IP-Telephony Quality of Service (QoS) - UNI …harald/multimedia/IP-Telephony_QoS.pdfl MPLS....

1Universtät Klagenfurt - IWASMultimedia Kommunikation (VK 622.776)Dr. Sebestyen/Dr. Hundt; Mai 2001

IP-TelephonyQuality of Service (QoS)Bernard HammerSiemens AG, Munich

© Siemens AG 2001

IP-Telephony – Quality of Service 2Universtät Klagenfurt - IWASMultimedia Kommunikation (VK 622.776)Dr. Sebestyen/Dr. Hundt; Mai 2001

Presentation Outline

n End-to-end OoS of VoIP services

n Quality of speech codecs

n Network-QoSl IntServl RSVPl DiffServl MPLS


Voice Quality in IP-Networksn Voice quality has an end-to-end relationship

n Voice quality is impacted by:l Media coding method (coding delay, lossy compression)l Delivery delay (packetization, IP-node buffering, terminal buffering)l Delay jitterl Packet loss

n the “E-Model” helps to predict QoS of voice services:Standards: ETSI ETR250; ITU-T G.107, G.108, G.108.01, G.109, G.113, G.114, P.833

Terminal A Network(s) Terminal B


MultimediaTerminal

MultimediaTerminal

Network QOSNetwork QOS Network QOS

Terminal-to-Terminal QOS• Speed, Accuracy, Dependability• Service Availability

• Voice• Video• Data• Call Control

Customer-Perceived QOS• Subjective Measures• Objective Measures

• Voice• Video• Data• Call Control

ControlNetwork

ControlNetwork

BearerNetwork

BearerNetwork

BearerNetwork

ControlNetwork

Multimedia QoS Elements


Why is QoS needed ?IP-networks are designed for non-realtime data

IP

optiClient 3xx

HiPath 5500

optiPoint 300

Data & Voice Queue

PC

PC

Delay, jitter and loss due to one queue for voice and data

DataVoice DataSignalling


Why is QoS needed ?End to End Delay in Today’s Networks

IP

HiPath 5500

optiPoint 300

Queuing0..50ms

Coding & Packetization

30..50ms

Processing20ms

Typical: 50..120ms

Decoding1ms

Jitter Buffer30..300ms

Processing20ms

Typical: 50..300ms

Typical: 1..50; ∞ ms

Queuing0..50; ∞ ms

Delay1ms

Delay, jitter and loss caused by queuing in the networkoptiClient 3xx

PC

PC

Terminal Delay Terminal Delay

Network Delay


Terminal Delay

n IP terminal buffering delay (hardware and software)

n Packetization/ buffering delays. Packetization delay may beintroduced while packets are being constructed. Buffering delay maybe introduced when they are being disassembled.

n Codec delay: Processing delay before the output frame is generated;l an algorithmic process called look-ahead in which some of the samples from the following frame

are used to improve the performance of the compression process; andl as a result of the rate at which the output frame is serially clocked out from the encoder output

buffer, if this rate is chosen to provide a continuous bit stream without gaps a further framedelay is involved.


Network Delay

Network delay is the time spent by packets to reach their destinationduring transmission through the network:

n the transmission delay, introduced by sending a packet over a link.(e.g. sending a 256 byte packet over a 64 kbit/s link takes 32 ms);

n the propagation delay, due to signal propagation over physical link.This delay is usually negligible if links are shorter than 1000 km;

n the node delay, due to router queuing and processing of packets;n the protocol delay, due to packet retransmissions (if used, like for

TCP) or network access (e.g. CSMA-CD for Ethernet);n gateway delay, introduced by interfacing between networks (e.g.

packet disassembly/assembly and speech coding/decoding).


End-to-End Delay in Next Generation Networks

Multimedia User

End-to-End Signal Delay < 150 ms

hiQ

MGCPMGCP

IP

Switch STP

PSTN / ISDNPSTN / ISDN

SS7SS7

H. 323

ITU-T G.114 : (one-way-delay-recommendation)0 to 150 ms: good quality150 to 400 ms: acceptable qualityabove 400 ms: unacceptable

hiGhiA


QoS - Objectives

n Distinguish traffic with strict timing requirements from those that cantolerate delay, jitter, and loss.

n QoS support does not create bandwidth, but manages it so it is usedmore effectively to meet a wide range of application requirements.

n The goal of QoS is to provide some level of predictability and controlbeyond the current IP best-effort service.

* Quality of Service Forum: http://www.stardust.com/qosforum/


Requirements for VoIP Speech Codecs

n Robustness of codecs:l Error concealment needed (use tools like unequal error protection)

n Robust against Packet losses:l Generally no time for requesting packet retransmissionl Graceful degradation of voice quality in case of loss (e.g. by generating

supplement voice and background information)

n Measures for getting higher compression:l IP Header compressionl Different type of packets for voice and background (incl. silence) noise

(transmission of background noise pattern only when needed)

These requirements are being taken care of in VoIP standardization


Speech Codecs für VoIP

n Speech Codecs (3.1 kHz)l ITU-T G.723.1 standard codec for PSTN, low bitrate but rel. high delay,

unpleasant IPR situationl ITU-T G.729 same as G.723.1, however due to smaller delay better suited

to packet-based transmissionl ITU-T G.711 standard codec for narrow-band ISDN (64 kbit/s, low delay)

- New annexes for VoIP applications, including packetizing and use of comfort noise.

- Increasing use for wireline VoIP systemsl ETSI AMR specified as mandatory codec for circuit switched UMTS by

3GPP, can be used for a wide range of data rates without needfor transcoding

n Wide-band Speech Codecs(7kHz)l ITU-T G.722.1 excellent quality at 24 kbit/s, 16 Kbit/s version plannedl ETSI AMR as above, compatible to narrow-band AMR codec

n Specification of System Parametersl packetizing & delay-times: ITU-T G.114l round trip delay & jitter: ITU-T G.177, G.114


How to achieve QoS in IP-networks

n Network over-provisioning - may not economically viable

n Quality feedback (IETF RTCP) - application centered, no network impact

n QoS Services:l Integrated Services: Application sets up path & per flow reservation of network resources

acc. to QoS management policy.Specifications: IETF IntServ (RFC 1633, 2210, 2211, 2212)

l Differentiated Services: Priorization of traffic aggregates; packets are classified &marked at network ingress routers and treated acc. their .resp. service classSpecifications: IETF DiffServ (RFC 2475), IEEE 802.1p

- RSVP (RFC 2205) is used as a signalling protocol for path set up & resource reservation- MPLS, a packet forwarding scheme, is used to control traffic flow- in an end-to-end OoS architecture both IntServ and DiffServ are applied

l Policy management— QoS policy framework & architecture (IETF POLICY/ RAP, QoS Forum)— Authentification, Accounting (IETF AAA)


Integrated Services (IntServ)

n RFC 1633 (Integrated Services) defines a service frameworkn Reserves resources in order to provide QoS for flows

⇒ requires flow specific state information in routers⇒ does not scale very well

n 3 service classes (as of today):l Guaranteed Service: bounded latencyl Predictive Service: reliable but not fixed latencyl Best Effort Service

n Consists of 4 components: packet scheduler, admission control,classifier, reservation setup protocol (usually RSVP)


Resource Reservation Protocol (RSVP)

n RSVP (RFC 2205) is a signaling protocol to configure QoSn Applications canl request End-to-End and per-flow QoS from the networkl indicate QoS requirements and capabilities to peer applications

n Not limited to per-flow-usage nor to IntServ semanticsn Information carried by RSVPl classification informationl traffic description parameters (date rate etc.)l service type requiredl policy and traffic engineering information


How RSVP Works

n Sender sends PATH message to receiver specifying the traffic characteristics.n Every intermediate router forwards the PATH message to the next hop router determined

by the routing algorithm.n Receiver responds with RESV message to request resources for the flow.n Intermediate router can accept or reject the request (based on available resources

and/or policies).n If the request is accepted, resources will be reserved for the flow and related flow state

information is installed in the router, otherwise the process terminates.

RouterSender Receiver

PATH

RESV

Router

Router

Router


RSVP + Policies

Does the user have authorization for reserving the ressource?

Cops PDP LDAP

SenderReceiver

PATHRESV

PATH PATH

Admin

IF user IN ApprovedUsers AND service IN VideoServices AND source IN VideoSources AND time IN ApprovedTimePeriods AND NWstate IN OK_NWStatesTHEN provide JitterFreeMPEG2


Differentiated Services (DiffServ)

n DiffServ defines the meaning of the DS field (6 Bit) in the IPheader.

n Packets will be processed based on their DS field (i.e. DiffServdefines a relative priority scheme).

n This allows ISPs to develop and tailor the service offerings, i.e.offer different service classes - Service-Level-Agreements (SLAs)

n SLAs may contain any combination of attributes including:latency, availability, packet loss rates, jitter.

n Classification, shaping, marking, authentication, policing onlynecessary at ingress router.

n Interior routers implement per-hop-behavior.n DIFFSERV is far simpler than RSVP however does not allow for

resource reservation but only for some sort of priorisation.DIFFSERV can be used "stand alone" or in conjunction with anRSVP-based INTSERV network.


Intserv vs. Diffserv

u Emulation of SCN in PSNu QoS per flowu State machineu Set up via RSVP signalingu No control on routingu Good for long duration transfer (slow setup (.3 -1 s)

u Align with PSN conceptu QoS per hopu Statelessu Priority by DS code u No control on routingu Good for short duration transfer

RSVP/Intserv Diffserv


QoS and Routing

n RSVP/Intserv and Diffserv are independent from routingn Explicit routing enables establishing a QoS path.n MPLS defines an underlying mechanism to provide an explicit routingn Explicit routing enables Traffic Engineering

Problem descriptionWithin a connectionless routed net, the router looks at a packet's destinationaddress each time the packet flows through a node. The packet's route isdetermined by the routing tables in each node. With this method, a packet'sroute can't be predicted, which makes it difficult to reserve resources orguarantee quality of service (QoS). Routing table lookups are also CPU-intensive and time-consuming


Multiprotocol Label Switching (MPLS)

Features:n Adding labels to packets and label swapping to routers as a means to aggregate

forwarding information at OSI layer 2n The label provides forwarding along an explicit pathn The label is added at ingress points and removed by egress pointsn by MPLS signaling protocols network (e.g. LDP) network resources for certain

traffic can be reserved.n RSVP and Diffserv can be mapped over MPLS

MPLS is a connection-oriented technology beingintegrated with connectionless IP networksMPLS lets a router or switch assign a tag to each of its routing table entries andcommunicate that tag to neighboring routers and switches. When one of thosedevices passes a packet to a neighbor, the router or switch adds to the packet atag associated with the routing table entry. The tag lets the router or switchidentify the next hop or hops in the path without looking up the address. The ideais to let tagged packets flow end to end without forcing other routers or switchesto perform any address lookups.


Concluding Remarks

n Lack of QoS is one of the barriers in VoIP deployment

n Speech quality: G.711 gets extended for VoIP usage, new G.722.1 &AMR are interesting alternatives for high quality speech

n RSVP related standards are mature and most routers support RSVPcurrently

n Diffserv may become a common QoS method

n Network QoS: is still in an infant state; work in progress at TIPHON,TIA, ITU-T, IETF

Further Information: www.qosforum.com

IP-Telephony Quality of Service (QoS) - UNI …harald/multimedia/IP-Telephony_QoS.pdfl MPLS....

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