Internet DRAFT - draft-cutler-megaco-mgc-cookie
draft-cutler-megaco-mgc-cookie
MEGACO Wayne Cutler
Internet Draft Marconi
Communications
Document: <draft-cutler-megaco-mgc-cookie-02.txt> July 2001
Category: Informational
MGC Cookie Package for Megaco/H248
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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1. Abstract
This documents provides a proposed definition for a supplemental
package to Megaco/H.248. The proposed package addresses support of
functionality to enable a MGC to store information on a MG which can
subsequently be retrieved via audit. The specific purpose for
storing / retrieving data in this way is regarded as being solely
the concern of the MGC. This draft merely proposes the means for
supporting such capability.
It is worth noting that one such use of this capability would be to
facilitate MGC recovery action in the event of an MGC restart. This
specific capability was described in a previous draft (draft-cutler-
megaco-recvpkg-01.txt) which was presented at IETF49 in San Diego.
This draft supercedes the previous one.
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. MGC Cookie Package
Package ID: mgcckie (0x????)
Version : 1
Extends: None
This package defines a property to enable the MGC to store a cookie
on a MG. The cookie may be stored against any MG termination (i.e.
both real and ephemeral). The cookie may be retrieved via the audit
mechanism. The cookie is treated by the MG as an opaque string.
3.1 Properties
MGC Cookie
Property ID : cookie (0x0001)
Type : STRING 1..64 Bytes
Possible Values : Any, as defined by the MGC
Defined in : Local Control Descriptor
Characteristics : Read/Write
3.2 Events
None.
3.3 Signals
None.
3.4 Statistics
None.
3.5 Procedures
The MGC may store a cookie against any MG termination. The cookie
may be subsequently updated at will by the MGC. In general, a cookie
may be stored against any existing termination irrespective of
whether that termination is in a (non-null) context or not. However,
since ephemeral terminations do not exist outside of a context, it
follows an ephemeral termination must be related to a context in
order for a cookie to be able to be stored against it.
As mentioned previously, a specific use of this capability would be
to facilitate MGC recovery action in the event of an MGC restart. As
an illustration of this usage, consider the following scenario :-
1) A MGC sets up a call between 2 ISUP trunk GWs.
2) The orig. MG (MG1) has a circuit termination(C1) and an ephemeral
termination (E1) in context CX1.
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3) The term. MG (MG2) has a circuit termination(C2) and an ephemeral
termination (E2) in context CX2.
4) At MG1, cookies are stored against C1 and E1 to identify the
billing reference and far end GW connection respectively. Similar
cookies are stored at MG2 against its terminations.
5) During the speech phase, the MGC is restarted and loses knowledge
of the active call. However, the RTP stream is unaffected and
continues between the 2 MGs.
6) Eventually the call releases and an ISUP-REL message is received
by the MGC. The CIC in the message identifies termination C1 on
MG1.
7) Via audit of MG1, the MGC discovers CX1 and E1, plus associated
cookies. This enables the billing reference to be re-learnt as
well as identifying the far end (MG2) connection.
8) Audit can be performed at MG2 to discover all related connection
information (CX2, C2 and E2),
9) MG2 can now be cleaned up and ISUP-REL message sent against the
CIC corresponding to termination C2.
10) Both MGs disconnected, both trunks released normally and billing
terminated correctly. End users oblivious to the fact that the
MGC restarted in mid call.
4. Formal Syntax
As in [4], the package described in this draft may be encoded as
ASN.1 or augmented Backus-Naur Form (BNF) [2].
5. Security Considerations
MGs may be untrusted and therefore the MGC MAY choose to encrypt the
stored cookie. For other security considerations, refer to [3].
9. References
1 Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
2 Crocker.D & Overell.P (editors), "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
3 Cuervo et al, "Megaco Protocol", RFC 3015, November 2000.
10. Acknowledgments
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11. Author's Addresses
Wayne Cutler
Marconi Communications
New Century Park
Coventry CV3 1HJ
England
Phone: +44 24 76562417
Email: wayne.cutler@marconi.com
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