[Nfd-dev] Fwd: Strategy for testbed routers

[Lan Wang (lanwang)]

Begin forwarded message:

From: Lan Wang <lanwang at memphis.edu<mailto:lanwang at memphis.edu>>
Subject: Re: [Nfd-dev] Strategy for testbed routers
Date: October 1, 2014 9:56:30 AM CDT
To: Junxiao Shi <shijunxiao at email.arizona.edu<mailto:shijunxiao at email.arizona.edu>>


On Sep 30, 2014, at 6:43 PM, Junxiao Shi <shijunxiao at email.arizona.edu<mailto:shijunxiao at email.arizona.edu>> wrote:

Hi Lan

1.
Yes, the root cause is that laptops are unable to register a precise prefix on the access router.
The most effective solution is to enable remote prefix registration on the access router.

2.
NCC strategy forwards an Interest to a nexthop, and that nexthop is never used again before InterestLifetime expires.
When there is a packet loss, even if the consumer is able to detect that and retransmit the Interest, the retransmission is suppressed by NCC strategy because it won't forward the Interest again to the same nexthop.
When a Data does not reach consumer before it's needed, the video frame cannot be constructed and cannot play out.

If the Interest was forwarded along some alternative paths by NCC, then it should still reach the producer and bring back the data, right?  And if the primary path is not working, sending the Interest there again probably won't help much either.  I just want to have a clear understanding of this problem for NDN-RTC on the testbed and then it's more clear how a more effective strategy should work.

3.
Link state routing can ensure all nexthops in FIB entry can reach the destination.
Backbone strategy is designed for this scenario.

Strategy choice depends on network environment and application needs.
Hyperbolic routing might need a different strategy.

I'm not sure if the forwarding strategy should make an assumption of what routing protocol is used.  After all, the routing protocol may be relying on the forwarding strategy to fix some of the temporary problems so that it doesn't have to respond as quickly as in an IP network (Cheng's paper).

4.
The distinction between remote prefixes and local site prefix is: remote prefixes have mostly reachable nexthops and less changes (when link state routing is used), local site prefix suffers more from unreachable nexthops and laptop mobility.
I don't know whether there is a major difference in the structure of those two forwarding strategies, but they will at least differ in some parameter settings.

It seems to me that as long as the forwarding strategy satisfies the requirement of "Make use of multiple paths in FIB entry, and learn the best path.", then it can handle various failure situations (whether they are caused by laptop mobility or link failures).  It would be better if you can make it clear what extra is required for local site prefix.

Lan

Yours, Junxiao

On Tue, Sep 30, 2014 at 10:00 AM, Lan Wang (lanwang) <lanwang at memphis.edu<mailto:lanwang at memphis.edu>> wrote:
Junxiao,

Just a few questions and comments:

1.  I remember the problem NDN-RTC had is the following: they have two producers connected to the same HUB, but the autoreg server gives them the same prefix even though they serve different content (each producer serves the data from a different camera).  Therefore, the forwarding strategy routes all the Interests to one of those producers (best route) or oscillates between the two producers (ncc).  They have to use broadcast strategy to get this work.  If this is the problem you are referring to, then the problem is not the forwarding strategy, but the lack of a way for the laptops to register their own prefixes with the hub (under the hub's prefix).  Is this the problem you are referring to?

2. Can you explain a bit the relationship between "NCC strategy suppresses all consumer retransmissions" and "any packet loss prevents playout of a video frame"?

3. Even on the backbone, you cannot be sure that all the available next hops in the FIB should lead you to the destination.  This really depends on the routing protocol.  If hyperbolic routing is used, it's possible that some of the next hops do not lead to the destination (due to local minima) and we have observed this.

4. Given the above, I do not feel that there is any major difference between the requirements for remote strategy and local strategy.   The following two seem to be enough:
>       • Make use of multiple paths in FIB entry, and learn the best path.
>       • Recovery from packet loss


Lan


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.lists.cs.ucla.edu/pipermail/nfd-dev/attachments/20141001/ebb72f4a/attachment.html>