QoS and Video Delivery

QoS and Video Delivery

Presented by Wei Wei

Internet QoS: A Big Picture[1][2][3][4]

• Current Internet approachBest effortNo guarantees

• Need of providing QoS for video applications

Introduction

• Integrated Services (InteServ) and Resource Reservation Protocol (RSVP)

• Differentiated Service (DiffServ)• Multiprotocol Label Switching (MPLS)• Traffic Engineering and Constraint Based

Routing

InteServ and RSVP

• Philosophy BehindRouters have to be able to reserve resources to provide special QoS for specific user packet streams

• Four components of IntServ ModelThe signaling protocol (e.g. RSVP)The admission control routineThe classifierThe packet scheduler

InteServ and RSVP

• How RSVP works?

InteServ and RSVP

• Sender sends a PATH Message to the receiver specifying the characteristics of the traffic

Every intermediate router along the path forwards the PATH Message to the next hop determined by the routing protocol

• The receiver responds with a RESV Message to request resources for the flow

InteServ and RSVP

• Every intermediate router along the path can reject or accept the request of the RESV Message

Rejected, the router send an error message to the receiver, the signaling process will terminate Accepted, Resources (link bandwidth and buffer space) are allocated for the flow and the related

flow state information will be installed in the router

InteServ and RSVP

• Admission controlDecide whether a request for resources can be granted

• ClassifierWhen a router receives a packet, the classifier will perform a Multi-Field (MF) classification and put the packet in a specific queue based on the classification result

• Packet schedulerSchedule the packet accordingly to meet its QoS requirements

InteServ and RSVP

• Problems– Not scalable

• Huge storage and processing overhead on the routers

• The amount of state information increases proportionally with the number of flows

– Requirement on routers is high• All routers must implement RSVP, admission control, MF

classification, and packet scheduling

DiffServ

• Main Idea– Push all complex functions to the edge routers

• Edge routers are responsible for multi-field classification and translating that into a DSCP

• Core routers treat packets through DS field– Marking the DS fields of packets differently,

then handling packets based on their DS fields

DiffServ

• Architecture

DiffServ

• Architecture– Ingress routers

• Police/shape traffic• Set Differentiated Service Code Point (DSCP) in

Diffserv (DS) field– Core routers

• Implement Per Hop Behavior (PHB) for each DSCP• Process packets based on DSCP

DiffServ

• Two types of service– Assured service– Premium service

• Plus, best-effort service

DiffServ

• Assured Service– Defined in terms of user profile, how much assured

traffic is a user allowed to inject into the network– Network: provides a lower loss rate than best-effort

• In case of congestion best-effort packets are dropped first

– User: sends no more assured traffic than its profile• If it sends more, the excess traffic is converted to best-effort

DiffServ

• Premium service– Provides the abstraction of a virtual pipe

between an ingress and an egress router– Network: guarantees that premium packets are

not dropped and they experience low delay– User: does not send more than the size of the

pipe• If it sends more, excess traffic is delayed, and

dropped when buffer overflows

DiffServ

• Advantage– Scalable

• Edge routers maintain per aggregate state• Core routers maintain state only for a few traffic classes

– Easy implementation• Incremental deployment is possible for Assured Forwarding

• Disadvantage– Provide weaker service than InteServ

MPLS

• Label Switching– Header of the packet contains a label that is

used to advance the packet toward its destination

– The label simplifies the forwarding decision a node must make for the packet

• A group of packets forwarded in the same manner are said to belong to the same Forwarding Equivalence Class (FEC)

MPLS

• Label Switched Paths (LSPs)– Within an MPLS domain, a path is set up for a

given packet to travel based on a Forwarding Equivalence Class (FEC)

– The LSP is set up prior to data transmission

MPLS

• MPLS improves packet forwarding performance– Enhances and simplifies packet forwarding through

routers that use layer-2 switching– Simplicity allows for easy implementation

• MPLS supports QoS for service differentiation– Use traffic-engineered path set-up and support QoS

guarantees– Classification and QoS service are determined by the

labels

Traffic Engineering and Constraint-Based Routing

• Traffic Engineering is the process of arranging how traffic flows through the network so that congestion caused by uneven network utilization can be avoided

• Constraint-Based Routing is used to compute routes that are subject to multiple constraints.

Traffic Engineering• Network congestion can be caused by lack of network

resources or by uneven distribution of traffic– In the first case, all routers and links are overloaded and the

only solution is to provide more resources by upgrading the infrastructure

– In the second case, uneven traffic distribution can be caused by the current Dynamic Routing protocols such as RIP and OSPF, because they always select the shortest paths to forward packets

– Traffic Engineering can be utilized to avoid congestion or to provide graceful degradation in case of congestion

Constraint-Based Routing

• Constraint-Based Routing with DiffServ– Select routes for flows so that their QoS

requirements are most likely to be met• Constraint-Based Routing with RSVP

– Select the path for RSVP messages• Constraint-Based Routing with MPLS

– MPLS is a forwarding scheme and constraint-based routing is a routing scheme

User-Oriented QoS in Packet Video Delivery[5]

• focuses on how the quality of service of video delivery is perceived by the end user

• What may affect the QoS– Encoding: Aritifacts and Delays

• All lossy compression schemes both distort and delay the signal• Degradations come from quantization. Generally, the higher the

quantization step, the higher the degradation.• The amount of delay introduced is related to the size of

encoding buffer. The bigger the buffer, the smoother the bit rate may become, but it is at the expense of higher delay. Trade-off

User-Oriented QoS in Packet Video Delivery

– Transmission: Loss and Delay• The quality degradation caused by data loss depends on the

importance of the lost information type.• Spatial propagation: variable-length coding• Temporal propagation: I- P- frame

• How to Improve QoS– Encoder side:

• Adaptive Quantization: allocate more bits to more important part.

• Syntatic protection: increase resynchronization point to reduce spatial and temporal error propagation.


– Layered coding: Video can be encoded into different layers, and each layer has different importance to the video quality.

• Unequal error protection: add more FEC to the more important layer

• DiffServ Network: classify video signal into different service class, and let the more important data receive higher service

• Rate Adaptation: adapt to the varying channel


• Network Adaptation– ARQ: causes delay– FEC: constant overhead– Hybrid ARQ and FEC

• Decoder side– Error Concealment Techniques: spatial

interpolation, temporal interpolation


• How to measure QoS– A popular metric is PSNR. Unfortunately, a

higher PSNR does not mean a higher quality.– Metirc based on the properties of the human

visual system:• metric based on a subjective rating function

obtained by psychovisual experiments• metrics relying on a model of the human visual

system (Sarnoff JND Vision Model, moving pictures quality metric (MPQM) and PDM )


• The Perceptual Impact of MPEG-2 Rate and Data Loss– The Impact of Encoding Rate on Video Quality

• The perceptual video quality increases as the bit rate increases, but it will saturate at some high bit rate point



• The Impact of Data Loss on Video Quality – The video quality first remains constant with

PLR. Then, beyond a certain PLR, the perceptual quality drops fast.



• Joint Impact Analysis – The relation between quality and the encoding

bit rate for a given nonzero PLR exhibits like Fig. 17. Video quality first increases with the average bit rate and then decreases after a certain point.


Dynamic Quality of Service Framework for Video in Broadband Networks[6]

• Key points:– Concept of Softness QoS– Client QoS renegotiation

Dynamic Quality of Service Framework for Video in Broadband Networks

• Softness refers to the ability of an application to gracefully scale its performance using the available network bandwidth.

• Appropriate QoS parameters specific to the network layer are negotiated at connection setup.

• Support terminal-initiated renegotiation for bandwidth on demand.


• Advantages:– Lower service blocking probability– Achieve network efficiency, while maintaining

an acceptable application-level performance.• Disadvantages:

– Increase setup delay


• System Model– Data Plane:

• Client: – Buffer: stores packets until the decoder is ready to process them,

smooth the display rate.– Decoding and display modules: error concealment module,

• Server– Source rate control module: adjust video’s rate to match the

available bandwidth.– Rate shaper: shapes the traffic to make sure that it fits the traffic

profile provided by the network


– Control Plane:• Client

– specify the terminal and the application requirements, and set up “QoS contract”

• Server– bandwidth renegotiation with the network control to

maintain the clients “QoS contract”

• Network– Connection admission:– Bandwidth (re)allocation:

QoS-Sensitive Flows[7]

• Concentrate on the issues and principles concerning router modification to provide QoS support in IP network– Packet marking– Packet classification– Scheduling and Queue Management– Traffic descriptions and Admission Control

A Management and Control Architecture for Providing IP Differentiated Services in

MPLS-Based Networks[8]

• Current DiffServ approach concentrates on control/data plane mechanisms to support QoS, while this paper focuses on management plane to support Diffserv-based QoS.


MPLS-Based Networks• Standalization of definition of Service-level

Specifications (SLS)• Architecture

– SLS Management• Subscribing and negotiating SLSs with users or

other peer ASs and performs admission control for the dynamic request of subscribed SLSs


MPLS-Based Networks– Traffic Engineering

• Selecting paths that are capable of meeting the QoS requirements for a given traffic demand.

– Policy management

Conclusions

• How to Provide QoS in current Internet?– Trying to make “some changes” to the current routers

to achieve some kind of QoS• User-Oriented QoS

– There exists gap between the provision of network-level QoS and the actual QoS requirements of applications. This gap causes distributed multimedia applications to inefficiently use network bandwidth, leading to poor end-to-end system performance.

References

[1] X. Xiao, et al. “Internet QoS: A Big Picture”, IEEE Network, Mar/April 1999

[2] L. Zhang, et al. "RSVP: A New Resource Reservation Protocol", IEEE Communications Magazine, 31(9):8-18, September 1993

[3] R. Braden, et al. "Integrated Services in the Internet Architecture: an Overview", RFC 1633, June 1994

[4] K. Nichols , et al. "A Two-bit Differentiated Services Architecture for the Internet",

References[5] O. Verscheure, et al. “User-Oriented QoS in Packet Video Delivery”,

IEEE Network, Nov./Dec. 1998, pp. 12-21[6] D. Reininger, et al. “A Dynamic Quality of Service Framework for

Video in Broadband Networks,” IEEE Network, Nov./Dec. 1998, pp. 22-34

[7] S.N. Bhatti, et al. “QoS-Sensitive Flows: Issues in IP Packet Handling”, IEEE Internet Computing, Jul./Aug. 2000, pp. 48-57

[8] P. Trimintzios, et al. “A Management and Control Architecture for Providing IP Differentiated Services in MPLS-Based Networks,” IEEE Communications Magazine, May 2001, pp. 80-88

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QoS and Video Delivery

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