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Internet Engineering Task Force                               Henry Houh
INTERNET DRAFT                                           NBX Corporation
                                                       February 25, 1999
                                                 Expires August 25, 1999


               DHCP Options for Call Control Servers
              <draft-ietf-dhc-callcontrolserv-00.txt>

Status of This Memo

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

   To learn the current status of any Internet-Draft, please check
   the ``1id-abstracts.txt'' listing contained in the Internet-Drafts
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   Europe), ftp.nis.garr.it (South Europe), munnari.oz.au (Pacific Rim),
   ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast).

   This document is a submission to the Dynamic Host Configuration
   Working Group of the Internet Engineering Task Force (IETF). Comments
   should be submitted to the dhcp-v4@bucknell.edu mailing list.

   Distribution of this memo is unlimited.

Abstract

   This document defines a new DHCP option for delivering configuration
   information to telephony enabled hosts in order to locate a call
   control/signalling server.  The option carries several operational
   parameters that allow multiple call control vendors to utilize this
   field.

1. Introduction

   Telephony is emerging as a network-based application.  The Call
   Control Server option allows telephony or gateway devices which
   cannot independently setup up and signal calls to automatically
   discover an address of a call control server.

   This specification describes a DHCP option [1] that can carry one or
   several Call Control Server sub-options.  Each sub-option is
   treated as a separate potential call control server by the hosts.




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   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. [2]

2. Call Control Server Option

   This option specifies one or more fields carrying Call Control
   Server information.  The fields that can be carried by this option
   are described in the sections that follow.

   The code for this option is TBD, and its maximum length is 255 octets.

      Code   Len        Sub-Option 1               Sub-Option 2
     +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+--
     | TBD |  n  |  a1 |  a2 |  a3 |  a4 |  a1 |  a2 |  a3 |  a4 |  ...
     +-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+--

   The 'Len' field specifies the number of octets containing sub-option
   information within the DHCP option.

   Each sub-option will contain a code followed by a length that
   specifies the number of octets containing configuration parameter
   information within the sub-option.

      Sub    Sub
      Code   Len        Configuration Parameter(s)
     +-----+-----+-----+-----+-----+-----+-----+-----+--
     |  x  |  n  |  a1 |  a2 |  a3 |  a4 |  a6 |  a7 |  ...
     +-----+-----+-----+-----+-----+-----+-----+-----+--

2.1. Call Control Servers

   This section describes the vendor-specific sub-options.

   Other types/vendors of call control servers can be added by using
   new sub-option fields.  See section 2.2 for the procedure for
   adding sub-option fields.

2.1.1 NBX Call Control Server Sub-option

   This sub-option specifies the network address of an NBX Call
   Control Server.

   The code for this sub-option is 1. The length specified in the 'Len'
   field of this sub-option MUST always be 4 octets.

      Code   Len    NBX Server Address
     +-----+-----+-----+-----+-----+-----+
     |  1  |  4  |  a1 |  a2 |  a3 |  a4 |
     +-----+-----+-----+-----+-----+-----+




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2.1.2 3Com Call Control Server

   This sub-option specifies the network address of a 3Com Call
   Control Server.

   The code for this sub-option is 2. The length specified in the 'Len'
   field of this sub-option MUST always be 4 octets.

      Code   Len    3Com Server Address
     +-----+-----+-----+-----+-----+-----+
     |  2  |  4  |  a1 |  a2 |  a3 |  a4 |
     +-----+-----+-----+-----+-----+-----+

2.1.3 MEGACO MGC

   This sub-option specifies the network address of a MEGACO Media
   Gateway Controller.

   The code for this sub-option is 3. The length specified in the 'Len'
   field of this sub-option MUST always be 4 octets.

      Code   Len     MEGACO MGC Address
     +-----+-----+-----+-----+-----+-----+
     |  3  |  4  |  a1 |  a2 |  a3 |  a4 |
     +-----+-----+-----+-----+-----+-----+

2.2 Procedure for adding call control server types

   A vendor may add a new sub-option field by issuing an internet
   draft that contains the new sub-option.  The new sub-option field
   code MUST be labeled "TBD."  This draft will then be submitted to
   the DHC working group, and, if accepted for inclusion in the DHCP
   specification, a sub-option field code is assigned and the
   sub-option specification is published as an RFC which updates this
   RFC.

3. Using Multiple Sub-options

   More than one sub-option field MAY be returned to the host.
   In addition, more than one of any sub-option type MAY be present.
   This allows the host to select the call control server appropriate
   to own its signaling protocol, allowing a single DHCP server to
   support multiple homogeneous call control servers as well as
   heterogeneous telephony and gateway devices.

4. References

   [1] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
       Extensions", RFC-2132, March 1997.

   [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
       Levels", RFC-2119, March 1997.


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   [3] Droms, R., "Dynamic Host Configuration Protocol", RFC-2131,
       March 1997.

5. Security Considerations

   DHCP currently provides no authentication or security mechanisms.
   Potential exposures to attack are discussed in section 7 of the DHCP
   protocol specification [3]. In particular, these DHCP options allow
   an unauthorized DHCP server to misdirect a telephone or gateway
   host to an unauthorized call control server.

6. Author's Address

   Henry Houh
   NBX Corporation
   100 Brickstone Square
   Andover, MA  01810

   Phone: +1 978 740 0000 x257

   EMail: hhouh@nbxcorp.com

































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