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Versions: 00 01 02 03 RFC 2886

Media Gateway Control                                       P.T. Taylor
Internet Draft                                          Nortel Networks
Document: draft-ietf-megaco-errata-03.txt                      May 2000
Category: Standards Track


                             Megaco Errata


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [1].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as Internet-
   Drafts. Internet-Drafts are draft documents valid for a maximum of
   six months and may be updated, replaced, or obsoleted by other
   documents at any time. It is inappropriate to use Internet- Drafts
   as reference material or to cite them other than as "work in
   progress."
   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt
   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.


1. Abstract

   This document records the errors found in the draft Megaco/H.248
   protocol document [2], along with the changes proposed in the text
   of that document to resolve them. After joint IETF/ITU-T Study Group
   16 approval of these corrections, they will be incorporated into the
   final decided version of H.248 and the corresponding Megaco protocol
   RFC.  The current status of approval is as follows:
   . IETF process is complete, and the IESG has granted its approval;
   . ITU-T process is complete except that the Members' comment period
     does not expire until June 8, 2000 and the final act of Decision
     is scheduled for June 15, 2000.

   This draft has been modified from the previous issue by
   strengthening the sentence in section D.1.3 which requires
   exponential backoff in the face of congestion.  The detailed list of
   changes from draft-ietf-megaco-errata-01.txt has been left intact
   for the user's convenience.


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].

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3. Errata

   All section numbers are those of the relevant text of [2].

3.1 Changes From draft-ietf-megaco-errata-01.txt

   Section 7.1: proposed change in the comment preceding production
   auditReturnItem in Annex B.2 (ABNF) has been deleted, because a
   later section actually proposes deletion of the comment.

   Section 7.2.5: issue has been expanded to note that the text of
   section 7.2.5 anticipates the possibility of return of multiple
   instances of the same descriptor.  Proposed remedy is to delete the
   restrictive comment in front of production auditReturnItem in Annex
   B.2 (ABNF), rather than just modify it to add exceptions.

   Section 7.2.5: to get the current dial string of an active digit
   map, the ObservedEvents descriptor must be audited rather than the
   Events descriptor.

   Section A.2: along with the addition of the protocol identifier
   field in the message header, the now-redundant version field is
   removed.  The need to add extensibility to more productions through
   use of ellipses is noted.

   Section A.2, B.2: the ASN.1 uses three values from contextId
   numbering space to denote NULL, CHOOSE, and ALL.  A comment is added
   to the ABNF to reserve the values concerned.

   Section A.2: format of H221NonStandard field does not properly
   reflect structure of T.35 country code.

   Annex C: changes to ATM-related sections are noted.  Alignment of
   sub-octet fields is stated to be at the low-order end of the octet.

   Section D.1.3: exponential backoff in the face of congestion made
   mandatory by replacing SHOULD with SHALL.

   Annex E: package serial numbers are revised to make them
   consecutive.

   Appendix A step 3: revised to use echo control as defined in the TDM
   package.


3.2 Complete List Of Corrections





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   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.


   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.

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   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.

   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"


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   Resolution: Add comment in B.2 that "true" in text corresponds to
   "on" in ABNF, and "false" corresponds to "off".

   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.


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   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.

   Section: 7.1.14 "DigitMap Descriptor"
   ----------

   Editorial: add the following subsections.

   7.1.14.1 DigitMap definition, creation, modification and termination

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   (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.

   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



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   . 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:

   AmmRequest ::= SEQUENCE
   {
           terminationID           TerminationIDList,
           descriptors             SEQUENCE OF AmmDescriptor,
           -- At most one descriptor of each type (see AmmDescriptor)
           -- allowed in the sequence
           ...
   }

   AmmDescriptor ::= CHOICE
   {
           mediaDescriptor         MediaDescriptor,
           modemDescriptor         ModemDescriptor,
           muxDescriptor           MuxDescriptor,
           eventsDescriptor        EventsDescriptor,
           eventBufferDescriptor   EventBufferDescriptor,
           signalsDescriptor       SignalsDescriptor,
           digitMapDescriptor      DigitMapDescriptor,

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           auditDescriptor         AuditDescriptor,
           ...
   }

   Section: 7.2.3 "Subtract"
   ----------
   Issue: cannot use the CHOOSE wildcard for terminationId of a
   Subtract command.

   Resolution: add this qualification to the second sentence, which
   indicates that terminationId may be wildcarded.

   Section: 7.2.4 "Move"
   ----------
   Issue: cannot use the CHOOSE wildcard for terminationId of a Move
   command.

   Resolution: add this qualification to the second sentence, which
   indicates that terminationId may be wildcarded.

   Section: 7.2.5 "AuditValue"
   ----------
   Issue: Not clear whether AuditValue of ObservedEventsDescriptor
   reports events captured in current dial string of active digit map.

   Resolution: Add text to indicate that if a digit map is active and
   ObservedEventsDescriptor is specified the response to an AuditValue
   includes a digit map completion event which shows the current dial
   string but does not show a termination method.

   Issue: Fails to indicate what AuditValue for EventBufferDescriptor
   returns

   Resolution: Add the following text: "EventBuffer returns the set of
   events and associated parameter values currently enabled in the
   EventBufferDescriptor."

   Issue: not clear whether wildcarded context includes the null
   context.

   Resolution: add statement that ALL as a contextID does not include
   the null context.

   Issue: the text of 7.2.5 allows retrieval of multiple digit maps
   with one AuditValue command if the terminationId is ALL.  Moreover,
   earlier text in the Annex anticipates that multiple instances of a
   descriptor may be returned.  The comment in front of production
   auditReturnParameter in Annex B.2 contradicts this text.  Note that
   Annex A has no restriction on the number of instances of any
   descriptor in either a command or a response.



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   Proposed Resolution: delete the"at-most-once" comment preceding ABNF
   production auditReturnParameter.

   Issue: Does not indicate how an audit of digit maps returns unnamed
   digit maps.

   Resolution: Change syntax of DigitMapDescriptor to allow return of
   unnamed digit maps as follows:

   digitMapDescriptor = DigitMapToken EQUAL
                        ( (LBRKT digitMapValue RBRKT)
                        / (digitMapname [ LBRKT digitMapValue RBRKT ])
                        )
   and

   DigitMapDescriptor ::= SEQUENCE
   {
           digitMapName    DigitMapName OPTIONAL,
           digitMapValue   DigitMapValue OPTIONAL
   }

   Issue: the text in section 7.2.5 mentions that using an empty Audit
   descriptor with a wildcarded terminationId is a way to get a list of
   the terminations in the context.  Annex A provides the possibility
   that the auditReply may be a contextAuditResult of type
   terminationIdList, and Annex B allows for an auditReply containing a
   contextTerminationAudit which in turn presents a terminationIdList.
   The connection between the text in 7.2.5 and these special forms of
   audit result is not clear.  Moreover, a note at the beginning of
   Annex A section A.2 limits terminationIdList to one terminationId.

   Proposed Resolution: add the following text in section 7.2.5 after
   the sentence "This may be useful to get a list of TerminationIDs
   when used with wildcard.":
   "Annexes A and B provide a special syntax for presenting such a list
   in condensed form, such that the AuditValue command tag does not
   have to be repeated for each terminationId."
   Also, in the Note at the beginning of section A.2 of Annex A,
   provide an exception on the length of type TerminationIdList when
   used in contextAuditResult.

   Section: 7.2.6 "AuditCapabilities"
   ----------
   Issue: Fails to indicate what AuditCapabilities for
   EventBufferDescriptor returns

   Resolution: Add the following text: "EventBuffer returns the same
   information as Events."

   Issue: Inconsistency regarding permissibility of DigitMap or
   Packages as capability audit items.


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   Resolution: Add comment to B.2 "auditItem" production indicating
   that DigitMap and Packages are not allowed in the AuditCapabilities
   command.

   Section: 7.2.8 "ServiceChange"
   ----------
   Issue: In point 1) describing the Graceful ServiceChange method, the
   scope of the recommendation against new connections is unclear.

   Resolution: at the end of the first sentence, add the phrase "on the
   termination(s) affected by the ServiceChange command".

   Issue: the explanatory string associated with ServiceChangeReason is
   optional in the syntax, but not in the text.

   Resolution: add "optional" before "explanatory string" in the
   explanation of the ServiceChangeReason" parameter.

   Issue: Paragraph beginning "A ServiceChange Command specifying the
   Root..." immediately following the description of ServiceChange
   Descriptor parameters erroneously states that the response to the
   ServiceChange command terminates the registration process.  This is
   so only if the response does not specify an alternate MGC.

   Resolution: Add text to the offending sentence, so that it reads:
   "Acknowledgement of the ServiceChange Command completes the
   registration process, except when the MGC has returned an
   alternative ServiceChangeMgcId as described in the next paragraph."

   Section: 7.3 "Command Error Codes"
   ----------
   Issue: Text for error code 403 should be consistent with that for
   404 and 405.

   Resolution: Change text to "Syntax error in TransactionRequest"

   Issue: There should be no error responses to TransactionReply or
   TransactionPending, lest they create response loops.

   Resolution: Delete codes 404, 405, 461-467

   Section: 8 "Transactions", A.2
   ----------
   Issue: state is unclear if a command fails.

   Resolution: add the following text:
   "If a command fails, the MG shall as far as possible restore the
   state which prevailed prior to the attempted execution of the
   command before continuing with transaction processing."

   Section: 8.1.1 "Transaction Identifiers"

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   ----------
   Issue: need a transaction identifier to use when reporting a syntax
   error such that the identifier is unavailable.

   Resolution: add text reserving transionId = 0 for this purpose.

   Section: 8.1.2 "Context Identifiers"
   ----------
   Issue: ALL as a context identifier does not include the null
   context.

   Resolution: add text to indicate that exclusion in the final
   sentence of the section.

   Section: 8.2.2 "TransactionReply"
   ----------
   Issue: Final para has wrong text for error code 442.

   Resolution: Change to "Syntax Error in Command"

   Section: 10.2 "Interim AH Scheme", B.2
   ----------
   Issue: The interim AH header can actually be as short as 24 hex
   digits (per RFCs 2403, 2404 which are indirectly referenced).  It is
   also unclear whether it is the source or destination UDP port which
   is prepended in the calculation.

   Resolution: Change 10.2 second para, second-last sentence to specify
   the destination port, in consistency with IPSEC.  In Annex B.2,
   change lower count for production AuthData to 24 from 32.

   Section: 11.2 "Cold Start"
   ----------
   Issue: First paragraph last sentence inadvertently modified --
   duplicates material in 11.3.

   Resolution: Restore original sentence: "If the MG is unable to
   establish a control relationship with any MGC, it shall wait a
   random amount of time as described in Section 9.2 and then start
   contacting its primary, and if necessary, its secondary MGCs again."

   Section: 11.4 "Failure Of an MG"
   ----------
   Issue: Second para: wrong MG is specified as the one to be used
   after failover.

   Resolution: Change fourth sentence to refer to "secondary MG" rather
   than "primary MG".

   Section: 12.1.2 "Properties"



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   ----------
   Issue: As indicated in 6.2.4, Properties occur in other descriptors
   besides LocalControl and TerminationState.

   Resolution: after the sentence mentioning TerminationState, add
   another sentence:
   "Although these are the most common cases, it is also possible for a
   property to be defined for other descriptors."

   Section: 12.1.4 "Signals"
   ----------
   Issue: Note says that default duration should be specified for BR
   signals.  This also applies to TO signals.

   Resolution: Add TO signals to note.

   Section: 12.2 "Guidelines to defining  Properties, Statistics and
   Parameters to Events and Signals", B.2
   ----------
   Issue: Text indicates that statistics can have the sub-list data
   type, but ABNF does not support that.

   Resolution: qualify the sublist type by adding the note:
   "(not supported for statistics)".

   Section: Annex A.1, ASN.1 Syntax
   ----------
   Issue: the ASN.1 uses the values 0x0, 0xFFFFFFFE, and 0xFFFFFFFF for
   the NULL context, a wildcard CHOOSE of context, and a wildcard ALL
   of context respectively.  Because of the possibility of a switch
   between binary and text encoding for messages relating to the same
   context, these values should be reserved in the text encoded syntax.

   Resolution: Add a comment preceding the ContextID production in
   Annex B.2 indicating that these values are reserved.

   Section: Annex A.2, ASN.1 Syntax
   ----------
   Issue: sloppy ASN.1 -- in production EventBufferControl the values
   "off" and "lockstep" should not be capitalized, and IA5STRING in
   production NonStandardIdentifier should be IA5String.  Both
   TransactionID and TransactionId are used.  A number of productions
   need ellipses to express extensibility.

   Resolution: fix them.








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   Issue: syntax for PropertyParm does not support sub-lists (i.e.
   parameters supporting multiple values simultaneously)

   Resolution: add a third choice to extrainfo in PropertyParm as
   follows:
            extraInfo   CHOICE
        {
                relation        Relation,
                range           BOOLEAN,
                sublist         BOOLEAN
        } OPTIONAL
   and add an appropriate note to the preceding comments.

   Issue: LocalControlDescriptor still contains reserve rather than
   reserveValue and reserveGroup.

   Resolution: Replace reserve with separate reserveValue and
   reserveGroup Booleans.

   Issue: EventBufferDescriptor is incorrectly portrayed as a SEQUENCE
   OF ObservedEvent.

   Resolution: replace with the following productions:

   EventBufferDescriptor ::= SEQUENCE OF EventSpec

   EventSpec ::= SEQUENCE
   {
        pkgdName                PkgdName,
        streamID                StreamID OPTIONAL,
        evParList               SEQUENCE OF EventParameter
   }

   Issue: Assigned object identifier missing.  It is usually present as
   a matter of convention.

   Resolution: Add object identifier line in the message header with
   content:
       "itu-t recommendation h 248 media-gateway-control(0)"
   Delete the version field, which this makes redundant.

   Issue: the T.35 country code in the H221NonStandard production does
   not have the right structure.

   Resolution: fix it.








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   Section: Annex B.2, ABNF Syntax
   ----------
   Issue: Syntax for parmValue and VALUE together make parsing of range
   ambiguous.  Furthermore, sub-lists and sets of alternative values
   have the same syntax, introducing possible ambiguity

   Resolution: Replace production alternativeValue by the following:
     "alternativeValue = ( VALUE
          / LSBRKT VALUE *(COMMA VALUE) RSBRKT     ; sub-list
          / LBRKT VALUE *(COMMA VALUE) RBRKT       ; alternatives
          / LSBRKT VALUE COLON VALUE RSBRKT )      ; range"

   Issue: EventBufferDescriptor content mistakenly shown as a sequence
   of observedEvent.

   Resolution: replace the production for eventBufferDescriptor with
   the following productions:

   eventBufferDescriptor = EventBufferToken LBRKT [ eventSpec
      *( COMMA eventSpec ) ] RBRKT

   eventSpec = pkgdName [ LBRKT  eventSpecParameter
                          *( COMMA eventSpecParameter ) RBRKT ]

   eventSpecParameter = ( eventStream / eventOther )

   Issue: Error in syntax for  digitMapDescriptor: value meant to be
   optional.

   Resolution: Change production:
   digitMapDescriptor = DigitMapToken EQUAL digitMapName
                [ LBRKT digitMapValue RBRKT ]

   Issue: VersionToken not defined.

   Resolution: Add ABNF:       VersionToken =  ("Version" / "V")

   Issue: DiscardToken not used.

   Resolution: Delete production.

   Section: Annex C
   ----------
   Issue: alignment of sub-octet fields within the octet is not
   indicated.

   Resolution: add note that fields of sub-octet length are placed in
   the low-order bits of the octet.





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   Section: Annex C, ATM-related sections C.4, C.7, C.8, C.10
   ----------
   Issue: direction of flow is segregated by outgoing (Remote
   descriptor) and incoming (Local descriptor).  Since forward and
   backward properties will not both reside in the same descriptor,
   need only the one set of prperties applicable to both directions.

   Resolution: replace with a single set of properties.

   Issue: miscellaneous problems of parameter specifications
   inconsistent with the relevant standards, unused parameters,
   distinction between ATM Forum and ITU-T usages, missing references.

   Resolution: fix them.

   Section: Annex C.8 "ATM AAL1"
   ----------
   Issue: Length of GIT is wrong.

   Resolution: ITU-T procedural problem, to be resolved by SG 16.
   Probable solution is to allow 29 octets, event though the relevant
   form requires only four octets.

   Section: Annex C.9 "Bearer Capabilities"
   ----------
   Issue: ITC has reference to missing note 2

   Resolution: Delete reference.

   Issue: Not clear that Q.931 Bearer Capability IE rather than Low
   Layer Compatibility IE is being used.

   Resolution: Specify that values are those valid for Bearer
   Capability IE

   Section: Annex D.1 "Transport over IP/UDP using Application Level
   Framing"
   ----------
   Issue: Even in the case of handoff or failover, the originating MGC
   needs confirmation that its command was received.

   Resolution: In the last sentence of the first paragraph, delete the
   excepting clause, so that the sentence reads: "Responses must be
   sent to the address and port from which the corresponding commands
   were sent."

   Section: Annex D.1.1 "Providing At-Most-Once Functionality"
   ----------
   Issue: Second para last sentence provides a procedural reference to
   8.2.3.  Should refer to UDP-specific procedures.

   Resolution: Add reference to D.1.4.

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   Section: Annex D.1.3 "Repeating Requests, Responses and
   Acknowledgements"
   ----------
   Issue: Make exponential backoff in the face of congestion mandatory.

   Resolution: To the paragraph just before the note, which begins "The
   specification purposely avoids specifying any value for the
   retransmission timers...", add the following sentence:

   "Implementations SHALL ensure that the algorithm used to calculate
   retransmission timing performs an exponentially increasing backoff
   of the retransmission timeout for each retransmission or repetition
   after the first one."

   In the paragraph in the middle of the note beginning "After any
   retransmission ...", capitalize the word SHOULD to emphasize the
   importance of the steps which follow.

   Issue: Last paragraph is equivocal about what ServiceChangeReason to
   use when recovering from loss of contact; it must always be
   "Disconnected".

   Resolution: Change the two sentences following the phrase "_ and it
   begins its recovery process" to read as follows: "The MG shall use a
   ServiceChange with ServiceChangeMethod set to disconnected so that
   the new MGC will be aware that the MG lost one or more
   transactions."

   Section: Annex D.1.4 "Provisional responses"
   ----------
   Issue: First paragraph, last sentence talks about when to send the
   Transaction Pending response.  When UDP/ALF is in use, the
   originator of a transaction may repeat it because it has not
   received an acknowledgement that the transaction was received.  An
   appropriate response to a duplicate transaction which is still being
   processed is to return Transaction Pending.

   Resolution: Add the sentence: "They SHOULD send this response if
   they receive a repetition of a transaction that is still being
   executed."

   Issue: Second para: transaction originator may not have received
   TransactionPending response(s) because they were lost, and may
   therefore not know that responder is expecting immediate
   acknowledgement of the TransactionReply.

   Resolution: add an optional field to TransactionReply allowing the
   responder to indicate if an immediate ACK is required.  Add text in
   the section indicating that when the responder has sent a
   provisional response, it shall also set the indicator in the final


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   transaction reply to indicate that an immediate acknowledgement is
   required.

   Section: Annex E "Basic Packages"
   ----------
   Issue: package numbering does not follow order of presentation.

   Resolution: renumber packages to follow order of numbering.

   Section: Annex E.2.1 "Base Root Package -- Properties"
   ----------
   Issue: the descriptor in which these properties occur is not
   specified.

   Resolution: in each case, indicate that the property is defined in
   the TerminationState descriptor.

   Section: Annex E.6.2 "DTMF detection Package -- Events"
   ----------
   Issue: "Long duration event modifier" is shown as "L" in parameter
   DigitString -- should be "Z".

   Resolution: Replace with "Z".

   Section: Annex E.9.2 "Analog Line Supervision Package -- Events"
   ----------
   Issue: Stated hook state reporting behaviour has race condition
   where same transition could be reported twice.

   Resolution: add an optional EventsDescriptor parameter and an
   optional ObservedEvents parameter to each of the on-hook and off-
   hook events.  Delete the second sentence of the existing event
   description (which indicates that the event is always reported if
   the hook state has already been achieved).

   The EventsDescriptor parameter is described as follows:

   Strict Transition
         ParameterID: strict (0x0001)
         Type: enumeration
         Possible values:
             "exact" means that only an actual hook state transition
             to on-hook (off-hook) is to be recognized

             "state" means that the event is to be recognized
             either if the hook state transition is detected or if the
             hook state is already on-hook (off-hook).  This is the
             default value if "strict" is unspecified.

             "failWrong" means that if the hook state is already what
             the transition would imply, the command fails and an error
             is reported [error code to be defined in the package].

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   The ObservedEvents parameter is described as follows:

   Initial State
         ParameterID: init (0x0002)
         Type: Boolean
         Possible values:
             true/"ON" means that the event was reported because the
             line was already on-hook (off-hook) when the events
             descriptor containing this event was activated

             false/"OFF" means that the event represents an actual
             state transition to on-hook (off-hook)


   Section: Annex E.10.3 "Basic Continuity Package -- Signals"
   ----------
   Issue: The rsp signal should continue until the MGC tells the MG to
   stop applying it.

   Resolution: change the type of signal from Timeout to ON/OFF.


   Section: Annex E.10.5 "Basic Continuity Package -- Procedures"
   ----------
   Issue: Wording of condition for generating cmp event with "success"
   does not cover case where test also requires successful removal of
   tone.

   Resolution: In the second paragraph of E.10.5 (dealing with test
   initiation), add the words "and any other required conditions are
   satisfied" in the second sentence, as part of the condition upon
   which success is reported.  Replace the third paragraph (dealing
   with test response) with the following text:

   "When a MGC wants the MG to respond to a continuity test, it sends a
   command to the MG containing a signals descriptor with the rsp
   signal. Upon reception of a command with the rsp signal, the MG
   either applies a loop-back or (for 2-wire circuits) awaits reception
   of a continuity test tone.  In the loop-back case, any incoming
   information shall be reflected back as outgoing information.  In the
   2-wire case, any time the appropriate test tone is received, the
   appropriate response tone should be sent.  The MGC will determine
   when to remove the rsp signal."









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                            Megaco Errata                     May 2000


   Section: Appendix A.1.2 "Example -- Collecting Originator Digits and
   Initiating Termination"
   ----------
   Issue: Step 3 uses a now-obsolete package DS0 for echo cancellation.

   Resolution: replace with echo cancellation via package TDM.

   Issue: Step 20 fails to show a returned TerminationStateDescriptor.
   It also contains the erroneous statement that an RTP termination
   does not support events and signals and fails to show a number of
   other descriptors.

   Resolution:
   Delete the sentence containing the erroneous statement.
   Add the following to the Media Descriptor preceding the line "Stream
   = 1_":
   "TerminationState { ServiceStates = InService, EventBufferControl =
   OFF },"

   Add lines showing Events, Signals, and DigitMap descriptors
   following the Media descriptor.

   "Events, Signals, DigitMap,"


6. Security Considerations

   This draft is a supplement to [2], which contains the required
   security section.


7. References

   [1] Scott Bradner, The Internet Standards Process -- Revision 3,
   IETF RFC 2026, October 1996.
   [2] Rosen et al, draft-ietf-megaco-protocol-08.txt, Megaco Protocol,
   work in progress, May 2000.
   [3] Scott Bradner, Key Words For Use In RFCs To Indicate Requirement
   Levels, IETF RFC 2119, March, 1997.

8. Acknowledgments

   This draft records the contributions of a number of people on the
   Megaco list and the H.248 faithful in ITU-T Study Group 16 who took
   the time to read the Megaco/H.248 draft with care and attention.
   Thanks to all of them.







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                            Megaco Errata                     May 2000


9. Author's Addresses

   Tom Taylor
   Nortel Networks
   P.O. Box 3511, Station C
   Ottawa, Ontario, Canada K1Y 4P7
   Phone: +1 613 736 0961
   Email: taylor@nortelnetworks.com





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   or assist in its implmentation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
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   followed, or as required to translate it into other languages.

   1  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997






















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