wdiff rfc7264.alt-original rfc7264.txt

P2PSIP
Internet Engineering Task Force (IETF) N. Zong, Ed.
Internet-Draft Zong
Request for Comments: 7264 X. Jiang
Intended status:
Category: Standards Track R. Even
Expires: April 24, 2014
ISSN: 2070-1721 Huawei Technologies
Y. Zhang
CoolPad
October 21, 2013 / China Mobile
June 2014

An Extension to the REsource LOcation And Discovery (RELOAD) Protocol
to Support Relay Peer Routing
draft-ietf-p2psip-rpr-11

Abstract

This document proposes defines an optional extension to the REsource LOcation
And Discovery (RELOAD) protocol to support the relay peer routing
mode. RELOAD recommends symmetric recursive routing for routing
messages. The new optional extension provides a shorter route for responses
responses, thereby reducing the overhead on intermediate peers and peers. This
document also describes the potential use cases where this extension can be
used.

Status of This Memo

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Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

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This Internet-Draft will expire on April 24, 2014.
http://www.rfc-editor.org/info/rfc7264.

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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 ....................................................3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 .....................................................4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 ........................................................5
3.1. RPR . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 ........................................................5
3.2. Scenarios where Where RPR can be used . . . . . . . . . . . . . 5 Can Be Used ............................6
3.2.1. Managed or closed Closed P2P systems . . . . . . . . . . . . 5 Systems .......................6
3.2.2. Using bootstrap nodes Bootstrap Nodes as relay peers . . . . . . . . 5 Relay Peers ................7
3.2.3. Wireless scenarios . . . . . . . . . . . . . . . . . 6 Scenarios ..................................7
4. Relationship between SRR and RPR . . . . . . . . . . . . . . 6 ................................7
4.1. How RPR works . . . . . . . . . . . . . . . . . . . . . . 6 Works ..............................................7
4.2. How SRR and RPR work together . . . . . . . . . . . . . . 6 Work Together ..............................7
5. RPR extensions Extensions to RELOAD . . . . . . . . . . . . . . . . . . 8 ........................................8
5.1. Basic requirements . . . . . . . . . . . . . . . . . . . 8 Requirements .........................................8
5.2. Modification to RELOAD message structure . . . . . . . . 8 Message Structure ...................8
5.2.1. State-keeping flag . . . . . . . . . . . . . . . . . 8
5.2.2. Extensive routing mode . . . . . . . . . . . . . . . 9 Routing Mode ..............................8
5.3. Creating a request . . . . . . . . . . . . . . . . . . . 9 Request .........................................9
5.3.1. Creating a request Request for RPR . . . . . . . . . . . . . 9 ..........................9
5.4. Request and response processing . . . . . . . . . . . . . 10 Response Processing ............................9
5.4.1. Destination peer: receiving Peer: Receiving a request Request and sending
Sending a
response . . . . . . . . . . . . . . . . . . . . . . 10 Response ..................................9
5.4.2. Sending peer: receiving Peer: Receiving a response . . . . . . . . . 11 Response .................10
5.4.3. Relay peer processing . . . . . . . . . . . . . . . . 11 Peer Processing ..............................10
6. Overlay configuration extension . . . . . . . . . . . . . . . 11 Configuration Extension ................................10
7. Discovery of relay peers . . . . . . . . . . . . . . . . . . 11 Relay Peers .......................................11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11 ........................................11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 ............................................11
9.1. A new New RELOAD Forwarding Option . . . . . . . . . . . . . 12 ............................11
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 ...............................................11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 ....................................................12
11.1. Normative References . . . . . . . . . . . . . . . . . . 12 .....................................12
11.2. Informative References . . . . . . . . . . . . . . . . . 12 ...................................12
Appendix A. Optional methods Methods to investigate peer connectivity . 13 Investigate Peer Connectivity .....13
Appendix B. Comparison on cost of Cost of SRR and RPR . . . . . . . . . .....................14
B.1. Closed or managed networks . . . . . . . . . . . . . . . 7 Managed Networks .................................14
B.2. Open networks . . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14 Networks ..............................................15

1. Introduction

The REsource LOcation And Discovery (RELOAD) protocol [I-D.ietf-p2psip-
base] [RFC6940]
recommends symmetric recursive routing (SRR) for routing messages and
describes the extensions that would be required to support additional
routing algorithms. Other than In addition to SRR, two other routing options: options --
direct response routing (DRR) and relay peer routing (RPR) -- are
also discussed in Appendix A of [I-D.ietf-p2psip-base]. [RFC6940]. As we show in section Section 3,
RPR is advantageous over SRR in some scenarios
reducing in that RPR can reduce
load (CPU and link bandwidth) on intermediate 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 provide benefits than if SRR is used alone.

Note that in this document, document we focus on the RPR routing mode and its
extensions to RELOAD to produce a standalone solution. Please refer
to DRR document [I-D.ietf-p2psip-drr] [RFC7263] for details on the DRR routing mode.

We first discuss the problem statement in Section 3, then how 3. 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 defined in Section 6. 5. Discovery of relay peers is
introduced in Section 7. Some optional methods to check peer
connectivity are introduced in Appendix A. In Appendix B, we give a
comparison of the cost of SRR and RPR in both managed and open
networks.

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 RELOAD base draft
[I-D.ietf-p2psip-base] RELOAD specification
[RFC6940] extensively in this document. We also use terms defined in
the NAT behavior discovery document [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: "publicly" "Publicly" does not mean that the peers must be on the
public Internet, because the RELOAD protocol may be used in a
closed network.

Relay Peer: A relay peer is 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 sender of the request.

Relay Peer Routing (RPR): "RPR" refers to a routing mode in which
responses to P2PSIP Peer-to-Peer SIP (P2PSIP) requests are sent by the
destination peer to a relay peer transport address who that will
forward the responses towards the sending peer. For simplicity,
the abbreviation RPR "RPR" is used instead in the rest of the this document.

Symmetric Recursive Routing (SRR): "SRR" refers to a routing mode
in which responses follow the reverse path of the request to get
to the sending peer. For simplicity, the abbreviation SRR "SRR" is
used
instead in the rest of this document.

Direct Response Routing (DRR): "DRR" refers to a routing mode in
which responses to P2PSIP requests are returned to the sending
peer directly from the destination peer based on the sending
peer's own local transport address(es). For simplicity, the
abbreviation "DRR" is used in the rest of this document.

3. Overview

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
Skype-like system intended to provide public service, while others
run in small-scale closed networks of small scale. networks. SRR works in any situation, but
RPR may work better in some specific scenarios.

3.1. RPR

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 types of illustrative
settings can be found in DRR document [I-D.ietf-p2psip-drr]. Appendix B.1 of [RFC7263].

If peer A knows it is behind a NAT or NATs, NATs and knows one or more
relay peers with whom they have a had prior connections, peer A can try
RPR. Assume that peer A is associated with relay peer R. When
sending the request, peer A includes information describing peer R R's
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
peer A on the existing connection. Figure 1 illustrates RPR. Note
that RPR also allows a shorter route for responses compared to SRR, which SRR;
this means less overhead on intermediate peers. Establishing a
connection to the relay with TLS Transport Layer Security (TLS) requires
multiple round trips. Please refer to
Section 5 Appendix B for a cost
comparison between SRR and RPR.

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

Figure 1. 1: RPR routing mode Mode

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

3.2. Scenarios where Where RPR can be used Can Be Used

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

3.2.1. Managed or closed Closed P2P systems Systems

As described in Section 3.2.1 of DRR draft [I-D.ietf-p2psip-drr], [RFC7263], 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 that 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
boundary, allowing external peers to send responses to peers inside
the managed network.

3.2.2. Using bootstrap nodes Bootstrap Nodes as relay peers Relay Peers

Bootstrap nodes are typically publicly reachable in a RELOAD
architecture. As a result, one possible architecture scenario would be to use the
bootstrap nodes as relay peers for use with RPR. A relay peer SHOULD
be publicly accessible and maintain a direct connection with its
client. As such, bootstrap nodes are well suited to play the role of
relay peers.

3.2.3. Wireless scenarios Scenarios

In some mobile deployments, using RPR may help reducing reduce radio battery
usage and bandwidth by the intermediate peers. The service provider
may recommend using RPR based on his/her his knowledge of the topology.

4. Relationship between SRR and RPR

4.1. How RPR works 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. method [RFC6940].

A requirement for RPR is for that the source peer to convey their its relay
peer peer's
(or peers) peers') transport address address(es) in the request, request so the destination
peer knows where the relay peer peers are and will send the response to a
relay peer first. The request SHOULD include request MUST also include the requesting peer
information enabling
peer's Node-ID or IP address, which enables 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 has
have more functionality than an ordinary peer. As discussed later, relay 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 Work Together

RPR is not intended to replace SRR. It is better to use these two
modes together to adapt to each peer's specific situation. Note that
the informative suggestions on for how to transition between SRR and RPR
are the same with that of as those for DRR. Please refer to DRR document [I-D
.ietf-p2psip-drr] Section 4.2 of
[RFC7263] for more details. If a relay peer is provided by the
service provider, peers MAY SHOULD prefer RPR over SRR. Otherwise,
using However, RPR
SHOULD NOT be discouraged used in the open Internet or if the administrator does
not feel he have has enough information about the
overlay. overlay network
topology. A new overlay configuration element specifying the usage
of
DRR RPR is defined in Section 7. 6.

5. RPR extensions Extensions to RELOAD

Adding support for RPR requires extensions to the current RELOAD
protocol. In this section, we define the extensions required to the
protocol, extensions,
including extensions to message structure and to message processing.

5.1. Basic requirements Requirements

All peers MUST be able to process requests for routing in SRR, SRR and MAY
support RPR routing requests.

5.2. Modification to RELOAD message structure Message Structure

RELOAD provides an extensible framework to accommodate future
extensions. In this section, we define a ForwardingOption structure
and present a an RPR routing option for the
extensive routing mode specified in [RFC7263]. The state-keeping
flag [RFC7263] is needed to support the RPR mode.

5.2.1. State-keeping flag

flag : 0x08 IGNORE-STATE-KEEPING

If IGNORE-STATE-KEEPING is set, any peer receiving this message and
which is not the destination of the message SHOULD forward the
message with the full via_list and SHOULD NOT maintain any internal
state.

5.2.2. Extensive routing mode

We first define a new type to define the new option,
extensive_routing_mode: Routing Mode

The option new RouteMode value for RPR is illustrated as below, defining defined below for the
ExtensiveRoutingModeOption structure:

enum {(0),DRR(1),RPR(2),(255)} RouteMode;
struct {
RouteMode routemode;
OverlayLinkType transport;
IpAddressPort ipaddressport;
Destination destinations<1..2^8-1>;
} ExtensiveRoutingModeOption;

Note that the DRR value in RouteMode is defined in DRR document [I-D
.ietf-p2psip-drr]. [RFC7263].

RouteMode: refers to which type of routing mode is indicated to the
destination peer.

OverlayLinkType: refers to the transport type which that 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. for sending responses. 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 items: the relay peer's
Node-ID and the sending peer's Node-ID.

5.3. Creating a request Request

5.3.1. Creating a request 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 ForwardingOption 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 ForwardingOption 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 through which the sender wishes the message to be relayed through. relayed.

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

5.4. Request and response processing 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] [RFC6940] for RELOAD base
procedures.

5.4.1. Destination peer: receiving Peer: Receiving a request Request and sending Sending a response Response

When the destination peer receives a request, it will check the
options in the forwarding header. If the destination peer can not cannot
understand the extensive_routing_mode option in the request, it MUST
attempt using to use SRR to return an "Error_Unknown_Extension" response
(defined in Section Sections 6.3.3.1 and Section 14.9 of [I-D.ietf-p2psip-
base]) [RFC6940]) to the sending
peer.

If the routing mode is RPR, the destination peer MUST construct a
destination_list for the response with two entries. entries as defined in
[RFC6940]. The first entry MUST be set to the relay peer peer's Node-ID
from the option in the request request, and the second entry MUST be the
sending peer peer's Node-ID from the option of in 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 Sections 6.3.3.1 and
Section
14.9 of [I-D.ietf-p2psip-base]) [RFC6940]) to the sending peer using SRR.

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

5.4.2. Sending peer: receiving Peer: Receiving a response Response

Upon receiving a response, the peer follows the rules in [I-D.ietf-
p2psip-base]. [RFC6940].
If the sender used RPR and does did not get a response until the timeout,
it MAY either resend the message using either RPR but (but with a different
relay peer (if available), peer, if available) or resend the message
using SRR.

5.4.3. Relay peer processing Peer Processing

Relay peers are designed to forward responses to peers who are not
publicly reachable. For the routing of the response, this document
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].
[RFC6940]. It receives the response, validates the message, re-adjust
readjusts the destination_list destination_list, and forward forwards the response to the next
hop in the destination_list based on the connection table. There is
no added requirement for the relay peer.

6. Overlay configuration extension Configuration Extension

This document uses the new RELOAD overlay configuration element,
"route-mode", inside each "configuration" element, as defined in
Section 7 6 of the DRR document [I-D.ietf-p2psip-drr]. [RFC7263]. The route mode MUST be "RPR".

7. Discovery of relay peers Relay Peers

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 the relay peer as a service and then service; some service
advertisement and discovery mechanism can then also be used for
discovering relay peers, peers -- for example, using the same mechanism as
that used in TURN Traversal Using Relays around NAT (TURN) server
discovery as discussed in base RELOAD [I-D.ietf-p2psip-base]. [RFC6940]. Another option is to let a peer
advertise its capability to be a relay in the response to ATTACH an Attach
or JOIN. Join [RFC6940].

8. Security Considerations

The normative security recommendations of Section 13 of base draft
[I-D.ietf-p2psip-base] [RFC6940] are
applicable to this document. As a routing alternative, the security
part of RPR conforms to Section 13.6 of the
base draft [RFC6940], which describes
routing security. RPR behaves like a DRR requesting node towards the
destination node. The RPR relay node peer is not necessarily an arbitrary
node but SHOULD be a trusted one (managed -- for example, a managed network, a bootstrap nodes node, or a
configured relay) which will make relay peer; it should be a trusted node, because a trusted
node will be less of a
risk risk, as outlined in section13 Section 13 of [RFC6940].

In order to address possible DoS attacks, the based draft. relay peer SHOULD also
limit the number of maximum connections; this is required in order to
also reduce load on the relay peer, as explained in Section 4.1.

9. IANA Considerations

9.1. A new New RELOAD Forwarding Option

A new RELOAD Forwarding Option type is has been added to the "RELOAD
Forwarding Option
Registry Registry" defined in [I-D.ietf-p2psip-base].

Type: 0x02 - [RFC6940].

Code: 2
Forwarding Option: extensive_routing_mode

10. Acknowledgments

David Bryan has helped extensively with this document, 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, Marc Petit-Huguenin Petit-Huguenin, and Carlos
Jesus Bernardos Cano for their constructive comments.

11. References

11.1. Normative References

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

[I-D.ietf-p2psip-base]

[RFC6940] Jennings, C., Lowekamp, B., Rescorla, E., Baset, S., and
H. Schulzrinne, "REsource LOcation And Discovery (RELOAD)
Base Protocol", draft-ietf-p2psip-base-26 (work in
progress), February 2013.

[I-D.ietf-p2psip-drr] RFC 6940, January 2014.

[RFC7263] Zong, N., Jiang, X., Even, R. R., and Y. Zhang, Y., "An extension Extension
to RELOAD the REsource LOcation And Discovery (RELOAD) Protocol
to support Support Direct Response Routing", draft-
ietf-p2psip-drr-11 (work in progress), October 2013. RFC 7263, June 2014.

11.2. Informative References

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

[RFC3424] Daigle, L., L. and IAB, "IAB Considerations for UNilateral
Self-Address Fixing (UNSAF) Across Network Address
Translation", RFC3424, RFC 3424, November 2002.

[RFC5780] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery
Using Session Traversal Utilities for NAT (STUN)",
RFC 5780, May 2010.

Appendix A. Optional methods Methods to investigate peer connectivity Investigate Peer Connectivity

This section is for informational purposes only for providing and provides some
mechanisms that can be used when the configuration information does
not specify if RPR can be used. It summarizes some methods which that can
be used for by 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
whether a peer is publically publicly reachable, other than via out-of-band
mechanisms. This document addresses the UNSAF UNilateral Self-Address Fixing
(UNSAF) [RFC3424] concerns considerations by specifying a fallback plan to SRR [p2psip-base-draft].
[RFC6940]. SRR is not an UNSAF mechanism. The This document does not
define any new UNSAF mechanisms.

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 to
preventing RPR from functioning properly. There are a number of
techniques by which a peer can get its reflexive address on 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 peer to which the address belongs can be a candidate
to serve as a relay peer. Peers which that are not publicly reachable may
still use RPR to shorten the response path path, with the help from relay
peers.

Some conditions that are unique in P2PSIP architecture which could be
leveraged to facilitate the tests. In a P2P overlay network, each
peer
only has partial only a partial view of the whole network, 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 reachable is reachable, are the same as the DRR case. those for DRR. Please refer to DRR
document [I-D.ietf-p2psip-drr]
Appendix A of [RFC7263] for more details.

Appendix B. Comparison on cost of Cost of SRR and RPR

The major advantage of the use of using RPR is that it reduces the number of
intermediate peers traversed by the response. By doing that, it This reduces the load on those peers' resources like load,
such as processing and communication bandwidth. bandwidth, on those peers'
resources.

B.1. Closed or managed networks Managed Networks

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

The number of hops for a response in SRR and in RPR are listed in the
following table. Note that the same types of illustrative settings
can be found in DRR document [I-D.ietf-p2psip-drr]. Appendix B.1 of [RFC7263].

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

Table 1. 1: Comparison of SRR and RPR in closed networks Closed Networks

From the above comparison, it is clear that:

1) In most cases when N the number of peers (N) > 4 (2^2), RPR uses
fewer hops than SRR. Using a shorter route means less overhead
and resource usage on intermediate peers, which is an important
consideration for adopting RPR in the cases where the resources such resources
as CPU and bandwidth are limited, e.g., the case of mobile,
wireless networks.

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

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

B.2. Open networks Networks

In open networks (e.g., the Internet) where RPR is not guaranteed to
work, RPR can fall back to SRR if it fails after trial, as described
in Section 4. 4.2. Based on the same settings of Section 5.1, as those listed in
Appendix B.1, the number of hops, as well as the number of messages
for a response in SRR and RPR RPR, are listed in the following table. table:

Table 2. 2: Comparison of SRR and RPR in open networks Open Networks

From the above comparison, it can be observed that trying to first
use RPR could still provide an overall number of hops lower than
directly using SRR. The detailed analysis is the same as that for
DRR case and can be found in DRR document [I-D.ietf-p2psip-drr]. [RFC7263].

Authors' Addresses

Ning Zong (editor)
Huawei Technologies

Email:

EMail: zongning@huawei.com

Xingfeng Jiang
Huawei Technologies

Email:

EMail: jiang.x.f@huawei.com

Roni Even
Huawei Technologies

Email:

EMail: roni.even@mail01.huawei.com

Yunfei Zhang
CoolPad

Email: / China Mobile

EMail: hishigh@gmail.com