Analisis Kualitas VoIP yang Berjalan di Atas Protokol Datagram Congestion Control Protocol

Abstrak Datagram Congestion Control Protocol (DCCP) adalah transport protocol yang didesain untuk aplikasi Internet multimedia. Protocol ini memiliki beberapa mekanisme congestion control dan dapat dipilih sesuai dengan karakteristik aplikasinya. CCID4 adalah salah satu mekanisme congestion control dari DCCP yang sesuai dengan aplikasi VoIP karena digunakan untuk mengirim paket yang berukuran kecil. Selain itu CCID4 mengatur jarak antar paket minimum sepanjang 10 ms sehingga paket VoIP tidak mendominasi penggunaan jaringan. Penelitian ini melakukan analisis terhadap protokol DCCP/CCID4 untuk mengetahui kualitas VoIP yang menggunakan protokol tersebut, membandingkan kualitas yang dihasilkan dengan penggunaan protokol UDP, serta melihat kualitas aliran TCP sebagai akibat dari terdapatnya aliran VoIP pada jaringan. Hasil simulasi memperlihatkan kualitas VoIP cenderung lebih baik dengan menggunakan protokol UDP dibandingkan dengan DCCP/CCID4 ketika tidak terdapat aliran TCP pada jaringan. Sebaliknya, ketika terdapat aliran TCP maka kualitas VoIP dengan protokol DCCP/CCID4 lebih baik dibandingkan dengan UDP. DCCP/CCID4 berhasil mencegah terjadinya congestion collapse dibandingkan dengan penggunaan UDP. Selain itu, kualitas TCP lebih baik ketika protokol DCCP/CCID4 digunakan untuk aplikasi VoIP pada jaringan yang mengalami congestion.   Kata kunci—mekanisme congestion control, Voice over Internet Protocol (VoIP), Datagram Congestion Control Protocol (DCCP), TCP, UDP, NS-2     Abstract Datagram Congestion Control Protocol (DCCP) is a transport protocol designed for multimedia Internet applications. This protocol has several congestion control mechanisms and can be selected according to application characteristics. CCID4 is a congestion control mechanism suitable for use with VoIP applications to send a small packet. CCID4 enforces a minimum interval of 10 milliseconds between data packets. This study conducted an analysis of DCCP/CCID4 protocol to determine the quality of VoIP that uses the protocol, comparing the quality produced by the used of UDP protocol, and see the quality of TCP flow as a result of the presence of the VoIP flow on the network. The simulation results show the quality of VoIP tend to do better by using the UDP protocol compared with DCCP/CCID4 when there is no TCP flow on the network. Conversely, when there are TCP flows, the quality of VoIP with DCCP/CCID4 protocol better than UDP. DCCP/CCID4 managed to prevent the congestion collapse compared with the use of UDP. In addition, the TCP quality is better when DCCP/CCID4 protocol used for VoIP applications that experiencing network congestion.   Keywords— congestion control mechanism, Voice over Internet Protocol (VoIP), Datagram Congestion Control Protocol (DCCP), TCP, UDP, NS-

Improvements in DCCP congestion control for satellite links

We propose modifications in the TCP-Friendly Rate Control (TFRC) congestion control mechanism from the Datagram Congestion Control Protocol (DCCP) intended for use with real-time traffic, which are aimed at improving its performance for long delay (primarily satellite) links. Firstly, we propose an algorithm to optimise the number of feedback messages per round trip time (RTT) rather than use the currently standard of at least one per RTT, based on the observed link delay. We analyse the improvements achievable with proposed modification in different phases of congestion control and present results from simulations with modified ns-2 DCCP and live experiments using the modified DCCP Linux kernel implementation. We demonstrate that the changes results in improved slow start performance and a reduced data loss compared to standard DCCP, while the introduced overhead remains acceptable

Rtp and the datagram congestion control protocol

We describe how the new Datagram Congestion Control Protocol (DCCP) can be used as a bearer for the Real-time Transport Protocol (RTP) to provide a congestion controlled basis for networked multimedia applications. This is a step towards deployment of congestion control for such applications, necessary to ensure the future stability of the best-effort network if high-bandwidth streaming and IPTV services are to be deployed outside of closed QoS-managed networks

Experimental performance of DCCP over live satellite and long range wireless links

We present experimental results for the performance over satellite and long range wireless (WiMax) links of the new TCP-Friendly Rate Control (TFRC) congestion control mechanism from the Datagram Congestion Control Protocol (DCCP) proposed for use with real-time traffic. We evaluate the performance of the standard DCCP/CCID3 algorithm and identify two problem areas: the measured DCCP/CCID3 rate is inferior to the rate achievable with standard TCP and a significant rate oscillation continuously occurs making the resulting rate variable even in the short term. We analyse the links and identify the potential causes, i.e. long and variable delay and link errors. As a second contribution, we propose a change in the DCCP/CCID3 algorithm in which the number of feedback messages is increased from the currently standard of at least one per return trip time. Although it is recognised that the increase in control traffic may decrease the overall efficiency, we demonstrate that the change results in higher data rates which are closer to what is achievable with TCP on those networks and that the overhead introduced remains acceptable

Transport Protocol Throughput Fairness

Interest continues to grow in alternative transport protocols to the Transmission Control Protocol (TCP). These alternatives include protocols designed to give greater efficiency in high-speed, high-delay environments (so-called high-speed TCP variants), and protocols that provide congestion control without reliability. For the former category, along with the deployed base of ‘vanilla’ TCP – TCP NewReno – the TCP variants BIC and CUBIC are widely used within Linux: for the latter category, the Datagram Congestion Control Protocol (DCCP) is currently on the IETF Standards Track. It is clear that future traffic patterns will consist of a mix of flows from these protocols (and others). So, it is important for users and network operators to be aware of the impact that these protocols may have on users. We show the measurement of fairness in throughput performance of DCCP Congestion Control ID 2 (CCID2) relative to TCP NewReno, and variants Binary Increase Congestion control (BIC), CUBIC and Compound, all in “out-of-the box” configurations. We use a testbed and endto- end measurements to assess overall throughput, and also to assess fairness – how well these protocols might respond to each other when operating over the same end-to-end network path. We find that, in our testbed, DCCP CCID2 shows good fairness with NewReno, while BIC, CUBIC and Compound show unfairness above round-trip times of 25ms

Simulasi dan Analisis Performansi Jaringan MANET Menggunakan Routing Protocol AODV dengan DCCP untuk Menangani Congestion

ABSTRAKSI: Mobile Ad-Hoc Network (MANET) merupakan pengembangan Ad-Hoc Network, dimana node dari jaringan ini memiliki mobilitas yang dinamis. Mobilitas dari node ini menyebabkan perubahan topologi jaringan sesuai dengan kondisi yang ada. Ad-Hoc On Demand Distance Vector (AODV) merupakan reactive routing protocol yang sangat sesuai diimplementasikan pada MANET karena pembangunan route pada AODV menyesuaikan dengan topologi jaringan. Penelitian membuktikan bahwa karakteristik mobilitas pada MANET akan menimbulkan congestion sebagai penyebab packet-loss yang lebih besar dan delay yang lebih panjang. Untuk itu, direkomendasikan DCCP (Datagram Congestion Control Protocol) sebagai transport protocol yang mengimplementasikan mekanisme congestion control pada MANET. Melalui skenario pengaruh nilai Packet Rate dan Pause Time, akan dibandingkan performansi UDP dan DCCP dalam menangani pemodelan traffic video streaming. Hasil simulasi menunjukkan performansi yang lebih baik pada DCCP dengan rata-rata nilai Packet Delivery Ratio sebesar 95%, Packet Loss Ratio sebesar 5%, End to End Delay sebesar 0.3s dan Routing Overhead sebesar 0.20.Kata Kunci : MANET, AODV, DCCP, congestion controlABSTRACT: Mobile Ad-Hoc Network (MANET) is an improvement of Ad-Hoc Network, which its node has capability of dynamic mobility. This feature will cause the topology changes in current condition. Ad-Hoc On Demand Distance Vector (AODV) is a relevant reactive routing protocol for MANET since the route is built based on the current network topology. Research proved that mobility characteristic of MANET will cause congestion as a trigger of frequent packet loss and longer delay. In that case, DCCP (Datagram Congestion Control Protocol) is suggested as a congestion control featured transport protocol for MANET. Through the scenario of different Packet Rate and Pause Time, simulation will compare the performance of UDP and DCCP when handling video streaming traffic model. Simulation result showed better performance of DCCP, where average mark of Packet Delivery Ratio reached 95%, Packet Loss Ratio reached 5%, End to End Delay reached 0.3s dan Routing Overhead reached 0.20.Keyword: MANET, AODV, DCCP, congestion contro

Performance of VoIP with DCCP for satellite links

We present experimental results for the performance of selected voice codecs using the Datagram Congestion Control Protocol (DCCP) with TCP-Friendly Rate Control (TFRC) congestion control mechanism over a satellite link. We evaluate the performance of both constant and variable data rate speech codecs (G.729, G.711 and Speex) for a number of simultaneous calls, using the ITU E-model and identify problem areas and potential for improvement. Our experiments are done on a commercial satellite service using a data stream generated by a VoIP application, configured with selected voice codecs and using the DCCP/CCID4 Linux implementation. We analyse the sources of packet losses which are a main contributor to reduced voice quality when using CCID4 and additionally analyse the effect of jitter which is one of the crucial parameters contributing to VoIP quality and has, to the best of our knowledge, not been considered previously in the published DCCP performance results. We propose modifications to the CCID4 algorithm and demonstrate how these improve the VoIP performance, without the need for additional link information other than what is already monitored by CCID4 (which is the case for Quick-Start). We also demonstrate the fairness of the proposed modifications to other flows. We identify the additional benefit of DCCP when used in VoIP admission control mechanisms and draw conclusions about the advantages and disadvantages of the proposed DCCP/ CCID4 congestion control mechanism for use with VoIP applications

Application-Level QoS: Improving video conferencing quality through sending the best packet next

In a traditional network stack, data from an application is transmitted in the order that it is received. An algorithm is proposed where information about the priority of packets and expiry times is used by the transport layer to reorder or discard packets at the time of transmission to optimise the use of available bandwidth. This can be used for video conferencing to prioritise important data. This scheme is implemented and compared to unmodified datagram congestion control protocol (DCCP). This algorithm is implemented as an interface to DCCP and tested using traffic modelled on video conferencing software. The results show improvement can be made to video conferencing during periods of congestion - substantially more audio packets arrive on time with the algorithm, which leads to higher quality video conferencing. In many cases video packet arrival rate also increases and adopting the algorithm gives improvements to video conferencing that are better than using unmodified queuing for DCCP. The algorithm proposed is implemented on the server only, so benefits can be obtained on the client without changes being required to the client

On the quality of VoIP with DCCP for satellite communications

We present experimental results for the performance of selected voice codecs using DCCP with CCID4 congestion control over a satellite link. We evaluate the performance of both constant and variable data rate speech codecs for a number of simultaneous calls using the ITU E-model. We analyse the sources of packet losses and additionally analyse the effect of jitter which is one of the crucial parameters contributing to VoIP quality and has, to the best of our knowledge, not been considered previously in the published DCCP performance results. We propose modifications to the CCID4 algorithm and demonstrate how these improve the VoIP performance, without the need for additional link information other than what is already monitored by CCID4. We also demonstrate the fairness of the proposed modifications to other flows. Although the recently adopted changes to TFRC specification alleviate some of the performance issues for VoIP on satellite links, we argue that the characteristics of commercial satellite links necessitate consideration of further improvements. We identify the additional benefit of DCCP when used in VoIP admission control mechanisms and draw conclusions about the advantages and disadvantages of the proposed DCCP/CCID4 congestion control mechanism for use with VoIP applications