draft-ietf-p2psip-rpr-04.txt   draft-ietf-p2psip-rpr-05.txt 
P2PSIP N. Zong, Ed. P2PSIP N. Zong
Internet-Draft X. Jiang Internet-Draft X. Jiang
Intended status: Standards Track R. Even Intended status: Standards Track R. Even
Expires: August 21, 2013 Huawei Technologies Expires: October 10, 2013 Huawei Technologies
Y. Zhang Y. Zhang
China Mobile April 08, 2013
February 17, 2013
An extension to RELOAD to support Relay Peer Routing An extension to RELOAD to support Relay Peer Routing
draft-ietf-p2psip-rpr-04 draft-ietf-p2psip-rpr-05
Abstract Abstract
This document proposes an optional extension to RELOAD to support This document proposes an optional extension to RELOAD to support
relay peer routing mode. RELOAD recommends symmetric recursive relay peer routing mode. RELOAD recommends symmetric recursive
routing for routing messages. The new optional extension provides a routing for routing messages. The new optional extension provides a
shorter route for responses reducing the overhead on intermediary shorter route for responses reducing the overhead on intermediate
peers and describes the potential cases where this extension can be peers and describes the potential use cases where this extension can
used. be used.
Status of this Memo Status of This Memo
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Backgrounds . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Backgrounds . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 5 3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. Relay Peer Routing (RPR) . . . . . . . . . . . . . . . 5 3.1.1. Relay Peer Routing (RPR) . . . . . . . . . . . . . . 4
3.2. Scenarios Where RPR Benefits . . . . . . . . . . . . . . . 6 3.2. Scenarios where RPR can be beneficial . . . . . . . . . . 5
3.2.1. Managed or Closed P2P System . . . . . . . . . . . . . 6 3.2.1. Managed or closed P2P systems . . . . . . . . . . . . 5
3.2.2. Using Bootstrap Peers as Relay Peers . . . . . . . . . 7 3.2.2. Using bootstrap nodes as relay peers . . . . . . . . 6
3.2.3. Wireless Scenarios . . . . . . . . . . . . . . . . . . 7 3.2.3. Wireless scenarios . . . . . . . . . . . . . . . . . 6
4. Relationship Between SRR and RPR . . . . . . . . . . . . . . . 7 4. Relationship between SRR and RPR . . . . . . . . . . . . . . 6
4.1. How RPR Works . . . . . . . . . . . . . . . . . . . . . . 7 4.1. How RPR works . . . . . . . . . . . . . . . . . . . . . . 6
4.2. How SRR and RPR Work Together . . . . . . . . . . . . . . 7 4.2. How SRR and RPR Work Together . . . . . . . . . . . . . . 7
5. Comparison on cost of SRR and RPR . . . . . . . . . . . . . . 8 5. Comparison on cost of SRR and RPR . . . . . . . . . . . . . . 7
5.1. Closed or managed networks . . . . . . . . . . . . . . . . 8 5.1. Closed or managed networks . . . . . . . . . . . . . . . 7
5.2. Open networks . . . . . . . . . . . . . . . . . . . . . . 9 5.2. Open networks . . . . . . . . . . . . . . . . . . . . . . 8
6. Extensions to RELOAD . . . . . . . . . . . . . . . . . . . . . 9 6. RPR extensions to RELOAD . . . . . . . . . . . . . . . . . . 8
6.1. Basic Requirements . . . . . . . . . . . . . . . . . . . . 9 6.1. Basic requirements . . . . . . . . . . . . . . . . . . . 8
6.2. Modification To RELOAD Message Structure . . . . . . . . . 9 6.2. Modification to RELOAD message structure . . . . . . . . 9
6.2.1. State-keeping Flag . . . . . . . . . . . . . . . . . . 10 6.2.1. State-keeping flag . . . . . . . . . . . . . . . . . 9
6.2.2. Extensive Routing Mode . . . . . . . . . . . . . . . . 10 6.2.2. Extensive routing mode . . . . . . . . . . . . . . . 9
6.3. Creating a Request . . . . . . . . . . . . . . . . . . . . 10 6.3. Creating a request . . . . . . . . . . . . . . . . . . . 10
6.3.1. Creating a request for RPR . . . . . . . . . . . . . . 10 6.3.1. Creating a request for RPR . . . . . . . . . . . . . 10
6.4. Request And Response Processing . . . . . . . . . . . . . 11 6.4. Request and response processing . . . . . . . . . . . . . 10
6.4.1. Destination Peer: Receiving a Request And Sending 6.4.1. Destination peer: receiving a request and sending a
a Response . . . . . . . . . . . . . . . . . . . . . . 11 response . . . . . . . . . . . . . . . . . . . . . . 10
6.4.2. Sending Peer: Receiving a Response . . . . . . . . . . 12 6.4.2. Sending peer: receiving a response . . . . . . . . . 11
6.4.3. Relay Peer Processing . . . . . . . . . . . . . . . . 12 6.4.3. Relay peer processing . . . . . . . . . . . . . . . . 11
7. Discovery Of Relay Peer . . . . . . . . . . . . . . . . . . . 12 7. Discovery of relay peers . . . . . . . . . . . . . . . . . . 12
8. Optional Methods to Investigate Peer Connectivity . . . . . . 13 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 13 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 9.1. A new RELOAD Forwarding Option . . . . . . . . . . . . . 12
10.1. A new RELOAD Forwarding Option . . . . . . . . . . . . . . 14 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14 11.1. Normative References . . . . . . . . . . . . . . . . . . 12
12.1. Normative References . . . . . . . . . . . . . . . . . . . 14 11.2. Informative References . . . . . . . . . . . . . . . . . 13
12.2. Informative References . . . . . . . . . . . . . . . . . . 14 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 Appendix A. Optional methods to investigate peer connectivity . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
1.1. Backgrounds 1.1. Backgrounds
RELOAD [I-D.ietf-p2psip-base] recommends symmetric recursive routing RELOAD [I-D.ietf-p2psip-base] recommends symmetric recursive routing
(SRR) for routing messages and describes the extensions that would be (SRR) for routing messages and describes the extensions that would be
required to support additional routing algorithms. Other than SRR, required to support additional routing algorithms. Other than SRR,
two other routing options: direct response routing (DRR) and relay two other routing options: direct response routing (DRR) and relay
peer routing (RPR) are also discussed in Appendix D in [I-D.ietf- peer routing (RPR) are also discussed in Appendix A of [I-D.ietf-
p2psip-base]. As we show in section 3, RPR is advantageous over SRR p2psip-base]. As we show in section 3, RPR is advantageous over SRR
in some scenarios reducing load (CPU and link BW) on intermediary in some scenarios reducing load (CPU and link bandwidth) on
peers. RPR works better in a network where relay peers are intermediate peers. RPR works better in a network where relay peers
provisioned in advance so that relay peers are publicly reachable in are provisioned in advance so that relay peers are publicly reachable
the P2P system. In other scenarios, using a combination of RPR and in the P2P system. In other scenarios, using a combination of RPR
SRR together is more likely to bring benefits than if SRR is used and SRR together is more likely to bring benefits than if SRR is used
alone. Some discussion on connectivity is in Non-Transitive alone.
Connectivity and DHTs [http://srhea.net/papers/ntr-worlds05.pdf].
Note that in this draft, we focus on RPR routing mode and its Note that in this document, we focus on RPR routing mode and its
extensions to RELOAD to produce a standalone solution. Please refer extensions to RELOAD to produce a standalone solution. Please refer
to DRR draft [I-D.ietf-p2psip-drr] for DRR routing mode. to DRR draft [I-D.ietf-p2psip-drr] for DRR routing mode.
We first discuss the problem statement in Section 3, then how to 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 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 comparison on the cost of SRR and RPR in both managed and open
networks. An extension to RELOAD to support RPR is proposed in networks. An extension to RELOAD to support RPR is proposed in
Section 6. Discovery of relay peers is introduced in Section 7. Section 6. Discovery of relay peers is introduced in Section 7.
Some optional methods to check peer connectivity is introduced in Some optional methods to check peer connectivity are introduced in
Section 8. Appendix A.
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
We use the terminology and definitions from the Concepts and We use the terminology and definitions from the Concepts and
Terminology for Peer to Peer SIP [I-D.ietf-p2psip-concepts] draft Terminology for Peer to Peer SIP [I-D.ietf-p2psip-concepts] draft
extensively in this document. We also use terms defined in NAT extensively in this document. We also use terms defined in NAT
behavior discovery [RFC5780]. Other terms used in this document are behavior discovery [RFC5780]. Other terms used in this document are
defined inline when used and are also defined below for reference. defined inline when used and are also defined below for reference.
Publicly Reachable: A peer is publicly reachable if it can receive Publicly Reachable: A peer is publicly reachable if it can receive
unsolicited messages from any other peer in the same overlay. Note: unsolicited messages from any other peer in the same overlay.
"publicly" does not mean that the peers must be on the public Note: "publicly" does not mean that the peers must be on the
Internet, because the RELOAD protocol may be used in a closed system. public Internet, because the RELOAD protocol may be used in a
closed system.
Relay Peer: A type of publicly reachable peer that can receive Relay Peer: A type of publicly reachable peer that can receive
unsolicited messages from all other peers in the overlay and forward unsolicited messages from all other peers in the overlay and
the responses from destination peers towards the request sender. forward the responses from destination peers towards the sender of
the request.
Relay Peer Routing (RPR): refers to a routing mode in which responses Relay Peer Routing (RPR): refers to a routing mode in which
to P2PSIP requests are sent by the destination peer to a relay peer responses to P2PSIP requests are sent by the destination peer to a
transport address who will forward the responses towards the sending relay peer transport address who will forward the responses
peer. For simplicity, the abbreviation RPR is used instead in the towards the sending peer. For simplicity, the abbreviation RPR is
following text. used instead in the rest of the document.
Symmetric Recursive Routing (SRR): refers to a routing mode in which Symmetric Recursive Routing (SRR): refers to a routing mode in
responses follow the request path in the reverse order to get back to which responses follow the reverse path of the request to get to
the sending peer. For simplicity, the abbreviation SRR is used the sending peer. For simplicity, the abbreviation SRR is used
instead in the following text. instead in the rest of the document.
3. Problem Statement 3. Introduction
RELOAD is expected to work under a great number of application RELOAD is expected to work under a great number of application
scenarios. The situations where RELOAD is to be deployed differ scenarios. The situations where RELOAD is to be deployed differ
greatly. For instance, some deployments are global, such as a Skype- greatly. For instance, some deployments are global, such as a Skype-
like system intended to provide public service. Some run in closed like system intended to provide public service, while others run in
networks of small scale. SRR works in any situation, but RPR may closed networks of small scale. SRR works in any situation, but RPR
work better in some specific scenarios. may work better in some specific scenarios.
3.1. Overview 3.1. Overview
RELOAD is a simple request-response protocol. After sending a RELOAD is a simple request-response protocol. After sending a
request, a peer waits for a response from a destination peer. There 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 are several ways for the destination peer to send a response back to
the source peer. In this section, we will provide detailed the source peer. In this section, we will provide detailed
information on RPR. information on RPR.
Note that the same illustrative settings can be found in DRR draft Note that the same illustrative settings can be found in DRR draft
skipping to change at page 5, line 41 skipping to change at page 5, line 4
RELOAD is a simple request-response protocol. After sending a RELOAD is a simple request-response protocol. After sending a
request, a peer waits for a response from a destination peer. There 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 are several ways for the destination peer to send a response back to
the source peer. In this section, we will provide detailed the source peer. In this section, we will provide detailed
information on RPR. information on RPR.
Note that the same illustrative settings can be found in DRR draft Note that the same illustrative settings can be found in DRR draft
[I-D.ietf-p2psip-drr]. [I-D.ietf-p2psip-drr].
3.1.1. Relay Peer Routing (RPR) 3.1.1. Relay Peer Routing (RPR)
If peer A knows it is behind a NAT or NATs, and knows one or more 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 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 RPR. Assume A is associated with relay peer R. When sending the
request, peer A includes information describing peer R transport request, peer A includes information describing peer R transport
address in the request. When peer X receives the request, peer X 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 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 the existing connection. Figure 1 illustrates RPR. Note that RPR
for responses compared to SRR, which means less overhead on also allows a shorter route for responses compared to SRR, which
intermediary peers. Establishing a connection to the relay with TLS means less overhead on intermediate peers. Establishing a connection
requires multiple round trips. Please refer to Section 5 for cost to the relay with TLS requires multiple round trips. Please refer to
comparison between SRR and RPR. 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 A B C D X R
| Request | | | | | | Request | | | | |
|----------->| | | | | |----------->| | | | |
| | Request | | | | | | Request | | | |
| |----------->| | | | | |----------->| | | |
| | | Request | | | | | | Request | | |
| | |----------->| | | | | |----------->| | |
| | | | Request | | | | | | Request | |
| | | |----------->| | | | | |----------->| |
| | | | | Response | | | | | | Response |
| | | | |---------->| | | | | |---------->|
| | | | Response | | | | | | Response | |
|<-----------+------------+------------+------------+-----------| |<-----------+------------+------------+------------+-----------|
| | | | | | | | | | | |
3.2. Scenarios Where RPR Benefits Figure 1, 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 a 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 message, the responding peer can
announce that it can serve as a relay peer.
3.2. Scenarios where RPR can be beneficial
In this section, we will list several scenarios where using RPR would In this section, we will list several scenarios where using RPR would
provide improved performance. provide an improved performance.
3.2.1. Managed or Closed P2P System 3.2.1. Managed or closed P2P systems
As described in Section 3.2.1, many P2P systems run in a closed or As described in Section 3.2.1 of DRR draft [I-D.ietf-p2psip-drr],
managed environment so that network administrators can better manage many P2P systems run in a closed or managed environment so that
their system. For example, the network administrator can deploy network administrators can better manage their system. For example,
several relay peers which are publicly reachable in the system and the network administrator can deploy several relay peers which are
indicate their presence in the configuration file. After learning publicly reachable in the system and indicate their presence in the
where these relay peers are, peers behind NATs can use RPR with the configuration file. After learning where these relay peers are,
help from these relay peers. Peers must also support SRR in case RPR peers behind NATs can use RPR with the help from these relay peers.
fails. Peers MUST also support SRR in case RPR fails.
Another usage is to install relay peers on the managed network Another usage is to install relay peers on the managed network
boundary allowing external peers to send responses to peers inside boundary allowing external peers to send responses to peers inside
the managed network. the managed network.
3.2.2. Using Bootstrap Peers as Relay Peers 3.2.2. Using bootstrap nodes as relay peers
Bootstrap peers must be publicly reachable in a RELOAD architecture. Bootstrap nodes are typically publicly reachable in a RELOAD
As a result, one possible architecture would be to use the bootstrap architecture. As a result, one possible architecture would be to use
peers as relay peers for use with RPR. The requirements for being a the bootstrap nodes as relay peers for use with RPR. A relay peer
relay peer are publicly accessible and maintaining a direct SHOULD be publicly accessible and maintaining a direct connection
connection with its client. As such, bootstrap peers are well suited with its client. As such, bootstrap nodes are well suited to play
to play the role of relay peers. the role of relay peers.
3.2.3. Wireless Scenarios 3.2.3. Wireless scenarios
In some mobile deployments, using RPR may help with reducing radio In some mobile deployments, using RPR may help reducing radio battery
battery usage and bandwidth by the intermediary peers. The service usage and bandwidth by the intermediate peers. The service provider
provider may recommend in the configuration using RPR based on his may recommend using RPR based on his knowledge of the topology.
knowledge of the topology. Such relay peers may also help
connectivity to external networks.
4. Relationship Between SRR and RPR 4. Relationship between SRR and RPR
4.1. How RPR Works 4.1. How RPR works
Peers using RPR must maintain a connection with their relay peer(s). Peers using RPR MUST maintain a connection with their relay peer(s).
This can be done in the same way as establishing a neighbor This can be done in the same way as establishing a neighbor
connection between peers by using the Attach method. connection between peers by using the Attach method.
A requirement for RPR is for the source peer to convey their relay 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 (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 knows where the relay peer are and send the response to a relay
peer first. The request should include also the requesting peer peer first. The request SHOULD include also the requesting peer
information enabling the relay peer to route the response back to the information enabling the relay peer to route the response back to the
right peer. right peer.
Note that being a relay peer does not require that the relay 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, more functionality than an ordinary peer. As discussed later, relay
relay peers comply with the same procedure as an ordinary peer to peers comply with the same procedure as an ordinary peer to forward
forward messages. The only difference is that there may be a larger messages. The only difference is that there may be a larger traffic
traffic burden on relay peers. Relay peers can decide whether to burden on relay peers. Relay peers can decide whether to accept a
accept a new connection based on their current burden. new connection based on their current burden.
4.2. How SRR and RPR Work Together 4.2. How SRR and RPR Work Together
RPR is not intended to replace SRR. As seen from Section 3, RPR has RPR is not intended to replace SRR. It is better to use these two
better performance in some scenarios, but have limitations as well, modes together to adapt to each peer's specific situation. Note that
see for example section 4.3 in Non-Transitive Connectivity and DHTs the informative suggestions on how to transition between SRR and RPR
[http://srhea.net/papers/ntr-worlds05.pdf]. As a result, it is (e.g. compute success rate of RPR, fall back to SRR, etc) are the
better to use these two modes together to adapt to each peer's same with that of DRR. Please refer to DRR draft [I-D.ietf-p2psip-
specific situation. Note that the informative suggestions on how to drr] for more details. Similarly, the peer can decide whether to try
transition between SRR and RPR (e.g. compute success rate of RPR, RPR based on other information such as configuration file
fall back to SRR, etc) are same with that on DRR and RPR. Please information. If a relay peer is provided by the service provider,
refer to DRR draft [I-D.ietf-p2psip-drr] for more details. peers MAY prefer RPR over SRR.
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 5. Comparison on cost of SRR and RPR
The major advantages in using RPR are in going through less The major advantage of the use of RPR is that it reduces the number
intermediary peers on the response. By doing that it reduces the of intermediate peers traversed by the response. By doing that, it
load on those peers' resources like processing and communication reduces the load on those peers' resources like processing and
bandwidth. communication bandwidth.
5.1. Closed or managed networks 5.1. Closed or managed networks
As described in Section 3, many P2P systems run in a closed or As described in Section 3, many P2P systems run in a closed or
managed environment (e.g. carrier networks) so that network managed environment (e.g. carrier networks) so that network
administrators would know that they could safely use RPR. administrators would know that they could safely use RPR.
The number of hops for a response in SRR and RPR are listed in the 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 following table. Note that the same illustrative settings can be
found in DRR draft [I-D.ietf-p2psip-drr]. found in DRR draft [I-D.ietf-p2psip-drr].
Mode | Success | No. of Hops | No. of Msgs Mode | Success | No. of Hops | No. of Msgs
---------------------------------------------------- ----------------------------------------------------
SRR | Yes | logN | logN SRR | Yes | log(N) | log(N)
RPR | Yes | 2 | 2 RPR | Yes | 2 | 2
RPR(DTLS) | Yes | 2 | 7+2 RPR(DTLS) | Yes | 2 | 7+2
Table 1, comparison of SRR and RPR in closed networks
From the above comparison, it is clear that: From the above comparison, it is clear that:
1) In most cases of N > 4 (2^2), RPR has fewer hops than SRR. 1) In most cases when N > 4 (2^2), RPR uses fewer hops than SRR.
Shorter route means less overhead and resource usage on intermediary Using a shorter route means less overhead and resource usage on
peers, which is an important consideration for adopting RPR in the intermediate peers, which is an important consideration for adopting
cases where the resource such as CPU and BW is limited, e.g. the case RPR in the cases where the resources such as CPU and bandwidth are
of mobile, wireless network. limited, e.g. the case of mobile, wireless networks.
2) In the cases of N > 512 (2^9), RPR also has fewer messages than 2) In the cases when N > 512 (2^9), RPR also uses fewer messages than
SRR. SRR.
3) In the cases where N < 512, RPR has more messages than SRR (but 3) In the cases when N < 512, RPR uses more messages than SRR (but
still has fewer hops than SRR). So the consideration to use RPR or still uses fewer hops than SRR). So the consideration on whether
SRR depends on other factors like using less resources (bandwidth and using RPR or SRR depends on other factors like using less resources
processing) from the intermediaries peers. Section 4 provides use (bandwidth and processing) from the intermediate peers. Section 4
cases where RPR has better chance to work or where the intermediary provides use cases where RPR has better chance to work or where the
resources considerations are important. intermediary resources considerations are important.
5.2. Open networks 5.2. Open networks
In open network where RPR is not guaranteed, RPR can fall back to SRR In open networks where RPR is not guaranteed to work, RPR can fall
If it fails after trial, as described in Section 4. Based on the back to SRR if it fails after trial, as described in Section 4.
same settings in Section 5.1, the number of hops, number of messages Based on the same settings in Section 5.1, the number of hops, number
for a response in SRR and RPR are listed in the following table. of messages for a response in SRR and RPR are listed in the following
table.
Mode | Success | No. of Hops | No. of Msgs Mode | Success | No. of Hops | No. of Msgs
----------------------------------------------------------- -----------------------------------------------------------
SRR | Yes | logN | logN SRR | Yes | logN | logN
RPR | Yes | 2 | 2 RPR | Yes | 2 | 2
| Fail&Fall back to SRR | 2+logN | 2+logN | Fail&Fall back to SRR | 2+logN | 2+logN
RPR(DTLS) | Yes | 2 | 7+2 RPR(DTLS) | Yes | 2 | 7+2
| Fail&Fall back to SRR | 2+logN | 9+logN | Fail&Fall back to SRR | 2+logN | 9+logN
From the above comparison, it can be observed that: Table 2, comparison of SRR and RPR in open networks
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, From the above comparison, it can be observed that trying to first
it is still possible that RPR has fewer messages than SRR. use RPR could still provide an overall number of hops lower than
Otherwise, the consideration to use RPR or SRR depends on other directly using SRR. The detailed analysis is same as DRR case and
factors like using less resources from the intermediaries peers. can be found in DRR draft [I-D.ietf-p2psip-drr].
6. Extensions to RELOAD 6. RPR extensions to RELOAD
Adding support for RPR requires extensions to the current RELOAD Adding support for RPR requires extensions to the current RELOAD
protocol. In this section, we define the changes required to the protocol. In this section, we define the extensions required to the
protocol, including changes to message structure and to message protocol, including extensions to message structure and to message
processing. processing.
6.1. Basic Requirements 6.1. Basic requirements
All peers implementing RPR MUST support SRR.
All peers MUST be able to process requests for routing in SRR, and All peers MUST be able to process requests for routing in SRR, and
MAY support RPR routing requests. MAY support RPR routing requests.
6.2. Modification To RELOAD Message Structure 6.2. Modification to RELOAD message structure
RELOAD provides an extensible framework to accommodate future RELOAD provides an extensible framework to accommodate future
extensions. In this section, we define a ForwardingOption structure extensions. In this section, we define a ForwardingOption structure
and present a state-keeping flag to support RPR mode. and present a state-keeping flag to support RPR mode.
6.2.1. State-keeping Flag 6.2.1. State-keeping flag
flag : 0x08 IGNORE-STATE-KEEPING flag : 0x08 IGNORE-STATE-KEEPING
If IGNORE-STATE-KEEPING is set, any peer receiving this message and If IGNORE-STATE-KEEPING is set, any peer receiving this message and
which is not the destination of the message SHOULD forward the which is not the destination of the message SHOULD forward the
message with the full via_list and SHOULD not maintain any internal message with the full via_list and SHOULD NOT maintain any internal
state. state.
6.2.2. Extensive Routing Mode 6.2.2. Extensive routing mode
We first define a new type to define the new option, We first define a new type to define the new option,
extensive_routing_mode: extensive_routing_mode:
The option value will be illustrated in the following figure, The option value is illustrated in the following figure, defining the
defining the ExtensiveRoutingModeOption structure: ExtensiveRoutingModeOption structure:
enum {(0),DRR(1),RPR(2),(255)} RouteMode; enum {(0),DRR(1),RPR(2),(255)} RouteMode;
struct { struct {
RouteMode routemode; RouteMode routemode;
OverlayLinkType transport; OverlayLinkType transport;
IpAddressPort ipaddressport; IpAddressPort ipaddressport;
Destination destinations<1..2^8-1>; Destination destinations<1..2^8-1>;
} ExtensiveRoutingModeOption; } ExtensiveRoutingModeOption;
Note that DRR value in RouteMode is defined in DRR draft [I-D.ietf- Note that DRR value in RouteMode is defined in DRR draft [I-D.ietf-
skipping to change at page 10, line 47 skipping to change at page 10, line 5
deliver responses from the destination peer to the relay peer. deliver responses from the destination peer to the relay peer.
IpAddressPort: refers to the transport address that the destination IpAddressPort: refers to the transport address that the destination
peer should use to send the response to. This will be a relay peer peer should use to send the response to. This will be a relay peer
address for RPR. address for RPR.
Destination: refers to the relay peer itself. If the routing mode is Destination: refers to the relay peer itself. If the routing mode is
RPR, then the destination contains two destinations, which are the RPR, then the destination contains two destinations, which are the
relay peer's Node-ID and the sending peer's Node-ID. relay peer's Node-ID and the sending peer's Node-ID.
6.3. Creating a Request 6.3. Creating a request
6.3.1. Creating a request for RPR 6.3.1. Creating a request for RPR
When using RPR for a transaction, the sending peer MUST set the When using RPR for a transaction, the sending peer MUST set the
IGNORE-STATE-KEEPING flag in the ForwardingHeader. Additionally, the IGNORE-STATE-KEEPING flag in the ForwardingHeader. Additionally, the
peer MUST construct and include a ForwardingOptions structure in the peer MUST construct and include a ForwardingOptions structure in the
ForwardingHeader. When constructing the ForwardingOption structure, ForwardingHeader. When constructing the ForwardingOption structure,
the fields MUST be set as follows: the fields MUST be set as follows:
1) The type MUST be set to extensive_routing_mode. 1) The type MUST be set to extensive_routing_mode.
skipping to change at page 11, line 26 skipping to change at page 10, line 33
2.2) transport set as appropriate for the relay peer. 2.2) transport set as appropriate for the relay peer.
2.3) ipaddressport set to the transport address of 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. that the sender wishes the message to be relayed through.
2.4) destination structure MUST contain two values. The first MUST 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. 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 The second MUST be defined as type node and set with the sending
peer's own values. peer's own values.
6.4. Request And Response Processing 6.4. Request and response processing
This section gives normative text for message processing after RPR is This section gives normative text for message processing after RPR is
introduced. Here, we only describe the additional procedures for introduced. Here, we only describe the additional procedures for
supporting RPR. Please refer to [I-D.ietf-p2psip-base] for RELOAD supporting RPR. Please refer to [I-D.ietf-p2psip-base] for RELOAD
base procedures. base procedures.
6.4.1. Destination Peer: Receiving a Request And Sending a Response 6.4.1. Destination peer: receiving a request and sending a response
When the destination peer receives a request, it will check the When the destination peer receives a request, it will check the
options in the forwarding header. If the destination peer can not options in the forwarding header. If the destination peer can not
understand extensive_routing_mode option in the request, it MUST understand extensive_routing_mode option in the request, it MUST
attempt to use SRR to return an "Error_Unknown_Extension" response attempt using SRR to return an "Error_Unknown_Extension" response
(defined in Section 6.3.3.1 and Section 14.9 in [I-D.ietf-p2psip- (defined in Section 6.3.3.1 and Section 14.9 of [I-D.ietf-p2psip-
base]) to the sending peer. base]) to the sending peer.
If the routing mode is RPR, the destination peer MUST construct a If the routing mode is RPR, the destination peer MUST construct a
destination_list for the response with two entries. The first MUST 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 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 the second MUST be the sending peer Node-ID from the option of the
request. request.
In the event that the routing mode is set to RPR and there are not 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 exactly two destinations, the destination peer MUST try to send an
"Error_Unknown_Extension" response (defined in Section 6.3.3.1 and "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 Section 14.9 of [I-D.ietf-p2psip-base]) to the sending peer using
SRR. SRR.
After the peer constructs the destination_list for the response, it After the peer constructs the destination_list for the response, it
sends the response to the transport address which is indicated in the sends the response to the transport address which is indicated in the
ipaddressport field in the option using the specific transport mode ipaddressport field in the option using the specific transport mode
in the Forwardingoption. If the destination peer receives a in the Forwardingoption. If the destination peer receives a
retransmit with SRR preference on the message it is trying to retransmit with SRR preference on the message it is trying to
response to now, the responding peer should abort the RPR response response to now, the responding peer SHOULD abort the RPR response
and use SRR. and use SRR.
6.4.2. Sending Peer: Receiving a Response 6.4.2. Sending peer: receiving a response
Upon receiving a response, the peer follows the rules in [I-D.ietf- 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 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 until the timeout, it MAY either resend the message using RPR but
with a different relay peer (if available), or resend the message with a different relay peer (if available), or resend the message
using SRR. using SRR.
6.4.3. Relay Peer Processing 6.4.3. Relay peer processing
Relay peers are designed to forward responses to peers who are not Relay peers are designed to forward responses to peers who are not
publicly reachable. For the routing of the response, this draft publicly reachable. For the routing of the response, this document
still uses the destination_list. The only difference from SRR is still uses the destination_list. The only difference from SRR is
that the destination_list is not the reverse of the via_list, instead that the destination_list is not the reverse of the via_list.
it is constructed from the forwarding option as described below. Instead, it is constructed from the forwarding option as described
below.
When a relay peer receives a response, it MUST follow the rules in When a relay peer receives a response, it MUST follow the rules in
[I-D.ietf-p2psip-base]. It receives the response, validates the [I-D.ietf-p2psip-base]. It receives the response, validates the
message, re-adjust the destination_list and forward the response to message, re-adjust the destination_list and forward the response to
the next hop in the destination_list based on the connection table. the next hop in the destination_list based on the connection table.
There is no added requirement for relay peer. There is no added requirement for relay peer.
7. Discovery Of Relay Peer 7. Discovery of relay peers
There are several ways to distribute the information about relay There are several ways to distribute the information about relay
peers throughout the overlay. P2P network providers can deploy some peers throughout the overlay. P2P network providers can deploy some
relay peers and advertise them in the configuration file. With the relay peers and advertise them in the configuration file. With the
configuration file at hand, peers can get relay peers to try RPR. 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 Another way is to consider relay peer as a service and then some
service advertisement and discovery mechanism can also be used for service advertisement and discovery mechanism can also be used for
discovering relay peers, for example, using the same mechanism as discovering relay peers, for example, using the same mechanism as
used in TURN server discovery in base RELOAD [I-D.ietf-p2psip-base]. 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 Another option is to let a peer advertise his capability to be a
relay in the response to ATTACH or JOIN. relay in the response to ATTACH or JOIN.
8. Optional Methods to Investigate Peer Connectivity 8. Security Considerations
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
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 As a routing alternative, the security part of RPR conforms to
section 13.6 in based draft [I-D.ietf-p2psip-base] which describes section 13.6 of the base draft [I-D.ietf-p2psip-base] which describes
routing security. routing security. RPR behave like a DRR requesting node towards the
destination node. The RPR relay node is not an arbitrary node but
SHOULD be a trusted one (managed network, bootstrap nodes or
configured relay) which will make it less of a risk as outlined in
section13 of the based draft.
10. IANA Considerations 9. IANA Considerations
10.1. A new RELOAD Forwarding Option 9.1. A new RELOAD Forwarding Option
A new RELOAD Forwarding Option type is added to the Forwarding Option A new RELOAD Forwarding Option type is added to the Forwarding Option
Registry defined in [I-D.ietf-p2psip-base]. Registry defined in [I-D.ietf-p2psip-base].
Type: 0x02 - extensive_routing_mode Type: 0x02 - extensive_routing_mode
11. Acknowledgements 10. Acknowledgements
David Bryan has helped extensively with this document, and helped David Bryan has helped extensively with this document, and helped
provide some of the text, analysis, and ideas contained here. The provide some of the text, analysis, and ideas contained here. The
authors would like to thank Ted Hardie, Narayanan Vidya, Dondeti authors would like to thank Ted Hardie, Narayanan Vidya, Dondeti
Lakshminath, Bruce Lowekamp, Stephane Bryant and Marc Petit-Huguenin Lakshminath, Bruce Lowekamp, Stephane Bryant, Marc Petit-Huguenin and
for their constructive comments. Carlos Jesus Bernardos Cano for their constructive comments.
12. References 11. References
12.1. Normative References 11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[I-D.ietf-p2psip-base] Jennings, C., Lowekamp, B., Rescorla, E., [I-D.ietf-p2psip-base] Jennings, C., Lowekamp, B., Rescorla, E.,
Baset, S., and H. Schulzrinne, "REsource LOcation And Discovery Baset, S., and H. Schulzrinne, "REsource LOcation And Discovery
(RELOAD) Base Protocol", draft-ietf-p2psip-base-22 (work in (RELOAD) Base Protocol", draft-ietf-p2psip-base-26 (work in
progress), July 2012. progress), February 2013.
12.2. Informative References 11.2. Informative References
[ChurnDHT] Rhea, S., "Handling Churn in a DHT", Proceedings of the [ChurnDHT] Rhea, S., "Handling Churn in a DHT", Proceedings of the
USENIX Annual Technical Conference. Handling Churn in a DHT, June USENIX Annual Technical Conference. Handling Churn in a DHT, June
2004. 2004.
[DTLS] Modadugu, N., Rescorla, E., "The Design and Implementation of [DTLS] Modadugu, N., Rescorla, E., "The Design and Implementation of
Datagram TLS", 11th Network and Distributed System Security Symposium Datagram TLS", 11th Network and Distributed System Security Symposium
(NDSS), 2004. (NDSS), 2004.
[RFC5780] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery [RFC5780] MacDonald, D. and B. Lowekamp, "NAT Behavior Discovery
Using STUN", RFC5780, May 2010. Using STUN", RFC5780, May 2010.
[I-D.ietf-behave-tcp] Guha, S., Biswas, K., Ford, B., Sivakumar, S., [RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.
and P. Srisuresh, "NAT Behavioral Requirements for TCP", Srisuresh, "NAT Behavioral Requirements for TCP", RFC5382, October
draft-ietf-behave-tcp-08 (work in progress), September 2008. 2008.
[I-D.lowekamp-mmusic-ice-tcp-framework] Lowekamp, B. and A. Roach, "A [I-D.lowekamp-mmusic-ice-tcp-framework] Lowekamp, B. and A. Roach,
Proposal to Define Interactive Connectivity Establishment for the "A Proposal to Define Interactive Connectivity Establishment for the
Transport Control Protocol (ICE-TCP) as an Extensible Framework", Transport Control Protocol (ICE-TCP) as an Extensible Framework",
draft-lowekamp-mmusic-ice-tcp-framework-00 (work in progress), draft-lowekamp-mmusic-ice-tcp-framework-00 (work in progress),
October 2008. October 2008.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation [RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127, RFC 4787, (NAT) Behavioral Requirements for Unicast UDP", BCP 127, RFC 4787,
January 2007. January 2007.
[I-D.ietf-p2psip-drr] Zong, N., Jiang, X., Even, R. and Zhang, Y., [I-D.ietf-p2psip-drr] Zong, N., Jiang, X., Even, R. and Zhang, Y.,
"An extension to RELOAD to support Direct Response Routing", "An extension to RELOAD to support Direct Response Routing", draft-
draft-ietf-p2psip-drr-04, February 2013. ietf-p2psip-drr-05, April 2013.
[I-D.ietf-p2psip-concepts] Bryan, D., Matthews, P., Shim, E., Willis, [I-D.ietf-p2psip-concepts] Bryan, D., Matthews, P., Shim, E., Willis,
D., and S. Dawkins, "Concepts and Terminology for Peer to Peer SIP", D., and S. Dawkins, "Concepts and Terminology for Peer to Peer SIP",
draft-ietf-p2psip-concepts-04 (work in progress), October 2011. draft-ietf-p2psip-concepts-04 (work in progress), October 2011.
12. References
Appendix A. 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
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 reachable is same as the DRR case. Please refer to DRR
draft [I-D.ietf-p2psip-drr] for more details.
Authors' Addresses Authors' Addresses
Ning Zong (editor) Ning Zong
Huawei Technologies Huawei Technologies
Email: zongning@huawei.com Email: zongning@huawei.com
Xingfeng Jiang Xingfeng Jiang
Huawei Technologies Huawei Technologies
Email: jiang.x.f@huawei.com Email: jiang.x.f@huawei.com
Roni Even Roni Even
Huawei Technologies Huawei Technologies
Email: even.roni@huawei.com Email: roni.even@mail01.huawei.com
Yunfei Zhang Yunfei Zhang
China Mobile
Email: zhangyunfei@chinamobile.com Email: hishigh@gmail.com
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