A few comments from Ari Keränen's review:

1.  Introduction

    COMEDIA is especially useful when an endpoint is located behind a
    NAT.  The endpoint can use the mechanism to indicate that it will
    create the media transport connection, in order for the media to
    traverse the NAT without the usage of relays, without being required
    to support more complex mechanims (e.g.  TCP Candidates with
    Interactive Connectivity Establishment (ICE)
    [I-D.ietf-mmusic-ice-tcp]).

Instead of "an endpoint" it would be better to say "one of the 
endpoints" since this does not help if both of the endpoints are behind 
a NAT.


4.2.1.  General

    An MSRP UA must support the a=setup "active", "actpass" and "passive"

s/must/MUST/

    An MSRP UA MUST NOT send the "holdconn" attribute,
    and MUST ignore it if received.

What to do when "ignoring" the attribute? Behave as if there was no 
"setup" attribute at all (i.e., assume COMEDIA isn't supported)?


4.2.2.  Attribute usage

    When the a=setup attribute value is "actpass" or "passive", the IP
    address and port values in the MSRP URI of the SDP a=path attribute
    MUST contain the actual address and port values on which the UA can
    receive a TCP Open request for the MSRP transport connection.

What is "TCP Open request" (found multiple times throughout the 
document)? TCP SYN perhaps? If not, a reference where this is defined 
would be nice.


    If an MSRP UA can provide a global IP address that the other endpoint
    can use as destination for a TCP Open request, the UA MUST use the
    a=setup "actpass" attribute value in SDP offers.

Would SHOULD be sufficient here? For the purpose of stateful firewall 
traversal, UA might want to use "active" even if it has a global IP 
address.

    - the UA has used Session Traversal Utilities for NAT (STUN)
    [RFC5389] signaling to retrieve NAT address and port through the
    local port to be used for the eventual transport connection, while
    also having determined that the NAT is not address restricted.

Could use RFC5382 (and 4787) terminology instead of "address 
restricted". And actually one should use RFC5780 to discover the behavior.


5.  Interoperability with connection model defined in RFC 4975

    [...] NAT traversal can only be achieved if the
    MSRP UA supports ICE [I.D.ietf-mmusic-ice-tcp] and the network
    provides TURN servers, or if the network supports SBC assisted NAT
    traversal for TCP.

While quite often useful, TURN (or even STUN) servers are not always 
needed for ICE-TCP to work (could just remove that part of the sentence).

  Nit: s/MRSP/MSRP/ in several places in the document.


Section 1., paragraph 2:
>    [RFC4145] defines a connection-oriended media mechanism, COMEDIA,

  Nit: s/connection-oriended/connection-oriented/


Section 1., paragraph 4:
>    to support more complex mechanims (e.g.  TCP Candidates with

  Nit: s/mechanims/mechanisms/


Section 9., paragraph 2:
>    o  Changes based on comments from Gonzalo Camrillo.

  Nit: s/Camrillo./Camarillo./


Section 9., paragraph 8:
>    Changes from draft-ietf-simple-mscp-acm-02

  Nit: s/draft-ietf-simple-mscp-acm-02/draft-ietf-simple-msrp-acm-02/

Acronyms need to be expanded in the main text on first usage (regardless
of their use in the Abstract).

---

Section 3

   Support of this specification is optional for MSRP user agents in

Is that "OPTIONAL"?

---

Section 4.2.2

   In accordance with [RFC4145], if the a=setup attribute value is
   "active", the port number value should be 9.

s/should/SHOULD/ ?

Sec 1: Spell out SDP on first usage.

Sec 3: r/optional/OPTIONAL?  It's specifying support requirements.

Sec 4.2.1: r/An MSRP UA must support the a=setup.../An MSRP UA MUST support the a=setup...