Network Working Group                                          T. Taylor
Request for Comments: 2886                               Nortel Networks
Category: Standards Track                                    August 2000

                             Megaco Errata

Status 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",
   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

   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

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

   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

     "emptyDescriptors               AuditDescriptor,"

   In the ABNF, add the choice auditItem to the production

   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

   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

   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. DigitMap definition, creation, modification and termination
   (before first paragraph) DigitMap Timers (after the first bullet list) DigitMap syntax (before the long paragraph starting "The
   formal syntax of the digit map [...]") DigitMap completion event (before the paragraph starting "A
   digit map is active while the events descriptor [...]") DigitMap procedures (before the sentence "Pending
   completion, successive events shall be processed [...]", preceding
   the numbered list) DigitMap activation (after the numbered list) Interaction of DigitMap and event processing (before the
   next paragraph, starting "While the digit map is activated, [...]") Wildcards (before the the next paragraph, starting "Note
   that if a package contains [...]") 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

   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]

RFC 2886                     Megaco Errata                   August 2000

   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,
           auditDescriptor         AuditDescriptor,

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

   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

   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.

Taylor                      Standards Track                     [Page 8]

RFC 2886                     Megaco Errata                   August 2000

   Issue: Fails to indicate what AuditValue for EventBufferDescriptor

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

   Issue: not clear whether wildcarded context includes the null

   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.

   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.

Taylor                      Standards Track                     [Page 9]

RFC 2886                     Megaco Errata                   August 2000

   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

   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.

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

   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."

Taylor                      Standards Track                    [Page 10]

RFC 2886                     Megaco Errata                   August 2000

   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"
   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.

Taylor                      Standards Track                    [Page 11]

RFC 2886                     Megaco Errata                   August 2000

   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

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

   Section: 12.1.2 "Properties"
   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)".

Taylor                      Standards Track                    [Page 12]

RFC 2886                     Megaco Errata                   August 2000

   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.

   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

            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:

Taylor                      Standards Track                    [Page 13]

RFC 2886                     Megaco Errata                   August 2000

   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
       "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.

   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

Taylor                      Standards Track                    [Page 14]

RFC 2886                     Megaco Errata                   August 2000

   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

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

   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 properties 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.

Taylor                      Standards Track                    [Page 15]

RFC 2886                     Megaco Errata                   August 2000

   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

   Section: Annex D.1 "Transport over IP/UDP using Application Level
   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

   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.

   Section: Annex D.1.3 "Repeating Requests, Responses and
   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

Taylor                      Standards Track                    [Page 16]

RFC 2886                     Megaco Errata                   August 2000

   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 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

   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".

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RFC 2886                     Megaco Errata                   August 2000

   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].

   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.

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RFC 2886                     Megaco Errata                   August 2000

   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

   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."

   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

   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,"

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RFC 2886                     Megaco Errata                   August 2000

4. Security Considerations

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

5. References

   [1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
       9, RFC 2026, October 1996.

   [2] Cuervo, F., Greene, N., Huitema, C., Rayhan, A., Rosen, B. and J.
       Segeret, "Megaco Protocol", RFC 2885, August 2000.

   [3] Bradner, S., "Key Words For Use In RFCs To Indicate Requirement
       Levels", BCP 14, RFC 2119, March 1997.

6. Acknowledgments

   This memo 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 document with care and attention.
   Thanks to all of them.

7. Author's Address

   Tom Taylor
   Nortel Networks
   P.O. Box 3511, Station C
   Ottawa, Ontario, Canada K1Y 4P7

   Phone: +1 613 736 0961

Taylor                      Standards Track                    [Page 20]

RFC 2886                     Megaco Errata                   August 2000

8.  Full Copyright Statement

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation 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 are
   included on all such copies and derivative works.  However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an


   Funding for the RFC Editor function is currently provided by the
   Internet Society.

Taylor                      Standards Track                    [Page 21]