Survey of error recovery techniques for ip based audio visual multicast applications
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Survey of Error Recovery Techniques for IP-Based Audio-Visual Multicast Applications. Georg Carle and Ernst W. Biersack lnstitut EURECOM. 2011. 05. 24 Kim, Dong Joo. 1 /28. Contents. 2 /28. Abstract. IP-based networks are inexpensive

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Survey of error recovery techniques for ip based audio visual multicast applications

Survey of Error Recovery Techniques for IP-Based Audio-Visual Multicast Applications

Georg Carle and Ernst W. Biersack

lnstitut EURECOM

2011. 05. 24

Kim, Dong Joo

1/28


Contents
Contents

2/28


Abstract
Abstract

  • IP-based networks

    • are inexpensive

    • offer no guarantees for loss or delay

  • For Audio-Visual Multicast

    • recovery from losses due to congestion is a key problem that must be solved

  • In this paper

    • overview of existing transport-layer error control mechanisms

    • suitability for use in IP-based networks

    • requirements of error control mechanisms

    • different network scenarios are used to assess the performance of retransmission-based error correction and forward error correction

3/28


Backgrounds; Transport Protocol Requirements

  • Web traffic

    • TCP that uses a closed loop congestion control algorithm

    • continuous media (CM) applications use UDP that does not have a congestion control mechanism

    • Goal : use of cheap network services, tolerating high loss rate, and delay violations by network and by servers

      • powerful real-time error control mechanisms for audio-visual applications are needed

  • Characteristics of CM streams

    • Strict timing requirements

      • arriving after a certain point in time, it is useless

    • Some tolerance of loss

      • the amount of loss that can be tolerated depends on the medium, the coding techniques used, and human perception

    • A certain periodicity

      • video, for instance, consists of a fixed number of frames per second. when transmitting CM across a network this periodicity is normally lost

4/28


Backgrounds; Transport Protocol Requirements

  • Multipoint Transport Services

    • Existing protocols is classified according to the degree of reliability they provide

    • 1:N or multicast service vs. M:N or multi-peer service

5/28


Backgrounds; Application Scenarios

  • For non-real-time application

    • reliably deliver a data stream

    • requirements are very general

    • a single protocol such as TCP to be used by a large variety of applications

  • For real-time application

    • specific requirements which make certain protocol mechanisms more suitable than others.

      • characteristics of the application data units(ADUs)

      • end-to-end delay requirement

      • reliability requirement

      • coding techniques

    • since it is difficult to design error recovery protocols that are well suited for the whole range of parameters, solutions are targeted for specific applications scenarios.

6/28


Backgrounds; Application Scenarios

  • Three different application scenarios

    • each application scenario is characterized by ADU size, availability, life span, priority, delay budget, and reliability requirements

7/28


Backgrounds; Mechanisms for Error Recovery

  • ARQ (Automatic Repeat Request)

    • Lost data detection (detected by the receiver; timeout)

    • Acknowledgment strategy (ACKs or NAKs)

    • the two best known retransmission strategies: Go-Back-N & selective retransmission

    • trade-off : simplicity of receiver implementation vs. transmission efficiency

  • FEC (Forward Error Correction)

    • reconstruction of lost packets at the receiver

    • add parity, Reed-Solomen codes

    • do not need a return path

    • require very little time of recovery

    • have overhead

    • a single parity packet can be used to repair the loss of different data packets seen by different receivers

8/28


Backgrounds; Mechanisms for Error Recovery

  • Hybrid Error Control (ARQ/FEC)

    • ARQ and FEC can be used in combination

9/28


Backgrounds; Mechanisms for Error Concealment

  • Approximation or interpolation

    • audio-video transmission disguises the loss

    • recovery and concealment can also be combined

    • buffering is used, it increase the end-to-end latency and may be in conflict with the real-time requirement.

10/28


Model of the End-to-End Delay of a CM Data Transmission

  • Retransmissions for real-time applications

    • In the past, it was not suitable, possible today due to technology advances

    • Exploitation of End-to-End Delay Budget

11/28


Network Properties

  • IP-Based Networks

    • offers a datagram service with best-effort service quality with no guarantees for loss rate, delay, and in-sequence delivery

    • TCP congestion control algorithm used

    • more open-loop applications based on UDP are used, higher losses can be observed

      • one solution is resource reservation offered by RSVP(Resource Reservation Protocol)

    • IP Best-Effort service model vs. IP integrated Service model

    • In a future Internet, reservation will allow the provisioning of IP services with guaranteed QoS that will need some kind of tariffing

    • powerful error control mechanisms will continue to play an important role

12/28


Network Properties

  • ATM-Based Networks

    • offers a connection-oriented network service

    • can be used to implement IP integrated services

    • Error Characteristics in ATM Networks

      • different error control mechanisms in a certain case

        • Fast Reservation Protocol with Immediate Transmission (FRP/IT)

        • different priorities to different virtual connections (VCs)

        • trade off additional overhead vs. higher network utilization

    • Special Properties of ATM Networks Relevant to CM Error Control

      • guarantee in-sequence delivery

      • bounds on delay and error probability

      • increased reliability for retransmissions or to ensure low-delay retransmissions

13/28


Network Properties

  • Comparison of ATM and IP Networks

    • ATM networks

      • for CBR, VBR, known delay bounds

      • for UBR, UBR, unknown delay bounds

        • mean delay and delay variation may be much smaller than they are in IP services

    • IP networks

      • provide a best-effort type service

      • no delay bounds are given

      • mechanisms for access control and scheduling exist that allow IP services to be provided with QoS guarantees

      • in IP/RSVP-based networks, delay bounds can also be given

14/28


Mechanisms for Multicast Error Control

  • Key challenges of reliable multicast services

    • Multiple receivers with heterogeneous connections and processing capabilities

    • Feedback implosion

    • Defending on where loss in the multicast tree happens, different error scenarios result

15/28


Mechanisms for Multicast Error Control

  • Basic Mechanisms(1/4)

    • The approaches can be classified according to the following questions:

      • Who detects loss: the sender (waiting for all ACKs) or the receiver (using NAKs)

      • How to send feedback: using unicast or multicast, with the option of applying algorithms for NAK suppression

      • What is retransmitted: original data or parity

      • Who retransmits: the source, servers within the network, or other group members

      • How to retransmit: using unicast, multicast, or subgroup-multicast

      • How to cope with heterogeneity: adapting to the slowest/most impaired receiver, or ignoring receivers that do not reach certain limits

    • Loss Detection

      • sender-initiated protocols :

        • receivers return positive ACKs

        • the sender is responsible for error detection

        • has problems in case of large groups; cause congestion and losses in the sender’s neighborhood

      • receiver-initiated protocols :

        • the receiver is responsible for error detection

        • receiver issues a NAK by unicast or multicast

        • far more scalable than sender-initiated protocols for large groups

16/28


Mechanisms for Multicast Error Control

  • Basic Mechanisms(2/4)

    • Feedback

      • Unicast vs. Multicast

        • Multicasting control messages proves useful when receivers are locally concentrated

        • When receivers are far apart, multicasting control messages has negative impact due to the large propagation delay, consuming significant network resources in comparison with unicast transmissions

      • NAK Suppression : Slotting and Damping Algorithms

        • NAK suppression reduces the amount of feedback the sender must process

        • Slotting describes a mechanism where receivers send feedback via multicast either immediately or after a delay of one or more time slots

        • Damping describes a mechanism in which a receiver suppresses its own feedback packet if feedback from other receivers corresponds to its own state

        • optimized this algorithm is employed on various protocols

        • It increases the mean delay until the first NAK reaches the transmitter (disadvantage)

17/28


Mechanisms for Multicast Error Control

  • Basic Mechanisms(3/4)

    • Data Retransmission vs. Parity Retransmission

      • Retransmission of missing original data (ARQ) is the most popular approach

      • Retransmission of parity results in much improved throughput and bandwidth usage for reliable multicast to a large number of receivers

        • In local networks, it is neither possible nor desirable

    • Source-Based vs. Decentralized Retransmission

      • Source-Based Retransmission

        • has advantage of simplicity

        • suffers from limited efficiency in large groups and much loss rates

        • XTP, MTP, RAMP employ source-based retransmission

      • Decentralized Retransmission

        • achieves better scalability using group communication servers (GCSs)

          • improves bandwidth efficiency and latency

18/28


Mechanisms for Multicast Error Control

  • Basic Mechanisms(4/4)

    • Heterogeneity

      • Applying a conservative policy, adapts to the needs of the slowest or most impaired receiver

      • provide several levels of service for different receivers

      • eject slow receivers that represent a performance bottleneck

    • Reliable Real-Time vs. Fully Reliable Multicast protocols

      • for real-time service, after a given deadline, successful delivery of data is no longer important, but protocols are based on the same basic mechanisms for feedback processing and error recovery

      • for non-real-time service, within the given delay budget, feedback processing and error recovery is subject to the same performance trade-offs

      • Transport protocols for real-time reliable multicast services have in common the trade-off between reliability and delay budget. By increasing the delay budget available for error recovery, the residual error probability in terms of no

19/28


Error Control Mechanisms for CM Data Transmission

  • ARQ-Based Error Control for CM Data Transmission

    • Audio Transmission :

      • Unicast interactive voice for small RTT (Slack ARQ by Dempsey and Liebeherr)

      • Non-interactive voice to multiple recipients with large RTT(STORM by Xu, Yavatkar et al.)Designated receiver (DR) for local recovery

    • Video transmission :

      • Challenge (Internet): rate control

        • Potential solution: layering

        • Receiver-driven layered multicast (RLM, by McCanne et al.)

      • Retransmission-based loss recovery protocol for non-interactive transmission to multiple receivers (LVMR by Li, Paul, Ammar)

20/28


Error Control Mechanisms for CM Data Transmission

  • FEC-Based Error Control for CM Data Transmission

    • FEC Schemes Suitable for IP Networks :

      • Video-specific FEC scheme ; applied to MPEG(Priority Encoding Transmission(PET) developed at ICSI, Berkely)

      • Transport layer protocol framework to support delivery of CM over the Internet(RTP developed by IETF, RTP+FEC, RTCP)

    • FEC Schemes Suitable for ATM Networks :

      • no plans are known for widespread use of any approach

      • For AAL, proposed schemes

        • Long-Interleaver Scheme (based on a Reed-Solomon code)

        • Short-Interleaver Scheme by ITU SG13; more limited error contol capabilities but better delay properties

21/28


Taxonomy of Protocol Mechanisms for Real-Time Audio-Visual Services

  • Overview

    • the suitability and performance of multicast protocol mechanisms depends on specific properties of the communication scenario

    • Network scenarios are determined by error and loss characteristics, delay characteristics and fan out characteristics.

  • Network Scenarios with Characteristic Properties (1/2)

    • Network Scenario 1:

      • losses on individual link

      • important role in many multicast scenarios

    • Examples:

      • losses occurred in subnets

      • point-to-multicast connections in wireless terminals

    • Problems:

      • lead to high bandwidth consumption & poor scaling for large groups

      • selective retransmission of missing packets requires a large amount of control messages and transmitter status information

    • Solutions:

      • hybrid error control scheme with parity retransmissions

      • local retransmission

22/28


Taxonomy of Protocol Mechanisms for Real-Time Audio-Visual Services

  • Network Scenarios with Characteristic Properties (2/2)

    • Network Scenario 2:

      • losses on shared link

      • heterogeneous RTTs

    • Examples:

      • Different distances to receivers

      • Large queueing delays for certain receivers

      • Occurs at IP multicast routers, ATM switches

    • Problems:

      • NACKs for common losses arrive within large time interval (implosion)

      • Local recovery not appropriate

    • Solutions:

      • RTT-aware NACK processing at the transmitter

      • Error detection and NACK processing close to location of error(Group Communication Servers)

23/28


Assessment of Error control Mechanisms for Different Scenarios

  • Scenario-specific Selection of Mechanisms

    • FEC is of particular benefit in the following scenarios:

      • Large groups

      • No feedback

      • Heterogeneous RTTs

      • Limited buffer

    • ARQ if of particular benefit in the following scenarios:

      • Heterogeneous loss

      • Loss on shared links of multicast tree dominates

      • small groups

      • Non-interactive applications

    • ARQ by local recovery:

      • large groups (good for individual losses, heterogeneous RTT)

24/28


Assessment of Error control Mechanisms for Different Scenarios

  • Assessment of Mechanisms Using Application Scenarios

25/28


Communication Subsystems Supporting Different Error Control Schemes

  • Selection of appropriate error control scheme

    • application-specific & network-specific parameters

    • two approaches exist

      • Design a single protocol that provides the full set of protocol mechanisms and can be configured with respect to application and network scenario.

        • supports all error control schemes

        • applicable for different CM applications

      • Use a communication subsystem which selects between different protocols for CM error control

        • feasibility complexity

        • can be integrated within either applicatio nor communication subsystem

    • Both approaches will most likely coexist in practice

26/28


Conclusion Schemes

  • ARQ-based schemes can be applied for real-time applications

  • ARQ adapted for real-time in combination with FEC is very promising

  • No mechanism works best for all scenarios

    • Selection of protocol mechanisms is highly challenging task

  • When network elements support different priorities, ARQ and FEC allow for recovery from excessive delays

  • Not yet exist a general solution under all network conditions and applicable for all CM applications

    • It is still an open question if there will ever be a single error recovery protocol

27/28


Thank you Schemes

Kim, Dong Joo

Hankuk University of Foreign Studies

Dept. of Information and Communications Engineering

[email protected]


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