ROMA: Reliable Overlay Multicast with Loosely Coupled TCP Connections
description
Transcript of ROMA: Reliable Overlay Multicast with Loosely Coupled TCP Connections
Computer Science
ROMA: Reliable Overlay Multicast with Loosely Coupled
TCP Connections
Gu-In Kwon and John ByersComputer Science Dept.Boston University
Computer ScienceIP Multicast
CMU
BerkeleyMIT
UCSD
routersend systemsmulticast flow
Highly efficient Challenges
Congestion Control Reliability
http://esm.cs.cmu.edu/Sigcomm2001/SigcommTalk.ppt
Computer ScienceOverlay Multicast
CMU2
UCSD
MIT1
MIT2Overlay Tree
Berkeley
CMU1
MIT1
MIT2
CMU1
CMU2
CMU
BerkeleyMIT
UCSD
http://esm.cs.cmu.edu/Sigcomm2001/SigcommTalk.ppt
Traditional Performance Metrics• Stretch
Relative Delay Penalty• Stress
# of identical packet over a physical link
Computer Science
Quick deployment ISP’s reluctant to turn on IP Multicast
All multicast state in end systems Routers maintain per-group state in IP Multicast
Congestion control easier on “unicast” end to end connections
Potential Benefits over IP Multicast
http://esm.cs.cmu.edu/Sigcomm2001/SigcommTalk.ppt
MIT1
MIT2
CMU1
CMU2
CMU
BerkeleyMIT
UCSD
Computer Science
Past Work on Overlay Multicast Yoid, Narada, Scattercast, Overcast,
NICE, ALMI, RMX, PRM, ZIGZAG, OMNI …….
Target Application Non-reliable Streaming Application
Design Goal Low overhead on tree construction. Optimize the performance metrics.
Stretch and Stress
Computer Science
Reliable Content Delivery Claim:
TCP on each overlay link is sufficient for reliable delivery.
A B C5Mbps 2Mbps
Available Bandwidth
Computer Science
Store-and-forward approach Back-pressure mechanism
If the application buffer is full, ask the parent to reduce the sending rate to avoid the buffer overflow.
ALMI(USITS’01) and MCC(NGC’02).
A
B C
D E F
S
1Mbps
10Mbps 6Mbps
8Mbps
Single rate Multicast
Congestion Control 1Mbp
s
10Mbps1Mbps
1Mbps
1Mbps
Computer Science
ROMA Contributions ROMA
Reliable Overlay Multicast Architecture. Multirate. TCP on each overlay link. Forward-when-feasible. Digital Fountain Approach.
Performance evaluation of the chains of TCP. Loosely coupled TCP connections. Conventional wisdom on overlay network is not correct.
Conventional wisdom: Increased latency and loss rate will reduce the performance of overlay node comparing to the direct unicast.
Computer ScienceForward-when-feasible
Digital Fountain Approach.• A sender encodes n packets of original content into an unbounded set of encoding packets. • A receiver can reconstruct the original content by receiving any n distinct encoding packets.
Digital Fountain Approach(Byers, Luby, Mitzenmacher, Rege: SIGCOMM ’98)
EncodingStream
Received
Message
Sourcen
n
n Can recover filefrom any set of n encoding packets.
Transmission
Computer ScienceOverview ROMA
A B C5Mbps 2Mbps
Computer Science
Candidate Architectures Limited Buffer Space solution
Back-pressure mechanism Unlimited Buffer Space Solution
Use a disk as an extra buffer. Limitations.
A separate application buffer for each downstream. Substantial complexity to support I/O access. The overlay cannot be adaptively reconfigured.
Memory Memory
Memory
Incoming TCP
Outgoing TCP
Computer Science
Adaptive reconfiguration Adaptive reconfiguration of overlay
network. Reconfigure when congestion or failures of
intermediate nodes occur.A
B C
D
10Mbps
10Mbps
5Mbps
5MbpsX
1Mbps
Memory
Shapeshifter BCMR’02
Computer Science
Overlay Node Implementation
Transport Layer
Application Layer
Incoming TCP
Outgoing TCP
Application Layer Buffer
Computer Science
Modeling Chains of TCP Connections
Computer Science
Chains of TCP Connections
Loosely coupled TCP connections. An upstream TCP connection may or may not
affect the performance of a downstream TCP. A downstream connection never affects the
performance of an upstream connection.
Computer Science
Modeling Chains of TCP flows I When the downstream transfer rate is slower than
the upstream transfer rate. The application layer buffer will grow without bound. Behaves like a normal TCP driven by an application
that always has data to send.
A B C5Mbps 2Mbps
Computer Science
Modeling Chains of TCP flows II When the downstream transfer rate is faster than the
upstream transfer rate. B will periodically drain the application level buffer. The throughput to C is limited to that of the
upstream rate into B.
A B C2Mbps 5Mbps
Computer Science
Expected throughput on ROMA
S 1 2 iRTT_1
P_1
RTT_2 RTT_i
P_2 P_i
• Local network condition limits the throughput of overlay node.• OR the upstream connection limits the throughput of overlay node.
Computer Science
Other Measurement Studies S. Savage et al.
The end-to-end effects of Internet path selection, ACM SIGCOMM 1999.
There often exists detour route with lower aggregate loss rate and shorter round-trip time than IP rounte.
D. Andersen et al. Resilient Overlay Networks, SOSP 2001. Use detour route both to improve performance and to
route around faults in the overlay.
• Conventional wisdom on overlay network follows this model. Increased latency and loss rate will reduce the performance of overlay node comparing to the direct unicast.
Computer Science
Example
Conservative Formula Our Formula
A C 9 Mbps 9 MbpsA B C 9Mbps 22.2Mbps
Computer Science
Experiments PlanetLab
160 machines hosted by 65 sites. Linux. We use University hosts in the U.S. Abilene.
Computer Science
Multirate Reliable Multicast• Slow link does not impact the performance either at upstream nodes, or at nodes in other regions of the tree
Effect of Link Stress
Computer Science
Multirate Overlay Multicast
Effect of Link Stress
Computer Science
Throughput Improvement
BU UIUC
GT26.4ms0.0049%54.7Mbps
15.8ms0.0295%37.2Mbps
33ms0.0236%19.9Mbps
Computer Science
How to construct the overlay tree Construct the single-source widest-path
tree. Maximize the minimum per-hop available
bandwidth to every destination. Simple variant of Dijkstra’s algorithm.
Weight on each hop is the available bandwidth.
Select the unvisited node with the widest path from the source.
Path width is measured by the minimum of the weights on the path.
Computer Science
Maximizing Overall Throughput
Computer Science
Throughput Advantage
Computer Science
Conclusion ROMA
New architecture for reliable distribution of large content across an overlay network using TCP.
Multiple-rate reception. Minimal amount of resources at the application
layer. Provides ability to adaptively reconfigure the
topology. Provides ability to speed up downloads with
collaborative peer-to-peer transfers. [BCMR’02] Analysis of chains of loosely coupled TCP
TCP chains offer an opportunity to increase performance.