1 / 38

IP Telephony Project

IP Telephony Project. By: Liane Lewin Shahar Eytan Guided By: Ran Cohen - IBM Vitali Sokhin - Technion. Agenda. What is IP Telephony The Jitter Buffer The Jitter Buffer Algorithm Implementation The Code Simulations Conclusions. Agenda. What is IP Telephony The Jitter Buffer

sovann
Download Presentation

IP Telephony Project

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. IP Telephony Project By: Liane Lewin Shahar Eytan Guided By: Ran Cohen - IBM Vitali Sokhin - Technion

  2. Agenda • What is IP Telephony • The Jitter Buffer • The Jitter Buffer Algorithm • Implementation • The Code • Simulations • Conclusions Network Lab - Technion

  3. Agenda • What is IP Telephony • The Jitter Buffer • The Jitter Buffer Algorithm • Implementation • The Code • Simulations • Conclusions Network Lab - Technion

  4. What is IP Telephony? • IP stands for Internet Protocol • Basically, it enables passing of audio data over the Internet. • The data is passed by UDP packets. Network Lab - Technion

  5. Why was that needed? • Imagine being able to call anywhere in the world for the cost of a local call… • Imagine being able to link your telephone system into your web page… • Imagine being able to give your customers a world wide toll-free number… • IP Telephony enables all that, and more... Network Lab - Technion

  6. Sounds easy? • Well, it’s not that easy! • We’re dealing with real time data, delays are critical • Remember the last time you talked to South America... • You would like a continuous conversation • You will not like to hear half words or sentences ( “ I ………….. you “ ) Network Lab - Technion

  7. Audio data is sent by UDP. • The network is not that reliable. • There are Routers on the way • Datagrams are delayed • Some times they change their order • Some times they just vanish • Some times they all come at once • Some one has to put an end to this mess... Network Lab - Technion

  8. Agenda • What is IP Telephony • The Jitter Buffer • The Jitter Buffer Algorithm • Implementation • The Code • Simulations • Conclusions Network Lab - Technion

  9. Jitter Buffer (JB) • Jitter - the speed variation between slowly and quickly traveling packets. • The JB stores packets, allowing most of the slower packets to catch up. • The less control in routing, the more jitter that results. Network Lab - Technion

  10. The Jitter Buffer Catch: More jitter means longer JB Longer JB introduces more latency Shorter JB loses too many packets Lose of packets cause voice to tumble Network Lab - Technion

  11. The Goal: How to control the Jitter Buffer? • Need to find a good algorithm that will control the JB. • A convenient Test Bench should be designed in order to simulate the algorithm. • The Test Bench will not be a full VoIP system (with gateways, routing, etc.) Network Lab - Technion

  12. Our Solution: The Packet Source The Network Module JB Destination Module Network Lab - Technion

  13. Agenda • What is IP Telephony • The Jitter Buffer • The Jitter Buffer Algorithm • Implementation • The Code • Simulations • Conclusions Network Lab - Technion

  14. The JB Algorithm: The frames number in the JB adjusts according to the High Water Mark (HWM) • Whenever the JB is empty, wait tillpackets will fill it to the HWM. • Whenever the jitter changes, check if the change is less then the last jitters. Network Lab - Technion

  15. By how much? Define consistent What is the Const ? • If the jitter is consistently shorter then reduce the HWM. • If the number of packets exceeds HWM X Const then throw the remains. • The HWM will increase whenever the Jitter exceeds a certain limit. • Remember, the goal is to have the shorter latency and the fewer breaks! What is the limit? Network Lab - Technion

  16. The Algorithm Parameters: • Prefetch - Initialized at the beginning of the JB operation. It is constantly updated according to the network behavior. • Stable History - Initialized at the beginning of the JB operation. It defines the time limit (in JB operations) needed to decide that the network is relatively stable. Network Lab - Technion

  17. The Algorithm Parameters (cont): • Prefetch reduction: Only when all the previous jitters during the last Stable History cycle where below the HWM. The Prefetch is reduced according to the difference between the current HWM and the maximal jitter. • Prefetch increment: Each time the jitter is higher then the Prefetch, it will increase to the jitter value. Network Lab - Technion

  18. The Algorithm Parameters (cont): • Packets are thrown whenever their number is 50% higher then the HWM. • The algorithm parameters are updated at every mode switch. Note: The parameters values are subject to change according to the packet size. The only well defined parameter is the Stable History. Network Lab - Technion

  19. Agenda • What is IP Telephony • The Jitter Buffer • The Jitter Buffer Algorithm • Implementation • The Code • Simulations • Conclusions Network Lab - Technion

  20. Implementation Notes • The project consist of 2 main blocks • The Packet Source and the Network module • It’s all part of the Test Bench • The Destination module • This is the main module. Improvement of this module is the goal of the project. Network Lab - Technion

  21. 2 ways to implement the Network module: 1. Simulation: • The path between source and destination is divided by Routers. • Number of Routers could be modeled by one queue as well. • For this queue we will add working parameters that characterize a network • Frequency of the breaks in its operation • The duration of a break Network Lab - Technion

  22. 2. Using the ‘Real’ Net • We used a Mirror Application • It runs on a far computer • All it does is replying the sender by sending his packets back immediately • While traveling through the net, packets: • where delayed • changed order • vanished away Network Lab - Technion

  23. The Destination: • Receives the voice packets • Uses the Jitter Buffer Algorithm • Tries to provide the user with smooth and short delayed voice Network Lab - Technion

  24. Agenda • What is IP Telephony • The Jitter Buffer • The Jitter Buffer Algorithm • Implementation • The Code • Simulations • Conclusions Network Lab - Technion

  25. The Code: • It contains 2 basic applications • The Network Simulator • The Destination • Each contains number of threads • Both NT and UNIX compatible • Few basic classes are being used to simplify the code (Sockets, Threads and Synchronization) Network Lab - Technion

  26. Implementing the Jitter Buffer • It’s basically a cyclic array • Allocated in memory at the beginning of the operation • Its size is a multiple of the Frame Size Get Put Wrap around Network Lab - Technion

  27. The JB Control • 3 Threads controls the JB I/O: 1. JB Input Thread: • Poles the network for incoming frames and inserts them to the JB according to their sequence number. 2. JB Output Thread: • Reads from the JB in constant frequency (equal to the sender’s), and plays the data to the user. 3. User Interaction Thread: • Gets the user commands Network Lab - Technion

  28. The Network Simulator • The Network is modeled as queue (Cyclic Queue) • 3 threads control its operation (Input, Output and User Interaction) • The input/output of the frames is done in order - FIFO Network Lab - Technion

  29. The Network Simulator (cont.) • The simulated network works according to the following parameters: • Breaks - Caused by heavy traffic in the net • Break frequency Those parameters could be entered by the user, or selected randomly Remember, if we want real data we still got the Mirror app. Network Lab - Technion

  30. Agenda • What is IP Telephony • The Jitter Buffer • The Jitter Buffer Algorithm • Implementation • The Code • Simulations • Conclusions Network Lab - Technion

  31. The Simulations Goal • Validate the code • Fix the constants values • Find the JB advantages over Simple algorithms Network Lab - Technion

  32. In each simulation we checked: • At any time: • Number of packets in the buffer (Buffer) • The number of input tries vs. output tries (Level) • The jitter (Jitter) • The HWM (Prefetch) • The approximate packet delay (Delay) • For comparison we managed also a simple buffer Network Lab - Technion

  33. Simulation Area: • Simulations ran on the “real net” using the Mirror application. It ran on computers in USA, Japan and closer. • To exercise the algorithm on different scenarios we used the network simulator. • For better view, we processed the data using Matlab. Network Lab - Technion

  34. Simulation Output Example Network Lab - Technion

  35. On the “Real” net with the Mirror Network Lab - Technion

  36. Agenda • What is IP Telephony • The Jitter Buffer • The Jitter Buffer Algorithm • Implementation • The Code • Simulations • Conclusions Network Lab - Technion

  37. Conclusions: • When coming to improve network connected applications, dynamic algorithms are needed. • Applying a JB to the destination improves the latency and breaks. • Its advantage is mainly when the net stabilizes. Not significant when it is static. Network Lab - Technion

  38. The End! Network Lab - Technion

More Related