Re: [Bier] BIER: draft-eckert-bier-cgm2-rbs-01 with performance analysis simulation

On Thu, Feb 10, 2022 at 09:16:28AM +0800, zhang.zheng@zte.com.cn wrote:
> Hi Toerless, 
> Haven't read the new version of CGM2/RBS, just have the same question with Jeffrey. 
> If I understand BIER-TE and CGM2/RBS solutions right, the forwarding tables of the two methods are only focus on the local links. 
> So the table's scale for the two solutions is almost same. 

Jeffrey wasn't asking about BIER-TE (i think).

> The commen issue of the two solution is the BSL limitation. 
> BIER-TE solution has an exclusive issue that the BP needs to be assigned globally. 
> But in CGM2/RBS solution, the BP needs not to be assigned globally. 
> So the main difference of the two solutions is: is it necessary to assign the BP globally, right?

That is one core difference, yes. And it eliminates IMHO all the scaling
challenges we have with BIER-TE (that we try to compensate for to some degree with
controller based bit optimizations). But as discussed in the answer to Jeffs message,
the fact that the encoding in CGM2/RBS is a tree means that we also eliminate
the BIER/BIER-TE issue that a bitstring can carry a lot of unnecessary (zero) bits
and need to make multiple copies just because some BFER or adjacencies have their
bits in different SI (in larger topologies).

Cheers
    Toerless

> Best regards,
> Sandy
> 
> 
> ------------------原始邮件------------------
> 发件人：Jeffrey(Zhaohui)Zhang
> 收件人：tte@cs.fau.de;bier@ietf.org;
> 抄送人：bing.xu@huawei.com;
> 日 期 ：2022年02月10日 04:50
> 主 题 ：Re: [Bier] BIER: draft-eckert-bier-cgm2-rbs-01 with performance analysis simulation
> Hi Toerless,
> Not sure if my understanding is correct, but it seems that RBS does not reduce the number of bits that are needed to encode the tree. Rather, it increases the number of bits (to encode the recursive structure).
> I agree that it reduces the size of BIFTs, but even current BIER-TE can reduce the number of copies if you use a longer bitstring?
> Jeffrey
> Juniper Business Use Only
> -----Original Message-----
> From: BIER <bier-bounces@ietf.org> On Behalf Of tte@cs.fau.de
> Sent: Wednesday, February 9, 2022 2:19 PM
> To: bier@ietf.org
> Cc: bing.xu@huawei.com
> Subject: [Bier] BIER: draft-eckert-bier-cgm2-rbs-01 with performance analysis simulation
> [External Email. Be cautious of content]
> Dear BIER-TE WG:
> Robin did add a section (6.3) describing an initial performance gain analysis of CGM2/RBS to the github source (https://urldefense.com/v3/__https://github.com/toerless/bier-cgm2-rbs__;!!NEt6yMaO-gk!WS49OT72vlonSWP3yLtLcW_RQARYP00KEiAWpH592AuDXmrOOJH_bgVzQZyfK9En$ ), and i just did a bit of editorial fixup and posted it as -01 of the draft.
> This actually is the first time i actually like the HTML'ized version of a draft, because the topology picture is so large it doesn't fit a single page:
> https://urldefense.com/v3/__https://www.ietf.org/archive/id/draft-eckert-bier-cgm2-rbs-01.html__;!!NEt6yMaO-gk!WS49OT72vlonSWP3yLtLcW_RQARYP00KEiAWpH592AuDXmrOOJH_bgVzQaBIgBPC$
> The interesting piece about the comparison is that it is actually comparing CGM2/RBS to BIER, and not BIER-TE. Because BIER itself should be requiring less copies than BIER-TE, so the gain of CGM2/RBS over BIER-TE should be even higher, but the fact alone that you get away with fewer packet copies to large receiver sets even though the bitstring also needs to encode the path/tree towards the receivers is really cool.
> Robin, two Q:
> 1. The new text mentions "in our graphs", but the text does not include any such graphs (yet).
> I guess such a graph would be even worse to convert to ASCII than the topology.
> Maybe post whatever format you have those results in to github (PDF, png...) and then we actually may want to see if/how a PDF version of the draft could include better than just ASCII art. Certainly a good reason to finally try it out.
> And short term we can just add references to such visuals to the draft.
> 2; Is it correct to assume that the hops through the topology that you simulated are "just" shortest-path, maybe with some ECMP choice - aka: the same paths that also BIER would choose given some "default" IGP routing setup ?
> Cheers
> Toerless
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