Re: [MEXT] the future of the MEXT working group

[<[e-mail]>]

Hi Jari,

Comments inline:

On Oct 28, 2011, at 7:21 AM, ext Jari Arkko wrote:

> And a follow-up on the charter. I'm describing a couple of different takes on what the new charter could be. Comments and alternative proposals are welcome. This is what the current charter says about DMM:
> 
>>   The working group will also work on operational considerations on
>>   setting up Mobile IPv6 networks so that traffic is distributed
>>   in an optimal way, for instance by using existing protocol mechanisms
>>   to select the closest home agents for new clients.
>> 
>>   Oct 2011 - Submit I-D 'Operational considerations for distributed use of Mobile IPv6' for publication as Informational.
> 
> Which is admittedly a bit short, but is also very concrete and achievable, if we work on it. I got another proposal from Hui Deng that extended this a bit, including going beyond mere operational considerations.
> 
>> In the past decade a fair number of mobility protocols have been standardized. Although the protocols differ in terms of functions and associated message format, we can identify a few key common features:
>> presence of a centralized mobility anchor providing global reachability and an always-on experience
>> extensions to optimize handover performance while users roam across wireless cells
>> extensions to enable the use of heterogeneous wireless interfaces for multi-mode terminals (e.g. cellular phones)

What does "extensions to enable the use of heterogeneous wireless interfaces for multi-mode terminals (e.g. cellular phones" this imply? The term always-on does not necessarily apply as well. If an MN is registered with an HA it is reachable but always-on would require the MN to be network-attached and registered with an HA which may not always be the case.


>> The presence of the centralized mobility anchor allows a mobile device to be reachable when it is not connected to its home domain.

What is a home domain for a user/MN? 

>> The anchor, among other tasks, ensures forwarding of packets destined to or sent from the mobile device. As such, most of the deployed architectures today have a small number of centralized anchors managing the traffic of millions of mobile subscribers.
>> 
>> To optimize handovers for mobile users, the base protocols have been extended to efficiently handle packet forwarding between the previous and new points of attachment. These extensions are necessary when applications impose stringent requirements in terms of delay. Notions of localization and distribution of local agents have been introduced to reduce signalling overhead. Unfortunately today we witness difficulties in getting such protocols deployed, often leading to sub-optimal choices. Moreover, all the availability of multi-mode devices and the possibility to use several network interfaces simultaneously have motivated the development of more new protocol extensions.

The comment about deployment of the Mobile IP protocols is irrelevant in this context. 

>> 
>> Mobile users are, more than ever, consuming Internet content, and impose new requirements on mobile core networks for data traffic delivery. When this traffic demand exceeds available capacity, service providers need to implement new strategies such as selective traffic offload (e.g. 3GPP work items LIPA/SIPTO) through alternative access networks (e.g. WLAN). Moreover, the localization of content providers closer to the Mobile/Fixed Internet Service Providers network requires taking into account local Content Delivery Networks (CDNs) while providing mobility services.  

Offloading to wifi or the fact that CDNs are used for content delivery are really not a motivator for DMM.

>> 
>> As long as demand exceeds capacity, both offloading and CDN techniques could benefit from the development of more flat mobile architectures (i.e., fewer levels of routing hierarchy introduced into the data path by the mobility management system).

Would you consider a P-GW/GGSN as introducing multiple levels of routing hierarchy? In Internet architecture terms the P-GW/GGSN is the NAS/Gateway router. 

>> This view is reinforced by the shift in users’ traffic behaviour, aimed at increasing direct communications among peers in the same geographical area.

This is highly speculative. What study shows that users traffic behavior displays such characteristics?

>> The development of truly flat mobile architectures would result in anchoring the traffic closer to point of attachment of the user and overcoming the suboptimal routing issues of a centralized mobility scheme.

What is a truly flat mobile architecture?

>> 
>> While deploying today’s mobile networks, service providers face new challenges. More often than not, mobile devices remain attached to the same point of attachment, in which case specific IP mobility management support is not required for applications that launch and complete while connected to the same point of attachment. However, the mobility support has been designed to be always on and to maintain the context for each mobile subscriber as long as they are connected to the network. This can result in a waste of resources and ever-increasing costs for the service provider. Infrequent mobility and intelligence of many applications suggest that mobility can be provided dynamically, thus simplifying the context maintained in the different nodes of the mobile network.
>> 
>> The proposed charter will address two complementary aspects of mobility management procedures: the distribution of mobility anchors to achieve a more flat design and the dynamic activation/deactivation of mobility protocol support as an enabler to distributed mobility management. The former has the goal of positioning mobility anchors (HA, LMA) closer to the user; ideally, these mobility anchors could be collocated with the first hop router. The latter, facilitated by the distribution of mobility anchors, aims at identifying when mobility must be activated and identifying sessions that do not impose mobility management -- thus reducing the amount of state information to be maintained in the various mobility anchors of the mobile network. The key idea is that dynamic mobility management relaxes some constraints while also repositioning mobility anchors; it avoids the establishment of non optimal tunnels between two anchors topologically distant. 
>> 
>> Considering the above, the working group will:
>> 
>> Define the problem statement and associated requirements for distributed mobility management. This work aims at defining the problem space and identifies the key functional requirements.
>> 
>> Produce a gap analysis mapping the above requirements against existing solutions.

Gap analysis is an academic exercise and not worth the effort of a WG.

>> 
>> Give best practices for the deployment of existing mobility protocols in a distributed mobility management and describe limitations of each such approach.

I think this is the most sane proposal in terms of how existing protocols can be deployed to address concerns that have been highlighted in various I-Ds.

>> 
>> Describe extensions, if needed, to current mobility protocols for their application in distributed mobility architectures

Yes. As needed.

-Basavaraj

> 
> Comments?
> 
> Jari
> 
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