Re: [DMM] Comments on draft-patil-dmm-issues-and-approaches2dmm-00

[Peter McCann <[e-mail]>]

Hi, Jouni,

jouni korhonen wrote:
> Pete,
> 
> On Mar 7, 2012, at 4:55 PM, Peter McCann wrote:
> 
>> Hi, Jouni,
>> 
>> jouni korhonen wrote:
>>> Pete,
>>> 
>>> Thanks for the review. Some thoughts inline.
>>> 
>>> On Mar 6, 2012, at 11:48 PM, Peter McCann wrote:
>>> 
>>>> Hi, Raj, Carl, and Jouni,
>>>> 
>>>> I have some comments on draft-patil-dmm-issues-and-approaches2dmm- 00.
>>>> 
>>>> I agree with most of Section 4, "Issues with current mobility
>>>> models". However, I'd like to point out that existing networks are
>>>> not just centralized in the manner you point out, they also tend to
>>>> have a hierarchical structure, e.g., the S-GW/P-GW split in 3GPP EPC.
>>>> Therefore, the issue you outline in
>>> Section 4.3
>>> 
>>> It is quite common to run combined nodes.
>> 
>> Sure, in that case the combined S-GW/P-GW is a centralized anchor
>> point and the excess signaling you point out in Section 4.3 would
>> indeed be a problem.
> 
> Actually, signaling due a handover (SGW/SGSN relocation or even L2
> handover) in PGW/GGSN is not the biggest issue.. It is the bearer
> management in general, which is not a problem for IETF to tackle.
> However, designing a system that is conservative on signaling is a good
> general guideline. And that is the reason we emphasize that. So not let
> us get too stuck with EPC, rather learn from it.

I agree.

>>>> ("Inefficient Routing and signaling overhead") is not quite true of
>>>> the 3GPP EPC, which can handle many mobility events in a localized
>>>> manner similar to HMIP.
>>> 
>>> Could you clarify which functionality in EPC you refer to from IP
>>> point of view?
>> 
>> I mean the ability to update a local S-GW with each eNB change, which
>> avoids the extra signaling to the P-GW.  It is architecturally similar
>> to HMIP (really, PMIP + HMIP).
> 
> Comparing against HMIP is not that straight forward. In HMIP you have
> IP exit points at AR, MAP and HA, also local mobility at the IP level
> under MAP and L2 mobility under AR. With EPC, you have one exist point
> at your gateway and L2 mobility under SGW.

If you combine HMIP with PMIP (as I think some would propose) it starts
to look very similar to the L2 mobility provided by GPRS.

>> We need to do some simulation/implementation experiments to see if this
>> is a problem.  Hopefully I'll have more to say on that soon.  But,
> intuitively,
> 
> That would be excellent.
> 
>> the UPDATE just has to propagate one hop to the crossover router to be
>> effective. We don't need the whole network to be converged for packets
>> to take the right path toward the currently serving AR.
> 
> You need to be careful on the deployment architecture you introduce
> stuff like this. I am just being conservative ;) Once the constraints
> and assumptions are better known it is easier to evaluate the solution.

Yes we need to do a simulation and play with the parameters to find out
engineering guidelines for how to dimension the network.  But, I think that's
generally true of any solution.

-Pete