APOHN: Subnetwork Layering to Improve TCP Performance over Heterogeneous Paths

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APOHNSubnetwork Layering to Improve TCP
Performance over Heterogeneous Paths
April 4, 2006
Dzmitry Kliazovich, Fabrizio Granelli, University
of Trento, Italy
Giovanni Pau, Mario Gerla University of
California, Los Angeles
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Presentation Outline

• TCP/IP in Heterogeneous Networks
• APOHN Architecture
• Techniques, Protocol, and Security
• Performance Evaluation
• In Satellite Wireless LAN Network
• Conclusions and Future Potential

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Background

• Nowadays Networks (Heterogeneous)

• TCP/IP protocol suite

• Wireless, Satellite links
• Terminal Mobility
• Limited Bandwidth
• Large Propagation Delays
• Signal Fading
• High Error Rates (10-3 10-1)

• Designed in late 70s (ARPANET)
• Strong Hierarchical structure
• Static Routing
• Stable Connectivity
• Small Propagation Delays
• Low Error Rates (BER 10-8 10-6)

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TCP/IP Improvements
Transparent Adaptation

• Hide from TCP undesirable physical
  characteristics
• Examples ARQ and FEC at the link layer
• Drawback Not all the characteristics can be
  compensated in transparent way

TCP Modification

• Modify TCP bringing desired behavior
• Examples TCP Westwood, TCP-DOOR, etc.
• Drawbacks Difficulty to maintain E2E semantics,
  requires modification of standardized and widely
  implemented TCP/IP stack

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TCP/IP Semantics
Connection Service for Applications
Connect Network Nodes
TCP
TCP
Connect Neighbor Nodes
Network (IP)
Network (IP)
Link
Link
Physical
Physical
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TCP/IP Semantics

• Heterogeneous Network?

Subnetwork
Subnetwork
Link
Link
Physical
Physical
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APOHN Architecture
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APOHN Architecture

• Optimize Subnetwork Communications
• Subnetwork Protocols (SBP)
• Split-Connection at Subnetwork Layer
• Preserve End-to-end Transport Layer
• No Changes for TCP/IP OS Implementation

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Protocol Booster

• Protocol Booster Transparent interface between
  TCP and Subnetwork layers

• Buffer TCP packets
• Control TCP with Receiver Advertise windows
  (rwnd)
• E2E Reliability keep a packet in buffer until
  its E2E acknowledged

D. Feldmeier at el., Protocol boosters, IEEE
JSAC, vol. 16, no. 3, pp. 437 444, 1998.
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Protocol Booster

• Implemented at Sender Node
• Protocol Booster completely disables TCP flow
  control mechanism without direct modifications on
  Transport layer
• TCP becomes a controlled source of packet data

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Subnetwork Flow Multiplexing

• Rate-based or Window-based flow control at
  Subnetwork layer
• Results in TCP flow speed up no need to probe
  the capacity with Additive Increase
  Multiplicative Decrease (AIMD)

• Network Utilization Increase

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Related Works

• Delay-Tolerant Network (DTN)
• Overlay network
• Adds Bundle layer above TCP
• E-mail style communications
• Drawbacks
• Modifies TCP/IP
• Requires dedicated (overlay) nodes
• Router nodes process whole protocol stack
• Can not handle delay sensitive traffic

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Related Works

• Performance Enhancement Proxy (PEP)

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Related Works

• Performance Enhancement Proxy (PEP)
• Designed for links or Subnetworks where TCP/IP
  performs poor
• Typically Satellite links
• Commonly Split-Connection approach
• End-to-end connection is split into two or more
  connections
• Use Optimized (non-TCP/IP) Protocol over a
  Problematic Link
• Drawbacks
• End-to-end Semantics not prevented
• Large Processing Buffer Overhead
• Inability to Handle IPSec

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Secure Communications

• Split-Connection on Transport Layer (like PEP)
  can not support IPSec
• Multilayer IP Security (by Zhang at el.) as an
  adaptation of IPSec for split-connection PEPs
• Divide network in the number of Zones
  (Subnetworks)
• Encrypt for every zone (not End-to-end)

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Secure Communications

• APOHN IPSec Support
• End-to-end IPSec (RFC 2401)
• Additional Subnetwork Security (Optional)

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Performance Evaluation

• Simulated network Satellite Wireless LAN
• Distributed Communications with no fixed
  infrastructure
• Disaster Recovery, Military Applications

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Performance Evaluation

• APOHN Subnetwork Protocols
• Satellite Transport Protocol (STP) over Satellite
  Link
• LLE-TCP (ACK suppression) over WLAN

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Performance Evaluation

• Ns-2 Simulation Scenario
• Satellite Link 20 Mb/s, 300 ms downstream 6
  Mb/s, 300 ms upstream
• Wireless LAN Link IEEE 802.11b (PHY 11 Mb/s)

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Performance Evaluation

• Single-Flow Scenario
• TCP Reno SACK triggers multiple timeouts
• SaTPEP is limited by WLAN bottleneck

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Performance Evaluation

• Congestion Window Evolution

Loss Detected with DupACKs
Loss Not Detected, Timeout
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Performance Evaluation

• Bottleneck Buffer

Multiple Overflow Drops
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Performance Evaluation

• Multi-Flow Scenario

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Performance Evaluation

• Cumulative Throughput

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Conclusions and Future Work

• Need for TCP/IP Adaptation to Heterogeneous
  Network Environment
• APOHN Architecture adds Subnetwork Layer to the
  protocol stack
• Optimized Subnetwork Protocols, Flow
  Multiplexing, and Protocol Speedup are keys for
  Performance enahncement
• IPSec is Supported

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Thank you!