Network Working Group                                       K. Chowdhury
Internet-Draft                                          Starent Networks
Expires: June 27, 2005                                         P. Yegani
                                                           Cisco Systems
                                                               L. Madour
                                                       December 27, 2004

       DHCPv4 Options for Broadcast and Multicast Control Servers

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
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   RFC 3668.

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Copyright Notice

   Copyright (C) The Internet Society (2004).


   This document defines new options for Broadcast and Multicast Service
   controller discovery in an IP network.  Broadcast service is being
   developed for 3G wireless networks.  Users of the service interact
   with a controller in the network to derive informations that are

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   required to receive broadcast service.  Dynamic Host Configuration
   Protocol can be used to configure the controller IPv4 addresses or
   fully qualified domain names in the user's devices.  This document
   defines the related options and option codes.

Table of Contents

   1.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Overview of the 3GPP2 BCMCS Network  . . . . . . . . . . . . .  4
   3.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Broadcast Service Controller Options . . . . . . . . . . . . .  6
     4.1   Broadcast Service Controller Domain Name list  . . . . . .  6
     4.2   Broadcast Service Controller IPv4 address option . . . . .  7
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   8.  Normative References . . . . . . . . . . . . . . . . . . . . . 10
       Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 10
       Intellectual Property and Copyright Statements . . . . . . . . 12

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1.  Motivation

   Dynamic Host Configuration Protocol [RFC2131] can be used to
   configure various non-IP address type of parameters.  These
   parameters are required for normal operation of various services that
   are offered over an IP network.

   Broadcast and multicast service (BCMCS) is one such service that is
   currently being standardized in various mobile wireless standard
   bodies such as 3GPP, 3GPP2 and OMA.  A description of the BCMCS, for
   example, in 3GPP2 can be found in [BCMCS].

   While DHCP offers necessary mechanisms for device configuration, it
   lacks the information elements required to configure a mobile device
   to support BCMCS.  This memo is an effort to define the extensions
   needed for DHCP to provide necessary configuration information to a
   mobile device in a BCMCS network.

   DHCP is being used in 3GPP2, for example, to assist with the
   discovery of the BCMCS Controller in a mobile operators IP network.
   The BCMCS includes a controller component that is responsible for
   managing the service via interaction with the users and other network

   An overview of the 3GPP2 BCMCS architecture is given in the next
   section.  It provides enough information to understand the basics of
   the 3GPP2 BCMCS operation.  Readers are encouraged to find a more
   detailed description in [BCMCS].

   As described in [BCMCS], the users of the service are required to
   know the IPv4 address of the controller entity so that they can
   download all the necessary information about a desired broadcast
   program.  In a roaming environment static configuration of the
   controller IPv4 address becomes unrealistic.  Therefore, DHCP is
   considered to be a method to dynamically configure the controller
   IPv4 address or the fully qualified domain name of the controller in
   the 3G wireless networks.

   In order to allow the users to discover the broadcast controllers,
   the clients request for appropriate option codes from the DHCP
   servers using Parameter Request List option.  The DHCP servers need
   to return the corresponding configuration options that carry either
   broadcast and multicast service controller IPv4 address or fully
   qualified domain name based on configuration.  The motivation for
   this document is to define the necessary option and option code.

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2.  Overview of the 3GPP2 BCMCS Network

   The Broadcast and Multicast Service architecture in a 3G wireless
   network such as 3GPP2 has the following model:

                              +------------+   +--------+
                              |            |   |        |
                              | Controller |   |  DHCP  |
                              |            |   | Server |
                              +------------+   +--------+
   +----+        +------------+    +------------+
   |    |        |            |    |            |
   | MN/| bearer |   Radio    |    | Broadcast  |
   |User|<-------|   Access   |<---| Content    |
   |    |        |   Network  |    | Server     |
   +----+        +------------+    +------------+

   Note that this figure is shown here for broad understanding of how
   Broadcast and Multicast service works in a 3G mobile wireless IP
   network.  The network elements except MN/user and the DHCP server are
   not relevant to the text in this document.

   The user interacts with the Controller to request for
   broadcast/multicast program information from the network (e.g.,
   scheduled time, multicast IP address, port numbers).  The User may
   also be authenticated by the Controller while downloading the
   relevant program security related information (such as encryption
   key).  These interactions happen via HTTP and XML.  There may be more
   than one controller in the network.  The user should discover the
   appropriate controller to request the relevant program information.
   For details of Broadcast and Multicast Service operation in 3GPP2,
   see [BCMCS]

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3.  Terminology

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   this document are to be interpreted as described in RFC 2119.

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4.  Broadcast Service Controller Options

   This section defines the configuration option for the controller of
   Broadcast Service.  The Configuration Option contains the IPv4
   address or the fully qualified domain names of the broadcast service

4.1  Broadcast Service Controller Domain Name list

   If the 'enc' byte has a value of 0, the encoding byte is followed by
   a sequence of labels, encoded according to Section 3.1 of RFC 1035

   The option MAY contain multiple domain names, but these domain names
   SHOULD be used to construct SRV lookups as specified in [BCMCS],
   rather than querying for different A records.  The client MUST try
   the records in the order listed, applying the mechanism described in
   [BCMCS] for each entry.  The client only resolves the subsequent
   domain names if attempts to contact the first one failed or yielded
   no common transport protocols between the client and the controller
   or denote a domain administratively prohibited by client's policy.

   Use of multiple domain names is not meant to replace the SRV records,
   but rather to allow a single DHCP server to indicate the broadcast
   controllers in the access provider's network.

   Clients MUST support compression according to the encoding in Section
   4.1.4 of "Domain Names - Implementation And Specification [RFC1035].

   Since the domain names are supposed to be different domains,
   compression will likely have little effect, however.  If the length
   of the domain list exceeds the maximum permissible within a single
   option (254 octets), then the domain list MUST be represented in the
   DHCP message as specified in [RFC3396] .

   The DHCP option for this encoding has the following format:

           Code  Len   enc   FQDN(s) of Broadcast Controller
         | TBD |  n  |  0  |  s1 |  s2 |  s3 |  s4 | s5  |  ...

   An example case when two controller domain names e.g., are returned will be:

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       |TBD|38 | 5 |'b'|'c'|'m'|'c'|'1'| 8 |'c'|'a'|'r'|'r'|'i'|'e'|'r'|
       |'1'| 3 |'c'|'o'|'m'| 5 |'b'|'c'|'m'|'c'|'2'| 8 |'c'|'a'|'r'|'r'|
       |'i'|'e'|'r'|'1'| 3 |'c'|'o'|'m'|

4.2  Broadcast Service Controller IPv4 address option

   If the 'enc' byte has a value of 1, the encoding byte is followed by
   a list of IPv4 addresses indicating broadcast controller IPv4
   addresses.  The controllers MUST be listed in order of preference.
   Its minimum length is 5, and the length MUST be a multiple of 4 plus
   one.  The DHCP option for this encoding has the following format:

          Code   Len   enc   Address 1               Address 2
         | TBD |  n  |  1  | a1  | a2  | a3  | a4  | a1  |  ...

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5.  Security Considerations

   The security considerations in the base DHCP spec [RFC2131] applies.
   An attacker may change information of the Broadcast Service
   Controller in packets that are in-tranist from DHCP server to the MN,
   if integrity protection is not in place.  In that event, the user of
   the Broadcast service may be diverted to a rogue broadcast service
   controller.  In the absence of a mutual authentication procedure
   between MN and the Broadcast controller, the MN may receive wrong or
   fraudulent information about Broadcast Service.

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6.  IANA Considerations

   The option code for Broadcast Service Controller option must be
   assigned by IANA.

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7.  Acknowledgements

   Thanks to the following indivduals for their review and constructive
   comments during the development of this document:

   AC Mahendran, Jun Wang, Raymond Hsu, Jayshree Bharatia, Ralph Droms,
   Ted Lemon.

8  Normative References

   [BCMCS]    3GPP2,, "X.S0022, Broadcast and Multicast
              Service in  cdma2000 Wireless IP Network.", February 2005.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol", RFC
              2131, March 1997.

   [RFC3396]  Lemon, T. and S. Cheshire, "Encoding Long Options in the
              Dynamic Host Configuration Protocol (DHCPv4)", RFC 3396,
              November 2002.

Authors' Addresses

   Kuntal Chowdhury
   Starent Networks
   2540 Coolwater Dr.
   Plano, TX  75025

   Phone: +1 214-550-1416

   Parviz Yegani
   Cisco Systems
   3625 Cisco Way
   San Jose, CA  95134

   Phone: +1 408-832-5729

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   Lila Madour
   8400, Decarie Blvd
   Town of Mount Royal, Quebec  H4P 2N2

   Phone: +1 514-345-7900

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