Voice over IP (VoIP) and QoS/QoE Professor Richard Harris School of Engineering and Advanced Technology (SEAT)
Presentation Outline Understanding jitter and methods to overcome problems with jitter Quality of Service issues for VoIP Concepts for NGN networks Quality of Service considerations Quality of Experience Computer Networks - 1/2
Learning Objectives You will be able to: Define jitter Demonstrate methods for overcoming jitter problems Explain Quality of Service issues as they relate to VoIP Explain Quality of Experience as an emerging issue in NGN networks Computer Networks - 1/3
References Forouzan, Data Communications and Networking, 4 th Edition Tanenbaum, Computer Networks, 4 th Edition Cisco CCNA1 Module 10 - part 1 Stallings, William 2000 Data and Computer Communications, Prentice Hall, Sixth Edition Russell, Travis 1997 Telecommunications Protocols, McGraw Hill Computer Networks - 1/4
The Perfect Time Relationship Computer Networks - 1/5
What is Jitter? Jitter is introduced in real-time data by the delay between packets. Computer Networks - 1/6
Time-stamping Packets To prevent jitter, we can time-stamp the packets and separate the arrival time from the playback time. Computer Networks - 1/7
A View of the Playback Buffer A playback buffer is required for real-time traffic. Computer Networks - 1/8
VoIP Issues Call Set-up Call set up response time : also called post dial delay The delay time between dialling and either hearing a dial tone or a busy tone. This should not exceed 3 seconds as this matches PSTN delay At end of the day every thing must be on par with the PSTN environment. Note the gateway issues : this results in a costing issue - PSTN to VoIP VoIP to PSTN Numbering is an issue : E-NUM is the current proposal Computer Networks - 1/9
What is ENUM? RFC 3761 Take the E.164 phone number +64 6 356 9099 Turn it into a FQDN by reversing the digits and inserting a dot as shown here, the domain "e164.arpa" is appended to the end: 9.9.0.9.6.5.3.6.4.6.e164.arpa. Return list of URI s sip:name@domain.tldn Eg: R.Harris@massey.ac.nz ask the DNS Phone number IN..URI OUT Computer Networks - 1/10 10
NGN Concepts Quality of Service Quality of Experience
Defining Quality of Service ITU Recommendation E.430 says: A typical user is not interested in how a particular service is implemented, but he/she is interested in comparing one service with another in terms of certain universal performance parameters which apply to any service. Quality of Service (QOS) is expressed by parameters which: do not depend on assumptions about the network internal design; are referred to in terms of user-perceivable effects and not by their causes in the network; are described in network independent terms and create a common language understandable by both the user and the provider; take into account all aspects of the service which can be objectively measured at the service access point. A network provider is concerned with the efficiency and effectiveness of the network. From the network providers point of view, network performance is best expressed by parameters which give information for: system development; network planning; operation and maintenance. Computer Networks - 1/12 12
Alternative Statement of QoS A network exists to service its users and their applications. We want to ensure that business-critical applications work effectively and efficiently for customers. Quality of service is all about the ability to service a given application efficiently without affecting its function or performance. Computer Networks - 1/13 13
A Network View of QoS A network is typically composed of: Hosts Routers/Switches Links QoS depends on these entities working correctly - together! Hosts Routers Links Computer Networks - 1/14 14
The Network Perspective of QoS What is a pipe? A path from A to B as perceived by a packet QoS is basically a set of techniques to manage the following four entities: Bandwidth How wide is the pipe? Delay How long is the pipe? Jitter What is the perceived variation in length of the pipe? Packet Loss How much leaks from the pipe? Delay Bandwidth Packet Loss Computer Networks - 1/15 15
QoS from a Business Perspective Each of the four parameters Bandwidth Delay Jitter Packet loss May be considered as resources available to a given user or application. QoS is simply an advanced form of resource management to enable the maximisation of the Return on Investment from the network infrastructure. Computer Networks - 1/16 16
Customer View How QoS in the network solves their problems QoS sets out to introduce varying levels of service relative to business priorities QoS provides control over delay and jitter sensitive traffic Eg. Multimedia and audio/video traffic Service providers can offer additional services to their customers Dept Applicn Priority Access Finance SAP Gold YES Sales Stock Bronze YES Computer Networks - 1/17 17
QoS Provisioning (Traffic prioritisation The DiffServ Model) Policing Is the flow conforming to the relevant contract? Marking Identify further treatment downstream for packets that comprise the flow Shaping This improves overall performance and enforces the conformance of packets in the stream Scheduler Ensures that the flow gets the desired bandwidth Computer Networks - 1/18 18
The Network Edge INGRESS EGRESS Mark Mark Packet Packet High Voice/Video /Data traffic Filter Police Police Packet Packet Mark Mark + + Police Police Packet Packet Mark Mark + + Shape Shape Packet Packet Medium Low Scheduler Outgoing Interface No service type Classification Forwarding Scheduling Computer Networks - 1/19 19
Where are all the delay components? (1) Voice packetisation (5 10 ms) (2) Node processing (6 ms) (3) Trunk queueing delay (4) Transmission delay (5) Propagation delay (6) Network delay (consists of steps 2 to 4) (2) Node processing (6 ms) (7) Dejitter Buffer delay TDM in Network TDM out Computer Networks - 1/20
Voice Quality Impairments Impairments in the PSTN Loss, frequency loss (due to filtering), distortion, side-tone, echo, delay, noise, Impairments in packet networks Delay, jitter, distortion, clipping, dropouts and echo Despite the fact that some of the impairments are similar in the two types of networks, they are usually caused by different processes Computer Networks - 1/21
So, why isn t bandwidth enough? What happens without QoS? Congestion! Why and where does congestion occur? Examples will be presented shortly! QoS for accountability and SLA s! Well, there are many new applications waiting in the wings Computer Networks - 1/22
Distortion of Voice If no congestion, voice clarity is fine For 12% packet loss and 142msec delay then the voice can be very irritating to listen to For 700msec delay and 12% loss the voice is incomprehensible. Computer Networks - 1/23
Problems for Data with no QoS Interactive traffic will experience freezes and timeouts! Non-critical applications could chew up bandwidth for the critical applications eg client-server applications. The goodput of bulk transfers can be seriously affected Eg FTP, database synchronisation etc Poor productivity! Computer Networks - 1/24
Anatomy of Congestion The main cause of congestion is the lack of bandwidth Demand > Capacity! May arise due to unexpected traffic fluctuations Familiar with congestion in other contexts including: Road networks and In the air Computer Networks - 1/25
Causes of Delay ( Latency ) Fixed delays Delays in switching Propagation delays Serialisation Variable delays Buffering of packets during congestion Computer Networks - 1/26
Causes of Jitter Congestion causes buffering and this results in packets being released onto links with varying delays Computer Networks - 1/27
Causes of Packet Loss Exhaustion of buffers in routers and switches Computer Networks - 1/28
Serialisation Delay Voice Packet 60 Bytes Every 20 msec Voice Packet 60 Bytes Every > 214 msec Voice Packet 60 Bytes Every 20 msec ~214 msec Serialisation Delay Voice 1500 Bytes of Data Voice Voice 1500 Bytes of Data Voice Voice 1500 Bytes of Data Voice 10 Mbps Ethernet 10 Mbps Ethernet 56 kbps WAN Computer Networks - 1/29
Congestion Scenario 1 Speed Mismatch 100Mbps 2Mbps WAN 1000Mbps 100Mbps Data Flow A speed mismatch is the primary reason for congestion: Most likely this is persistent when moving from LAN to WAN Usually transient when going from LAN to LAN Computer Networks - 1/30
Congestion Scenario 2 - Aggregation Headquarters 2Mbps Choke Points 512Kbps Data Flow FR/ATM N*56Kbps Remote 1000Mbps S 1 1000Mbps S 2 Data Flow Choke Point Computer Networks - 1/31
Congestion Scenario 3 - Confluence Core 1 Core 2 STM-64/OC 64/OC-192c STM-16/OC 16/OC-48c Mechanisms needed to provide guarantees Transient congestion occurs in this situation Computer Networks - 1/32
Effects of a 1% Packet Drop Link E1 E2 E3 OC-3 OC-12 OC-48 OC-192 10GE Link-speed 2.048Mbps 8.448Mbps 34.368Mbps 155Mbps 622Mbps 2.4Gps 9.6Gps 10Gps Bits dropped per second 20.48kbps 84.48kbps 343.6kbps 1.55Mbps 6.22Mbps 24Mbps 96Mbps 0.1Gbps Computer Networks - 1/33
Quality of Experience for Users d Network d Codec V Codec Codec V Network Codec d Jitter V Jitter Play-out Network e Network Coding delay Jitter buffer delay e Jitter Computer Networks - 1/34
Demonstration Comparison of PSTN and VoIP quality
Sound Samples Sound Sample 1: First: Speech sampled at 44.1 khz. Second: Speech sampled at 20 khz. Sound Sample 2: First: Narrowband speech. Second: Encoded with G.729. Sound Sample 3: First: Music sampled at 44.1 khz. Second: Music sampled at 8 khz. Third: Music encoded with G.729. Sound Sample 4: First: Speech sampled at 44.1 khz. Second: Narrowband speech. Third: Telephony band speech. Sound Sample 5: First: Narrowband speech. Second: Wideband speech. Computer Networks - 1/36