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Versions: 00 01 02 03 04 05 draft-ietf-pcp-port-set

PCP WG                                                      M. Boucadair
Internet-Draft                                            France Telecom
Intended status: Standards Track                            S. Sivakumar
Expires: October 21, 2012                                          Cisco
                                                          April 19, 2012


                   Reserving N and N+1 Ports with PCP
                    draft-boucadair-pcp-rtp-rtcp-04

Abstract

   This document defines a new PCP Option to reserve a pair of ports (N
   and N+1) by a PCP-controlled device while preserving the parity and
   contiguity.  This PCP Option eases the NAT traversal for applications
   having requirements on the port parity and contiguity (e.g., RTP/
   RTCP).

Requirements Language

   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 [RFC2119].

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on October 21, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents



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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Why N/N+1 Option is Needed?  . . . . . . . . . . . . . . . . .  3
   3.  Definition of the Port Reservation Option  . . . . . . . . . .  4
     3.1.  Requirements . . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Rationale  . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.3.  PCP Port Reservation Option  . . . . . . . . . . . . . . .  4
   4.  Client Behaviour . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Server Behaviour . . . . . . . . . . . . . . . . . . . . . . .  6
   6.  Illustration Examples  . . . . . . . . . . . . . . . . . . . .  7
     6.1.  Port Reservation Option Not Supported by The PCP Server  .  7
     6.2.  Port Reservation Option Is Supported by The PCP Server . .  8
     6.3.  Delete the Mappings  . . . . . . . . . . . . . . . . . . . 10
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 12
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 13
     10.2. Informative References . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13





















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1.  Introduction

   This document defines a new PCP Option [I-D.ietf-pcp-base] which aims
   to ease the traversal of RTP/RTCP based applications [RFC3550] when a
   NAT is involved in the path.

   The main advantage of using PCP is it does not need any further
   feature to be supported by the outbound proxy to assist the remote
   endpoint to successfully establish media sessions.  In particular,
   ALGs are not required in the NAT for this purpose and no dedicated
   functions at the media gateway are needed.

   The base PCP specification allows to retrieve the external IP address
   and external port to be conveyed in the SIP signaling messages
   [RFC3261].  Therefore SIP Proxy Servers do not need to support means
   to ease the NAT traversal of SIP messages (e.g., [RFC5626],
   [RFC6223], etc.).  Another advantage of using the external IP address
   and port is this provides a hint to the proxy server there is no need
   to return a small expire timer (e.g., 60s).


2.  Why N/N+1 Option is Needed?

   Traditionally the voice/video applications that use RTP and RTCP
   would specify only the RTP port that the application would use for
   streaming the RTP data.  The inherent assumption is that the RTCP
   traffic will be sent on the next higher port.  Below is provided an
   excerpt from [RFC3550]:

      "RTP relies on the underlying protocol(s) to provide de-
      multiplexing of RTP data and RTCP control streams.  For UDP and
      similar protocols, RTP SHOULD use an even destination port number
      and the corresponding RTCP stream SHOULD use the next higher (odd)
      destination port number.  For applications that take a single port
      number as a parameter and derive the RTP and RTCP port pair from
      that number, if an odd number is supplied then the application
      SHOULD replace that number with the next lower (even) number to
      use as the base of the port pair.  For applications in which the
      RTP and RTCP destination port numbers are specified via explicit,
      separate parameters (using a signaling protocol or other means),
      the application MAY disregard the restrictions that the port
      numbers be even/odd and consecutive although the use of an even/
      odd port pair is still encouraged."

   [RFC3605] defines an explicit "a=RTCP" SDP attribute for some
   applications using a distinct port than RTP+1.  Even though [RFC3605]
   defines a new attribute for explicitly specifying the RTCP attribute
   for the SDP based applications, but since it is not a MUST to use



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   this attribute, there are still applications that are not compliant
   with this RFC.  There are also non-SDP based applications that use
   RTP/RTCP like H323, that make the assumption that RTCP streaming will
   happen on RTP+1 port.

   In order for these applications to work across NAT, the NAT device
   must have an application layer gateway, that would allocate two
   consecutive ports.  In a PCP context, a similar functionality need to
   be provided for the PCP Client to request two consecutive ports and
   the PCP Server to allocate and respond with the information of the
   allocated port.

   This document describes the mechanism to request a pair of
   consecutive ports for a PCP-controlled device and the corresponding
   mechanism for the PCP Server to allocate and respond to the port
   allocation request.

   It is acknowledged that modern applications adopt new approaches
   (e.g., use the same port for both RTP and RTCP) which does not
   encounter the problem raised above.  This document do not target
   those applications but "legacy" ones.


3.  Definition of the Port Reservation Option

3.1.  Requirements

   The PCP Option used to reserve a port pair should meet the following
   requirements:

   1.  Preserve the port parity as discussed in Section 4.2.2 of
       [RFC4787].

   2.  Preserve port contiguity as discussed in Section 4.2.3 of
       [RFC4787] (i.e., RTCP = RTP+1).

3.2.  Rationale

   Since PCP does not support a mechanism to include multiple port
   numbers in the same request/response, only the RTP port is explicitly
   signaled in PCP messages.  The companion port (i.e., RTCP port) is
   reserved too by the PCP Server.

3.3.  PCP Port Reservation Option

   The format of the PCP Port Reservation Option is defined in Figure 1.





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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |PORT_RESRV_OPT |  Reserved     |           0..0                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        This Option:

        Option Name: Port Reservation Option (PORT_RESRV_OPT)
        Number: TBA (IANA)
        Purpose: Used to retrieve a pair of ports
        Valid for Opcodes: MAP
        Length: 0
        May appear in: both request and response
        Maximum occurrences: 1


          Figure 1: Port Reservation Option (a.k.a., N/N+1 port)


4.  Client Behaviour

   To retrieve a pair of ports following the requirements listed in
   Section 3.1, the PCP Client adds the Port Reservation Option to its
   PCP MAP request.  The PCP Client MAY indicate its preferred external
   port.  This port number is likely to be equal to the internal port
   indicated in the PCP request.

   Once a response is received from the PCP Server, the PCP Client
   checks whether the Port Reservation Option is supported by the peer
   PCP Server following the procedure defined in Section 7.3 of
   [I-D.ietf-pcp-base].

      If the answer is positive, the PCP Client retrieves the mapping
      returned by the PCP Server; in particular the external port number
      should be even.  For the RTP case, this port is indicated to the
      remote peer as the port number used for RTP flows; RTCP is assumed
      to use the returned external port number + 1.

      If the Port Reservation Option is not supported by the PCP Server,
      and according to the port quota, only the RTP port can be signaled
      to the remote endpoint (e.g., SDP offer/answer [RFC4566]).  RTCP
      flows are likely to fail if no mechanism to assist the traversal
      of RTCP flows is supported (e.g., "a=RTCP" attribute).

   When a pair of ports is retrieved from the PCP Server, two mappings
   are instantiated in both the PCP Server and PCP Client.  For explicit
   deletion of these mappings, the PCP Client and PCP Server follow the



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   procedure defined in Section 11.5 of [I-D.ietf-pcp-base] for each
   port mapping.

   To reduce the delay to establish media sessions, the PCP Client MAY
   reserve a pair of ports once the (SIP) registration phase has been
   successfully completed.  These pair of ports will be included in SDP
   offers/answsers for instance.


5.  Server Behaviour

   Upon receiving the Port Reservation Option in a PCP request, the PCP
   Server validates the request for the supported OpCode values.  If an
   unrecognized value is received a Invalid request error is returned to
   the PCP Client (e.g., using MALFORMED_REQUEST error).  The reason for
   rejecting the request could be an invalid internal IP address,
   invalid Internal port, etc.

   For a valid request, the PCP Server collects the Internal port and
   the hinted external port and verify against any administrative rules
   to allow or disallow the PCP Client from making this request.  An
   example of an administrative rule will be by fulfilling the request
   it would put the client over its administratively allowed limits.  In
   those cases, the PCP Server will treat this as an error and this is
   handled the same way as described in [I-D.ietf-pcp-base] for the
   denial of honoring the request with the appropriate Opcode.

   To handle the PCP Reservation Option by the PCP Server, the procedure
   defined in Section 7.3 of [I-D.ietf-pcp-base] should be followed.
   When PCP Reservation Option is not supported, the PCP Server MUST
   treat the request as any PCP request to create an individual mapping.
   If port parity preservation is supported by the PCP Server, an even
   port is likely to be returned to the PCP Client.  Otherwise, a port
   is returned if the port quota is not reached.

   The following describes the behavior of the PCP Server when the PCP
   Reservation Option is supported.

   The PCP Server should request the controlling NAT device to allocate
   a pair of consecutive ports.  If there is a hinted external port
   present in the request, the server MAY try to honor the request.  The
   PCP Server MUST honor the parity by requesting the allocation of
   ports that match the parity.  However, there is no guarantee that the
   hinted external ports are available or be allocated.  Two mappings
   are therefore instantiated by the PCP Server with the same lifetime
   value.  These mappings are treated as any individual mapping.

   If a mapping already exists and the PCP Reservation Option can be



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   honored, the PCP Server instantiate the companion mapping and sends
   back a positive answer to the requesting PCP Client.

   If the port allocation failed either because of the unavailability of
   ports or the port parity could not be honored, the PCP Server SHOULD
   reserve only one external port.  The PCP Server SHOULD indicate in
   the response that the PCP Reservation Option has not been honored as
   specified in Section 6.3 of [I-D.ietf-pcp-base].

   If the request contains the PREFER_FAILURE option and one or both
   hinted external ports (i.e., the hinted external port number and
   hinted external port number + 1) cannot be allocated, the PCP Server
   MUST reply with result code CANNOT_PROVIDE_EXTERNAL_PORT.


6.  Illustration Examples

   This section provides a list of examples to illustrate the usage of
   PCP Port Reservation Option.

6.1.  Port Reservation Option Not Supported by The PCP Server

   Figure 2 shows an example of the flow exchange which is observed when
   the PORT_RESERVATION_OPTION is not supported by the PCP Server.



























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                       +------+                           +------+
                       | PCP  |                           | PCP  |
                       |Client|                           |Server|
                       +------+                           +------+
                          |       (1) PCP MAP Request         |
                          |           protocol= UDP           |
                          | internal-ip-address= 198.51.100.1 |
                          |       internal-port= 6000         |
                          |      PORT_RESERVATION_OPTION      |
                          |---------------------------------->|
                          |                                   |
                          |      (2) PCP MAP Response         |
                          |           protocol= UDP           |
                          | internal-ip-address= 198.51.100.1 |
                          |       internal-port= 6000         |
                          |   external-ip-address= 192.0.2.1  |
                          |        external-port= 15659       |
                          |       assigned-lifetime= 3600     |
                          |   UNSUPP_OPTION(PORT_RESRV_OPT)   |
                          |<----------------------------------|
                          |                                   |

     Figure 2: Flow Example of a PCP Server which does not support the
                          Port Reservation Option

6.2.  Port Reservation Option Is Supported by The PCP Server

   Figure 3 and Figure 4 illustrate two examples of the flow exchanges
   which are observed when the PORT_RESERVATION_OPTION is supported by
   the PCP Server.  Figure 3 shows an example of a PCP Server supporting
   the option and honoring the requested external port number.  Figure 4
   shows an example of a PCP Server supporting the option but not
   honoring the requested external port number.


















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                       +------+                           +------+
                       | PCP  |                           | PCP  |
                       |Client|                           |Server|
                       +------+                           +------+
                          |       (1) PCP MAP Request         |
                          |           protocol= UDP           |
                          | internal-ip-address= 198.51.100.1 |
                          |       internal-port= 6000         |
                          |      PORT_RESERVATION_OPTION      |
                          |---------------------------------->|
                          |                                   |
                          |      (2) PCP MAP Response         |
                          |           protocol= UDP           |
                          | internal-ip-address= 198.51.100.1 |
                          |       internal-port= 6000         |
                          |   external-ip-address= 192.0.2.1  |
                          |        external-port= 6000        |
                          |       assigned-lifetime= 3600     |
                          |      PORT_RESERVATION_OPTION      |
                          |<----------------------------------|
                          |                                   |

     Figure 3: Flow Example of a PCP Server supporting the option and
                     honoring the hinted external port



























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                       +------+                           +------+
                       | PCP  |                           | PCP  |
                       |Client|                           |Server|
                       +------+                           +------+
                          |       (1) PCP MAP Request         |
                          |           protocol= UDP           |
                          | internal-ip-address= 198.51.100.1 |
                          |       internal-port= 6000         |
                          |      PORT_RESERVATION_OPTION      |
                          |---------------------------------->|
                          |                                   |
                          |      (2) PCP MAP Response         |
                          |           protocol= UDP           |
                          | internal-ip-address= 198.51.100.1 |
                          |       internal-port= 6000         |
                          |   external-ip-address= 192.0.2.1  |
                          |        external-port= 12000       |
                          |       assigned-lifetime= 3600     |
                          |      PORT_RESERVATION_OPTION      |
                          |<----------------------------------|
                          |                                   |

   Figure 4: Flow Example of a PCP Server supporting the option but not
                     honoring the hinted external port

6.3.  Delete the Mappings

   Figure 5 and Figure 6 shows the exchanges that occur to delete the
   created mappings.






















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                       +------+                           +------+
                       | PCP  |                           | PCP  |
                       |Client|                           |Server|
                       +------+                           +------+
                          |          PCP MAP Request          |
                          |           protocol= UDP           |
                          | internal-ip-address= 198.51.100.1 |
                          |       internal-port= 6000         |
                          |   external-ip-address= 192.0.2.1  |
                          |        external-port= 6000        |
                          |       requested-lifetime= 0       |
                          |---------------------------------->|
                          |                                   |
                          |          PCP MAP Request          |
                          |           protocol= UDP           |
                          | internal-ip-address= 198.51.100.1 |
                          |       internal-port= 6001         |
                          |   external-ip-address= 192.0.2.1  |
                          |        external-port= 6001        |
                          |       requested-lifetime= 0       |
                          |---------------------------------->|
                          |                                   |

               Figure 5: Flow example to delete the mappings



























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                       +------+                           +------+
                       | PCP  |                           | PCP  |
                       |Client|                           |Server|
                       +------+                           +------+
                          |                                   |
                          |          PCP MAP Request          |
                          |           protocol= UDP           |
                          | internal-ip-address= 198.51.100.1 |
                          |       internal-port= 6000         |
                          |   external-ip-address= 192.0.2.1  |
                          |        external-port= 12000       |
                          |       requested-lifetime= 0       |
                          |---------------------------------->|
                          |                                   |
                          |          PCP MAP Request          |
                          |           protocol= UDP           |
                          | internal-ip-address= 198.51.100.1 |
                          |       internal-port= 6001         |
                          |   external-ip-address= 192.0.2.1  |
                          |        external-port= 12001       |
                          |       requested-lifetime= 0       |
                          |---------------------------------->|
                          |                                   |

             Figure 6: Flow example to delete the mappings (2)


7.  IANA Considerations

   This document requests the assignment of a new PCP Option code:
                                   Option Name Value
                             ----------------- -----
                       PORT_RESERVATION_OPTION TBA


8.  Security Considerations

   This document does not introduce any security issue in addition to
   what is taken into account in [I-D.ietf-pcp-base].


9.  Acknowledgments

   Many thanks to S. Perrault for his comments.


10.  References




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10.1.  Normative References

   [I-D.ietf-pcp-base]
              Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
              Selkirk, "Port Control Protocol (PCP)",
              draft-ietf-pcp-base-24 (work in progress), March 2012.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC3605]  Huitema, C., "Real Time Control Protocol (RTCP) attribute
              in Session Description Protocol (SDP)", RFC 3605,
              October 2003.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC4787]  Audet, F. and C. Jennings, "Network Address Translation
              (NAT) Behavioral Requirements for Unicast UDP", BCP 127,
              RFC 4787, January 2007.

10.2.  Informative References

   [RFC5626]  Jennings, C., Mahy, R., and F. Audet, "Managing Client-
              Initiated Connections in the Session Initiation Protocol
              (SIP)", RFC 5626, October 2009.

   [RFC6223]  Holmberg, C., "Indication of Support for Keep-Alive",
              RFC 6223, April 2011.













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Authors' Addresses

   Mohamed Boucadair
   France Telecom
   Rennes,   35000
   France

   Email: mohamed.boucadair@orange.com


   Senthil Sivakumar
   Cisco
   7100 Kit Creek Road
   Research Triangle Park, North Carolina  27709
   USA

   Email: ssenthil@cisco.com


































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