't think that
>>the difference in packet formats makes it a substantially different
>>spec from low latency.  Also, the other case you are considering 
>>involves an L3 handoff that happens after the MN attaches to the new 
>>link. This cannot really be considered a "fast" handoff, which would 
>>instead be where the handoff happens before or in parallel with the L2

>>handoff.
>>  
>>
>Perhaps you have missed something.. The FMIP design allows movement
>detection and router/FA discovery phases to be done prior to L2 
>handover. The "reactive" handover we refer to is the one where the FBU 
>is sent from the
>new link. But, the MN uses the neighborhood information via Proxy
Router
>messages to determine movement detection and router/FA config
>information of the
>new subnet. So, your description above is not accurate.

Note that I first addressed the L3-movement-before-L2 (where I am saying that FMIPv4 is no different from LLH) and then I wrote "the other case you are considering....". Am I incorrect in saying that FMIPv4 also supports the L3-handoff-after-L2-handoff case? I think I had read that case in FMIPv4 (i.e. FBU sent from new link). That's why I had asked about PFANE.

>>This L3-handoff-after-L2-handoff was already covered in the route
>>optv4 spec using PFANE. You may have missed the question so I'll 
>>repeat it: did you consider the PFANE? Why aren't you just reusing the

>>PFANE (Previous FA Notification
>>Extension) work for that scenario?
>>  
>>
>Please see above. The key difference with respect to Previous FA (what 
>used to be Previous AR notification in v6) Notification is that you 
>don't incur delays due to movement detection and
>router/FA discovery.

If you are only considering the L3-handoff-before-L2-handoff case then there are very little differences between FMIPv4 and LLH for the reasons given above.

>So, apart from the independence from L2 to provide L3 information, the
>other crucial difference is the decoupling of neighborhood discovery 
>from the actual
>handover signaling. This not only reduces the number of signaling
>messages
>during the handover itself, but also makes the reactive fast handovers 
>possible.

Again I can't see the crucial difference from LLH.
The ND messages are basically the same (even almost called the same): PrRtSol and PrRtAdv. LLH uses standard MIPv4 naming (Registration Request and Reply) while FMIPv4 achieves the same result but calls this an FBU. Tunnelling between FAs is supported in both specs. LLH furthermore supports anticipated HA updating or "local" HA updating (regional registrations). It seems to me that to make things "faster" one would want to update the local/global HA directly if possible since FA-FA routing can be inefficient in a tree-like network structure compared to updating a local HA. I am curious to understand why you have eliminated that option in FMIPv4 compared to LLH. Measurements performed on FMIPv6+HMIPv6 integration prove that it makes sense to combine local/global HA updating with the FMIP mechanism. /Karim

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