Internet DRAFT - draft-zong-p2psip-rpr
draft-zong-p2psip-rpr
P2PSIP N. Zong
Internet-Draft X. Jiang
Intended status: Standards Track R. Even
Expires: March 22, 2012 Huawei Technologies
Y. Zhang
China Mobile
September 19, 2011
An extension to RELOAD to support Relay Peer Routing
draft-zong-p2psip-rpr-01
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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This Internet-Draft will expire on March 22, 2012.
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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) . . . . . . . . . . . . . . . 6
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 . . . . . . . . . . . . . . 8
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 . . . . . . . . . 10
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 . . . . . . . . . . 12
6.4.3. Relay Peer Processing . . . . . . . . . . . . . . . . 12
7. Discovery Of Relay Peer . . . . . . . . . . . . . . . . . . . 12
8. Optional Methods to Investigate Node Connectivity . . . . . . 12
9. Security Considerations . . . . . . . . . . . . . . . . . . . 13
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
12.1. Normative References . . . . . . . . . . . . . . . . . . . 14
12.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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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.zong-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 node connectivity
described in DRR draft [I-D.zong-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 node 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 [I-D.ietf-behave-nat-behavior-discovery]. Other
terms used in this document are defined inline when used and are also
defined below for reference.
There are two types of roles in the RELOAD architecture: peer and
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client. Node is used when describing both peer and client. In
discussions specific to behavior of a peer or client, the term peer
or client is used instead.
Publicly Reachable: A node is publicly reachable if it can receive
unsolicited messages from any other node in the same overlay. Note:
"publicly" does not mean that the nodes 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 nodes 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 node waits for a response from a destination node. There
are several ways for the destination node to send a response back to
the source node. In this section, we will provide detailed
information on RPR.
Note that the same illustrative settings can be found in DRR draft
[I-D.zong-p2psip-drr].
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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
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 nodes 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 nodes 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
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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.
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
While some mobile deployments may use clients, in mobile networks
using peers, RPR may reduce radio battery usage and bandwidth usage
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.
(Editor's Note: 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
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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
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.zong-p2psip-drr] for more details.
Similarly, the node 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, nodes 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.zong-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.
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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.
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.zong-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.zong-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.zong-p2psip-drr].
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6.2. Modification To RELOAD Message Structure
RELOAD provides an extensible framework to accommodate future
extensions. In this section and in DRR[I-D.zong-p2psip-drr], we
define a ForwardingOption structure to support RPR mode.
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.zong-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.zong-p2psip-drr]. The definition of
the fields is as follow:
Route mode: refers to which type of routing mode is indicated to the
destination peer. Currently, only DRR (specified in DRR draft
[I-D.zong-p2psip-drr]) and RPR are defined.
Transport: 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 node'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_TYPE.
2) The ExtensiveRoutingModeOption structure MUST be used for the
option field within the ForwardingOptions structure. The fields MUST
be defined as follows:
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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.
2.4) Destination structure MUST contain two values. The first MUST
be defined as type peer and set with the values for the relay peer.
The second MUST be defined as type peer 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 5.3.3.1 and Section 13.9 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 node 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 5.3.3.1 and
Section 13.9 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.
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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.
6.4.3. Relay Peer Processing
Relay peers are designed to forward responses to nodes 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.
Editor note: This section will be extended if we adopt RPR, but like
other configuration information, there may be many ways to obtain
this.
8. Optional Methods to Investigate Node 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 node to determine its own network location compared
with NAT. These methods may help a node to decide which routing mode
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it may wish to try. Note that there is no foolproof way to determine
if a node 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 node 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 node 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 nodes to which the address belongs can be a candidate
to serve as a relay peer. Nodes 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 node
only has partial a view of the whole network, and knows of a few
nodes in the overlay. P2P routing algorithms can easily deliver a
request from a sending node to a peer with whom the sending node has
no direct connection. This makes it easy for a node to ask other
nodes to send unsolicited messages back to the requester.
The approaches for a node 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.zong-p2psip-drr] for more details.
9. Security Considerations
TBD
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
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authors would like to thank Ted Hardie, Narayanan Vidya, Dondeti
Lakshminath and Bruce Lowekamp for their constructive comments.
12. References
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-18 (work in
progress), August 2011.
[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-03 (work in progress), October 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[I-D.zong-p2psip-drr] Zong, N., Jiang, X., Even, R. and Zhang, Y.,
"An extension to RELOAD to support Direct Response Routing",
draft-zong-p2psip-drr-01, September 2011.
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.
[I-D.ietf-behave-nat-behavior-discovery] MacDonald, D. and B.
Lowekamp, "NAT Behavior Discovery Using STUN",
draft-ietf-behave-nat-behavior-discovery-04 (work in progress), July
2008.
[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.
Zong, et al. Expires March 22, 2012 [Page 14]
Internet-Draft P2PSIP relay September 2011
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127, RFC 4787,
January 2007.
Authors' Addresses
Ning Zong
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
Zong, et al. Expires March 22, 2012 [Page 15]
