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Network Working Group T. TaylorRequest for Comments: 2886 Nortel NetworksCategory: Standards Track August 2000 Megaco ErrataStatus of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.Copyright Notice Copyright (C) The Internet Society (2000). All Rights Reserved.1. Abstract This document records the errors found in the Megaco/H.248 protocol document [2], along with the changes proposed in the text of that document to resolve them.2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [1].3. Errata All section numbers are those of the relevant text of [2]. Section: 2 "References" ---------- Editorial: Add missing references to I.363.5 (AAL5) and RFC 1661 (PPP). Editorial: delete unused reference to Q.724. Editorial: Leave Recommendations referred to in Annex C undated, implying latest issue. Editorial: add reference to RFC 2805, the Megaco requirements document.Taylor Standards Track [Page 1] RFC 2886 Megaco Errata August 2000 Section: 4 "Abbreviations" ---------- Editorial: delete unused abbreviation BRI. Editorial: add explanations for GSM and IVR. Section: 6.2.2 "TerminationIDs" ---------- Issue: Not clear what wildcard union responses look like. Resolution: Add the following text: "ie. Given termination Ta with properties p1=a, p2=b, and termination Tb with properties p2=c, p3=d a UNION response would be T* p1=a, p2=b,c, p3=d." Section: 6.2.4 "Termination Properties and descriptors" ---------- Issue: Says that property values set in Null context are remembered and reinstated when termination returns to Null. Contradicts latest text in 7.2.3. Resolution: Rewrite the first paragraph from the third sentence onward, to read: "Most properties have default values, which are explicitly defined in this standard or in a package (see Section 12) or set by provisioning. If not provisioned otherwise, all descriptors except for TerminationState and LocalControl default to empty/"no value" when a termination is first created or is returned to the null context. The default contents of the two exceptions are described in sections 7.1.5 and 7.1.7." Issue: DigitMap entry in table makes explicit reference to DTMF tones, but is also intended to apply to other in-band signalling systems. Resolution: Change existing text to new one as follows: "Defines patterns against which sequences of a specified set of events are to be matched so they can be reported as a group rather than singly." Section: 6.2.5 "Root Termination" ---------- Issue: Root can have statistics as well as properties and events. Resolution: add "statistics" to the fourth sentence of the first paragraph, listing what is valid for Root. Add "statistics" to what AuditValue can return for Root.Taylor Standards Track [Page 2] RFC 2886 Megaco Errata August 2000 Section: 7.1 "Descriptors" ---------- Issue: it is unclear how to express empty descriptors in responses to the MGC. Proposed resolution: In section 7.1, add the following text after the sentence: "Descriptors may be returned as output from a command.": "In any such return of descriptor contents, an empty descriptor is represented by its name unaccompanied by any list." In the ASN.1, add the following choice to the AuditReturnParameter production: "emptyDescriptors AuditDescriptor," In the ABNF, add the choice auditItem to the production auditReturnParameter. Section: 7.1.1 "Specifying Parameters" ---------- Issue: Third paragraph (discussing unspecified parameters): not clear which parameters are mandatory. Resolution: Replace the first two sentences (each beginning with the word "unspecified") with the following text: "If a required descriptor other than the Audit descriptor is unspecified (i.e. entirely absent) from a command, the previous values set in that descriptor for that termination, if any, are retained. A missing Audit descriptor is equivalent to an empty Audit descriptor. The behaviour of the MG with respect to unspecified parameters within a descriptor varies with the descriptor concerned, as indicated in succeeding sections." Section: 7.1.6 "Stream Descriptor", ABNF (Annex B.2) ---------- Issue: Text indicates use of "true" and "false" values while ABNF uses "on" and "off" Resolution: Add comment in B.2 that "true" in text corresponds to "on" in ABNF, and "false" corresponds to "off".Taylor Standards Track [Page 3] RFC 2886 Megaco Errata August 2000 Section: 7.1.8 "Local and Remote Descriptors" ---------- Issue: case where reserveGroup or reserveValue is true, last bulleted item beginning: "If the Mode property of the LocalControl descriptor is RecvOnly or SendRecv,...", could also have DSP involvement in the case of loopback mode. Resolution: Add "loopback". Section: 7.1.9 "Events Descriptor" ---------- Issue: EventDM is part of syntax but not mentioned in section. Resolution: Add text: "If a digit map completion event is present or implied in the EventsDescriptor, EventDM is used to carry either the name or the value of the associated digit map. See section 7.1.14." Issue: Not clear whether events trigger side effects (e.g. signal termination) at time of detection, at time of processing (whether or not in active Events Descriptor) or at time of notification. Also, the third paragraph of the section fails to mention these side effects and limits MG action to notification. Resolution: Modify the third paragraph of the section, so that it reads: "When an event (either newly detected or buffered) is processed against the contents of an active Events descriptor and found to be present in that descriptor ("recognized"), the default action of the MG is to send a Notify command to the MG. Notification may be deferred if the event is absorbed into the current dial string of an active digit map (see section 7.1.14). Any other action is for further study. Moreover, event recognition may cause currently active signals to stop, or may cause the current Events and/or Signals descriptor to be replaced, as described at the end of this section." Replace "detection" with "recognition" in the fourth paragraph from the end, so that it reads: "Normally, recognition of an event shall cause any active signals to stop. When KeepActive is specified in the event, the MG shall not interrupt any signals active on the Termination on which the event is detected." In the third-last paragraph, replace all three instances of "detected" with "recognized". Leave the word "detected" as is in the final paragraph.Taylor Standards Track [Page 4] RFC 2886 Megaco Errata August 2000 Issue: Case 1, step 2(a) is incorrectly formulated. Existing logic may result in an infinite loop. Also, the step excludes side effect actions such as signal termination. Resolution: Modify step 2(a) to read: "If the event in the queue is in the events listed in the new EventsDescriptor, the MG acts on the event and removes it from the EventBuffer. The time stamp of the Notify shall be the time the event was actually detected. The MG then waits for a new EventsDescriptor. While waiting for a new EventsDescriptor, any events detected which appear in the current EventsBufferDescriptor will be placed in the EventBuffer. When a new EventDescriptor is received, event processing repeats from step 1." Section: 7.1.11 "Signals Descriptor" ---------- Issue: There is a need for the MGC to be aware of signalling failures. It is not possible to use the signal completion event to monitor for signalling failures only, without also having to process successes. Proposed Resolution: In section 7.1.11, replace the current text on completion notification, beginning: "Finally, the optional parameter "notifyCompletion" ..." and continuing to the end of the paragraph with the following text: "Finally, the optional parameter "notifyCompletion" allows a MGC to indicate the circumstances under which it wishes to be notified when the signal finishes playout. The possible cases are that the signal timed out, that it was interrupted by an event, that it was halted when a Signals descriptor was replaced, or that it stopped or never started for other reasons. If "notifyCompletion" is absent, notification is generated in the "other reasons" case only. For reporting to occur the signal completion event (see section E.1.2) must be enabled in the currently active Events descriptor." In Annex A.2, make notifyCompletion a BIT STRING with the four cases. In B.2, make it a parameter consisting of a name and a list of values representing the possible completion methods. Section: 7.1.13 "ServiceChange Descriptor" ---------- Issue: Missing "extension" component in the API. Resolution: Add missing component.Taylor Standards Track [Page 5] RFC 2886 Megaco Errata August 2000 Section: 7.1.14 "DigitMap Descriptor" ---------- Editorial: add the following subsections. 7.1.14.1 DigitMap definition, creation, modification and termination (before first paragraph) 7.1.14.2 DigitMap Timers (after the first bullet list) 7.1.14.3 DigitMap syntax (before the long paragraph starting "The formal syntax of the digit map [...]") 7.1.14.4 DigitMap completion event (before the paragraph starting "A digit map is active while the events descriptor [...]") 7.1.14.5 DigitMap procedures (before the sentence "Pending completion, successive events shall be processed [...]", preceding the numbered list) 7.1.14.6 DigitMap activation (after the numbered list) 7.1.14.7 Interaction of DigitMap and event processing (before the next paragraph, starting "While the digit map is activated, [...]") 7.1.14.8 Wildcards (before the the next paragraph, starting "Note that if a package contains [...]") 7.1.14.9 Example (before the example) Issue: incorrect statements regarding the interaction of the dot symbol with default timing rules. Resolution: last sentence of the paragraph beginning "The letter "x" is used as a wildcard, ..." should be modified to read: "As a consequence of the third timing rule above, inter-event timing while matching a terminal dot symbol uses the short timer by default." In the next paragraph, the third sentence, which begins: "A timer specifier following a dot ...", should be deleted. Issue: Step 5 in second numbered list understates conditions for digit map completion when single candidate remains. Resolution: Add the words "and it has been fully matched" to the existing sentence. Also remove the parenthetical remark: "... (because the candidate set still contains more than one alternative event sequence)" from step 6.Taylor Standards Track [Page 6] RFC 2886 Megaco Errata August 2000 Issue: Not clear when unmatched events are recognized and trigger side effects (e.g. signal termination). Resolution: Modify the final sentence of the paragraph following procedural step 6 to read as follows: "Normal event behaviour (e.g. stopping of signals unless the digit completion event has the KeepActive flag enabled) continues to apply for each such event detected, except that . the events in the package containing the specified digit map completion event other than the completion event itself are not individually notified, and . an event which triggers a "partial match" completion is not recognized and therefore has no side effects until reprocessed following the recognition of the digit map completion event." Issue: the last paragraph before the example is misleading if the package containing the digit map completion event is different from the package containing the actual digits. Resolution: qualify the second sentence of the paragraph as follows: "Regardless of whether a digit map is activated, if the package also contains the digit events themselves, this form of event specification ...". Section: 7.1.18 "Topology Descriptor" ---------- Issue: Third bullet attached to third para: says loopback achieved by manipulating TerminationMode, which no longer has that name. Resolution: Delete the clause "; loopbacks are created by setting the TerminationMode" Section: 7.2 ---------- Issue: The order in which descriptors are processed within a command matters, but is not clear. Moreover, it is fixed in the ASN.1 but variable in the ABNF. Resolution: Add text stating that descriptors are processed in the order in which they are provided. Change ASN.1 in Annex A.2 to allow the MGC to specify ordering:Taylor Standards Track [Page 7]⌨️ 快捷键说明
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