[MEDIACTRL] Review of draft-ietf-mediactrl-call-flows-10
worley@ariadne.com (Dale R. Worley) Wed, 19 December 2012 20:10 UTC
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Subject: [MEDIACTRL] Review of draft-ietf-mediactrl-call-flows-10
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Review of draft-ietf-mediactrl-call-flows-10 The first thing that comes to mind is that this is a massive body of work, and tremendously useful for the implementer! I've listed the items in the order they appear in the draft. Almost all of them are editorial rather than technical. The technical questions are: item 15 (is the listing of control packages in the SDP important or not) item 17 (the negotiation of the timeout value is vague) item 35 (mixing of playback of two recordings) item 38 (semantics of setgain) item 53 (how does AS send media INVITE to the correct MS) item 55 (how does the MS know which AS sent each request) item 1) various The indentation of the header lines identifying various messages is inconsistent. I can find the following lines in various places: 1. AS -> MS (SIP INVITE) A1. AS -> MS (CFW CONTROL, createconference) A1. AS1 -> MS (CFW CONTROL, audit IVR) 1. AS -> MS (CFW SYNC) However, it may be easiest to have the RFC Editor fix that by giving them an appropriate instruction, as they are likely to manually adjust the indentation of the examples anyway. item 2) various There are a lot of places where an arrow seems to go from a network entity to itself, such as "create conf and its ID" below: AS MS | | | 1. CONTROL (create conference) | |++++++++++++++++++++++++++++++++>>| | |--+ create | | | conf and | 2. 200 OK (conferenceid=Y) |<-+ its ID |<<++++++++++++++++++++++++++++++++| However, the event described on the label, "create conf and its ID", is not the transmission of a message, and so it doesn't seem like it should be represented by an arrow. A more accurate alternative would be: AS MS | | | 1. CONTROL (create conference) | |++++++++++++++++++++++++++++++++>>| | | create | | conf and | 2. 200 OK (conferenceid=Y) | its ID |<<++++++++++++++++++++++++++++++++| item 3) section 1 "self-sustained" should be "self-contained". item 4) section 2 Note that due to RFC formatting conventions, this document often splits SIP/SDP and CFW across lines whose content would exceed 72 characters. "whose content ..." is applied to the wrong referent, a "lines", but those lines are the post-split lines, not the pre-split lines. Perhaps: Note that due to RFC formatting conventions, SIP/SDP and CFW lines whose content exceeds 72 characters are split across lines. This line folding is marked by a backslash at the end of the first line. This backslash, the preceding whitespace, the following CRLF, and the whitespace beginning the next line would not appear in the actual protocol contents. item 5) section 2 Due to the same 72 characters limitation, this document also sometimes splits the content of XML elements across lines: please beware that, when this happens, no whitespace is actually meant to be neither at the beginning nor at the end of the element content. This seems to be incorrect, as in many places, an XML *element*, that is, everything from the start tag to the end tag (see XML spec, rule "element"), is quite long and is necessarily split across lines, but is also valid. (However, that interpretation depends on entities respecting the common convention that whitespace character content is to be ignored if it appears immediately within an element that does not admit immediate character content.) I believe you meant "start tag" instead of "element". But in that case, line breaks between the attributes of a start tag are valid in XML (see XML spec, rule "STag"). If this is correct, the above sentence can be omitted. However, the message B1 in section 7.1 may be an exception. See the appropriate item. item 6) section 3 This document makes use of the same terminology as the one that can be found in the referenced documents. This is awkward. Perhaps: This document makes use of the same terminology as the referenced documents [RFC6230] [RFC6231] [RFC6505] [I-D.ietf-mediactrl-mrb]. item 7) section 4 This section starts with a paragraph over one page long. Could it be broken into multiple paragraphs? item 8) section 4 It seems overly complicated to explicitly describe "categories" to contain only four things. Also, the text needs to mention that Figure 3 contains *two* diagrams, otherwise the accounting seems to be incorrect. Perhaps: Four diagrams are provided. Two of them (Figure 1 and Figure 2) describe normal operation of the framework. Figure 3 contains two diagrams describing asynchronous event notifications. Figure 1 embraces the MS perspective, whereas Figure 2 is on on the AS side. The upper part of Figure 3 shows how events are generated, on the MS side, by issuing a CONTROL message addressed to the AS; events are acknowledged by the AS through standard 200 responses. Hence, the behavior of the AS, which mirrors that of the MS, is depicted in the lower part of the figure. item 9) section 4 figure 1 I think the state machine could be clarified: - Replace the event "API 200" in "API 200/200" with "API terminate", which is how the API termination is described on other arcs. - Replace the event "API 202" in "API 202/202" with "API update", which is how the API non-termination is described on other arcs. - Further, change "API update" to "timer" or something like that, to indicate that the MS CFW state machine must generate a 202 *based on the passage of time*, not based on the API providing some sort of "update". If these time intervals are globally fixed for the CFW protocol, their fixed values could be written in. - The states "'202' sent" and "'update' sent" have the same outgoing transitions, so they should probably be merged. - Is there truly an "Error" message that is comparable to the "200" and "202" messages? Or is sending "Error" a shorthand for a cluster of numeric response codes? If the latter, it would help to make that clearer here in the introductory material. - What happens if the API detects an error after 202 has been sent? There is no "API Error" arc from "'202' sent"/"'update' confirmed". item 10) section 4 figure 2 Clarifications of the state machine: - There is no "Error" arc from the "202 received" and "'update'" states. Are errors impossible here? - The states "202 received" and "'update'" have the same outward arcs and so could be merged. - The two figures are inconsistent regarding whether response numbers (200, 202) are within quotes '...'. - The two figures are inconsistent regarding whether report categories (update, terminate) are within quotes '...'. - The two figures are inconsistent regarding whether the sending of a request or response in an arc's label is indicated using "send" or not. item 11) section 4 figure 3 There are similar inconsistencies between figure 3 and figures 1 and 2. item 12) section 5 The term "COMEDIA" is used, and a reference is given to RFC 4145. But that RFC does not use the term "COMEDIA" at all. The framework I-D also uses "COMEDIA" without explicitly defining it. It would be helpful to insert here a definition of "COMEDIA", which seems to be synonymous with "media of type application/cfw". item 13) section 5.1 If the request is fine, the MS answers with its own offer, shouldn't this be: If the request is fine, the MS answers with its answer, item 14) section 5.1 The MS replies with the list of packages it supports, by adding a dummy example package to the list provided by the AS. The "by" should be removed, as the replying is not done "by adding"; instead, the MS replies and also adds. item 15) section 5.1 It is worth noting that this exchange of information is not meant as a strict or formal negotiation of packages: in case the AS realizes that one or more packages it needs are not supported according to the indications sent by the MS, it may, or may not, choose not to open a control channel with the MS at all, if its application logic leads to such a decision. The actual negotiation of control packages is done subsequently through the use of the framework SYNC transaction. This confuses me: Either the list of packages in the SDP offer/answer is significant or it is not. If it is not, why is it provided? In particular, if the MS may support packages that it does not admit to in the answer, then when the AS sees an answer that does not contain the needed packages, it will have to continue with the control channel connection in order to determine if the MS *actually* supports the needed packages or not. Thus, the MS could omit all ctrl-package attributes in its answers all the time. Also, it's not clear whether the AS is required to provide the list of packages it will need. If it is required, then the SDP can be used to choose the correct MS based on MS capabilities. If it is not required, a different architectural mechanism is needed. item 16) section 5.3 Whether "keep alive" is hyphenated is not consistent. item 17) section 5.3 In the previous section it has been described how a timeout value for the keep alive mechanism is negotiated. Specifically, in the example the AS and the MS agreed on a value of 100 seconds. In fact, that section does not describe how the value is negotiated (since it is not clear what happens if the MS dislikes the value proposed by the AS). However, this is correct: In example in the previous section, the AS and the MS agreed on a value of 100 seconds. item 18) section 6 Besides, unless stated otherwise, the same UAC session is referenced in all the above mentioned examples. Is "above mentioned" the correct modifier? The previous paragraph refers to "the following scenarios". item 19) section 6 figure 10 It would be useful at this point to make it clear that the two INVITEs are different SIP dialogs (as these scenarios are constructed). (Or, if the AS may be inline and acting as a proxy, describe that there may be two dialogs or only one.) Including, replace the second "INVITE (X)" with "INVITE (Y)" to show that the URIs need not be the same. Also, why not include the establishment of the Control Channel in the figure, as that will not need to be duplicated in any further figure. item 20) section 6 figure 11 Figure 11 appears to be only a caption. Or is it the SIP signaling? Expositions of protocol messages are rarely considered to be figures. item 21) section 6 The phrase "These three identifiers" is confusing because the text has just introduced four identifiers. I assume that if the SDP from AS to MS also contains label attributes, the Mediactrl framework specifies how they will be used (or ignored), so that the "addressing" of media streams is not made ambiguous. item 22) section 6.1.2 The 202+REPORT(s) mechanism is used whenever the MS wants to tell the AS that the requested operation might take some more time than expected. This is probably incorrect. What you mean is, "the requested operation might take more than *** seconds". The fixed or variable time limit should be specified here. In this example, the preparation ends before the timeout, and so the transaction is concluded with a 'REPORT terminate', which acts as the 200 message in the previous example. The last clause is rather confusing, as 'REPORT terminate' is a request, not a response, and thus doesn't "act like" a 200 message. Perhaps: "which reports the end of the transaction (as did the 200 message in the previous example)". item 23) section 6.2 figure 18 It might be useful to distinguish the four(?) SIP dialogs involved. item 24) section 6.2.2 Three hours is 10,800 seconds, not 1,800 seconds. I think the easiest fix is to replace "3 hours" with "30 minutes". RFC 6230 section 6.2 An entity acting as a Control Server, on receiving a request, MUST generate a response [...]. The response MUST conform to the ABNF Responses MUST NOT include the 'Status' or 'Timeout' message headers, [...] RFC 6230 section 6.3.2.1 A Control Server issuing a 202 response MUST ensure the message contains a 'Timeout' message header. item 25) section 6.2.3 This section is rather difficult to follow. I'm not sure why, but partly it's because the text doesn't rigorously make clear what events are "before", that is, when the two audio channels of the original conference are being recorded, and "after", when the two recordings are being played back. For instance, in the second paragraph, the last sentence is "after", but the first two sentences are "before". Instead, there should be a paragraph break there, and starting "Later, when we desire to play the whole conversation to UAC, the AS may take...". It would help if the UAC which is listening to the playback was called "UAC3" or something like that, as "UAC" is also a generic term, and it's not immediately clear that it is unrelated to UAC1 and UAC2. It would also help if the two *recordings* had names different from the UACs during the recording. In particular "play UAC1 on confY" is hard for the naive reader to understand until he realizes that "UAC1" means the recording file of the audio generated by UAC1. item 26) section 6.3 o The AS invokes the creation of a new conference instance by means of a CONTROL request (1); this request is addressed to the conferencing package (msc-mixer/1.0) and contains in the body the directive (createconference) with all the desired settings for it; The antecedent of "it" is not particularly clear. The antecedent is "a new conference", which is the 6th preceding noun phrase, which is only determined because it is the first preceding noun phrase which has settings. Better to say "... the desired settings for the new conference instance". item 27) section 6.3.1 figure 30 This figure uses "UAC1" and "UAC2", but the other figures in 6.3 use "UAC A", "UAC B", and "UAC C". Ditto for figure 31 and some of the text. item 28) section 6.3.4 figure 38 The notation "D+[a+c]" is clever, but "D+(A+C)/2" would be more accurate. (And see the following item regarding the volume level.) item 29) section 6.3.4 The volume level at which the main conference is heard in the sidebar is not stated consistently: the main conference. The mix of the conference, instead, must be attached to the sidebar, but with a lower volume (50%), being just a background to the actual conversation. This would allow both B and D 2. then, the main conference mix is attached to it as 'sendonly' and with a -5dB gain to limit the volume of its own contribution to 30% (so that B and D can hear each other louder, while still listening to what's happening in the main conference in background); | | | B1. CONTROL (join confX-->confY) | | | |++++++++++++++++++++++++++++++++>>| | | | |--+ join confX | | | | | & confY | | | B2. 200 OK |<-+ sendonly | | |<<++++++++++++++++++++++++++++++++| (50% vol) <mscmixer version="1.0" xmlns="urn:ietf:params:xml:ns:msc-mixer"> <join id1="2f5ad43" id2="519c1b9"> <stream media="audio" direction="sendonly"> <volume controltype="setgain" value="-5"/> </stream> </join> </mscmixer> Of these, two references say 50% (-3dB) and two references say 30% or -5dB. item 30) section 6.3.5 figure 43 Is it intended that UAC (FCC) does not have any RTP going to the MS? (Indeed, is it necessarily a UAC? But perhaps SIP is needed to set up BFCP.) item 31) section 6.3.5 The participant UAC is labeled inconsistently as "UAC", "UAC (FCP)", and "UAC1". ("UAC" may be correct, as the context for that term my be describing a generic or abstract UAC.) Similarly, "UAC (FCC)" and "UAC2" are used for the chair UAC. item 32) section 6.3.5 It might be desirable to mention that the previous speaker should be muted before UAC1 can be un-muted. Usually, this muting will happen between the Accepted and Granted BFCP messages, so it probably should be illustrated in the sequence of events. item 33) section 6.4 It might be helpful to expand "VCR" the first time it is used. (Apparently it does not mean "video cassette recorder", and I see no suitable meaning on the Wikipedia "disambiguation" page for "VCR".) item 34) section 6.4.2 In fact, rather than having the AS build different framework messages according to the current time to build an announcement, This is difficult to read. Perhaps In fact, rather than having the AS build an announcement according to the current time using different framework messages, item 35) section 6.4 The discussion of mixing in the background music should be contrasted with the mixing of the two recordings during playback in section 6.2.3. Naively, it would seem that the same mixing techniques could be used in both cases, but the two sections implement mixing in entirely different ways. item 36) section 6.4.3 An example contains XML elements that seem to be unnecessarily complex: <rule id="action" scope="public"> <item> * <item><ruleref uri="#digit"/></item> </item> </rule> As far as I can tell from the SRGS specification, <item> functions more-or-less as a type of parenthesis, and is needed only when (1) a "weight" or "repeat" attribute needs to be applied to the group, (2) delimiting one alternative of a <one-of> element, or (3) constructing the "null" regular expression (that consumes no input and always matches). Thus, these examples can be simplified to: <rule id="action" scope="public"> * <ruleref uri="#digit"/> </rule> Then again, if the example is taken from a real interaction, perhaps it is best to leave it as it really happened. item 37) section 6.4.3 to implement is a <collect>, and we are only interested in two- digits DTMF strings (maxdigits); the AS is not interested in a "two-digits" should be "two-digit". (Because this phrase is used as a modifier of "DTMF strings", the "digit" is not plural.) instructs the MS into modifying the volume of the UAC-->conference "into modifying" would better be "to modify". audio flow (setgain=-5dB sendonly); notice how the request also This is probably intended to be "-3dB", as all other uses of setgain in this section (including the displayed messages) use a 3 dB increment. item 38) section 6.4.3 This section leads to a question about the semantics of the <volume controltype="setgain" ...> operation: Clearly, initially the stream is output at the same volume as the input media. But when "<volume controltype='setgain' value='+1'>" is applied, does that cause the stream's output volume to be set to +1 dB *relative to the input media* or to +1 dB *relative to the previous volume setting*? E.g., if I apply that operation twice, does the second application leave the amplification at +1 dB or raise it to +2 dB? The examples in section 6.4.3 suggest the second interpretation. The text in draft-ietf-mediactrl-mixer-control-package-14 is not clear on this point: "setgain" is only discussed in section 4.2.2.5.1, and it says "use the value of the "value" attribute as a specific gain measured in dB to apply". That would be most likely to mean "as a specific gain measured in dB to apply to the input", which suggests the first interpretation. In any case, the semantics of this need to be clarified and the example adjusted accordingly. item 39) section 7.1 Each MS makes use of the publishing interface to provide an MRB with relevant information. In the relationship between the MRB and MS, the MRB initiates the relationship. Thus, it would be clearer to express this: An MRB makes use of the MS's publishing interface to acquire relevant information. It is enough to point out that, in this case, the MRB adds a new voice to the 'Packages' it needs support for (mrb-publish/1.0). "voice" should be "item". All this messages flow through the control channel as all the messages in ---^^^^ should be "these" ----------------------------------------------------^ insert "do" this document. item 40) section 7.1 message B1 This seems to be the only place in the draft where whitespace has been introduced where character content is valid, and so there is a question whether the draft needs to indicate that the whitespace would not be present on the wire. The relevant elements are: <mixing-modes> <audio-mixing-modes> <audio-mixing-mode package="msc-ivr/1.0"> nbest </audio-mixing-mode> </audio-mixing-modes> <video-mixing-modes activespeakermix="true" vas="true"> <video-mixing-mode package="msc-mixer/1.0"> single-view </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> dual-view </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> dual-view-crop </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> dual-view-2x1 </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> dual-view-2x1-crop </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> quad-view </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> multiple-5x1 </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> multiple-3x3 </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> multiple-4x4 </video-mixing-mode> </video-mixing-modes> </mixing-modes> I'm not sure if the schema defining urn:ietf:params:xml:ns:mrb-publish indicates that the whitespace before and after the mixing mode names is to be ignored. But this might be a place to use the backslash-line-folding convention specified in section 2: <mixing-modes> <audio-mixing-modes> <audio-mixing-mode package="msc-ivr/1.0"> \ nbest \ </audio-mixing-mode> </audio-mixing-modes> <video-mixing-modes activespeakermix="true" vas="true"> <video-mixing-mode package="msc-mixer/1.0"> \ single-view \ </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> \ dual-view \ </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> \ dual-view-crop \ </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> \ dual-view-2x1 \ </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> \ dual-view-2x1-crop \ </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> \ quad-view \ </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> \ multiple-5x1 \ </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> \ multiple-3x3 \ </video-mixing-mode> <video-mixing-mode package="msc-mixer/1.0"> \ multiple-4x4 \ </video-mixing-mode> </video-mixing-modes> </mixing-modes> item 41) section 7.1, section 7.2, section 7.2.1 In the Inline mode, instead, the MRB is in the path between the AS and the pool of MSs it is handling. Anyway, the MRB is also conceived to work with ASs that are unaware of its functionality, and the SIP addresses of the chosen MSs. Generally, "AS" and "MS" are used as the plurals of "AS" and "MS", but in these instances, "ASs" and "MSs" are used. item 42) section 7.1 request itself and an SDP related to related to either the creation -----------------------------^^^^^^^^^^^^^^^^^^^^^ "related to" is duplicated. item 43) section 7.2.1 MS the MRB has deemed better capable to fulfill the AS requirements), -------------------------^^^^^^ This should be "best". -------------------------------------------------------^^ This should be "AS's" or "AS'" (depending on which spelling convention we are using). targeting the request, and as a consequence picks up two MS which --------------------------------------------------^^^^^^^^ I think you want "picks" here. after the Query the AS<->interaction becomes 1:1, UAC media dialogs ----------------------------^ Something appears to be missing here. item 44) section 7.2.2.1, section 7.2.2.2, section 7.2.3 I think it would make the diagrams a little easier for the naive reader to follow if the media types specified in the SDP of the message bodies were given. E.g., if an INVITE or 200 carries an application/sdp body for audio media, that is shown on the diagram. This would be particularly helpful in 7.2.3, where it takes the reader more consideration to deduce what the media types must be. Updated in this way, the diagrams are as follows. (But this has removed the comments noting where the SDP has been copied from one message to another. That may need to be improved.) 7.2.2.1. Inline-aware Mode: CFW-based approach AS MRB MS | | | | 1. INVITE | | | (multipart/mixed: | | | audio, | | | application/mrb-consumer+xml) | |---------------------->| | | 2. 100 (Trying) | | |<----------------------| | | |--+ Extract SDP and | | | | MRB payloads; handle | | |<-+ Consumer request to | | | pick MS | | | | | | 3. INVITE | | | (audio) | | |-------------------------->| | | 4. 100 (Trying) | | |<--------------------------| | | |--+ Negotiate | | | | CFW Control | | |<-+ Channel | | 5. 200 OK | | | (audio) | | |<--------------------------| | | 6. ACK | | |-------------------------->| | Prepare new +--| | | payload with | | | | SDP from MS and +->| | | Consumer reply | | | | | | 7. 200 OK | | | (multipart/mixed: | | | audio, | | | application/mrb-consumer+xml) | |<----------------------| | | 8. ACK | | |---------------------->| | | | | |--+ Read Cons. reply | | | | and use SDP to | | |<-+ create CFW Chn. | | | | | | | |<<############## TCP CONNECTION #################>>| | | | CFW SYNC | |++++++++++++++++++++++++++++++++++++++++++++++++++>| | | 7.2.2.2. Inline-aware Mode: Media dialog-based approach UAC AS MRB MS | | | | | 1. INVITE | | | | (audio) | | | |-------------->| | | | 2. 100 Trying | | | |<--------------| | | | | 3. INVITE | | | | (multipart/mixed: | | | | audio, | | | | application/mrb-consumer_xml) | | |---------------------->| | | | 4. 100 (Trying) | | | |<----------------------| | | | |--+ Extract SDP and | | | | | MRB payloads; handle | | | |<-+ Consumer request to | | | | pick Media Servers | | | | | | | | 5. INVITE | | | | (audio) | | | |------------------------->| | | | 6. 100 (Trying) | | | |<-------------------------| | | | +--| | | | Handle media dialog | | | | | (connection-id) +->| | | | | | | | 7. 200 OK | | | | (audio) | | | |<-------------------------| | | | 8. ACK | | | |------------------------->| | | Prepare new +--| | | | payload with | | | | | SDP from MS and +->| | | | Consumer reply | | | | | | | | 9. 200 OK | | | | (multipart/mixed: | | | | audio, | | | | application/mrb-consumer+xml) | | |<----------------------| | | | 10. ACK | | | |---------------------->| | | | | | | |--+ Read Cons. reply | | | | | and send SDP | | | |<-+ back to UAC | | | 11. 200 OK | | | | (audio) | | | |<--------------| | | | 12. ACK | | | |-------------->| | | | | | | |<<*************************** RTP ******************************>>| | | | | | |--+ Negotiate | | | | | CFW channel | | | |<-+ towards MS | | | | (if needed) | | | | | | | |<<############## TCP CONNECTION ################>>| | | | | | CFW SYNC | | |+++++++++++++++++++++++++++++++++++++++++++++++++>| | | | 7.2.3. Inline-unaware Mode AS MRB MS | | | | 1. INVITE | | | (application/cfw) | | |---------------------->| | | 2. 100 (Trying) | | |<----------------------| | | |--+ Pick a MS | | | | and redirect | | |<-+ INVITE there | | | | | | 3. INVITE | | | (application/cfw) | | |-------------------------->| | | 4. 100 (Trying) | | |<--------------------------| | | |--+ Negotiate | | | | CFW Control | | |<-+ Channel | | 5. 200 OK | | | (application/cfw) | | |<--------------------------| | | 6. ACK | | |-------------------------->| | | | | 7. 200 OK | | | (application/cfw) | | |<----------------------| | | 8. ACK | | |---------------------->| | | | | | | |<<############## TCP CONNECTION #################>>| | | | CFW SYNC | |++++++++++++++++++++++++++++++++++++++++++++++++++>| | | item 45) section 7.2.2 An AS willing to issue a Concumer request by means of SIP, has to do ----------------------------^ This should be "Consumer". envisages two kind of SIP dialogs a Consumer request may be sent -----------------^ This should be "kinds". setup a control channel) or a UAC media dialog (a SIP dialog the AS ---^ This should be "set up". ("set up" functions like a verb; "setup" functions like a noun.) The behaviour in the two cases, which are called respectively CFW- -------^ Probably better to say "behaviours" here. based and Media dialog-based approach, is only slightly different, ------------------------------------------^ Use "are", to go with "behaviors". item 46) section 7.2.2.1, section 7.2.2.2 Please note that, to ease the reading of the protocol contents, a simple '=_Part' is used whenever a boundary for a 'multipart/mixed' payload is provided, instead of the actual boundary that would be inserted in the SIP messages. This seems like a poor strategy, as the resulting figures are not strictly correct. Perhaps use "Part" as the boundary value, which would result in figures that look like the following, which strictly correct and are just as easy to read: [..] Content-Type: multipart/mixed;boundary="Part" --Part Content-Type: application/sdp v=0 o=- 2890844526 2890842807 IN IP4 as.example.com [...] --Part Content-Type: application/mrb-consumer+xml <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <mrbconsumer version="1.0" xmlns="urn:ietf:params:xml:ns:mrb-consumer"> [...] </mrbconsumer> --Part-- In both of these sections, just before the message listings, there is a line containing only: o In the following message titles, "SDP" appears in lower case: section 7.2.2.1: 3. MRB -> MS (INVITE sdp only) 5. MRB <- MS (200 OK sdp) section 7.2.2.2: 5. MRB -> MS (INVITE sdp only) 7. MRB <- MS (200 OK sdp) 11. UAC <- AS (200 OK sdp) item 47) section 7.2.3 pick a MS rather than another. --------^ Probably should be "one", to contrast with "another". item 48) section 7.2.3 This example does not give the content of the messages, unlike the previous two examples. item 49) section 7.3.1 This section is titled "Query/IAMM". The call flow does mesh with the call flow in section 7.2.1, "Query Mode", but it does not mesh with the call flow in section 7.2.2.1, "Inline-aware Mode: CFW-based approach" nor with the call flow in section 7.2.2.2, "Inline-aware Mode: Media dialog-based approach". It would probably be best to change the title of the section to "Query". If necessary, an additional section should be added giving examples relevant to inline-aware mode. item 50) section 7.3.1, section 7.3.2 The use of "IAMM" and "IUMM" is a bit opaque here, as those acronyms are not explicitly expanded anywhere in this document. They seem to mean what is called "inline-aware mode" and "inline-unaware mode", but the acronyms of those phrases aren't the same as the acronyms used. Perhaps these section titles could be changed to resemble those of 7.2.*, "7.3.1. Query and Inline-aware Mode" and "7.3.2. Inline-unaware Mode". That doesn't fix the problem with the acronyms per se but does make the titles clearer. item 51) section 7.3.1 We might want to mention that in this scenario, the AS obtains assignment of an MS *before* any UAC makes a request, in order to have facilities to satisfy future SIP requests. That is probably how AS's operate in practice, but a naive reader might expect that the AS will make the consumer request only after the AS receives a demand for its services. Nevertheless, there are cases when having an MRB in the signalling path ... You might want to say "the SIP signalling path" here. By my count, there are *three* different signalling paths: the COMEDIA negotiation (INVITE with application/cfw SDP), the CFW connection, and the SIP signalling (INVITE with audio/etc. SDP). item 52) section 7.3.2 As mentioned previously, in such a case the AS would interact with What case is "in such a case"? (This is the first sentence of a section.) It seems that this paragraph is trying to contrast "such a case" with "IUMM", but it's not clear what is going on. That said, the IUMM case is also very interesting with respect to the media dialogs management. In fact, in the MRB-unaware mode there ---------^ This should be "dialog". would be no Consumer request and an AS would actually see the MRB as an MS. This means that, unlike the previous scenarios, there is actually no choice, meaning the MRB would likely be in the signaling ------------^ What is there "no choice" of? The obvious choice is that of a MS, but the MRB clearly can choose which MS to sent the request to. path anyway. The MRB could either redirect the AS to a MS directly or transparently act a proxy/B2BUA and contact a MS (according to implementation-specific policies) on behalf of the unaware AS. To overcome the scalability limitations of such an approach, the MR --------------------------------------------------------------^ You should add here "at least in regard to the MRB being in the SIP signalling path for all calls" -- as far as I can tell, this is the only scaling problem this approach removes. (The major one is that all calls handled by the AS have to be handled by only one MS.) Rather than recurring to explicit redirection, or always ---------------^ This isn't the right word. Perhaps "resorting" was intended? item 53) section 7.3.2 While apparently not a problem, this raises an issue when the same unaware AS has several sessions with different MS: the AS would only see one "virtual" MS (the MRB) and so it would relay all calls there, making it hard for the MRB to understand where these media dialogs should belong: specifically, whether the UAC calling belongs to the AS application logic leading to MS1 or MS2, or wherever else. This seems to be a deficiency in the CFW protocol: If the AS establishes a CFW channel with the MS (via a SIP URI to an MRB), and then later the AS wants to addresses a SIP INVITE to the MS, it has no choice but to use the same SIP URI (which routes to the MRB). This makes it impossible for the MRB to associate the SIP INVITE with the CFW connection, and thus it is difficult for the MRB to route the INVITE to the same MS. What seems to be needed is for either the COMEDIA response (application/cfw) or CFW connection to provide a SIP URI that is the "real" SIP URI of the far-end of the CFW channel. Actually, this seems to be a problem even if an AS is addressing an MS URI, but the URI resolves to a redundant set of MSs: There seems to be no way to ensure that when a CFW channel is established that a subsequent SIP INVITE can be sent to the same MS. This issue seems to be discussed in RFC 6230 section 3, but I can't find any solution there. item 54) section 8 receiving requests that may cross the bounds each AS is constrained into. ---^ Probably better as "within". item 55) section 8 The detailed discussion of how the MS enforces security against the ASs is helpful, but it does not mention how the MS discerns which requests come from AS1 and which come from AS2. Dale
- [MEDIACTRL] Review of draft-ietf-mediactrl-call-f… Dale R. Worley
- Re: [MEDIACTRL] Review of draft-ietf-mediactrl-ca… Lorenzo Miniero
- Re: [MEDIACTRL] Review of draft-ietf-mediactrl-ca… Eric Burger
- Re: [MEDIACTRL] Review of draft-ietf-mediactrl-ca… Lorenzo Miniero
- Re: [MEDIACTRL] Review of draft-ietf-mediactrl-ca… Lorenzo Miniero
- Re: [MEDIACTRL] Review of draft-ietf-mediactrl-ca… Dale R. Worley
- Re: [MEDIACTRL] Review of draft-ietf-mediactrl-ca… Lorenzo Miniero
- Re: [MEDIACTRL] Review of draft-ietf-mediactrl-ca… Lorenzo Miniero