Monday, May 1, 2017

Reducing delay in multimedia transmission application

Reducing delay in multimedia transmission application

Savita Saini
Assistant Professor, RRMK Arya Mahila Mahavidyalaya, Pathankot
Assistant Professor, RRMK Arya Mahila Mahavidyalaya, Pathankot                                                                                             

In multimedia transmission application we use transmission control protocol to send video packets that ensures the reliability but experiences delays.  There are abundant techniques that are to be to enhance the performances during transmission. In this paper we surveyed various techniques which are aimed to reduce the acknowledgement delay during the multimedia transmission. Here in this we evaluate various simulations that reduces the existing TCP delay.

Keywords- Transmission Control Protocol(TCP), multimedia traffic, Re-transmission

The Transmission Control Protocol (TCP) is one of the main protocols of the internet protocol. TCP is a standard that define how to establish and maintain a network conversation via which application program can exchange data. TCP works with internal Protocol (IP), which defines how computer send packets of data to each other. TCP and IP are the basic rules defining the internet.
There are two standard end-to-end communication protocols: transmission control protocol (TCP) and user datagram protocol (UDP). TCP provides reliable communication and resends every loss packets. TCP guarantees data transmissions by using acknowledgement packets. Even though, the acknowledgement packet and data retransmission generate additional delays, moreover if TCP delivers real-time multimedia traffics, delay increment will be a concern [1]. Therefore, various researches have been carried out to improve TCP performance. Among them, various TCP variants such as TCP Reno and TCP Vegas were emerged. Further, TCP Friendly Rate Control (TFRC) [2] was  by using window rate control techniques to determine network conditions. TCP split [3] was  to enhance TCP performances in different media. TCP multipath was also  for the same reason [4]. Besides TCP, UDP has also been used for multimedia communications such as video streaming [5].  However, packet loss generates problems as UDP is not responsive to network conditions. UDP keeps sending packets despite those packets are dropped by the congested network. UDP potentially causes poor network worsen. UDP improvements are performed in many ways. For instance, by adopting TCP properties [6], by using congestion control [7], by utilizing error correcting code [8], and by using negative acknowledgement [9, 10] This paper focuses on TCP performance improvement by reducing acknowledgement delay, so that the overall delay can
be reduced. Acknowledgement delay reduction is achieved by shortening acknowledgement packet route. The method may also be applied to other types of TCP.

Simulation Configuration
This paper evaluates the impact of the  method on TCP performances by using NS-2 simulations [11]. The Evalvid was integrated to the NS-2 simulator as the multimedia transmission evaluation framework [12]. The assessed network configuration consists of 22 nodes as shown in Figure 1. The configuration is set to avoid the NS-2 simulator from over capacity. The evaluated node is Node 9, which is set as the sender. Node 8 is set as the receiver. Node 9 sends multimedia traffic (akiyo_cif.yuv) which is encoded to MPEG4 with IPP packet sequence by using Evalvid [13]. Other nodes are assigned background traffics using constant bit rate (CBR) generators. Every link is set to be duplex which has varying bandwidth from 1.5 to 5 Mbps, and transmission delay 2 to 10 ms.

Fig.1. Simulated network configuration

The observed traffic specifications are shown in Table 1, where bitrates are changed during simulations from 541.47 to 601.12 Mbps. 

Video trace
Frame speed
Frame type
bitrates (kbps)
541, 47; 548, 16; 561, 22; 581, 57; 601, 12

Video traffics have speeds of 30 frames per second, and are encoded by using mpeg4 with frame sequences IPP.
Meanwhile, the background CBR traffics have 200 bit length which are periodically sent within 0.1 s interval.

Research Gap

The basic idea is to improve TCP performances by reducing the acknowledgement packet delay. The reduction is achieved by shortening acknowledgement route. This is can be realized by adding an alternative low speed direct link connecting the sender and the receiver.  Figure 2 describes that the video packets sent from Node 9 to Node 8 through the existing internet connection. Meanwhile, the acknowledgement packets sent from Node 8 to Node 9 are routed directly through the additional link. The additional link is the low cost and low speed connection. In the simulation, the speed of video are adjusted from 541.47-601.12 kbps sent through internet connection with speeds between 1.5 and 5 Mbps. The additional link for the acknowledgement packets is a low speed link, in this case 0.2 Mbps, about 40% of the traffic rates. In order to ensure that additional link is only transmitting the acknowledgement packets; this paper uses a simplex/duplex setting rather than routing method. The configuration is illustrated in Figure 2.

Fig. 2 The network adjustment
An additional direct link means additional cost. However, the link cost may not be significant as the required speed is as low as possible. For instance, live report of an event uses internet connection can be improved by adding a cell phone call or a cheap high frequency (HF) radio connection, connecting sender and receiver using data connections or modems as shown in Figure 3.

(a)                                                                                   (b)

Fig. 3. Additional link illustration (a) Without additional link  (b) With additional link

The enhancement is evaluated by using delay, jitter, and packet loss parameters. Beside impact of the additional link to standard TCP, impact to TCP variant (TCP\vegas) is also presented. Logically, the additional link can also be used for sending video packets; the paper also evaluates this option. Even though, the cost considerations of the additional link as well as the bandwidth requirements are out of the scope of this paper.

A. TCP Performances Using Separated Acknowledgement Route
(a) Delay
(b) Jitter
(c) Packet loss


Fig. 4. Delay, jitter and packet loss characteristics of TCP 

Delay characteristics of TCP before and after adding acknowledgement route are plotted in Figure 4a. The method is able to reduce TCP delay significantly about 1.14% to 11.16%. The method is failed to consistently improve jitter, however the average jitter difference is only about 0.64% (Figure 4b). The packet loss characteristics remain similar(Figure 4c).

Various Method Impact on TCP Vegas
Since TCP Vegas is also using acknowledgement, direct route of acknowledgement packets also has positive impact on TCP Vegas. TCP Vegas delays are reduced about 4.18% in average with jitter reduction is about 3.63%(Figure5). Packet loss characteristics remain similar (Figure 4c).
(a) delay
(b) jitter


Fig. 5. Delay and jitter characteristics of TCP Vegas and  method

C. Impact of Additional Link Without Acknowledgement Route Separation
The link addition may be considered unfair as the end to end connection experiences total bandwidth increment.
However, the simulation shows that such link does not improve the performance if it is used for transmitting video
packets. When video packets flow through the additional link, the overall delay increases up to 37.47-40.09 ms. Video packets experience higher delay up to 159% although its jitter reduced to 62.4% as the connection be redirected to the shortest link (Figure 6, 7). The tremendous delay increment is caused by the default network simulators employ the open shortest path first (OSPF) routing so that all video packets chose the direct path which has lower bandwidth than its traffic.

Fig. 6: Delay characteristics of TCP without acknowledgement separation
Fig. 7. Jitter characteristics of TCP without acknowledgement separation

Based on the evaluation results, it is proven that TCP and TCP Vegas performances are positively improved in term of delay when acknowledgement route is separated. TCP delays are corrected in average 8.12% lower than the original network configuration, while jitter characteristic is not consistent. TCP Vegas delay is reduced in average 4.18% and its jitter is decreased 3.63% in average. The additional link has positive impact only if it is dedicated for the acknowledgement packets; otherwise, delay worsens up to 159%. Future work may implement the method on real networks, consider network costs, and examine the minimum bandwidth requirement.


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