[sfc] Specifying chains of network functions [Re: Figures in draft-quinn-sfc-arch-05]

[Sevil Mehraghdam <[e-mail]>]

Hello,

I am new to this mailing list, and regarding the discussion about 
representing the chained functions, I would like to draw your attention 
to our work:

"Specifying and Placing Chains of Virtual Network Functions" 
(http://arxiv.org/abs/1406.1058)

We have defined a language for specifying the chaining among network 
functions. We use it for describing an optimization problem for 
placement of chained functions in a geographically distributed network 
based on given deployment requests. The paper is currently under review, 
and we are working on extending our model and language as new 
requirements and details about virtual network functions and the chains 
become available. Comments and suggestions are welcome!

Best regards,
Sevil Mehraghdam



On 05/30/2014 05:03 PM, Eric Gray wrote:
>
> Linda,
>
> It may be a mathematically correct expression (depending on interpretation
>
> of the notation used), but networking is not necessarily (possibly 
> even usually) a
>
> mathematical operation.
>
> There is nothing "intuitively obvious" in this expression that makes 
> it clear
>
> that "load sharing" is taking place between the sets of sf2 and sf4 
> instances, or how
>
> the "or" operation takes place.
>
> One literal way to interpret this notation (as a mathematical 
> expression) is
>
> that each the functions sf2, sf2' and sf2" are "visited" sequentially 
> and passed on
>
> to sf3 ­*/as soon as it succeeds in any of the functions/*. With this 
> interpretation, since
>
> the service function performed at each sf2 instance is presumed to be 
> identical,
>
> what the expression means is that either the service function will 
> succeed at sf2
>
> (and always skip sf2' and sf2"), or that it will fail at each sf2 
> instance.
>
> An equally legitimate "parallel computing" (not exactly mathematical, but
>
> possibly viewed as more closely analogous to networking) 
> interpretation would
>
> be that processing passes (on success at sf1) to */each/* of sf2, sf2' 
> and sf2" in parallel
>
> and then proceeds to sf3 on success at any of the sf2 instances.
>
> None of these interpretations corresponds to  "load sharing" -- yet 
> all are
>
> perfectly legitimate interpretation of your suggested expression/notation.
>
> And yet, these are actually more common interpretation of the usage of
>
> an "or" operation to computing folks (which many of us are), depending 
> on their
>
> specific background in computing.
>
> As I said before, I have no objection to the suggested notation you and
>
> Lucy proposed -- provided that the notation is explained.  I am 
> unclear as to what
>
> value this usage -- and included explanation may have -- but this is 
> largely a style
>
> issue, and best left up to the draft editors at this point.
>
> And, as I also said, there may be others who would prefer not to have too
>
> much textual explanation necessary in order to understand a figure.
>
> Finally, you must realize that there are a fairly large number of 
> folks who
>
> read-over mathematical expressions as if they were written in a 
> foreign language.
>
> For this reason, even if it were a perfectly useful/correct 
> mathematical expression,
>
> a number of folks would */still/* need a picture.
>
> --
>
> Eric
>
> *From:*Linda Dunbar [mailto:[e-mail]]
> *Sent:* Thursday, May 29, 2014 5:42 PM
> *To:* Eric Gray; Lucy yong; Jakob Heitz (jheitz); Joel Halpern; Paul 
> Quinn (paulq)
> *Cc:* [e-mail]
> *Subject:* RE: Figures in draft-quinn-sfc-arch-05
> *Importance:* High
>
> Eric,
>
> How about this shorter one?
>
> ->{sf1}->{sf2|sf2'|sf2''}->{sf3}->{sf4|sf4'|sf4''}->{sf5}->
>
> The intent is pretty simple: If a service function on a chain has 
> multiple instances, one of the service function's instances is 
> selected to treat packets belonging to the service chain.
>
> This is a correct mathematics expression.
>
> There is really no need draw all those boxes.
>
> Linda
>
> *From:*Eric Gray [mailto:[e-mail]]
> *Sent:* Thursday, May 29, 2014 4:23 PM
> *To:* Linda Dunbar; Lucy yong; Jakob Heitz (jheitz); Joel Halpern; 
> Paul Quinn (paulq)
> *Cc:* [e-mail] <mailto:[e-mail]>
> *Subject:* RE: Figures in draft-quinn-sfc-arch-05
>
> Linda,
>
> By the way, your proposal for Figure 5 would require a column width of 
> at least 80
>
> characters (more than you are supposed to have in an ID), and the 
> situation would
>
> be worse if it were applied to figure 6.
>
> For figure 5, you can improve the width slightly by fixing up a few of 
> your arrows,
>
> and even more by wrapping the figure.  Wrapping  might detract from 
> simplicity,
>
> however.
>
> --
>
> Eric
>
> *From:*Linda Dunbar [mailto:[e-mail]]
> *Sent:* Thursday, May 29, 2014 4:49 PM
> *To:* Lucy yong; Eric Gray; Jakob Heitz (jheitz); Joel Halpern; Paul 
> Quinn (paulq)
> *Cc:* [e-mail] <mailto:[e-mail]>
> *Subject:* RE: Figures in draft-quinn-sfc-arch-05
> *Importance:* High
>
> I like the Figures drawn by Lucy.
>
> Actually why can't Figure 5 be simplified as
>
> enter 
> -->{sf1}-->-{sf2|sf2'|sf2''}->--{sf3}-->-{sf4|sf4'|sf4''}->--{sf5}--> exit
>
> ??
>
> Linda
>
> *From:*sfc [mailto:[e-mail]] *On Behalf Of *Lucy yong
> *Sent:* Thursday, May 29, 2014 1:12 PM
> *To:* Eric Gray; Jakob Heitz (jheitz); Joel Halpern; Paul Quinn (paulq)
> *Cc:* [e-mail] <mailto:[e-mail]>
> *Subject:* Re: [sfc] Figures in draft-quinn-sfc-arch-05
>
> For readability on these figures, propose:
>
> Figure 5:
>
> +-sf2-+       +-sf4-+
>
> |     |       |     |
>
> enter -->sf1-->-sf2->--sf3-->-sf4->--sf5--> exit
>
> |     |       |     |
>
> +-sf2-+       +-sf4-+
>
> Figure 6:
>
> +-sf2-+              +-sf4-+
>
> |     |              |     |
>
> enter -->{sf1|sf1'}-->-sf2->--{sf3|sf3'}-->-sf4->--{sf5}--> exit
>
> |     |              |     |
>
> +-sf2-+              +-sf4-+
>
> lucy
>
> *From:*sfc [mailto:[e-mail]] *On Behalf Of *Eric Gray
> *Sent:* Thursday, May 29, 2014 12:54 PM
> *To:* Jakob Heitz (jheitz); Joel Halpern; Paul Quinn (paulq)
> *Cc:* [e-mail] <mailto:[e-mail]>
> *Subject:* Re: [sfc] Figures in draft-quinn-sfc-arch-05
>
> HaHa, funny man. J
>
> *From:*Jakob Heitz (jheitz) [mailto:[e-mail]]
> *Sent:* Thursday, May 29, 2014 1:43 PM
> *To:* Eric Gray; Joel Halpern; Paul Quinn (paulq)
> *Cc:* [e-mail] <mailto:[e-mail]>
> *Subject:* RE: Figures in draft-quinn-sfc-arch-05
> *Importance:* High
>
> You could turn the whole picture right by 90 degrees.
>
> If you don't like top to bottom instead of left to right, make a note 
> that it's in landscape.
>
> --Jakob
>
> *From:*sfc [mailto:[e-mail]] *On Behalf Of *Eric Gray
> *Sent:* Thursday, May 29, 2014 8:31 AM
> *To:* Joel Halpern; Paul Quinn (paulq)
> *Cc:* [e-mail] <mailto:[e-mail]>
> *Subject:* [sfc] Figures in draft-quinn-sfc-arch-05
>
> Paul/Joel,
>
>                 Pretty sure that Figures 5 and 6 don't actually fit 
> the width expected for an
>
> Internet Draft (Figure 5 is more than 80 characters wide and Figure 6 
> is wider still).
>
>                 Depending on how a reader tries to read the draft, 
> this can turn complicated
>
> illustrations into a _/real/_ fun time. J
>
>                 Also, I am unsure what the figures are trying to 
> convey with some of "dotted
>
> lines" crossing the service functions.  If the intent is to show that 
> a service function is
>
> a virtual instance hosted by some network device, perhaps this will be 
> better shown
>
> in a separate figure and this aspect of Figures 5 and 6 can be eliminated?
>
> I would suggest replacing Figure 5 with a figure along the lines of:
>
> source             +-----+       +-----+
>
>   |            +-->| sf2 +--+   +-->| sf4 +--+
>
>   |            |   |     |  |            |   | |  |
>
>   |  +------+--+   +-----+  +-->+-----+--+ +-----+  +->+-----+
>
>   |  | sf1  |      +-----+      | sf3 | +-----+     | sf5 |
>
>   +->|      +----->| sf2 +----->| |----->| sf4 +---->|     |-+
>
>      |      |      |     |      |     |      | |     |     | |
>
>      +------+--+   +-----+  +-->+-----+--+ +-----+  +->+-----+ |
>
>                |   +-----+  |            | +-----+  |          |
>
>                +-->| sf2 +--+   +-->| sf4 +--+     +----+
>
>                    |     |                   | |        |
>
>                    +-----+       +-----+        V
>
>                                           destination
>
>                    Figure 5: Load Balancing
>
> (67 characters?)
>
>                 Similarly, I would suggest replacing Figure 6 with a 
> figure along the
>
> lines of:
>
>     source
>       |               +-----+-+                   +-----+-+
>   +---+           +-->| sf2 |-|+              +-->| sf4 |-|+
>   |           +---|-->|     | ||          +------>|     | ||
>   |   +------+|---+   +-----+ |+-->+-----+|---+   +-----+ |+-->+-----+
>   |   | sf1  ||       +-----+ +--->| sf3 ||       +-----+ +--->| sf5 |
>   +-->|      +|------>| sf2 |+---->|     ||------>| sf4 |+---->|     |--+
>   |   |      || +---->|     |-+    |     || +---->|     |-+    |     |  |
>   |   +------+|-|-+   +-----+ |+-->+-----+|-|-+   +-----+ |+-->+-----+  |
>   |           | | |   +-----+ ||          | | |   +-----+ ||            |
>   |   +------++ | +-->| sf2 |-|+   +-----++ | +-->| sf4 |-|+   +-----+  |
>   |   | sf1' |  | +-->|     | +--->| sf3'|  | +-->|     | +--->| sf5'|  |
>   +-->|      +--+ |   +-----+----->|     |--+ |   +-----+----->|     |--+
>       |      |    |                |     |    |                |     |  |
>       +------+----+                +-----+----+                +-----+  |
>                                                                         |
>                                                                +--------+
>                                                                |
>                                                                V
>                                                           destination
>   
>                      Figure 6: Load Balancing and HA
>
> (72 characters?)
>
>                 In both cases, the figure has all the same connection 
> complexity (fixed up in a few
>
> places), but seems to be less busy.
>
> --
>
> Eric
>
>
>
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-- 
Sevil Mehraghdam
University of Paderborn
Computer Networks group -- http://wwwcs.upb.de/cs/ag-karl
Tel.: +49 5251 / 601755
Room: O3.161