DECADE L. Chen
Internet-Draft H. Liu
Intended status: Informational Yale University
Expires: October 31, 2011 April 29, 2011
Leveraging In-network Storage in P2P LiveStreaming
draft-ietf-decade-integration-example-00
Abstract
DECADE is an in-network storage infrastructure which is under
discussions and constructions. It can be integrated into Peer-to-
Peer (P2P) applications to achieve more efficient content
distributions. This document represents a detailed example of how to
integrate DECADE into P2P live streaming (a popular P2P application).
Specifically, it describes mainly about: 1) a preliminary DECADE
client API; 2) a P2P live streaming integration with DECADE; 3) a
testing on our DECADE integrarion and 4) an application performance
analysis from the test.
Status of this Memo
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Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. DECADE Server . . . . . . . . . . . . . . . . . . . . . . 3
2.2. DECADE Module . . . . . . . . . . . . . . . . . . . . . . 3
2.3. P2P LiveStreaming Client (P2PLS Client) . . . . . . . . . 4
2.4. DECADE Client . . . . . . . . . . . . . . . . . . . . . . 4
3. DECADE Client API . . . . . . . . . . . . . . . . . . . . . . 4
4. DECADE Integration of P2P LiveStreaming Client . . . . . . . . 5
4.1. DECADE Integration Architecture . . . . . . . . . . . . . 5
4.1.1. Data Access . . . . . . . . . . . . . . . . . . . . . 5
4.1.2. Message Control . . . . . . . . . . . . . . . . . . . 6
4.2. Challenges in DECADE Integration . . . . . . . . . . . . . 6
4.2.1. Limited Connection Slot . . . . . . . . . . . . . . . 6
4.2.2. Additional Control Latency . . . . . . . . . . . . . . 7
5. Test Environment and Settings . . . . . . . . . . . . . . . . 7
5.1. Test Settings . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Platforms and Components . . . . . . . . . . . . . . . . . 8
5.2.1. EC2 DECADE Server . . . . . . . . . . . . . . . . . . 9
5.2.2. PlanetLab P2P Live Streaming Client . . . . . . . . . 9
5.2.3. Tracker . . . . . . . . . . . . . . . . . . . . . . . 9
5.2.4. Source Server . . . . . . . . . . . . . . . . . . . . 9
5.2.5. Test Controller . . . . . . . . . . . . . . . . . . . 9
6. Performance Analysis . . . . . . . . . . . . . . . . . . . . . 9
6.1. Performance Metrics . . . . . . . . . . . . . . . . . . . 9
6.2. Result and Analysis . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Normative References . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
DECADE is an in-network storage infrastructure under discussions and
constructions. It can be integrated into Peer-to-Peer (P2P)
applications to achieve more efficient content distributions.
This draft introduces an instance of application integration with
DECADE. In our example system, the core component includes DECADE
servers and DECADE-enabled P2P live streaming clients. A DECADE
server provides data storage and transport service with interactive
control to DECADE clients. We extended a P2P live streaming
application, P2PLS (P2P LiveStreaming), to leverage DECADE service
provided by the servers. P2PLS clients are DECADE-enabled. For our
implementation, we used a preliminary API (Application Programming
Interface) set, which is supposed to be provided by DECADE, to enable
P2PLS clients to use DECADE in their data transmission. In this
draft, we introduce the design of the DECADE-P2PLS integration
system, the main control flow for DECADE-enabled data transmission,
and the testing performance with this system.
Please note that P2PLS in this draft only represents the usage case
of "live streaming" out of a large number of P2P applications, while
DECADE itself can support other applications. The API set used in
this system is an experimental design and implementation. It is not
a standard and is still under development. Currently, DECADE in this
draft is only a preliminary framework of in-network storage for P2P.
It is designed to test the pros and cons of in-network storage
utilized by P2P applications rather than to reach a final solution.
2. Concepts
2.1. DECADE Server
A DECADE server is implemented with DECADE protocols, management
mechanism, and storage strategies. It is a core element to provide
DECADE service. Each DECADE server manages a number of Data Lockers,
each of which is a virtual account and corresponds to private storage
space for clients.
2.2. DECADE Module
DECADE module is a functional component for application clients to
utilize DECADE. This component serves as an application-specific
interface between a particular application and DECADE servers. It
can be a simple implementation of basic DECADE access APIs, or a more
intelligent integration, e.g. consider application-specific control
strategies when using DECADE APIs.
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2.3. P2P LiveStreaming Client (P2PLS Client)
P2P LiveStreaming Client (P2PLS Client) is our self-maintained
version of a native P2P live streaming application. It is one
example out of a large number of P2P applications.
2.4. DECADE Client
DECADE client is an integration of a native P2PLS Client and a DECADE
module. It is not required to embed DECADE module into native P2P
clients, since it can also be an independent component running at a
remote server.
3. DECADE Client API
In order to simplify the DECADE integration with P2P clients, we
provide an API set which covers the communications with DECADE
servers and token-generation. On top of this API, a P2P client can
develop its own application-specific control and data distribution
policies.
There are five basic interfaces:
o Get_Object: to get an object from a DECADE server with an
authorized token. The get operation can be classified into two
categories: Local Get and Remote Get. Local Get is to get an
object from a local DECADE server. Remote Get is to use a
client's local DECADE server to indirectly get an object from a
remote DECADE server. The object will be firstly passed to the
local DECADE server, then returned to the application client
o Put_Object: to store an object into a DECADE server with an
authorized token. A client can either store an object into its
local DECADE server or into other clients' DECADE servers, if it
has an authorized token. Both of the operations are direct, for
we don't provide indirectly storing (i.e. remote put).
o Delete_Object: to delete an object in a DECADE server explicitly
with an authorized token. Note that an object can also be deleted
implicitly by setting an expired time or a specific TTL.
o Status_Query: to query current status of an application itself,
including listing stored objects, resource usage, etc.. Such
information is private.
o Generate_Token: to generate an authorized token. The token can be
used to access an application client's local DECADE server, or
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passed to other clients to allow them to access the client's local
DECADE server.
4. DECADE Integration of P2P LiveStreaming Client
We integrate a DECADE module into a P2P live streaming application--
P2PLS, in order that clients of this application can easily leverage
DECADE in their data distributions.
4.1. DECADE Integration Architecture
The architecture of the P2PLS application and DECADE integration is
shown in Figure 1:
+---------------+ +---------------+
| DECADE | | DECADE |
| Peer | | Peer |
|+-------------+| +---------------+ |+-------------+|
||DECADE Module||---| DECADE Server |---||DECADE Module||
|+------^------+| +---------------+ |+------^------+|
| API | | | API | |
|+------v------+| +---------------+ |+------v------+|
||Native Client||---| Tracker |---||Native Client||
|+-------------+| +---------------+ |+-------------+|
+---------------+ +---------------+
Figure 1
A DECADE-integrated P2PLS client uses DECADE client to communicate
with its DECADE server and transmit data between itself and its
DECADE server. It is compatible with its original P2P protocol,
while it also uses a DECADE protocol to exchange DECADE related
messages with other peers.
4.1.1. Data Access
DECADE module is called whenever a client wants to get data objects
from (or put data objects into) its DECADE server. Each data object
transferred between a client and its DECADE server should go through
DECADE module. Neither the DECADE server and the original client
knows each other. A data object is a data transfer unit between
DECADE servers and application clients. Its size can be application-
customized, according to variable requirements of performance or
sensitive factors (e.g. low latency, high bandwidth utilization).
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4.1.2. Message Control
Control and data plane decoupling is a design principle of DECADE.
Control messages are propagated in an original P2P way. DECADE only
introduces an additional control message between DECADE module which
carries DECADE authorized token. By exchanging DECADE authorized
tokens, P2P live streaming clients can retrieve or store data objects
into or from others' DECADE servers.
4.2. Challenges in DECADE Integration
One essential objective of DECADE integration is to improve (or at
least not to hurt) the application performance. However, as a brand
new architecture, DECADE has some inherit challenges which will
potentially be harmful to application performance. In our P2P live
streaming case, we met mainly two such limitations of DECADE:
4.2.1. Limited Connection Slot
Limited Connection Slot: In native P2P systems, a peer can establish
tens or hunderds of concurrent connections with other peers.
However, this situation can hardly be ture when the application is
integrated with DECADE, because it is too expensive for a DECADE
server to maintain so many connections for each peer. Typically,
each DECADE peer only have m connection slots, which means it can
only at most have m active connections with its DECADE server
simultaneously. A potential "side effect" of limited connection slot
is that the content availability and downloading rate might be
impacted negatively by fewwer connections carrying data traffic.
This requests us to adjust the peer's behavior in resource
allocation, downloading/uploading scheduling, etc. to fully utilize
the connection slots to archieve a satisfying and robust data
downloading.
In our integration, we mainly employed two technical strategies:
o Batch Request: In order to fully utilize the connection bandwidth
of a DECADE server and reduce overhead, a P2PLS client may combine
multiple requests in a single request to DECADE server. Note that
for the sake of improving data transfer efficiency in P2P live
streaming, we may combine multiple data requests into a batch
request. Generally, a batch may consist of different kinds of
access requests.
o Larger Data Object Size: In typical P2P live streaming
application, the size of a data block is relatively small,
considering to reduce end-to-end transport latency. However,
existing data size may incur large control overhead and low
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transport utilization. A larger data object size may be needed to
utilize DECADE more efficiently.
4.2.2. Additional Control Latency
Addtional Control Latency: In native P2P systems, when an uploader
decides to reply a request for a piece, it sends the piece out
directly. Nevertheless, in DECADE-aware P2P systems, the uploader
typically only replies with a token of the piece. And then the
downloader will leverage this token to fetch the piece from the
uploader's DECADE server. This process obviously introduces
additional control latency compared with native P2P systems. It is
even more serious in latency sensitive applications such as P2P live
streaming. We need to consider how to reduce such additional delay
or how to compensate the lose with other inherit advantages of
DECADE.
In our integration, we addressed this challenge by multiplexing
pieces into one token:
o Range Token: One way to reduce request latency is to use range
token. A P2PLS client may piggyback a range token when it
propagates its bitmap to its neighbors, to indicate that all
available pieces in the bitmap are accassable by this range token.
Then instead of requesting specific pieces from this client and
waiting for response, the neighbors can directly use this range
token to access data in DECADE servers. Note that this method not
only reduce request latency, but also reduce message overhead.
With these adjustments and strategies (it is not necessary to use
"Batch Request" and "Larger Object Size" both), DECADE clients'
performance was not impacted by the liminations of DECADE and was
even better than native clients' as we will see in following
sections.
5. Test Environment and Settings
In order to demonstrate the performance of our DECADE implementation
and DECADE-integrated P2P live streaming application, we conduct some
experimental tests in Amazon EC2 and PlanetLab. We perform a pair of
comparative experiments: DECADE integrated P2P live streaming v.s.
native P2P live streaming, in the same environment using the same
settings.
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5.1. Test Settings
Our tests ran on a wide-spread area and diverse platforms, including
a famous commercial cloud platform, Amazon EC2 and a well-known test
bed, PlanetLab. The environment settings are as following:
o EC2 Regions: we setup DECADE servers in Amazon EC2 cloud,
including all four regions around the world, US east, US west,
Europe and Asia.
o PlanetLab: we run our P2P live streaming clients (both DECADE
integrated and native clients) on PlanetLab of a wild-spread area.
o Arrival pattern: we made all the clients join into the system
within a short duration to simulate a flash crowd scenario.
o Total Bandwidth: for a fair comparison, we set the system's total
supply bandwidth to be exact the same in both test.
5.2. Platforms and Components
In the tests, we have different functional components running in
different platforms, including DECADE servers, P2P live streaming
clients(DECADE integrated or Native), Tracker, Source server and Test
Controller, as shown in Figure 2.
+----------+ +------------+ +------------+
| P2PLS | /| DECADE |----| DECADE |
| Manager | / | Server | | Server |
+--------^\+ / +-----|------+ +------|-----+ EC2
___________\/_________|__________________|_______
/\ | |
+---------/+ \ +-----|------+ +------|-----+
| P2PLS ^ \ | P2PLS ^ ^ P2PLS |
| Source |\ \| Client |\ /| Client |
+-----|----+ \ \------^-----+ \/ +------^-----+ PlanetLab
______|_______\__\_____|_______/\________|_______
| \ \ | / \ |
+-----|----+ v--v---v-----v v------v-----+
| Streaming| | P2PLS | | Test |
| Files | | Tracker | | Controller |
+----------+ +------------+ +------------+ Yale Lab
P2PLS represents to P2P Live Streaming.
Figure 2
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5.2.1. EC2 DECADE Server
DECADE Servers ran on Amazon EC2 small instances, with bandwidth
constraint.
5.2.2. PlanetLab P2P Live Streaming Client
Both DECADE integrated and Native P2P live streaming clients ran on
PlanetLab which spreads in various locations around the world. The
DECADE integrated P2P live streaming clients connect to the closest
DECADE server according to its Geo-location distance to the servers.
DECADE integrated P2P live streaming clients use their DECADE servers
to upload to neighbors, instead of their own "last-mile" bandwidth.
5.2.3. Tracker
A native P2P live streaming tracker ran at Yale's laboratory and
served both DECADE integrated clients and native clients during the
test.
5.2.4. Source Server
A native P2P live streaming source server ran at Yale's laboratory
and serve both DECADE integrated clients and native clients during
the test. The capacity of source is equivalently constrain for both
cases.
5.2.5. Test Controller
Test Controller is a manager to control all machines' behaviors in
both EC2 and PlanetLab during the test.
6. Performance Analysis
During the test, DECADE integrated P2P live streaming clients
achieved an impressively better performance than native clients.
6.1. Performance Metrics
To measure the performance of a P2P live streaming client, we employ
mainly four metrics:
o Startup Delay: the duration from a peer joins the channel to the
moment it starts to play.
o Piece Missed Rate: the number of pieces a peer loses when playing
over the total number of pieces.
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o Freeze Times: the number of times a peer re-buffers during
playing.
o Average Peer Uploading Rate: Average uploading bandwidth of a
peer.
6.2. Result and Analysis
o Startup Delay: In the test, DECADE integrated P2P live streaming
clients startup around 35~40 seconds. some of them startup at
about 10 seconds. Native P2P live streaming clients startup
around 110~120 seconds. less than 20% of them startup within 100
seconds.
o Piece Missed Rate: In the test, both DECADE integrated P2P live
streaming clients and native P2P live streaming clients achieved a
good performance in pieces missed rate. Only about 0.02% of total
pieces missed in both cases.
o Freeze Times: In the test, native P2P live streaming clients
suffered from more freezing than DECADE Integrated P2P live
streaming clients by 40%.
o Average Peer Uploading Rate: In the test, according to our
settings, DECADE integrated P2P live streaming clients had no
upload in their "last-mile" access network. While in the native
P2P live streaming system, more than 70% of peers uploaded in a
rate that is much more than streaming rate. In another word,
DECADE can shift uploading traffic from clients' "last-mile" to
in-network devices, which saves a lot of expensive bandwidth on
access links..
7. Security Considerations
This document does not contain any security considerations.
8. IANA Considerations
This document does not have any IANA considerations.
9. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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Authors' Addresses
Lijiang Chen
Yale University
Email: lijiang.chen@yale.edu
Hongqiang Liu
Yale University
Email: hongqiang.liu@yale.edu
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