An extension to RELOAD to support Relay Peer Routing
draft-ietf-p2psip-rpr-03

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P2PSIP                                                      N. Zong, Ed.
Internet-Draft                                                  X. Jiang
Intended status: Standards Track                                 R. Even
Expires: April 25, 2013                              Huawei Technologies
                                                                Y. Zhang
                                                            China Mobile
                                                        October 22, 2012

          An extension to RELOAD to support Relay Peer Routing
                        draft-ietf-p2psip-rpr-03

Abstract

   This document proposes an optional extension to RELOAD to support
   relay peer routing mode.  RELOAD recommends symmetric recursive
   routing for routing messages.  The new optional extension provides a
   shorter route for responses reducing the overhead on intermediary
   peers and describes the potential cases where this extension can be
   used.

Status of this Memo

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Backgrounds  . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  5
       3.1.1.  Relay Peer Routing (RPR) . . . . . . . . . . . . . . .  5
     3.2.  Scenarios Where RPR Benefits . . . . . . . . . . . . . . .  6
       3.2.1.  Managed or Closed P2P System . . . . . . . . . . . . .  6
       3.2.2.  Using Bootstrap Peers as Relay Peers . . . . . . . . .  7
       3.2.3.  Wireless Scenarios . . . . . . . . . . . . . . . . . .  7
   4.  Relationship Between SRR and RPR . . . . . . . . . . . . . . .  7
     4.1.  How RPR Works  . . . . . . . . . . . . . . . . . . . . . .  7
     4.2.  How SRR and RPR Work Together  . . . . . . . . . . . . . .  7
   5.  Comparison on cost of SRR and RPR  . . . . . . . . . . . . . .  8
     5.1.  Closed or managed networks . . . . . . . . . . . . . . . .  8
     5.2.  Open networks  . . . . . . . . . . . . . . . . . . . . . .  9
   6.  Extensions to RELOAD . . . . . . . . . . . . . . . . . . . . .  9
     6.1.  Basic Requirements . . . . . . . . . . . . . . . . . . . .  9
     6.2.  Modification To RELOAD Message Structure . . . . . . . . .  9
       6.2.1.  State-keeping Flag . . . . . . . . . . . . . . . . . . 10
       6.2.2.  Extensive Routing Mode . . . . . . . . . . . . . . . . 10
     6.3.  Creating a Request . . . . . . . . . . . . . . . . . . . . 10
       6.3.1.  Creating a request for RPR . . . . . . . . . . . . . . 10
     6.4.  Request And Response Processing  . . . . . . . . . . . . . 11
       6.4.1.  Destination Peer: Receiving a Request And Sending
               a Response . . . . . . . . . . . . . . . . . . . . . . 11
       6.4.2.  Sending Peer: Receiving a Response . . . . . . . . . . 11
       6.4.3.  Relay Peer Processing  . . . . . . . . . . . . . . . . 12
   7.  Discovery Of Relay Peer  . . . . . . . . . . . . . . . . . . . 12
   8.  Optional Methods to Investigate Peer Connectivity  . . . . . . 12
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 14
     12.2. Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14

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1.  Introduction

1.1.  Backgrounds

   RELOAD [I-D.ietf-p2psip-base] recommends symmetric recursive routing
   (SRR) for routing messages and describes the extensions that would be
   required to support additional routing algorithms.  Other than SRR,
   two other routing options: direct response routing (DRR) and relay
   peer routing (RPR) are also discussed in Appendix D in [I-D.ietf-
   p2psip-base].  DRR is specified in [I-D.ietf-p2psip-drr].  As we show
   in section 3, RPR is advantageous over SRR in some scenarios reducing
   load (CPU and link BW) on intermediary peers.  RPR works better in a
   network where relay peers are provisioned in advance so that relay
   peers are publicly reachable in the P2P system.  In other scenarios,
   using a combination of RPR and SRR together is more likely to bring
   benefits than if SRR is used alone.  Some discussion on connectivity
   is in Non-Transitive Connectivity and DHTs
   [http://srhea.net/papers/ntr-worlds05.pdf].

   Note that in this draft, we focus on RPR routing mode and its
   extensions to RELOAD.  Some text such as modification to RELOAD
   message structure, optional methods to investigate peer connectivity
   described in DRR draft [I-D.ietf-p2psip-drr] are also relevent to
   RPR.

   We first discuss the problem statement in Section 3, then how to
   combine RPR and SRR is presented in Section 4.  In Section 5, we give
   comparison on the cost of SRR and RPR in both managed and open
   networks.  An extension to RELOAD to support RPR is proposed in
   Section 6.  Discovery of relay peers is introduced in Section 7.
   Some optional methods to check peer connectivity is introduced in
   Section 8.

2.  Terminology

   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].

   We use the terminology and definitions from the Concepts and
   Terminology for Peer to Peer SIP [I-D.ietf-p2psip-concepts] draft
   extensively in this document.  We also use terms defined in NAT
   behavior discovery [RFC5780].  Other terms used in this document are
   defined inline when used and are also defined below for reference.

   Publicly Reachable: A peer is publicly reachable if it can receive
   unsolicited messages from any other peer in the same overlay.  Note:

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   "publicly" does not mean that the peers must be on the public
   Internet, because the RELOAD protocol may be used in a closed system.

   Relay Peer: A type of publicly reachable peer that can receive
   unsolicited messages from all other peers in the overlay and forward
   the responses from destination peers towards the request sender.

   Relay Peer Routing (RPR): refers to a routing mode in which responses
   to P2PSIP requests are sent by the destination peer to a relay peer
   transport address who will forward the responses towards the sending
   peer.  For simplicity, the abbreviation RPR is used instead in the
   following text.

   Symmetric Recursive Routing (SRR): refers to a routing mode in which
   responses follow the request path in the reverse order to get back to
   the sending peer.  For simplicity, the abbreviation SRR is used
   instead in the following text.

3.  Problem Statement

   RELOAD is expected to work under a great number of application
   scenarios.  The situations where RELOAD is to be deployed differ
   greatly.  For instance, some deployments are global, such as a Skype-
   like system intended to provide public service.  Some run in closed
   networks of small scale.  SRR works in any situation, but RPR may
   work better in some specific scenarios.

3.1.  Overview

   RELOAD is a simple request-response protocol.  After sending a
   request, a peer waits for a response from a destination peer.  There
   are several ways for the destination peer to send a response back to
   the source peer.  In this section, we will provide detailed
   information on RPR.

   Note that the same illustrative settings can be found in DRR draft
   [I-D.ietf-p2psip-drr].

3.1.1.  Relay Peer Routing (RPR)

   If peer A knows it is behind a NAT or NATs, and knows one or more
   relay peers with whom they have a prior connections, peer A can try
   RPR.  Assume A is associated with relay peer R. When sending the
   request, peer A includes information describing peer R transport
   address in the request.  When peer X receives the request, peer X
   sends the response to peer R, which forwards it directly to Peer A on
   the existing connection.  Note that RPR also allows a shorter route

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   for responses compared to SRR, which means less overhead on
   intermediary peers.  Establishing a connection to the relay with TLS
   requires multiple round trips.  Please refer to Section 5 for cost
   comparison between SRR and RPR.

   This technique relies on the relative population of peers such as A
   that require relay peers and peers such as R that are capable of
   serving as a relay peers.  It also requires mechanism to enable peers
   to know which peers can be used as their relays.  This mechanism may
   be based on configuration, for example as part of the overlay
   configuration an initial list of relay peers can be supplied.
   Another option is in a response to ATTACH request the peer can signal
   that it can be used as a relay peer.

   A            B            C             D           X           R
   |  Request   |            |            |            |           |
   |----------->|            |            |            |           |
   |            | Request    |            |            |           |
   |            |----------->|            |            |           |
   |            |            | Request    |            |           |
   |            |            |----------->|            |           |
   |            |            |            | Request    |           |
   |            |            |            |----------->|           |
   |            |            |            |            | Response  |
   |            |            |            |            |---------->|
   |            |            |            |  Response  |           |
   |<-----------+------------+------------+------------+-----------|
   |            |            |            |            |           |

3.2.  Scenarios Where RPR Benefits

   In this section, we will list several scenarios where using RPR would
   provide improved performance.

3.2.1.  Managed or Closed P2P System

   As described in Section 3.2.1, many P2P systems run in a closed or
   managed environment so that network administrators can better manage
   their system.  For example, the network administrator can deploy
   several relay peers which are publicly reachable in the system and
   indicate their presence in the configuration file.  After learning
   where these relay peers are, peers behind NATs can use RPR with the
   help from these relay peers.  Peers must also support SRR in case RPR
   fails.

   Another usage is to install relay peers on the managed network
   boundary allowing external peers to send responses to peers inside
   the managed network.

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3.2.2.  Using Bootstrap Peers as Relay Peers

   Bootstrap peers must be publicly reachable in a RELOAD architecture.
   As a result, one possible architecture would be to use the bootstrap
   peers as relay peers for use with RPR.  The requirements for being a
   relay peer are publicly accessible and maintaining a direct
   connection with its client.  As such, bootstrap peers are well suited
   to play the role of relay peers.

3.2.3.  Wireless Scenarios

   In some mobile deployments, using RPR may help with reducing radio
   battery usage and bandwidth by the intermediary peers.  The service
   provider may recommend in the configuration using RPR based on his
   knowledge of the topology.  Such relay peers may also help
   connectivity to external networks.

4.  Relationship Between SRR and RPR

4.1.  How RPR Works

   Peers using RPR must maintain a connection with their relay peer(s).
   This can be done in the same way as establishing a neighbor
   connection between peers by using the Attach method.

   A requirement for RPR is for the source peer to convey their relay
   peer (or peers) transport address in the request, so the destination
   peer knows where the relay peer are and send the response to a relay
   peer first.  The request should include also the requesting peer
   information enabling the relay peer to route the response back to the
   right peer.

   Note that being a relay peer does not require that the relay peer
   have more functionality than an ordinary peer.  As discussed later,
   relay peers comply with the same procedure as an ordinary peer to
   forward messages.  The only difference is that there may be a larger
   traffic burden on relay peers.  Relay peers can decide whether to
   accept a new connection based on their current burden.

4.2.  How SRR and RPR Work Together

   RPR is not intended to replace SRR.  As seen from Section 3, RPR has
   better performance in some scenarios, but have limitations as well,
   see for example section 4.3 in Non-Transitive Connectivity and DHTs
   [http://srhea.net/papers/ntr-worlds05.pdf].  As a result, it is
   better to use these two modes together to adapt to each peer's
   specific situation.  Note that the informative suggestions on how to

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   transition between SRR and RPR (e.g. compute success rate of RPR,
   fall back to SRR, etc) are same with that on DRR and RPR.  Please
   refer to DRR draft [I-D.ietf-p2psip-drr] for more details.
   Similarly, the peer can decide whether to try RPR based on other
   information such as configuration file information.  If a relay peer
   is provided by the service provider, peers may prefer RPR over SRR.

5.  Comparison on cost of SRR and RPR

   The major advantages in using RPR are in going through less
   intermediary peers on the response.  By doing that it reduces the
   load on those peers' resources like processing and communication
   bandwidth.

5.1.  Closed or managed networks

   As described in Section 3, many P2P systems run in a closed or
   managed environment (e.g. carrier networks) so that network
   administrators would know that they could safely use RPR.

   The number of hops for a response in SRR and RPR are listed in the
   following table.  Note that the same illustrative settings can be
   found in DRR draft [I-D.ietf-p2psip-drr].

     Mode      | Success | No. of Hops | No. of Msgs
     ----------------------------------------------------
     SRR       |  Yes    |     logN    |    logN
     RPR       |  Yes    |     2       |    2
     RPR(DTLS) |  Yes    |     2       |    7+2

   From the above comparison, it is clear that:

   1) In most cases of N > 4 (2^2), RPR has fewer hops than SRR.
   Shorter route means less overhead and resource usage on intermediary
   peers, which is an important consideration for adopting RPR in the
   cases where the resource such as CPU and BW is limited, e.g. the case
   of mobile, wireless network.

   2) In the cases of N > 512 (2^9), RPR also has fewer messages than
   SRR.

   3) In the cases where N < 512, RPR has more messages than SRR (but
   still has fewer hops than SRR).  So the consideration to use RPR or
   SRR depends on other factors like using less resources (bandwidth and
   processing) from the intermediaries peers.  Section 4 provides use
   cases where RPR has better chance to work or where the intermediary
   resources considerations are important.

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5.2.  Open networks

   In open network where RPR is not guaranteed, RPR can fall back to SRR
   If it fails after trial, as described in Section 4.  Based on the
   same settings in Section 5.1, the number of hops, number of messages
   for a response in SRR and RPR are listed in the following table.

     Mode      |       Success         | No. of Hops | No. of Msgs
     -----------------------------------------------------------
     SRR       |         Yes           |     logN    |    logN
     RPR       |         Yes           |     2       |    2
               | Fail&Fall back to SRR |     2+logN  |    2+logN
     RPR(DTLS) |         Yes           |     2       |    7+2
               | Fail&Fall back to SRR |     2+logN  |    9+logN

   From the above comparison, it can be observed that:

   1) Trying RPR would still have a good chance of fewer hops than SRR.
   The detailed analysis is same as DRR case and can be found in DRR
   draft [I-D.ietf-p2psip-drr].

   2) In the cases of large network and the success rate of RPR is good,
   it is still possible that RPR has fewer messages than SRR.
   Otherwise, the consideration to use RPR or SRR depends on other
   factors like using less resources from the intermediaries peers.

6.  Extensions to RELOAD

   Adding support for RPR requires extensions to the current RELOAD
   protocol.  In this section and in DRR[I-D.ietf-p2psip-drr], we define
   the changes required to the protocol, including changes to message
   structure and to message processing.

6.1.  Basic Requirements

   The basic requirements to peers for supporting RPR are same as DRR
   case.  Please refer to DRR draft [I-D.ietf-p2psip-drr].

6.2.  Modification To RELOAD Message Structure

   RELOAD provides an extensible framework to accommodate future
   extensions.  In this section and in DRR[I-D.ietf-p2psip-drr], we
   define a ForwardingOption structure to support RPR mode.

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6.2.1.  State-keeping Flag

   The state-keeping flag to support RPR is same as DRR case.  Please
   refer to DRR draft [I-D.ietf-p2psip-drr].

6.2.2.  Extensive Routing Mode

   The ForwardingOption structure to support RPR is same as DRR case.
   Please refer to DRR draft [I-D.ietf-p2psip-drr].  The definition of
   the fields is as follow:

   RouteMode: refers to which type of routing mode is indicated to the
   destination peer.  Currently, only DRR (specified in DRR draft
   [I-D.ietf-p2psip-drr]) and RPR are defined.

   OverlayLinkType: refers to the transport type which is used to
   deliver responses from the destination peer to the relay peer.

   IpAddressPort: refers to the transport address that the destination
   peer should use to send the response to.  This will be a relay peer
   address for RPR.

   Destination: refers to the relay peer itself.  If the routing mode is
   RPR, then the destination contains two destinations, which are the
   relay peer's Node-ID and the sending peer's Node-ID.

6.3.  Creating a Request

6.3.1.  Creating a request for RPR

   When using RPR for a transaction, the sending peer MUST set the
   IGNORE-STATE-KEEPING flag in the ForwardingHeader.  Additionally, the
   peer MUST construct and include a ForwardingOptions structure in the
   ForwardingHeader.  When constructing the ForwardingOption structure,
   the fields MUST be set as follows:

   1) The type MUST be set to extensive_routing_mode.

   2) The ExtensiveRoutingModeOption structure MUST be used for the
   option field within the ForwardingOptions structure.  The fields MUST
   be defined as follows:

   2.1) routemode set to 0x02 (RPR).

   2.2) transport set as appropriate for the relay peer.

   2.3) ipaddressport set to the transport address of the relay peer
   that the sender wishes the message to be relayed through.

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   2.4) destination structure MUST contain two values.  The first MUST
   be defined as type node and set with the values for the relay peer.
   The second MUST be defined as type node and set with the sending
   peer's own values.

6.4.  Request And Response Processing

   This section gives normative text for message processing after RPR is
   introduced.  Here, we only describe the additional procedures for
   supporting RPR.  Please refer to [I-D.ietf-p2psip-base] for RELOAD
   base procedures.

6.4.1.  Destination Peer: Receiving a Request And Sending a Response

   When the destination peer receives a request, it will check the
   options in the forwarding header.  If the destination peer can not
   understand extensive_routing_mode option in the request, it MUST
   attempt to use SRR to return an "Error_Unknown_Extension" response
   (defined in Section 6.3.3.1 and Section 14.9 in [I-D.ietf-p2psip-
   base]) to the sending peer.

   If the routing mode is RPR, the destination peer MUST construct a
   destination_list for the response with two entries.  The first MUST
   be set to the relay peer Node-ID from the option in the request and
   the second MUST be the sending peer Node-ID from the option of the
   request.

   In the event that the routing mode is set to RPR and there are not
   exactly two destinations the destination peer MUST try to send an
   "Error_Unknown_Extension" response (defined in Section 6.3.3.1 and
   Section 14.9 in [I-D.ietf-p2psip-base]) to the sending peer using
   SRR.

   After the peer constructs the destination_list for the response, it
   sends the response to the transport address which is indicated in the
   ipaddressport field in the option using the specific transport mode
   in the Forwardingoption.  If the destination peer receives a
   retransmit with SRR preference on the message it is trying to
   response to now, the responding peer should abort the RPR response
   and use SRR.

6.4.2.  Sending Peer: Receiving a Response

   Upon receiving a response, the peer follows the rules in [I-D.ietf-
   p2psip-base].  If the sender used RPR and does not get a response
   until the timeout, it MAY either resend the message using RPR but
   with a different relay peer (if available), or resend the message
   using SRR.

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6.4.3.  Relay Peer Processing

   Relay peers are designed to forward responses to peers who are not
   publicly reachable.  For the routing of the response, this draft
   still uses the destination_list.  The only difference from SRR is
   that the destination_list is not the reverse of the via_list, instead
   it is constructed from the forwarding option as described below.

   When a relay peer receives a response, it MUST follow the rules in
   [I-D.ietf-p2psip-base].  It receives the response, validates the
   message, re-adjust the destination_list and forward the response to
   the next hop in the destination_list based on the connection table.
   There is no added requirement for relay peer.

7.  Discovery Of Relay Peer

   There are several ways to distribute the information about relay
   peers throughout the overlay.  P2P network providers can deploy some
   relay peers and advertise them in the configuration file.  With the
   configuration file at hand, peers can get relay peers to try RPR.
   Another way is to consider relay peer as a service and then some
   service advertisement and discovery mechanism can also be used for
   discovering relay peers, for example, using the same mechanism as
   used in TURN server discovery in base RELOAD [I-D.ietf-p2psip-base].
   Another option is to let a peer advertise his capability to be a
   relay in the response to ATTACH or JOIN.

8.  Optional Methods to Investigate Peer Connectivity

   This section is for informational purposes only for providing some
   mechanisms that can be used when the configuration information does
   not specify if RPR can be used.  It summarizes some methods which can
   be used for a peer to determine its own network location compared
   with NAT.  These methods may help a peer to decide which routing mode
   it may wish to try.  Note that there is no foolproof way to determine
   if a peer is publically reachable, other than via out-of-band
   mechanisms.  As such, peers using these mechanisms may be able to
   optimize traffic, but must be able to fall back to SRR routing if the
   other routing mechanisms fail.

   For RPR to function correctly, a peer may attempt to determine
   whether it is publicly reachable.  If it is not, RPR may be chosen to
   route the response with the help from relay peers, or the peers
   should fall back to SRR.  NATs and firewalls are two major
   contributors preventing RPR from functioning properly.  There are a
   number of techniques by which a peer can get its reflexive address on

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   the public side of the NAT.  After obtaining the reflexive address, a
   peer can perform further tests to learn whether the reflexive address
   is publicly reachable.  If the address appears to be publicly
   reachable, the peers to which the address belongs can be a candidate
   to serve as a relay peer.  Peers which are not publicly reachable may
   still use RPR to shorten the response path with the help from relay
   peers.

   Some conditions are unique in P2PSIP architecture which could be
   leveraged to facilitate the tests.  In P2P overlay network, each peer
   only has partial a view of the whole network, and knows of a few
   peers in the overlay.  P2P routing algorithms can easily deliver a
   request from a sending peer to a peer with whom the sending peer has
   no direct connection.  This makes it easy for a peer to ask other
   peers to send unsolicited messages back to the requester.

   The approaches for a peer to get the addresses needed for the further
   tests, as well as the test for learning whether a peer may be
   publicly reacheable is same as the DRR case.  Please refer to DRR
   draft [I-D.ietf-p2psip-drr] for more details.

9.  Security Considerations

   As a routing alternative, the security part of RPR conforms to
   section 13.6 in based draft[I-D.ietf-p2psip-base] which describes
   routing security.

10.  IANA Considerations

   No IANA action is needed.

11.  Acknowledgements

   David Bryan has helped extensively with this document, and helped
   provide some of the text, analysis, and ideas contained here.  The
   authors would like to thank Ted Hardie, Narayanan Vidya, Dondeti
   Lakshminath, Bruce Lowekamp, Stephane Bryant and Marc Petit-Huguenin
   for their constructive comments.

12.  References

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12.1.  Normative References

   [I-D.ietf-p2psip-base] Jennings, C., Lowekamp, B., Rescorla, E.,
   Baset, S., and H. Schulzrinne, "REsource LOcation And Discovery
   (RELOAD) Base Protocol", draft-ietf-p2psip-base-22 (work in
   progress), July 2012.

   [I-D.ietf-p2psip-concepts] Bryan, D., Matthews, P., Shim, E., Willis,
   D., and S. Dawkins, "Concepts and Terminology for Peer to Peer SIP",
   draft-ietf-p2psip-concepts-04 (work in progress), October 2011.

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

   [I-D.ietf-p2psip-drr] Zong, N., Jiang, X., Even, R. and Zhang, Y.,
   "An extension to RELOAD to support Direct Response Routing",
   draft-ietf-p2psip-drr-03, October 2012.

12.2.  Informative References

   [ChurnDHT] Rhea, S., "Handling Churn in a DHT", Proceedings of the
   USENIX Annual Technical Conference.  Handling Churn in a DHT, June
   2004.

   [DTLS] Modadugu, N., Rescorla, E., "The Design and Implementation of
   Datagram TLS", 11th Network and Distributed System Security Symposium
   (NDSS), 2004.

   [RFC5780] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery
   Using STUN", RFC5780, May 2010.

   [I-D.ietf-behave-tcp] Guha, S., Biswas, K., Ford, B., Sivakumar, S.,
   and P. Srisuresh, "NAT Behavioral Requirements for TCP",
   draft-ietf-behave-tcp-08 (work in progress), September 2008.

   [I-D.lowekamp-mmusic-ice-tcp-framework] Lowekamp, B. and A. Roach, "A
   Proposal to Define Interactive Connectivity Establishment for the
   Transport Control Protocol (ICE-TCP) as an Extensible Framework",
   draft-lowekamp-mmusic-ice-tcp-framework-00 (work in progress),
   October 2008.

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

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Authors' Addresses

   Ning Zong (editor)
   Huawei Technologies

   Email: zongning@huawei.com

   Xingfeng Jiang
   Huawei Technologies

   Email: jiang.x.f@huawei.com

   Roni Even
   Huawei Technologies

   Email: even.roni@huawei.com

   Yunfei Zhang
   China Mobile

   Email: zhangyunfei@chinamobile.com

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