CHAPTER 3 PERFORMANCE ANALYSIS OF TRANSPORT PROTOCOLS TCP, UDP, SCTP AND DCCP VARIANTS

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1 53 CHAPTER 3 PERFORMANCE ANALYSIS OF TRANSPORT PROTOCOLS TCP, UDP, SCTP AND DCCP VARIANTS 3.1 INTRODUCTION In general, the performance of the congestion control algorithms of the presently available internet transport protocols for wired, wireless and mobile ad hoc networks, are found highly reliable under certain scenarios. Also, their performance is not found satisfactory under a high density sensor network application since, they are not designed for sensor networks in mind. To determine a best suited algorithm for a sensor network it is proposed to analyze the performance of some of the standard transport protocols on a congested sensor network environment. The protocols selected for this purpose in this research work are TCP, UDP, SCTP, DCCP-TCP-like and DCCP-TFRC. To estimate the performance of any proposed system in the field of engineering and technology, finding a suitable model of the system using any of the proven modeling techniques, with the minimum permitted deviation from the actual scenario, is the first step. This is followed by simulating the model using a simulation tool with a degree of compromise such that the results obtained from the simulation by and large reflects the actual values. Hence, a brief overview of the NS2 simulation scenario over which the proposed transport protocols are to be implemented and the standard metrics used to estimate their performances are also given in this chapter.

2 PROPOSED WSN SCENARIO A typical WSN scenario over which the proposed protocols are to be implemented to estimate their performances is depicted in Figure 3.1. There are 57 nodes in the proposed scenario with one sink node or base station and 50 normal nodes with relatively lesser transmission range. Seven gateway nodes are provided to facilitate the information exchange between sink node and normal nodes Node 0 Sink Node Nodes 1 to 7: Gateway Nodes Nodes 8 to 57: Normal Sensor Nodes Figure 3.1 Proposed wireless sensor network In the simulated sensor field the 0 th node is the sink node. Nodes 1 to 7 are sensor nodes capable of communicating to sink node with relatively higher transmission power. All other nodes are normal sensor nodes and can transmit only for a short distance. The Transmission power of the sensor

3 55 nodes and sinks are set based on the required transmission range, signal frequency and other related parameters. Table 3.1 Transmission range of nodes S.No Node Type Range 1 Sink Node (Node 0) 150m 2 Gateway Nodes (Nodes 1 to 7) 150m 3 Normal Sensor Nodes (Nodes 8 to 57) 60 m Table 3.2 Specification of sensor field S.No. Parameter Value 1 Channel Wireless Channel 2 Propagation Two Ray Ground 3 Physical Medium Wireless medium 4 Antenna Omni Antenna 5 Routing Protocol AODV 6 MAC Type Queue Drop Tail / PriQueue 8 Queue Size 50 9 Traffic Application CBR 11 Number of Nodes Topographical Area m 13 Simulation Time 100 sec The energy model of NS2 is used to study the power drain characteristics of the node. In the network simulated, sensor nodes send the

4 56 data to the sink in a periodic fashion as in the case of practical networks and no cross traffic is taken into account during evaluation of the protocols. So, the total sent and received packets will increase with respect to the increase in reporting interval since, the overall simulation time is kept constant. The different attributes of the various components of the sensor field are set to the default values as specified by NS2. The transmission range of different types of nodes and the specifications for sensor field are given in Tables 3.1 and 3.2 respectively. 3.3 OVERVIEW OF PERFORMANCE METRICS To estimate the performance of a system there are certain metrics associated with the system under consideration and a range of desired values for those metrics. These values of the metrics determine the quality of the system and its suitability for the proposed objective. In similar lines, the standard metrics considered in this work to evaluate the performance of WSN employed with different protocols are Throughput, Energy Consumption, Routing Load, MAC Load, Dropped Packets and End-to-End Delay Throughput This metric defines the number of packets received by a destination or sink over the given period of time. Obviously, a better congestion control algorithm results in the delivery of good number of packets with respect to time always. The unit for throughput is kilo bits per sec (Kbps) Energy Consumption The average energy consumed by all the nodes of the network is considered as a metric to assess the performance of the congestion control algorithms. The energy consumption of a node depends on several parameters

5 57 such as sensor data reporting interval, routing protocol, transport protocol, congestion control algorithm of the transport protocol etc., and it is obvious that the lower energy consumption signifies better congestion control algorithm. The unit for this metric is Joules Routing Load It is the number of routing packets required to transmit a data packet successfully from a source to sink. A better congestion algorithm provides a relatively lower routing load for the given amount of data packets. The unit for Routing Load is Packets, i.e. the number of routing packets MAC Load MAC load means the average number of MAC messages generated for the successful delivery of each data packet to the destination. Hence, lower MAC load signifies better congestion control algorithm. The unit for MAC load is packets Dropped Packets The data packets that fail to reach sink due to congestion during transmission are dropped packets. In a better congestion control algorithm the count of dropped packets should be significantly low. The unit for this metric is Packets per Second End to End Delay End to End Delay (EED) is the cumulative delay that might arise as a result of buffering during discovery of routes over sensor network, queuing at interfaces of the sensor nodes, delays in retransmission at MAC, and the time taken for propagation and transfer over the sensor field.

6 58 Evidently a better algorithm will deliver the packets with minimum delay. The unit for EED is milliseconds. N EED= (r n, s n ) n=1 (3.1) where -the time that data packet n was sent -the time that data packet n was received -the total number of data packets received. 3.4 PERFORMANCE ANALYSIS OF TRANSPORT PROTOCOLS TCP, UDP and SCTP are well suited for efficient streaming communication over unreliable internet but they need to be improved for better performance over a typical wireless sensor network scenario. A typical wireless sensor network is highly unstable as it is error-prone due to various reasons such as interference of radio signal, radio channel contention, and survival rate of nodes (Yao-Nan Lien 2009).This error rate is increased significantly in a multi-hop network due to channel contention. Further, in a sensor network error rate is much higher and bandwidth is smaller than that of fixed networks. As a consequence, running conventional TCP, UDP or SCTP protocol on a wireless sensor network will potentially suffer from severe performance degradation (Zhaojuan Yue et al 2012). It is obvious that the capabilities of wireless sensor nodes are much less than that of their fixed network counterparts, due to various reasons (Jang-Ping Sheu et al 2009). The complexity in implementing a standard TCP or SCTP protocol inside the tiny sensor nodes further degrades the

7 59 performance of wireless nodes. However, the capabilities of the modern sensor nodes have improved so much to accommodate a fully functional TCP like protocol stack inside them. Protocol DCCP is having some interesting properties, which makes it possible to use it in an error-prone sensor network scenario. To evaluate the performance of DCCP, when implemented over a congested WSN, it is necessary to conduct experiments under various environmental conditions. UDP is a simple open systems interconnection transport layer protocol for client-server network applications based on Internet protocol and was introduced in 1980 as a main alternative to TCP. UDP is an unreliable protocol as it does not include any congestion control mechanism. The messages, to be sent by the sender, are split in to datagrams and these datagrams are sent as packets on the network layer, without any buffer support on both sending and receiving sides. UDP is mainly for real-time performance oriented applications such as video-conferencing and computer games. To achieve higher performance, as preferred by the applications, dropping of individual packets without any retries and reception of packets in a different order than they were sent are permitted. So, evaluating these classical protocols on wireless sensor networks may provide an opportunity to understand and estimate their performance in wireless sensor networks. An in-depth analysis, based on the above study, may help us to include the necessary modifications and improvements so as to accommodate those protocols for wireless sensor networks. More experiments and evaluations are needed to understand the behavior of these protocols under congested sensor network scenario which may lead to the selection of a better congestion control algorithm for wireless sensor networking.

8 Transmission Control Protocol A basic strategy for communication among dissimilar networks called as TCP. The evolution that followed provides a reliable and ordered delivery of a data among the communicating nodes. Internet protocol suite comprises two core protocols viz. TCP and IP and commonly referred to as TCP/IP. In the event of data transmission between two computers, TCP, staying between an application program and the Internet protocol, provides reliable and ordered delivery of a stream of bytes from a program on one computer to another program on another computer (Bennett et al 1999). That is, when an application program desires to send a large chunk of data across the internet using IP, instead of breaking the data into IP-sized pieces and issuing a series of IP requests, the software can issue a single request to TCP and let TCP to handle the IP details. TCP is a byte-stream protocol as its flow control and acknowledgement are based on byte number rather than packet number. However, the smallest unit of data transmitted over the internet is a data segment or packet and each packet is identified by a data octet number. When a destination receives a data segment, it acknowledges the receipt of the segment by issuing an ACK with the next expected data octet number. The time elapsed between moment a data segment is sent and the moment an ACK for that segment is received is known as the RTT of the communication between the source and the destination, which is the sum of the propagation, transmission, queuing, and processing delays at each hop of the communication, along with the time taken to process a received segment and generate an ACK for the segment at the destination. The flow control mechanism used by TCP is a credit allocation scheme. To avoid overwhelming its buffer space, a destination advertises to the associated source the size of a window, called as advertised window,

9 61 which indicates the number of data bytes, beyond the acknowledged data, the source can send to the destination. This information is included in the header of each TCP (data or control) segment sent to the source. Suppose that based on the ACKs received, a source knows that Byte is the last data byte received by the destination. The source can send data up to Byte +, where W is the size of the advertised window. The scenario of the source s sequence number space is exhibited in Figure 3.2. Sent but Unacknowledged Not yet Sent x Advertised Window x + W Sequence Number Figure 3.2 An illustration of the source sequence number space and advertised window in TCP Congestion Control Operations of TCP To achieve good performance, it is necessary to control network congestion so that the number of packets lost within the internet is well below the level at which the network performance drops significantly. Various congestion control measures (Stefan Savage et al 1999) have been implemented in TCP to limit the sending rate of data entering the internet by regulating the size of the congestion window cwnd, and the number of unacknowledged segments permitted over the link. These measures include slow start, congestion avoidance, fast retransmit, and fast recovery. When a new connection is established, TCP initializes the cwnd size to 1. In slow start, the value of cwnd is incremented by one each time an ACK is received until it reaches the slow start threshold, ssthresh.

10 62 TCP uses segment loss as an indicator of network congestion. To characterize a segment as being lost in transit, a source has to wait long enough without receiving an ACK for the segment. Therefore, a retransmission timer is associated with each transmitted segment and a timer timeout signals a segment loss. The Retransmission Timeout Period (RTO) is determined by the sum of the smoothed exponentially weighted moving average and a multiple of the mean deviation of RTT (Leung et al 2007). When a timeout occurs, ssthresh is set to half of the amount of outstanding data sent to the network. The slow start process is performed starting with cwnd set to one and changes the size of it using AIMD technique, until it reaches ssthresh. The congestion avoidance phase is then carried out where cwnd is increased by one for each RTT. When the data octet number of an arriving segment is greater than the expected one, the destination finds it as a sequence hole, i.e. a gap in the sequence number space. Then the receiver immediately sends out a duplicate ACK, i.e., an ACK with the next expected data octet number in the cumulative acknowledgement field, to the source, instead of the ACK for the segment received with sequence hole. If the communication channel is an in-order channel, the reception of a duplicate ACK implies the loss of a segment. When the source receives three duplicate ACKs, fast retransmit is triggered such that the inferred loss segment is retransmitted before the expiration of the retransmission timeout. Fast recovery works as a companion of fast retransmit. A fast retransmission suggests the presence of mild network congestion. To handle this, ssthresh is set to half of the amount of outstanding data sent to the network. Since the reception of a duplicate ACK indicates the departure of a segment from the network, cwnd is set to the sum of ssthresh and the number

11 63 of duplicate ACKs received. When an ACK for a new segment arrives, cwnd is reset to ssthresh and then congestion avoidance takes place. Packet reordering refers to the network behavior where the relative order of some packets in the same flow is altered when these packets are transported in the network. In other words, the receiving order of a flow of packets or segments differs from its sending order. The presence of persistent and substantial packet reordering violates the in-order or near in-order channel assumption made in the design principles of some traffic control mechanisms in TCP. This can result in a substantial degradation in application throughput and network performance (Laor and Gendel 2002). Modern TCP implementations also include congestion control mechanisms that adapt the source transmission behaviour to network conditions by dynamically computing the congestion window size. The goal of TCP congestion control is to increase the congestion window size, if there is additional bandwidth available on the network, and decrease the congestion window size upon congestion. It is widely agreed that the congestion control schemes in TCP provide stability for the best effort internet. These mechanisms increase network utilization, prevent starvation of flows, and ensure inter-protocol fairness (Floyd and Fall 1999). With TCP as the benchmark, a transport mechanism in WSN should have basic functionalities such as reliable transport of data, better congestion control means, reasonable rate-control and acceptable fairness (Xiaohua Luo 2004) User Datagram Protocol The UDP is another protocol with TCP/IP suit which can send messages, or datagrams in this protocol, to other nodes on IP network without

12 64 requiring prior communications to set up special transmission channels or data paths. UDP does not guarantee reliability or ordering in the way that TCP does. Datagrams may arrive out of order, appear duplicated, or go missing without notice. Avoiding the overhead of checking whether every packet actually arrived makes UDP faster and more efficient, at least for applications that do not need guaranteed delivery. Time-sensitive applications often use UDP because dropped packets are preferable to delayed packets. UDP's stateless nature is also useful for servers that answer small queries from huge numbers of clients. Unlike TCP, UDP supports packet broadcast i.e. sending to all on local network and multicasting i.e. send to all subscribers. UDP assumes that error checking and correction is either not necessary or performed in the application, thus avoiding the overhead of such processing at the network interface level. Due to this, the arrival of datagrams may not be in the same order in which they were transmitted and some of the transmitted datagrams may not reach the receiver and hence, lost during transmission. The QoS is further deteriorated by data duplication and data loss. UDP is more appropriate for applications where time is precious than data loss and hence, seldom suitable for real-time applications Stream Control Transmission Protocol In SCTP the transmission of a message is in the form a stream instead of individual data packets and hence, considered as a single operation. Similarly the reception of the exact message is also considered as a single operation (Boussen et al 2009, Maria-Dolores Cano 2011). Multi-homing

13 65 and Multi-streaming are the two special features of SCTP and a connection between two endpoints in this context is called an association. Multi-homing is defined as the ability of an association to support multiple IP addresses or interfaces at a given end point. Use of more than one address permits re-routing of packets in the event of failure and also provide an alternate path for retransmissions, thus resulting in greater survivability of the session. Multi-streaming represents a sequence of messages, either long or short, within a single association and different from multiple streams. The messages include control flags for segmentation and reassembly. Stream Identifiers and Stream Sequence numbers are included in the data packet to allow sequencing of messages on a per-stream basis which eliminates the unnecessary head-of-line blocking between independent streams of messages, in case of loss in any of the streams. In addition SCTP provides mechanism for designating order-of-arrival delivery as opposed to ordered delivery Datagram Congestion Control Protocol With UDP as the base, DCCP is developed for effective and efficient handling of congestion, resulting in more reliable transmission of datagrams or packets. It is highly promising that DCCP will become the defacto standard for multimedia rich content delivery over IP-based networks (Stanimir Statev et al 2008). The main objective of DCCP is to extend support for implementing different congestion control schemas out of which the most suitable one may be selected by the applications, particularly multimedia streams, so as to provide efficient congestion control.

14 66 Hence, according to the type of data being transmitted a schema will be selected to assure a better flow of packets. A mechanism, known as CCID, is implemented in DCCP, enabling it to assign separate CCID for each direction of data flow. The nature of congestion is defined by CCID and the source and destination select appropriate mechanism to handle this congestion by feature negotiation (Kohler et al 2006), a method that selects the best suited algorithm for the present scenario. DCCP congestion control structure is so designed that the addition of new congestion control algorithms or the deletion/modification of existing algorithms takes place, regardless of the core of the protocol. Presently DCCP-TCP-like and DCCP-TFRC are two such standard mechanisms DCCP-TCP-like Congestion Control The DCCP-TCP-like Congestion Control mechanism implements an algorithm that controls the congestion through tracking a transmission window, and regulating the transmit rate similarly to that of TCP and designated as CCID 2. CCID 2 takes the advantage of available bandwidth in a rapidly changing environment and is suitable for senders who can adapt to the abrupt changes in congestion window, typical to that of TCP s AIMD congestion control (Floyd and Kohler 2006). CCID 2 is also appropriate for DCCP flows, that would like to receive as much bandwidth as possible over long term and consistent with the use of end-to-end congestion control and tolerates large sending rate variations characteristic of AIMD congestion control, including halving of the congestion window in response to a congestion event. Hence, CCID 2 is most suitable for applications that simply need to transfer as much data as possible over a short period of time.

15 DCCP-TFRC Congestion Control Congestion control is implemented in DCCP-TFRC by tracking the packet loss rate and varying the transmission rate in a smoother manner using AIMD, and this technique of congestion control is designated as CCID 3. DCCP-TFRC is a receiver-based congestion control mechanism that provides a TCP-friendly sending rate while minimizing the abrupt-ratechange characteristic of TCP or TCP-like congestion control. Upon receiving a loss event rate sent by the receiver, the sender sets its allowed sending rate appropriately (Floyd et al 2006). CCID 3's TFRC congestion control is most suitable for flows that would prefer to minimize abrupt changes in the sending rate, including streaming media applications with small or moderate receiver buffering before playback. 3.5 PERFORMANCE ANALYSIS Sensor networks with protocols TCP, UDP, SCTP, DCCP-TCP-like and DCCP-TFRC have been simulated with different data reporting intervals and the results obtained are plotted with respect to the data reporting intervals and metrics concerned. The individual performances of all the five protocols with respect to the desired metrics are given in Tables 3.3 through Table 3.7. The performance of each protocol is analyzed in this section along with the comparison of the performances of other protocols. Table 3.3 shows that the performance of TCP for different metrics taken for consideration. It is observed from the table that TCP does not perform well in terms of EED delay. The average EED delay obtained by TCP is which are very higher when compared with other protocols taken for analysis. TCP provides second worst results in terms of Average

16 68 Routing Load, Average MAC Load and Average Dropped Packets, with the value of 56.49, and respectively. Interval (seconds) EED Delay (ms) Table 3.3 Performance of TCP Routing Load (pkts) Mac Load (pkts) Dropped Packets (pkts /sec) Throughput (bytes/sec) Consumed Energy (Joules) Average The performance of TCP is found to be poor in terms of average energy consumption with the value of 1.43 Joules. TCP provides second best result for throughput next to UDP when Average throughput is considered. Thus, on the whole except for average throughput, TCP provides poor results with respect to the metrics considered. Table 3.4 Performance of UDP Interval (seconds) EED Delay (ms) Routing Load (pkts) Mac Load (pkts) Dropped Packets (pkts /sec) Throughput (bytes/sec) Consumed Energy (Joules) Average

17 69 It is noticed from the Table 3.4 that UDP provides third best result in terms of EED delay next to DCCP-TCP-like and DCCP-TFRC approach with the delay of ms. UDP also provides third best results in terms of Average Routing Load, Average MAC Load and Average Dropped Packets, with the value of 8.66, and respectively. UDP provides moderate results in terms of average consumed battery energy with the value of 1.37 Joules. UDP outperforms other protocols with highest throughput. Thus, on the whole UDP provides moderate results with all the metrics taken for consideration. Table 3.5 shows the overall performance of the SCTP. SCTP does not provide significant EED delay and the delay is very high, ms. The average routing load of SCTP is 82 and it is the highest routing load when compared with other protocols. The average MAC load obtained is which is also higher than other protocols. The packets dropped by the SCTP is very large than the other protocols. Table 3.5 Performance of SCTP Interval (seconds) EED Delay (ms) Routing Load (pkts) Mac Load (pkts) Dropped Packets (pkts /sec) Throughput (bytes/sec) Consumed Energy (Joules) Average

18 70 In terms of Average consumed energy, SCTP does not provide significant results as it consumes higher energy next to TCP. Average throughput by the SCTP is also very less when compared with other algorithms. Average Through put of DCCP-TCP-like is kbps which is the better than SCTP. From the foregoing discussion it may be observed that SCTP fails in all aspects with respect to WSN, and hence not a suitable protocol for WSN. Table 3.6 Performance of DCCP-TCP-like Interval (seconds) EED Delay (ms) Routing Load (pkts) Mac Load (pkts) Dropped Packets (pkts /sec) Throughput (bytes/sec) Consumed Energy (Joules) Average It is observed from the Table 3.6 that the average energy consumed by DCCP-TCP-like is 1.23 Joules which is the second best result, and next to DCCP-TFRC approach. The routing load is also very less for DCCP-TCPlike. It is the second least value next to DCCP-TFRC. When the MAC load is considered DCCP-TCP-like provides a relatively lower value, The packets dropped by the DCCP-TCP-like approach is also very less when compared with the protocols TCP, UDP and SCTP.

19 71 Table 3.7 Performance of DCCP-TFRC Interval (seconds) EED Delay (ms) Routing Load (pkts) Mac Load (pkts) Dropped Packets (pkts /sec) Throughput (bytes/sec) Consumed Energy (Joules) Average When EED delay is considered, DCCP-TCP-like produces the least delay among all the five protocols with ms. Thus DCCP-TCP-like approach provides significant results with all the metrics found to be next to DCCP-TFRC Table 3.7 shows the overall performance of the DCCP-TFRC with respect to performance metrics taken for consideration. It is observed from the Table that the DCCP-TFRC outperforms all the other protocols taken for consideration and provides a fairly acceptable result along with DCCP-TCP-like Throughput Figure 3.3 show the throughputs of all the five protocols against different data reporting intervals. Upon considering the individual performances, it is noticed that during low data reporting intervals the throughputs are better for all protocols, comparing their corresponding high data reporting interval response.

20 Data Reporting Interval Vs. Throughput Throughput (Kbps) TCP UDP SCTP DCCP-TCP-like DCCP-TFRC Data Reporting Interval (sec) Figure 3.3 Data reporting interval Vs throughput of all protocols As TCP is reliable and byte oriented, the throughput is relatively better as it assures the delivery of all the data bytes. Though SCTP is also reliable, it is stream oriented and hence, even a loss of single byte in a stream necessitates the retransmission of entire stream again, bringing down the throughput. Further, in SCTP, the life time of the data to be transmitted is specified by the application and hence, in case if the life time expires, the data will be discarded even if it is not sent, which deteriorates throughput. Unlike TCP and SCTP which use dedicated paths, UDP is permitted to send the data through all the available paths which increases the probability of the data delivery and so the throughput. It is found that the throughputs of all the protocols converge as the data reporting time increases. It is also observed that when the data reporting interval is too low UDP outplays other protocols. As the data reporting interval increases the performance of TCP improves and provides best throughput at high data reporting intervals among all protocols, which is closely followed by UDP. Figure 3.4 shows the average throughput of the

21 73 protocols and it may be concluded that the performance of TCP protocol based networks, baring low data interval periods, is the best and UDP dominates during low data reporting intervals due to highest delivery rate during that period. Average Throughput Throughput (Kbps) TCP UDP SCTP DCCP-TCP-like DCCP-TFRC Protocols Figure 3.4 Average throughput of all protocols Energy Consumption The amount of energy consumed in Joules by all five protocols over the data reporting intervals are given in Figure 3.5 and the average of energy consumed by the protocols is given in Figure 3.6. At lower data reporting intervals, the reporting is more frequent which results in higher energy consumption for all the protocols as shown in Figure 3.5. It is found that UDP consumes maximum energy during low data reporting intervals in view of higher throughput. The energy consumption falls significantly on moving towards higher data reporting intervals for UDP, resulting in moderate average energy consumption over the entire period with respect to UDP as shown in Figure 3.6.

22 74 As TCP and SCTP are reliable protocols, it is necessary for them to retransmit the data when data is discarded, reordered, duplicated or corrupted. Due to this it is obvious that the energy requirement is higher for them in view of additional overheads to assure proper delivery of data, as shown in Figures 3.5 and 3.6. Energy Consumed (Joules) Data Reporting Interval Vs. Energy Consumed TCP UDP SCTP DCCP-TCP-like DCCP-TFRC Data Reporting Interval (sec) Figure 3.5 Data reporting interval Vs energy consumed by all protocols With respect to the variants of DCCP, the energy consumption is relatively lesser than other three protocols, as the retransmission is permitted only for control packets and not for data packets in those protocols. Among the protocols DCCP-TCP-like and DCCP-TFRC, protocol DCCP-TCP-like found to consume lesser energy over the entire time period considered due to its abrupt nature i.e. the window size is reduced suddenly on sensing congestion, as observed from Figures 3.5 and 3.6. The smooth transmission behavior of DCCP-TFRC, on sensing congestion, forces it to consume bit higher energy than that of DCCP-TCP-like.

23 75 Average Energy Consumed Energy Consumed (Joules) TCP UDP SCTP DCCP-TCP-like DCCP-TFRC Protocols Figure 3.6 The average energy consumed by all protocols Routing Load The amount of routing load over different data reporting intervals for the five protocols are shown Figure 3.7. With respect to the protocols SCTP and TCP, it is found from the Figure 3.8, the routing load is prohibitively higher in view of their additional overheads to assure reliable transmission. With respect to other three protocols, as there is no retransmission of data the required routing load falls significantly. It is observed that DCCP-TFRC and DCCP-TCP-like protocols result in almost equal routing load over the entire time interval and also the lowest among all the protocols. UDP protocol closely follows DCCP based protocols at low reporting intervals and marginally increases with reporting time.

24 76 Routing Load (pkts) Data Reporting Interval Vs. Routing Load Data Reporting Interval (sec) TCP UDP SCTP DCCP-TCP-like DCCP-TFRC Figure 3.7 Data reporting interval Vs. routing load of all protocols Average Routing Load Routing Load (pkts) TCP UDP SCTP DCCP-TCP-like DCCP-TFRC Protocols Figure 3.8 Average routing load of all protocols The average routing load for all five protocols is shown in Figure 3.8 and it is clear from it that DCCP based protocols provide best performance among all the protocols considered MAC Load Comparing Figure 3.7 with Figures 3.9 and 3.8 with 3.10 it may be easily concluded that the performance of MAC load is similar to that of Routing load for all the five protocols.

25 77 Data Reporting Interval Vs. MAC Load 250 MAC Load (pkts) TCP UDP SCTP DCCP-TCP-like DCCP-TFRC Data Reporting Interval (sec) Figure 3.9 Data reporting interval Vs MAC Load of all protocols Hence, from the discussions given in section 3.5.3, it may be arrived that the performances of the networks, based on DCCP are better than all other protocols with respect to MAC load also. Average MAC Load MAC Load (pkts) TCP UDP SCTP DCCP-TCP-like DCCP-TFRC Protocols Figure 3.10 The average MAC load of all protocols

26 Dropped Packets Figure displays the number of dropped packets during different data reporting intervals for the five protocols considered in this work. Data Reporting Interval Vs. Dropped Packets Dropped Packets (pkts/sec) Data Reporting Interval (sec) TCP UDP SCTP DCCP-TCP-like DCCP-TFRC Figure 3.11 Data reporting interval vs. dropped packets by all protocols TCP and SCTP protocols transmit data from a source to a destination only through a dedicated path and hence, when congestion occurs the probability of data loss is high. The life time specific data packets in SCTP increase the count of dropped packets further, due to which the amount of dropped packets in SCTP is always high. UDP transmits data through all the available paths and hence, if data is lost in one path due to congestion or any other reason, the same data which is travelling over other paths may reach the destination successfully, thus reducing the amount of dropped packets. On the other hand DCCP variants, after establishing a connection between a sender and a receiver after negotiation, start data transmission and in case of congestion they reset the connection and reestablish it. Due to this

27 79 in DCCP protocol based networks the amount of data loss is minimized as shown in Figures 3.11 and Upon considering the average loss over the data reporting interval as given in Figure 3.12, it is found that the data loss with respect to DCCP based protocols is the least. Average Dropped Packets Dropped Packets (pkts/sec) TCP UDP SCTP DCCP-TCP-like DCCP-TFRC Protocols Figure 3.12 Average dropped packets by all protocols End-to-End Delay From Figure 3.13 it is obvious that the EED is higher with respect to TCP and SCTP as the average amount of data loss is prohibitively higher than other three protocols as shown in Figure Though the average data loss is higher in case of the TCP than that of SCTP, former takes relatively longer time to deliver data as given in Figure 3.13 for all the data reporting intervals considered. The reason is that, TCP is byte oriented protocol and the delivery of each byte is to be assured by it where as SCTP is stream oriented protocol and it is related to the delivery stream of bytes rather than individual byte and hence, the latter involves relatively lesser overheads.

28 Data Reporting Interval Vs. End-to-End Delay End-to-End Delay (ms) TCP UDP SCTP DCCP-TCP-like DCCP-TFRC Data Reporting Interval (sec) Figure 3.13 Data reporting interval Vs. end-to-end delay of all protocols With respect to the remaining three protocols, EED is relatively very low and constant over the reporting intervals considered. It may further be noticed that DCCP-TCP-like and DCCP-TFRC protocols based networks exhibit almost same delay time where as that of UDP based networks is marginally higher. These facts are evident on considering average EED as given Figure Average End-to-End Delay End-to-End Delay (ms) TCP UDP SCTP DCCP-TCP-like DCCP-TFRC Protocols Figure 3.14 Average end to end delay of all protocols

29 RESULT ANALYSIS The consolidated performance of WSN based on the transport protocols TCP, UDP, SCTP and DCCP-TCP-like and DCCP-TFRC is given in Table 3.8. Table 3.8 Average performance of protocols TCP, UDP, SCTP and DCCP variants S.No. Metric TCP UDP SCTP DCCP- TCP-like DCCP- TFRC 1 Throughput(Kbps) Energy (Joules) Routing Load (pkts) MAC Load (pkts) EED Delay (sec) Dropped Packets (pkts/sec) As TCP is a reliable protocol, which ensures in-order delivery of packets with congestion control, the overheads involved are high, which results in underutilization of resources which is reflected as poor performance indices, as shown in Table 3.8. On the other hand, it is found that UDP is far better than TCP, but at the cost of reliability and congestion. As SCTP too is a reliable protocol, it also attracts more overheads as given in Table 3.8. DCCP includes congestion control mechanisms as in the case of TCP and unreliable transmission like UDP and hence, the performance of DCCP variants found to be the best, bearing the transmission loss, which is not a main criterion in WSNs, as only the recent information are preferred than older ones in WSN.

30 SUMMARY A brief overview of the simulation scenario over which all proposed algorithms in this work are implemented to analyze their performance, is presented in this chapter. The specifications of different parameters of the nodes and sensor field are also given. The standard metrics prescribed to validate the performance of the networks, with different algorithms are also discussed. The congestion control behavior of the wireless sensor networks based on five protocols TCP, SCTP, UDP, DCCP-TFRC, DCCP-TCP-like with respect to six metrics viz. throughput, pocket-loss or dropped packets, routing load, MAC load and EED have been analyzed in this chapter. To analyze the congestion control performance of the networks based on the above protocols, the scenario given earlier in this chapter has been successfully simulated under the package NS2 for a range of data reporting intervals and the results thus arrived have been tabulated and plotted. The performances of the networks based on the metrics considered have been analyzed in detail. The throughputs of TCP and UDP protocols based networks are relatively higher at low data reporting intervals where as the throughputs are almost equal for all the five protocols at high data reporting intervals. Hence, it may be concluded that DCCP-TFRC and DCCP-TCP-like protocols based networks behave almost similar to other protocols at high data reporting intervals. It may also be observed that the average energy consumption is low with respect to DCCP based networks despite the initial fluctuations and that of TCP and SCTP are much higher. The energy consumption is high for UDP

31 83 based networks at low reporting intervals and almost equal to that of DCCP based networks and hence, it may be arrived that the DCCP networks, on average, consume energy lesser than other protocols. With respect to the remaining metrics routing load, MAC load, dropped packets and EED it may be observed that the performance of DCCP based networks are far better that TCP and SCTP based networks and just above UDP based networks. Hence, from the arrived results it is concluded that DCCP protocol may be the best suited protocol among the protocols considered for wireless sensor networks.

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