Subject: [MMUSIC] Some comments on draft-ietf-mmusic-ice-08

From: Philip Matthews <[email-masked]>
Date: Tue, 18 Apr 2006 10:31:53 -0400

Jonathan:

Here are some comments. They are mostly pretty minor.
I am still re-reading the draft to more fully understand it,
so more may follow.

General comments:
- The grammar given in section 12 specifies that a colon (":") is to  
immediately follow the word "candidate"
in the "a=candidate" line. This is consistent with the SDP syntax for  
an attribute with a value as specified in
draft-ietf-mmusic-sdp-new-26.
However, none of the examples given elsewhere in the document use a  
colon.

Section 1:
- (First PP) Misspelling - "Descrption" should be "Description".

Section 2:
- I found it difficult to understand much of the terminology on my  
first pass through
   the document, even though I had a basic understanding of how ICE  
works. In the end,
   I just skipped over it and then came back later.
   Perhaps consider placing the introductory sections before the  
terminology section,
   perhaps by making sections 3 - 6 subsections of section 1.  If you  
did this,
   then the terminology section would clearly divide the Informative  
text from the Normative text.
- It would be nice if the definitions of Reflexive Transport Address  
and Relayed Transport Address
   could make it clearer that these are subclasses of Derived  
Transport Addresses
   (for example, the definition text could start "A type of Derived  
Transport Address where ...").
- I found the definitions of the various Transport Address forms  
difficult to understand
   (I was familiar with the concepts, but hadn't see the terms  
before, and was uncertain for a while
   which term matched which concept).
   I might be useful to add a diagram (perhaps somewhere in sections  
3-6) that illustrates the
   various forms  (Derived, Reflexive, etc...)

Section 3:
- "in addition to private networks connected to the public Internet  
through NAT".
   The wording here suggests  that the combination of the Internet  
plus various private networks
   connected to it via NAT boxes is one realm.
- (top of page 10) "reply from that target Section 7.13".
   There is some sort of grammatical error here.

Section 7.1:
- In the case of a candidate whose components are all server- 
reflexive or relayed, must the component
   transport addresses all be derived from the same local address?
   I suspect so, but you don't say this.
- (page 13)
       "Local candidates are obtained by binding to ephemeral ports  
on an interface ..."
    AND
      "... obtain a set of candidates (one for each interface) by  
binding to N ephemeral UDP ports ..."
   This text seems to imply that the UDP ports must be ephemeral.  
This seems overly restrictive.
   I believe that the specification will work fine if a well-known  
port is used instead.
   I suggest replacing these with the following:
       "Local candidates are obtained by binding to ports (typically  
ephemeral ports) on an interface ..."
   AND
      "... obtain a set of candidates (one for each interface) by  
binding to N UDP ports ..."
- (page 14, indented paragraph)
   "The ability to process STUN connectivity checks allows for  
clients to obtain peer reflexive transport
    addresses that can be used by the network server to reach them  
without a relay, even through NATs
    with restrictive mapping and filtering policies."
   I don't understand this sentence.
   In general, I found the wording in this indented paragraph to be  
much below the very high standard
   set by the rest of the document. Perhaps you might rewrite this  
entire paragraph.
- (page 15)
    "... where there are multiple layers of NAT,  and that layering  
is known to the provider of the client."
   Suggest adding an extra "where", so it reads
    "... where there are multiple layers of NAT,  and where that  
layering is known to the provider of the client."

Section 7.8:
-  "symmetric NAT". Replace with BEHAVE terminology?

Section 12:
- In addition to all the SDP examples in section 11, it would be nice  
to see one or two examples of SDP
   that do NOT use $L1, $L-PRIV-1.IP, $STUN-PUB-2.PORT, etc.
   This would help the reader understand the grammar rules.

- Philip

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