Subject: [RRG] Will the flat ID and its corresponding resolution infrastracture be practicable? [RRG] Renumbering...

From: Xu Xiaohu <[email-masked]>
Date: Wed, 20 Aug 2008 15:47:07 +0800

It's true that the address (as the role of identifier) is hard to be in
accordance with the topologically aggregatability requirement. However, it
is still workable to be aggregatable in the overlay or virtual topology,
e.g. DNS or home agent in MIP. As for DHT, is it workable to support
global-scope resolution for the flat id (or host- granularity PI address)
based on the assumption that every host will need a unique entry in the DHT
system? I believe it's a big difference in the scale between the above
resolution infrastracture and the current structured P2P system, like Skype.
Besides the scalability concern, there is also a business and trust model
issue, that is, who will run this infrastracture?
 
Xiaohu  

  _____  

发件人: [email-masked] [mailto:[email-masked]] 代表 Heinrich Hummel
发送时间: 2008年8月20日 16:56
收件人: [email-masked]
主题: RE: [RRG] Renumbering...

Tony Li wrote: 

I think the real question is whether aggregates are required at all. If so, 
then I think we have an issue that leads us down the NAT path. 

Now, if someone has some mapping technology that does not require 
aggregation at all (DHTs?), then there is a possible alternate to NATs. 

In answering: 
This is exactly the key point of my approach: forwarding without being based
on aggregates of Unicast user addresses. 
Address aggregation is a problem just because of the huge quantity.
Additionally, it is principally wrong in view of user mobility and
eventually router mobility. 

Heiner

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From: Scott Brim <[email-masked]>
Date: Wed, 20 Aug 2008 10:51:57 -0400

On 8/20/08 3:47 AM, Xu Xiaohu allegedly wrote:

I can't find Tony's original mail but replying to your reply ...

> aggregation at all (DHTs?), then there is a possible alternate to

To scale, DHTs would simply transform aggregation into iterative lookup.
 There is no difference in the amount of effort.

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From: Brian E Carpenter <[email-masked]>
Date: Thu, 21 Aug 2008 09:31:15 +1200

>  There is no difference in the amount of effort.

In terms of joules per second, perhaps not, but surely the question
is about practicality. Will the "D" in DHT mean that a DHT-based map
is fast enough in practice? I'm not sure that question is really
different from one we've already discussed inconclusively: can
a caching mapping system cache enough entries close enough to
the ITRs?

    Brian

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From: Xu Xiaohu <[email-masked]>
Date: Thu, 21 Aug 2008 11:40:13 +0800

>  There is no difference in the amount of effort.

Agree.  However, if the IDs are not allocated in any hierarchy and they are
randomly scattered across the DHT overlay, the lookup speed will be
decreased heavily. Of course, the tree-like mapping system like DNS or ALT
has the same issue. So no matter DNS like mapping system or DHT, to make it
scale better(in aspect of lookup speed) , the id should be allocated in some
geographically aggregatable manner. Strict hierarchy is not flexible to
support ID roaming since it may require some renumbering work, while the
full flat structure is also not feasible. It's better to make some tradeoff.
For example, you don't need to renumber the ID if you migrate from one city
to another city within the same country. However, you'd better to renumber
it if you migrate from one country to another country.

Xiaohu Xu

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From: "Rolf Winter" <[email-masked]>
Date: Thu, 21 Aug 2008 10:14:00 +0200

Hi,

> Agree.  However, if the IDs are not allocated in any 
> hierarchy and they are randomly scattered across the DHT 
> overlay, the lookup speed will be decreased heavily. 

In general it has to be noted that in a DHT the number of lookup hops is a function of the number of nodes participating in the DHT not a function of the ID space.  

> Of 
> course, the tree-like mapping system like DNS or ALT has the 
> same issue. So no matter DNS like mapping system or DHT, to 
> make it scale better(in aspect of lookup speed) , the id 
> should be allocated in some geographically aggregatable 
> manner. Strict hierarchy is not flexible to support ID 
> roaming since it may require some renumbering work, while the 

I am not sure I follow you here. A geographic allocation of IDs would increase the look-up speed, that is what you are saying right? What are the underlying assumptions of this? If look-ups have an inherent locality property maybe. That is, end-host communicate with higher probability with nodes that are geographically close AND the node that is responisble for the lookup is in the same geographic region AND the underlying network topology follows this geographic constraints ONLY then this statement it true. Considering a popular application such as BitTorrent which also opens many connections simulatneously (i.e. would trigger numberous lookups), my personal experience is that locality does not impact the peer choice an awful lot. To deal with non-locality today we employ caches and CDNs (that's at least partly why we do it). And I think in general it is safe to say that we will continue to do it. 

	Rolf

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