Scheduling TCP-Friendly Flows over a Satellite Network

IWSSC 2008 – Oct 3rd 2008 Raffaello Secchi

Scheduling TCP-Friendly Flows over a Satellite Network

R. Secchi, A. Sathiaseelan, and G. Fairhurst

Electronics Research GroupUniversity of Aberdeen

Aberdeen, United Kingdom{raffaello, arjuna, gorry}@erg.abdn.ac.uk


Outline

• QoS in Satellite Networking – System Requirements– Architecture Components

• Scenarios and Results– Criteria for performance evaluation– Relevant cross-layer interactions

• Conclusions & Future work

QoS in Satellite Networks

• Features & goals of the global Internet – Universal Interconnection– Decentralization– Heterogeneous Networking – Multiservice & IP oriented

• Objectives of QoS-Sat management– Integration in a large-scale network– Support of a wide range of applications



Approaches to QoS provisioning

• Limitations of hard QoS approaches (IntServ)– Traffic must be classified– A layer-3 to layer-2 mapping is required– Lack of network policies standardization: the end-to-end

behavior is difficult to guarantee– Subjectivity of policies: one provider’s gold traffic can be

bronze for another– The capacity argument

• End-to-end QoS schemes – High service levels under normal traffic conditions– Preventing collapse under high traffic loads


System Requirements

• A transport framework able to support multimedia applications

– Satisfying multimedia QoS requirements

– Compatibility with existing TCP services

– Network stability

DCCP

AQM, Fair queuing

BoD, Framing

• Active participation of IP layer– Fast feedback to upper-layer congestion control– Flow isolation & intelligent scheduling

• Effective use of satellite capacity – TCP/IP oriented design– Tuning knobs for efficiency vs. performance tradeoffs– Appropriate burst assignment across long

superframes

DCCP: The State of Art

• DCCP provides a framework for congestion control for multimedia flows– RFC 5348 (TFRC) proposed standard

• Suited for streaming media • Rate-based protocol• Requires sender and receiver participation• Periodic feedback reports• Smoothly variable sending rate

– RFC 4828 (TFRC-SP)• Small packet variant of TFRC• Suited for VoIP


TFRC development process


2000 20082006 2007

RFC 3448

RFC 4342

RFC 4828

RFC 5348

TFRC specifications

CCID3 in DCCP

TFRC-SP variant

Revision of TFTC

• Expanding TFRC framework (new CCID?)

• TFRC-SP in DCCP framework

future


SAL

MAC

IP

L4

Segmentation (ULE)

data signalling

Framing ATM, MPEG-2

flow control

To/From NCC

CR

buffer monitoring

DRADVB-Frames

TBTP

User applications

Transport (TFRC, TFRC-SP)

Packet SchedulingDrop Tail, DRR, SFQ, CBQ

Active Queue ManagementRED (Byte/Packet mode)

Bandwidth on DemandRBDC, CRA

VoIP packets

Architecture Components

Explicit/Implicit feedback

Bandwidth/Delay tradeoffs

Intra-flow & Inter-flow fairness

Simulation methodology

• Simulation scenario– Individual terminal scenario

– MF-TDMA over return link

– TDM over forward link

• Algorithms considered– DCCP: TFRC, TFRC-SP

– AQM: RED byte/packet mode

– IP layer: DropTail, DRR, SFQ, Prio

– BoD: RCDC, CRA

• Evaluation Criteria– R-score (objective quality estimation)

– Max-min fairness



Effects of flow isolation on TFRC

•A single TFRC streaming application may not achieve fairness when sharing with multiple data TCP flows• DRR is able to restore fairness and improve performance

Effect of AQM and Packet scheduling


Effects of Bandwidth on Demand



Conclusions

• The soft QoS concept for satellite networks– Architecture definition and its purpose– Identifying main elements, their scope and cross-

layer interactions– Strong points and weaknesses

• Ideas for the future research– Parametric optimization of arch. elements– Towards an emulative testbed?

Documents

Scheduling TCP-Friendly Flows over a Satellite Network