[Sip] draft-ietf-sip-rph-new-namespaces

[Henning Schulzrinne <hgs at cs.columbia.edu>]

Keith asked me to review the draft; here are a few quick comments:

While the mechanics and namespaces defined seem relatively  
straightforward, it is hard to evaluate anything beyond the syntax  
and editorial issues without knowing something about what motivated  
the design. Why 50 namespaces and not 42 or 99? Is this based on some  
existing PSTN technology or is this an attempt to have 50 departments  
in the DoD share some resource, without declaring who is more  
important than the other fiefdom or assistant vice deputy director?  
Why priority values that are even only?

Depending on the motivation and background, there could well be other  
designs, such as 250 levels, where preemption is only within groups  
of 5. I'm not arguing that this is a better design, but it's hard to  
say anything even vaguely interesting without knowing the requirements.

The wording is somewhat redundant, with the same information repeated  
three times, but in slightly different ways. In particular, the  
notion of non-preemption across namespaces seems to be couched in  
caveats. It seems that preemption across namespaces is sometimes  
permitted and sometimes not, which makes it rather difficult to build  
an implementation for the namespace without either a lot of  
configuration options or special software versions for each policy.  
We have seen in other areas that excessive configurability leads to  
interoperability problems and code complexity. I have a hard time  
picturing how to build such a configurable system without a monster  
language and all kinds of strange interactions. What happens if  
namespace 30 can preempt namespace 28, and vice versa? What about  
circular preemption chains (30 -> 17 -> 10)? In those cases, do  
namespaces have absolute priority, i.e., any priority in 30 beats any  
priority in 28? You'd have to create a matrix with 250 by 250 entries

Paragraph breaks appear to be random, with a single thought split  
into three paragraphs (introduction).

I can't parse sentences such as "matter of local policy. However,  
this policy is a known requirement..." What policy? The local policy,  
undefined?

Henning


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