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QoS of Voice over 802.11 with NS simulator

QoS of Voice over 802.11 with NS simulator. Presented by: SaiKamal Neeli Avinash Thota. VoIP-Introduction . VoIP-Voice over internet protocol. - Transfers voice using IP packets over the internet. How VoIP works-

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QoS of Voice over 802.11 with NS simulator

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  1. QoS of Voice over 802.11with NS simulator Presented by: SaiKamal Neeli Avinash Thota

  2. VoIP-Introduction VoIP-Voice over internet protocol. - Transfers voice using IP packets over the internet. How VoIP works- - conversion of analog voice to digital signal bits using ADC. - Compression of the digital bits in to a proper format for easy transmission. Protocols like PCM etc are used. - Inserting VoIP packets into data packets. VoIP data packets are packed in real time transport protocol packets which are inside UDP-IP packets. -H323 is the signaling protocol used to call the users. - In the receiver the received packets are converted in to analog voice signals and then the signals are transferred in to the sound card.

  3. Network Simulator Network simulator can be a software or hardware which can be used for predicting the behavior of the network. Different versions of the network simulators are ns-1, ns-2, ns-3. Ns-3 is the latest version of the network simulator.

  4. Overview • 802.11 - applies to wireless LANs and provides 1 or 2 Mbps transmission in the 2.4 GHz band using either frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS). • 802.11a - an extension to 802.11 that provides theoretically up to 54 Mbps in the 5GHz band, but realistically achieves 20-25 Mbps under normal conditions. 802.11a uses an orthogonal frequency division multiplexing encoding scheme (OFDM) • 802.11b (802.11 High Rate or Wi-Fi) - an extension to 802.11 that provides 11 Mbps transmission in the 2.4 GHz band. 802.11b uses only DSSS. Problem: No QoS

  5. Overview Both 802.11a and 802.11b have two channel accessing mechanisms: • PCF - Point Coordination Function Based on polling technique – each station is polled in turn and stations with a packet pending for transmission sends the packet upon being polled. A dynamic list of stations may be maintained by the AP in order to increase efficiency. • DCF - Distributed Coordination Function Based on CSMA/CA – stations contend for the channel. Two basic schemes are used: • Two way handshake: Acknowledgement is sent by the receiver to the sender upon successful reception of a packet. The acknowledgement is needed since the sender cannot determine whether its transmission was successful only by listening to it. • Four way handshake: RTS/CTS mechanism, and then proceed with ACKs as above.

  6. 802.11e – An extension of 802.11 designed to improve its • medium access mechanism and to add support for service • differentiation. Uses the HCF – hybrid coordination function • which is queue based service differentiation scheme that uses • both DCF and PCF enhancements - EDCF and EPCF.

  7. Goal • Investigate QoS indications (for voice packets), • Average Throughput (per voice connection). • Average Latency. • Packet Loss percentage.

  8. Simulated Network

  9. Setting Connections • Each wireless station has a different wire line station it “talks” to. • There are N + 4 connections: half from a wireless node to a wire line node • and half the other way (the connections are in one-direction) • There are N voice connections. The parameters we investigate are taken only from these connections

  10. Average Throughput as function of VOIP Calls ----- 802.11e ----- 802.11b Throughput is the average rate of successful message delivery over a communication channel.

  11. Average Latency as function of VOIP Calls ----- 802.11e ----- 802.11b • Latency: It is the time between the moment a voice packet is transmitted and the moment it reaches its destination • It slows down your phone conversations • Untimeliness can results in overlapping noises, with one speaker interrupting the other • Causes echo. • Disturbs synchronization between voice and other data types, especially during video conferencing

  12. Percentage of dropped packets as function of VOIP Calls ----- 802.11e ----- 802.11b

  13. Conclusions • When the number of voice connection becomes large, the performance of 802.11b • and 802.11e is very much alike. • QoS is not guaranteed by 802.11 standards because of the poor performance. • 802.11e is the only standard offering QoS to those applications which are time sensitive like video and audio communications.

  14. Thank You

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