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Quality of Experience and Quality of Service
Quality of Experience and Quality of Service
Quality of Experience and Quality of Service
Quality of Experience and Quality of Service
Quality of Experience and Quality of Service
Quality of Experience and Quality of Service
Quality of Experience and Quality of Service
Quality of Experience and Quality of Service
Quality of Experience and Quality of Service
Quality of Experience and Quality of Service
Quality of Experience and Quality of Service
Quality of Experience and Quality of Service
Quality of Experience and Quality of Service
Quality of Experience and Quality of Service
Quality of Experience and Quality of Service
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Quality of Experience and Quality of Service

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  • 1. Communicate Simply White Papers by Polycom Quality of Experience and Quality of Service For IP Video Conferencing Timothy M. O’Neil Director of Technical Marketing Polycom Video Communications
  • 2. Table of Contents Introduction ..........................................................................................................1 Information Sources .............................................................................................2 Application-based Quality of Service [1] ............................................................2 AQoS and Signaling ......................................................................................3 AQoS and Media Handling ............................................................................3 AQoS Summary .............................................................................................5 Network-based Quality of Service [2] ................................................................ 5 NQoS Architectures ...................................................................................... 6 Differentiated Service [3] (Diffserv) .......................................................6 Integrated Services [3] (Intserv)/RSVP ...................................................6 NQoS Process ................................................................................................7 Packet Marking ........................................................................................7 Packet Classification ................................................................................7 Admission/Policy .....................................................................................7 Scheduling/Queuing .................................................................................8 NQoS Summary .............................................................................................8 Quality of Experience and Polycom’s IPriority Facilities ...................................8 IPriority Summary .............................................................................................10 Terminology .......................................................................................................10 References ..........................................................................................................12 Additional Information ......................................................................................12 Contact Information ...........................................................................................13 Communicate Simply White Papers by Polycom
  • 3. QoE and QoS - IP Video Conferencing It is important to note that while tradi- Introduction tional discussions of QoS discuss only the networking facilities related to H.323 video and voice applications dif- QoE, not all networks are NQoS-capa- fer from traditional data applications in ble or NQoS-enabled, and it often falls that they are real-time applications, and to the AQoS services to provide what- in that they require higher bandwidth ever QoE is available for voice/video than traditional data applications. Real- sessions. Ensuring QoE is also difficult time applications, especially H.323 because there is no mandatory QoS applications, require more stringent defined within the H.323 standard packet handling than non-real-time specification. This results in the manu- (traditional IP-based) applications. facturers of different video terminals This, in turn, necessitates more net- applying different solutions for AQoS work management resources to assure services, if they provide AQoS at all. predictable video and voice transmis- sion. The combination of stringent The quality of an end user’s experience packet handling and large volume net- is the true litmus test of a proper video/ work data flow are defined by Quality voice deployment. Only by under- of Service (QoS). standing both the application and net- work facilities for QoE can you Another term pertinent to the discus- absolutely ensure the highest quality sion is Quality of Experience (QoE). user experience. The following discus- QoE is defined as the totality of Qual- sion about AQoS and NQoS allows for ity of Service (QoS) mechanisms, pro- a greater understanding of just how vided to ensure smooth transmission of important the interplay of application audio and video over IP networks. and network QoS mechanisms are in These QoS mechanisms can be further the overall scheme of QoE. distinguished as application-based QoS (AQoS) and network-based QoS (NQoS). AQoS includes those services provided by voice and video applica- tions to enhance the desired end-to-end performance, while NQoS includes those services provided by the network and networking devices (like routers and switches) to enhance end-to-end QoS. Communicate Simply 1 White Papers by Polycom
  • 4. QoE and QoS - IP Video Conferencing Information Sources Application-based Quality of Service [1] This white paper has derived some of its information from existing publica- Application-based Quality of Service tions, such as other white papers and (AQoS) relates to the facilities embed- RCFs. In addition, some terminology ded within an application that preserve and descriptions directly pertain to a the quality of its intended use. For specific publication. In these cases, a H.323 video/VoIP applications, AQoS number, in brackets, follows the term relates to two main areas: or description. The number identifies • Call signaling the specific publication that contains • Terminal handling of media flows, the information about that term or both video and audio. description. The publications are num- bered and listed in “References” on The following sections review each of page 12. For example, this white paper these areas and discuss the step-by-step contains the term Application-based process of the application flow. Appli- Quality of Service [1]. The [1] identi- cation flow is the process that voice fies the number of the publication that and video applications undergo during contains the information about Appli- the process of media acquisition, com- cation-based Quality of Service pression, packetization, transmission (AQoS). In this case, the AQoS infor- decompression, and playback. Under- mation is derived from IP Telephony standing the application flow process is with H.323 Architectures for Unified a simple way of separating the func- Networks and Integrated Services. tions of AQoS from those associated with NQoS in an overall QoE solution. Communicate Simply 2 White Papers by Polycom
  • 5. QoE and QoS - IP Video Conferencing AQoS and Signaling AQoS and Media Handling Signaling is the low level communica- H.245 is also used to provide AQoS by tion that happens between applications. measuring packet loss and then Signaling utilizes industry standard instructing the application to react. protocols. The three main signaling Inter-arrival packet jitter and one-way mechanisms in H.323 are: delay (latency) are also measured. In • H.225-RAS - Responsible for com- situations where no NQoS exists, munication between the terminal H.245 is the only QoS facility reacting and the gatekeeper. Additionally, to packet loss, jitter, and latency. There terminals use H.225-RAS to obtain are several techniques employed by services from the gatekeeper. Polycom that leverage these facilities, • H.225-Q.931 - Used between ter- such as dynamic jitter buffers, minals for call setup and call termi- Dynamic Bandwidth Allocation nation. (DBA), and Polycom Video Error Con- • H.245 - Used between terminals cealment (PVEC) technology. See for the multimedia portion of call Table 1 on page 4 for a listing of AQoS setup and negotiation. facilities. Additional information about the specifics of Polycom AQoS can be obtained from the white paper titled Application-based Quality of Service, posted on http://esupport.polycom.com/ whitepapers.html. Communicate Simply 3 White Papers by Polycom
  • 6. QoE and QoS - IP Video Conferencing Table 1: H.323 Application Process [1] from Media Acquisition (at Sender) to Transmission Over the Network to Media Playback (at Receiver) QoS Step Description Type --- 1 Input to camera and microphone (media) is digitized and buffered at sender AQoS 2 Media is retrieved from buffer and entered into Codec AQoS 3 Compression of media AQoS 4 Output of compression is sent to Real-Time Transport Pro- tocol (RTP) for packetization AQoS 5A RTP output is sent to User Datagram Protocol (UDP) IP layers for packetization AQoS/ 5B Application marks for NQoS signaling NQoS NQoS 6 IP datagram is transmitted NQoS 7A Routing occurs (injection of propagation-serialization delay based on queuing) AQoS 7B H.245 via RTP measures loss, jitter, latency and instructs application to react AQoS 8 Media is de-packetized at receiver’s buffer AQoS 9 Codec retrieves from buffer and adjusts delay to account for loss and jitter --- 10 Output is played Communicate Simply 4 White Papers by Polycom
  • 7. QoE and QoS - IP Video Conferencing AQoS Summary The following is a short list of the ser- Network-based Quality vices obtained via signaling and media of Service [2] handling: • Gatekeeper discovery/registration NQoS can be provided in two different • Endpoint registration ways: hard QoS or soft QoS. Hard QoS • Call admission absolutely guarantees QoS and soft • Capabilities exchange QoS provides best effort QoS. Both • Bandwidth negotiation methods provide service to marked • AQoS relative to network loss, jit- packets over other packets. ter and latency The two fundamental purposes of • Call disengagement. NQoS as it relates to IP voice and video applications are: All of these services are areas of poten- • Reduce the likelihood of packet tial AQoS and optimization. The time loss for each of these services to complete • Allow IP voice and video applica- as well as the accuracy and reliability tions to operate on the network of these services directly affects QoE. while other applications are also Imagine if the user had to continually using the network. redial a call because the call admission phase had no reliability mechanisms NQoS can be broken down into a four- employed to guarantee the call. If an step process as it relates to IP voice and NQoS-enabled network has packet video applications: loss, and the application cannot com- • Marking pensate for the loss, the user’s QoE can • Classification not be preserved. Polycom improves • Admission (policy) these scenarios by employing leading • Scheduling (queuing). edge AQoS services to enhance the user’s QoE. These processes can be accomplished using one of several different, standard architectures, which are summarized below. Communicate Simply 5 White Papers by Polycom
  • 8. QoE and QoS - IP Video Conferencing NQoS Architectures be deployed at both the edge and core of IP networks. Differentiated Service [3] (Diffserv) This is considered soft QoS. Traffic Integrated Services [3] (Intserv)/ flows (applications/protocols) are RSVP grouped into classes based on the level This is considered hard QoS. This ser- of service they require to operate most vice type requires a reservation of net- efficiently/effectively. Network work resources in order to meet devices then characterize flows and specified service classification require- apply services according to policy and ments. scheduling of resources for the marked • Allows for preferential treatment of class of flow. flows, in two ways: • Allows for preferential treatment of 1. Without an absolute guarantee flows without an absolute guaran- service known as Controlled tee Load Service. • Works well for bandwidth-inten- 2. With a guarantee known as sive data applications like video Guaranteed Service. • Marking is provided by IP prece- • Works well for bandwidth-inten- dence and Differentiated Services sive data applications like video Code Points (DSCP). • Marking is accomplished via the RSVP signaling protocol, not a lit- IP Precedence eral mark, actually a definition of a The IP precedence field in an IP pack- Path and Reservation requirements. ets header is used to indicate the prior- ity with which a packet should be Intserv is considered by most to be handled. IP precedence is made up more difficult to scale than Diffserv from three bits in the IP headers Type and not suitable for implementation in of Service (ToS) byte. the core of IP networks. Intserv is cur- Diffserv rently being promoted as a comple- Diffserv defines a field in the IP header mentary method of interoperating called the Differentiated Services Code between RSVP at the edge and Diff- Point (DSCP). The DSCP is a six-bit serv within the core. field, spanning the fields formerly uti- lized by type-of-service and IP prece- dence services in the Type of Service (TOS) byte. Diffserv is considered to be the most scalable architecture for NQoS. It can Communicate Simply 6 White Papers by Polycom
  • 9. QoE and QoS - IP Video Conferencing NQoS Process tions can mark or be trusted, the policy The four steps involved in NQoS are: of the network should decide and thus 1. Packet marking write/rewrite all markings at the near- 2. Classification est network node. Every installation is 3. Admission/policy different and options for application or 4. Scheduling. network node marking exist. Some- times, a mix of both application and These steps are all part of a continuous network marking is deployed. Polycom process that occurs over the varied data terminals have the ability to mark the paths traversed by the application data. IP precedence bit from within the The data path is from the first router application and via the Global Manage- encountered at the very edge of a net- ment System™ network management work, closest to the sender, through the software. core and border routers, back to the edge router closest to the receiver. It Packet Classification should be noted that most layer three Packet classifiers determine the flow or switches provide routing facilities Behavior Aggregate of a packet, based within the layer three switch itself. on its marking. Classification is the Cisco calls these Route Switch Mod- function of a network node. Classifica- ules (RSM). tion can be done either by parsing mul- tiple fields of the IP header (for The four steps of NQoS are summa- example, source/destination address, rized below. protocol ID, source/destination port ID) or by parsing the ToS byte for class Packet Marking of service/precedence (for example, Packet marking is accomplished in two Diffserv code points, precedence bits). ways: • The marking of packets is accom- Admission/Policy plished by the terminal itself Admission control consists of band- • The marking or lack of marking is width control and policy control. written/overwritten at the nearest Applications like Polycom video com- network node (router). munications terminals can request a particular QoS for their traffic. The Some schools of thought believe that devices in the network through which the further from the core the applica- this traffic passes can either grant or tion is, mark there; the network edge deny the request depending on various (for example, the application does the factors, such as capacity, load, policies, marking). Other schools of thought etc. If the request is granted, the appli- believe that because not all applica- cation has a contract for that service, Communicate Simply 7 White Papers by Polycom
  • 10. QoE and QoS - IP Video Conferencing which will be honored in the absence of disruptive events, such as network Quality of Experience outages. and Polycom’s IPriority Facilities Scheduling/Queuing Traffic flows/classes can be assigned to Polycom’s IPriority™ (see Table 2 on different queues based on their classifi- page 9) initiative is a portfolio of all cation. The placement or switching of facilities relating to QoE. Within the packets into different queues provides IPriority portfolio are facilities that are for the diverse service needs of marked supported between terminals within packets. Special requirements, such as network infrastructure, Multipoint low delay can be provided to packets Control Units (MCUs), Gateways by servicing their queue more fre- (GW), and signaling capabilities for quently. The selection of queue is standards-based network QoS mecha- based on a packets marked classifica- nisms. These facilities work with, and tion. The QoS queuing discipline that in some instances, improve upon stan- is implemented determines and/or dards-based implementations in an schedules which queued packets enter effort to provide the highest quality or exit the queues. user experience. Polycom is committed to continually provide leadership in the NQoS Summary areas of improved quality and usability NQoS can potentially increase the QoE of their market-leading video and voice for the user of IP voice and video appli- technologies. cations. Polycom terminals can mark the IP precedence bit for NQoS. The default setting is five with a range from zero to seven; with zero indicating no priority and seven indicating the high- est priority. iPower™ sets independent precedence bits for audio and video. For a more detailed discussion about NQoS, see the white paper Network- based Quality of Service, posted on http://esupport.polycom.com/ whitepapers.html. Communicate Simply 8 White Papers by Polycom
  • 11. QoE and QoS - IP Video Conferencing Table 2: Polycom IPriority Facilities Video Network Network Terminal Infra- IPriority Facility Traffic Mgmt Support structure Support IP precedence (ToS) / DSCP X X N1 (CoS) Dynamic bandwidth allocation X X2 N1 Polycom video error X X3 N1 concealment Proactive network monitoring X X X X Packet and jitter control X X X NAT support X X4 X Asymmetric speed control X X N1 Fixed port firewall supported X X H.323/H.320 interop testing X X X Remote diagnostics X X X On-screen diagnostics X X X Transcoding: Frame rate, audio X X protocols, video format, video protocols Lip synchronization X X X Echo cancellation X X Echo suppression X X 1. Scheduled development for 2002. 2. ViewStation SP ver 6.0, ViewStation FX ver 2.0, and ViaVideo ver 1.0. 3. ViewStation FX ver 4.0. Scheduled development for ViaVideo and iPower in 2002. 4. iPower does not support. Communicate Simply 9 White Papers by Polycom
  • 12. QoE and QoS - IP Video Conferencing IPriority Summary Terminology The quality a user experiences using Table 3 explains the various terms used voice or video application is based on in this white paper. more than just one method of QoE. NQoS and AQoS are required to ensure the highest level of user satisfaction. Polycom is committed to working with their networking partners to maintain interoperability in the areas of NQoS. (See www.polycom.com/custPartners/ partners/partners_family.html) for a list of Polycom’s networking partners.) Polycom is also committed to continu- ous innovation and implementation of AQoS mechanisms within their mar- ket-leading terminal and infrastructure technologies. Table 3: Terminology Term Definition Application Quality The facilities provided within an application to provide of Service (AQoS) Quality of Experience to users. Implemented to provide a quality user experience. Behavior aggregate A collection of packets with the same DS codepoint (BA) crossing a link in a particular direction. Classifier An entity that selects packets based on the content of packet headers according to defined rules. Differentiated A specific value of the DSCP portion of the DS field, Services Code Point used to select a PHB. (DSCP) Communicate Simply 10 White Papers by Polycom
  • 13. QoE and QoS - IP Video Conferencing Table 3: Terminology Term Definition DS field The IPv4 header ToS octet or the IPv6 Traffic Class octet when interpreted in conformance with the defini- tion given in [DSFIELD]. The bits of the DSCP field encode the DS codepoint, while the remaining bits are currently unused. Marker A device that performs marking. Marking The process of setting the DS codepoint in a packet based on defined rules; pre-marking, re-marking. Network Quality of Typically referred to as IP QoS. Derived from Inte- Service (NQoS) grated services (IETF Intserv working group) and/or Differentiated Services (RFC 2475). Per-Hop-Behavior The externally observable forwarding behavior applied (PHB) at a DS-compliant node to a DS behavior aggregate. Policy A set of administrative rules used to classify the response afforded a marked packet, Behavior Aggre- gate, PHB group. Quality of The measure of the facilities of Quality of Service Experience (QoE) applied to a voice/video communication session. Application QoS or network alone or a combination of the two. Communicate Simply 11 White Papers by Polycom
  • 14. QoE and QoS - IP Video Conferencing References Additional Information 1. IP Telephony with H.323: Architec- 1. Resource ReSerVation Protocol tures for Unified Networks and (RSVP) Version 1 Functional Spec- Integrated Services ification [RFC 2205] Wiley R. Braden, L. Zhang, S. Berson, Vineet Kumar, Markku Korpi, S. Herzog, S. Jamin Senthil Sengodan September 1997 April 2001 2. An Expedited Forwarding PHB 2. IP Quality of Service [RFC 2598] Srinivas Vegesna V. Jacobson, K. Nichols, K. Poduri Cisco Press June 1999 2001 3. An Assured Forwarding PHB 3. Definition of the Differentiated Ser- [RFC 2597] vices Field (DS Field) in the IPv4 J. Heinanen, F. Baker, W. Weiss, and IPv6 Headers (RFC 2474) J. Wroclawski K. Nichols, S. Blake, F. Baker, June 1999 D. Black 4. Internetworking Technologies December 1998 Handbook, Third Edition 4. An Architecture for Differentiated Cisco Press Services (RFC 2475) December 2000 S. Blake, D. Black, M. Carlson, E. Davies, Z. Wang, W. Weiss December 1998 Communicate Simply 12 White Papers by Polycom
  • 15. QoE and QoS - IP Video Conferencing Contact Information Corporate Headquarters Polycom, Inc. 1565 Barber Lane Milpitas, CA 95035 USA Phone: +1.408.526.9000 Fax: +1.408.526.9100 European Headquarters Polyspan Ltd. Whichford House Parkway Court Oxford Business Park South Oxford 0X4 2JY United Kingdom Phone: +44 (0) 1865 335500 Fax: +44 (0) 1865 335501 Asia Pacific Headquarters Polycom Solutions Pte. Ltd. 16 Raffles Quay #40-02A, Hong Leong Building Singapore 048581 Phone: +65.323.3882 Fax: +65.323.3022 For additional information, please visit the Polycom web site at: www.polycom.com Polycom® and the Polycom logo design are registered trademarks, and ViewStation™, ViaVideo™, IPriority™, iPower™, and Global Management System™ are trademarks of Polycom, Inc. in the United States and various other countries. All other trademarks are the property of their respective owners. ©2002 Polycom, Inc. All rights reserved. Communicate Simply 13 White Papers by Polycom

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