Analysis of Congestion Control Protocols (TCP, XCP, RCP) in Multi-Hop Wireless Network. Dr. Atul M Gosai 1, Udit Narayan Kar 2 and Bhargavi H Goswami 3, Assistant Professor 1 Research Fellow 2, Research Scholar 3 Department of Computer Science, Saurashtra University, Rajkot 1,2 Department of Computer Science and Applications, NIMS University, Jaipur 3 ------------------------------------------------------------ɚ------------------------------------------------------------- Abstract:- TCP is one of the most widely used congestion protocol in the world of Internet. Though, TCP has some limitations, even in the wired world, such as not providing high utilizations in high bandwidth-delay product networks, and introducing high load and overhead in the network. Due to these limitations, several congestion protocols have been proposed. explicit Control protocol (XCP) and Rate Control Protocol(RCP) are most well known protocols developed to control the congestion in an efficient manner in a wired networking environments.xcp has already been modified to work in the wireless environment known as XCP-b (blind), but RCP has not yet been implemented tested in the wireless networking scenarios Multi-hop Wireless networks are undergoing a rapid progress, it is important to evaluate how XCP and RCP behave in these networks, as com-pared to TCP under the presence of different routing protocols used in wireless multi-hop network Like Ad-Hoc on Demand Distance Vector (AODV), Dynamic Sequence Distance vector (DSDV), and Dynamic Source Routing(DSR). This paper presents an throughput evaluation study of TCP, XCP and RCP in Multi-hop Wireless Network in both static and dynamic topology. Surprisingly, the results show that TCP is more efficient in multi-hop scenarios, as compared to XCP and RCP. To obtain the available network throughput, both XCP and RCP need that all nodes in the network cooperate, which increases network overhead, and reduces the throughput Moreover, their capacity evaluation is not accurate in wireless networks. Key Words: TCP, XCP,XCP-b, RCP, DSDV, AODV, DSR,802.11 ------------------------------------------------------------ɚ------------------------------------------------------------- IJISAER 3IS0100013 www.ijisaer.com 1
1. Introduction The use of wireless networks has increased significantly in the past years. Wireless networks are more flexible, easy to deploy and scalable than traditional wired networks. Multi-hop wireless network such as wireless mesh network and wireless ad-hoc network has emerged as a promising wireless technology for a large verity of applications. Multi-hop wireless network are being used in broadband home networking, community networking, enterprise networking, defense networking and building automations [1]. The Transmission Control Protocol (TCP) is the most widely used congestion control protocol as far as internet is concerned. It has been adopted widely in most of the communication network as far as the reliable data transfer is concerned. TCP used Van Jacobson algorithm [2] to control congestion and became highly successful as far as internet technology is concerned. This phenomenon of TCP was developed for wired networks. Multi-hop wireless network has several characteristics that differ from the wired networks. A typical wireless network uses IEEE 802.11 MAC protocol and the packets may be dropped due to either buffer overflow or link layer contention. Such losses may directly affect the performance of TCP. Another problem is that a wireless channel is a scarce and the resources in these networks are always shared. Hence, by the increasing demand of the internet band and wireless network, TCP proved to be unsuitable for highly dynamic environments. Due to this factor various numbers of congestion control protocols developed. The explicit Control Protocol (XCP) [3] and the Rate Control Protocol (RCP) [4] are two of those protocols which use feedback mechanism to control the congestion. These protocols need intermediate nodes like router to work and act together to control the congestion. These protocols worked perfectly in the wired networks and not yet being implemented in the wireless network. Wireless multi-hop network are undergoing rapid progress as they are very easy to deploy. In wireless multi-hop network node can act as a router and also contains additional routing functions. A huge amount of efforts have been done in improving the performance of TCP in the multi-hop wireless networks. The XCP protocol is a very popular mechanism and is widely renowned as being a major advance in internet congestion. XCP normally tries to achieve maximum link utilization and bandwidth waste is approximately zero due to minimum packet losses. RCP is an advanced version of XCP and is much efficient than XCP too. Both XCP and RCP were designed and implemented in the wired networks and both of them are very popular. It is very important to know and analyze how these two protocol will work in the wireless network in comparison to TCP. All the mechanisms proposed or developed for the congestion control in the wireless network have some specific drawbacks. Especially in the mobile wireless network, the mobile nodes may be attached to the different types of networks along the time. Therefore the various congestion control mechanisms designed for multi-hop wireless network are not that efficient. TCP however is the most widely used congestion control protocol in both wireless and wired network. Both XCP and RCP are designed to improve the performance of TCP. But both the protocol XCP and RCP is not yet implemented in the multi-hop wireless network. It is very much of essential to know how RCP and XCP behaves in the wireless network both in the static and dynamic topology. Hence the next part of the paper describes the simulation study of TCP, XCP, and RCP in multi-hop wireless network.in this paper we analyzed the throughput performance of TCP, XCP and RCP in the wireless multihop network. The base results have been obtained by using a set of simulation under NS-2.35 by using both static and dynamic topology. The presented scenarios are not complex, but sufficient enough to draw the conclusions between these protocols. This work still shows that a much work is needed in the wireless multi-hop network to increase the throughput performance. In the rest of paper Section-1 describes the popular congestion control protocols TCP, XCP amd RCP used for analysis, Section-3 describes the routing protocols under which TCP, XCP and RCP are simulated in the multi-hop wireless networking scenario, Section-4 describes a brief about the enhanced version of TCP used congestion control protocol in multi-hop wireless network, Section-5 describes simulation setup and methodology, section-6 describes about the performance analysis, Section-7 describes the results and finally conclude with conclusion in Section-8 2. Congestion Control Protocols (TCP, XCP, RCP) A. Transport Control Protocol Transport control protocol is most widely used congestion control protocol in today s networking scenario. TCP used additive increase and multiplicative decrease (AIMD) and slow start phenomenon to avoid congestion. When congestion is detected through time out or selective acknowledgements the congestion window is updated as This is known as multiplicative decrease of the TCP protocol. Due to its AIMD approach TCP is having unstable throughput, high queuing delay and limited amount of fairness especially in wireless networks. In a wireless network the wireless channel impairments cause bit error and packet drops due to mobility and leads to congestion. TCP mechanism does not respond well and its performance degrades. Due to weak signal strength and noise in wireless network the burst error occurs and packet drop occurs. If a single packet is dropped, TCP will detect it as a time out and resume slow start. This phenomenon heavily degrades the network performance. explicit Congestion Control Protocol- XCP 1 2 IJISAER 3IS0100013 www.ijisaer.com 2
XCP was designed to extract the congestion information directly from the routers. XCP achieves fairness; link utilization is minimum and utilizes the bandwidth in an efficient manner. However XCP has its own disadvantages because it is very difficult to deploy as the end systems and routers of a network need some changes. A XCP network consists of the XCP sender hosts, XCP receiver hosts and intermediate nodes where queuing from sender to receiver occurs [5]. XCP is a feedback based protocol and uses feedback mechanism to inform the sender about the best network conditions. By utilizing this phenomenon it achieves maximum throughput. The congestion header associated with each and every packet sent stores the feedback. In between the transmission of the packets the intermediate node updates the congestion header. In the due time the packets reaches receiver it copies all the network information obtained from the last intermediate router. The figure 1 shows a normal XCP system. The sender tries to increase the congestion window by Delta1 and this information is stored in XCP congestion header. The first router analyzes and forwards the packet to the second router. Although there is enough capacity to deal with the request, the first router does not modify the congestion header and the second router considers that Delta1 increase I excessive and modifies the congestion header by replacing Delta1 with Delta2. The maximum allowed throughput changes for this single flow and where Delta 2 is smaller than Delta 1. The receiver copies Delta 2 and sends it to the sender. The sender then modifies the congestion window and the proceeds to transfer the data. The calculation of the bandwidth adjustment is done in the following manner. Where c is the link capacity, input_bw is the actual bandwidth used before the time period T and q is the minimum queue length observed in the last T seconds. T is the average RTT and and are constants. To implement this equation number 3 in the wireless network like 802.11 a lots of problems arrived because of capacity errors in the shared access media. Hence further XCP equation has been modified to XCP-b (XCP-blind) where spare bandwidth is measured from the variations of the persistent queue [6]. This means to measure the queue variations the medium used in the wireless network should be fully utilized. Therefore this is the measure drawback of XCP-b as it will take a lot of resource and time to calculate the actual bandwidth. Hence XCP-b is not a suitable option for the large scale deployments. B. Rate Control Protocol (RCP) RCP is very similar to XCP, is a congestion control algorithm. The main aim of RCP is to deliver fast flow completion times or download times. RCP was also designed having in mind typical flows of typical users in today s network. RCP aims to improve web user s flows, distributed computing and distributed file-systems and decreasing their transfer time. RCP uses the same feedback principle as that of XCP and tries to imitate a processor sharing. However, it uses a different approach. Routers along the path don t determine incremental changes to the end-system s throughput, but determine the available capacity and the rate at which the end system should operate [4]. The Fig.2 shows a general operation of RCP. Here the sender sets a desired rate with an infinite value and the first router calculates the available rate. The first router overwrites the value of rate in RCP congestion header. The second router compares the rate calculated by the first router. If the value compared by the final router is smaller than the available rate, the router does not change the value of rate in the congestion header. The rate value is only modified if the available rate has a smaller value. After analyzing the required rate, the receiver feedbacks the rate value to the sender in the acknowledgement packet. Fig-2- RCP Operation Figure 1:- XCP operation If the flow completion time is greater than one RTT then the subsequent rates are piggy-backed in the acknowledgement and data packets. So to determine the rate the RCP depends upon the router information and depending upon the correct information and zero delay the rate is analyzed by C/N(T) 4 IJISAER 3IS0100013 www.ijisaer.com 3
Where R (T) is the given rate, N (T) is the number of flows and C is the link capacity. Due to any reason if there is a delay, it becomes very difficult to analyze ). Hence an adaptive algorithm is used to analyze the updated rate assigned to the flows. This allows emulating processor sharing. Processor sharing allows calculating the updated rate without depending upon the number of flows as given in the equation 5. Where is the is the moving average of RTT measured across all the flows, is the last updated rate, C is the link capacity, y(t) is the input traffic rate, q(t) is the instantaneous queue size, and N(t) is the router s estimate number of on-going flows. are the performance and stabilization parameters. This RCP protocol works very well for burst traffic, but the bandwidth allocation is instantaneous. TCP is still the most used congestion control protocol, in wired and wireless networking environments and XCP and RCP are developed to improve the performance of TCP. It is very important to know how XCP and RCP works in multi-hop wireless networking scenario. Both XCP an d RCP are not tested in wireless networking scenario. Therefore the authors decided to simulate XCP and RCP under the presence of different routing protocols (Demand Driven and Table driven) for this evaluation. This will allow us to find further direction for defining a new congestion control mechanism that will work efficiently in multi-hop wireless networking scenario. Routing protocols in Multi-Hop Wireless Networks The routing protocol in the wireless multi-hop network can be classified as follows A. Table Driven Protocol: This protocol basically contains reliable and up-to-date routing information from each node to every other node provided in the network. They maintain the routing tables and broadcast the updates throughout the network. Various tables driven routing protocols vary in the number of methods by which the changes in the network topology are broadcasted. Destination Sequenced Distance Vector (DSDV), Optimized Link State Routing (OLSR), etc are the examples of table driven protocol. In DSDV routing protocol each and every node maintains a routing table. The routing table consists of available destinations along with the number of hops needed to reach the destinations. For each new entry in the routing table it is tagged with a sequence number that is originated by the destination node. These sequence numbers normally avoid the routing loops. A brief detail of the DSDV routing protocol is given in [7]. The basic disadvantage of these protocols are that they require a huge amount of memory to maintain the routing table and due to any reason if the network fails the reaction of these protocols are very slow and time consuming. B. Demand Driven Routing Protocols The routes are created by these protocols whenever it is required by the sender. The demand driven routing protocols are dependent upon two basic phases. a. Route Discovery: The sender initiates the route discovery whenever it is required to send a packet to the receiver. When all the possible routes are examined this process gets completed. b. Route Maintenance: It maintains all the required routes until the destination becomes unavailable or the established routing path is no longer required. Ad-Hoc on Demand Distance Vector (AODV), Dynamic Source Routing (DSR), etc is the basic examples of the demand driven routing protocols. The AODV routing protocol reduces system wide broadcasting of the routes and is the modified version of DSDV protocol [7]. Again like the table driven protocols demand driven protocols also maintains the sequence number that increases periodically These sequence number makes sure that most recent route discovery is initiate whenever it is required by the sender. The basic disadvantage of these protocols are they take a lot of time to analyze the real route and establish it before sending the actual data packets and due to this reason the routing over head increases. 3. Congestion in Multi-Hop Wireless Networks A lot of research is going on congestion control mechanisms in multi-hop wireless network. Various protocols like TCP-F [8], TCP- ELFN [9], TCP-BUS [10], ATCP [11], not only enhances the features of original TCP but also tries to control the congestion in the wireless network. The protocol like ATP [12] is a rate based congestion control protocol that uses explicit rate feed back to network resources. The authors K.Tan, F.Jiang, Q.Zahang, and X.Shen in the year 2006 discussed about Explicit Wireless Congestion protocol (EWCCP) [13]. This mechanism identified the set of flows that shared a channel capacity through the congested node. This EWCCP analyzed that rate region in 802.11 wireless network the rate region is absolutely convex and proportionally fair. But this protocol is not yet implemented in the real time scenarios. 4. Simulation Setup and Methodology The results obtained in this paper is based upon the simulation done by using NS-2.35 [16]. To obtain the results and analyze them both static and dynamic topologies are taken into consideration. A. Static Topologies We have designed the static topology which is very similar to that of [14]. The topology consists of 10 nodes with a single TCP connection. The topology has a variable number of hops from node number 1 to 9. All these nodes are configured to use IEEE 802.11 MAC protocol. After testing the performance of TCP a single XCP and RCP connection is being established to analyze the performance. The transmission range between the two nodes is set as default which IJISAER 3IS0100013 www.ijisaer.com 4
is 250 meters. The data rate set is 11 Mbps and the packet size is fixed to 1500 bytes. All the simulation last for 300 seconds and for data transmission FTP application is configured with packets. B. Mobile Topology We have designed the mobile topology consisting of 30 nodes in a flat 1500x1500 rectangular area. The mobility pattern used sre generated by using set-dest function and random way-point mobility model given in NS-2.35. The average speed with which nodes move is 10 m/s. 5. Performance Analysis We used throughput as our only performance metric in our simulation study. In static topologies we have measured the throughput of TCP connection and then compared with the throughput of the XCP and RCP connection. It should be noted that no RTC/CTS control packets are used in this simulation. But in the mobile topologies we have used another performance metric known as expected throughput. Because in the mobile topologies the distance between the source and destination keeps on varying [15]. The expected throughput is calculated as follows. 6 Where is the obtained throughput, i is the number of hops and 1 i. And is the duration for which the shortest distance between the source and destination is covered. The actual throughput is obtained by using the simulations and actual throughput is compared with the expected throughput. 6. Results I. Static Topologies 6 612.29 603.42 712.05 7 593.34 512.88 535.04 8 478.06 447.65 449.01 9 398.80 159.20 166.05 B. in (KBPS) using DSDV Number of Hops TCP XCP RCP 1 3997.52 2689.81 2743.25 2 3452.19 2125.025 2247.05 3 2997.51 1674.05 1728.83 4 1613.69 1206.084 1349.45 5 917.43 751.83 895.42 6 710.04 598.03 613.29 7 689.39 437.23 445.02 8 565.06 379.25 397.07 9 488.39 127.892 135.04 C. in (KBPS) using DSR Number of Hops TCP XCP RCP Number of Hops A. in KbpS using AODV TCP XCP RCP 1 3996.52 2705.72 2819.63 2 3052.17 2029.81 2127.52 3 2808.51 1693.27 1725.06 4 1507.82 1217.82 1452.52 5 898.50 769.73 967.58 1 3996.52 1689.81 2641.25 2 2052.17 1123.25 2138.05 3 1708.51 1012.05 1617.83 4 1317.82 916.084 1229.45 5 717.50 649.83 775.42 6 502.29 358.03 528.29 7 332.34 237.23 378.02 8 278.06 179.25 267.07 9 178.80 77.892 165.04 IJISAER 3IS0100013 www.ijisaer.com 5
The tables given above shows the throughput of TCP, XCP, and RCP tested in the multi-hop wireless networks under the presence of AODV, DSDV and DSR routing protocol. decreases as the number of hop increases. The TCP protocol performs consistently better in the DSDV routing protocol. This is because DSDV protocol maintains a routing table and hence avoids the initial delay. The two other protocols XCP and RCP also perform well in DSDV and AODV protocol, but in all the scenarios RCP is performing better than XCP as far as the simulations results are concerned. Under DSR routing protocol TCP doesn t perform as compared to DSDV and AODV. This is because in DSR protocol carries the entire route information from the source to destination in its header. This leads to severe degradation of throughput. Under AODV protocol XCP and RCP performs comparatively good because in both the protocol the rate is selected by the router. The delay based component used in AODV protocol normally reduces the sending rate to avoid the packet drops and increases the throughput. II. Mobile Topologies A. Table-4: in Kbps Using AODV Congestion Control Protocols Expected Actual TCP 1585.606 1372.5324 XCP 1276.243 645.1164 RCP 1389.356 884.4412 B. Table-4: in Kbps Using DSDV Congestion Control Protocols Expected Actual TCP 1625.179 972.236 XCP 1319.008 699.5872 RCP 1420.152 872.644 C. Table-6: in Kbps using DSR Congestion Control Protocols Expected Actual TCP 1326.714 1310.200 XCP 1124.606 789.417 RCP 1376.606 981.231 In the table-4 to table-6 we have analyzed the actual throughput and expected throughput of the TCP, XCP and RCP with AODV, DSDV and DSR respectively. We found that the throughput obtained under DSR protocol is comparatively better as compared to AODV and DSDV. The actual throughput obtained for TCP, XCP and RCP in the presence of AODV is lower than DSR but better than DSDV. This is because mobility causes frequent route failure and DSDV like protocol don t send the data packets until the routing table is updated with new routes. This phenomenon introduces larger delays and degrades the overall throughput of the network. AODV and DSR are the demand driven routing protocols and they don t need the routing table to be updated frequently. Hence, the delay in AODV and DSR is not as large as compared to DSDV. In all the comparative results TCP has a very regular and fair throughput as compared to the XCP and RCP. The irregular behavior of XCP and RCP is because of incorrect evaluation of the link capacity, channel utilization and frequent channel losses. 7. Conclusion and Future Work The work presented in this paper clearly shows that TCP has a better throughput as compared to XCP and RCP. We know that TCP is not a good congestion control protocol and is not suitable enough for the wireless environments. TCP also does not behave correctly where there is a weak signal strength and interference. When XCP and RCP is implemented in the multi-hop wireless network, one of the basic problem is that there is wrong interference of the available band width. Finally we concluded that the nodes in XCP and RCP are not e valuating precisely network capacity and therefore leading to the degradation of the network performance. For this purpose the cross layer communication may help. MAC layer can be a good source for the available planning rate. We still believe that new congestion control techniques can be developed to control the congestion in the multi-hop wireless network. We are currently studying and analyzing new congestion control techniques and making use of the cross layer communications to provide accurate mechanisms for evaluating the throughput in the multi-hop wireless networking environment. 8. Acknowledgement We thank to the anonymous reviewers for their helpful comments and suggestions. This work is sponsored by UGC (University of Grant Commission, New Delhi) as a major research project and we are very thankful to UGC for all the economic assistance and support provided to us by them. IJISAER 3IS0100013 www.ijisaer.com 6
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