Browsing by Subject "TCP"

Now showing 1 - 11 of 11

Open Access
Analysis and mitigation of interference in multi-radio multi-channel wireless mesh networks
(2013) Uluçınar, Alper Rifat
Wireless mesh networking, which is basically forming a backbone network of mesh routers using wireless links, is becoming increasingly popular for a broad range of applications from last-mile broadband access to disaster networking or P2P communications, because of its easy deployment, self-forming, self-configuration, and self-healing properties. The multi-hop nature of wireless mesh networks (WMNs) aggravates inter-flow interference and causes intra-flow interference and severely limits the network capacity. One technique to mitigate interference and increase network capacity is to equip the mesh routers with multiple radios and use multiple channels. The radios of a mesh router can then simultaneously send or receive packets on different wireless channels. However, careful and intelligent radio resource planning, including flow-radio and channel assignment, is necessary to efficiently make use of multiple radios and channels. This first requires analyzing and modeling the nature of co-channel and adjacent channel interference in a WMN. Through real-world experiments and observations made in an indoor multihop multi-radio 802.11b/g mesh networking testbed we established, BilMesh, we first analyze and model the nature of co-channel and adjacent channel interference. We conduct extensive experiments on this testbed to understand the effects of using multi-radio, multi-channel relay nodes in terms of network and application layer performance metrics. We also report our results on using overlapping in addition to orthogonal channels for the radios of the mesh routers. We then turn our attention to modeling and quantifying adjacent channel interference. Extending BilMesh with IEEE 802.15.4 nodes, we propose computational methods to quantify interference between channels of a wireless communication standard and between channels of two different standards (such as Wi-Fi and ZigBee). Majority of the studies in the literature on channel assignment consider only orthogonal channels for the radios of a multi-radio WMN. Having developed quantitative models of interference, next we propose two optimization models, which use overlapping channels, for the joint flow-radio and channel assignment problems in WMNs. Then we propose efficient centralized and distributed heuristic algorithms for coupling flows and assigning channels to the radios of a WMN. The proposed centralized and distributed schemes make use of overlapping channels to increase spectrum utilization. Using solid interference and capacity metrics, we evaluate the performances of the proposed schemes via extensive simulation experiments, and we observe that our schemes can achieve substantial improvement over single-channel and random flow-radio and channel assignment schemes.
Open Access
Analysis of an Adaptive Modulation and Coding scheme with HARQ for TCP traffic
(IEEE, 2015-04) Öztürk, Onur; Akar, Nail
In this paper, we analyze the aggregate TCP throughput performance of a wireless link utilizing Active Queue Management (AQM) and an Adaptive Modulation and Coding (AMC) scheme with Hybrid ARQ (HARQ) based on the probability of failure in the first transmission attempt. We assume packets arriving out-of-order at the wireless receiver due to random retransmissions are resequenced before being released to the network. For this reason, an approximate model for the delay experienced at the resequencing buffer is also presented. In the light of the results obtained from the presented analysis, we propose a threshold for the aforementioned probability of failure making the investigated AMC scheme work at an overall performance close to that of the optimum policy. © 2015 IEEE.
Open Access
Combined use of prioritized AIMD and flow-based traffic splitting for robust TCP load balancing
(2005) Alparslan, Onur
In this thesis, we propose a multi-path TCP load balancing traffic engineering methodology in IP networks. In this architecture, TCP traffic is split at the flow level between the primary and secondary paths in order to prevent the adverse effect of packet reordering on TCP performance occuring in packet-based load balancing schemes. Traffic splitting is done by using a random early rerouting algorithm that controls the queuing delay difference between the two alternative paths. We apply strict priority queuing in order to prevent the knock-on effect that arises when primary and secondary path queues have equal priority. Probe packets are used for getting congestion information from the output queues of links along the paths and AIMD (Additive Increase/Multiplicative Decrease) based rate control using this congestion information is applied to the traffic routed over these paths. We compare two queuing architectures, namely first-in-first-out (FIFO) and strict priority. We show through simulations that strict priority queuing has higher performance, it is relatively more robust than FIFO queuing and it eliminates the knock-on effect. We show that avoiding packet reordering by flow level splitting significantly improves the performance of long flows. The capabilities of ns-2 simulator is improved bu using optimizations in order to apply the simulator to relatively large networks. We show that incorporating a-priori knowledge of the traffic demand matrix into the proposed architecture can further improve its performance in terms of load balancing and byte rejection ratio.
Open Access
Combined use of prioritized AIMD and flow-based traffic splitting for robust TCP load balancing
(Springer, 2004) Alparslan, O.; Akar, N.; Karasan, E.
In this paper, we propose an AIMD-based TCP load balancing architecture in a backbone network where TCP flows are split between two explicitly routed paths, namely the primary and the secondary paths. We propose that primary paths have strict priority over the secondary paths with respect to packet forwarding and both paths are rate-controlled using ECN marking in the core and AIMD rate adjustment at the ingress nodes. We call this technique "prioritized AIMD". The buffers maintained at the ingress nodes for the two alternative paths help us predict the delay difference between the two paths which forms the basis for deciding on which path to forward a new-coming flow. We provide a simulation study for a large mesh network to demonstrate the efficiency of the proposed approach in terms of the average per-flow goodput and byte blocking rates. © Springer-Verlag Berlin Heidelberg 2004.
Open Access
Delay-bounded rate adaptive shaper for TCP traffic in DiffServ Internet
(2002) Balkaş, Yakup
Applications with different quality requirements set out the need for different Qualities of Service (QoS) to be provided in Internet. Differentiated Services (DiffServ) model is an architecture proposed to provide QoS in the Internet in a scalable way. Assured Forwarding Per Hop Behavior (AF PHB) is a QoS service class which provides a loss sensitive service. The DiffServ Service Provider (SP) delivers services to customers where traffic parameters are quantified in a Service Level Agreement (SLA). The incoming traffic from customers are policed in order to make sure that they meet the specifications in the SLA. The portion of traffic that is nonconformant with the SLA is not guaranteed to receive the service quality specified in the SLA. Shapers delay nonconformant packets in order to increase the ratio of traffic that is within the bounds specified in the SLA. If nonconformant traffic is tolerated in the SP network up to some extent, increasing the ratio of traffic that is complying with specifications in the SLA may lead to unnecessary delaying of packets and may decrease throughput. In this thesis, a shaper, called Delay-Bounded Rate-Adaptive Shaper (DBRAS), is introduced which tries to increase the ratio of traffic that conforms to the SLA while satisfying an upper-bound (Dmax) in the amount of delay it can apply to incoming packets (shaping delay). By avoiding unnecessarily large shaping delays, it is shown that throughput is increased. In order to have the shaper to adapt to changes in network topology, traffic, and different propagation delays, an adjustment algorithm is proposed where the shaper dynamically adjusts its Dmax value in order to increase throughput. The resulting shaper is called Dynamic DBRAS (D-DBRAS). The heuristic adjustment algorithm is greedy in that it adapts the maximum shaping delay in the direction where throughput increases. Results obtained from simulations show that throughput of TCP in AF PHB shaped by D-DBRAS can be increased by up to 65% compared with unshaped traffic. Simulations are performed in order to analyze effects of parameters such as propagation delay, buffer threshold levels, and offered traffic on the performance of D-DBRAS. It is also shown through simulations that by using the adjustment algorithm, the maximum shaping delay, Dmax, converges to regimes where throughput increases in response to changes in offered traffic.
Open Access
Effects of physical channel separation on application flows in a multi-radio multi-hop wireless mesh network: an experimental study on BilMesh testbed
(Academic Press, 2014) Ulucinar, A. R.; Korpeoglu, I.; Karasan, E.
In this paper, we introduce BilMesh, an indoor 802.11 b/g mesh networking testbed we established, and we report about our performance experiments conducted on multi-hop topologies with single-radio and multi-radio relay nodes. We investigate and report the effects of using multi-radio, multi-channel relay nodes in the mesh networking infrastructure in terms of network and application layer performance metrics. We also study the effects of physical channel separation on achievable end-to-end goodput perceived by the applications in the multi-radio case by varying the channel separation between the radio interfaces of a multi-radio relay node. We have observed that the difference between TCP and UDP goodput performances together with the delay and jitter performance depends on the hop count. We also observed that assigning overlapping channels with a central frequency separation of 5-15 MHz may render the CSMA mechanism used in 802.11 MAC ineffective and hence reduce the overall network performance. Finally, we provide some suggestions that can be considered while designing related protocols and algorithms to deal with the observed facts.
Open Access
Fixed-point analysis of a network of routers with persistent TCP/UDP flows and class-based weighted fair queuing
(Springer New York LLC, 2017) Tunc C.; Akar, N.
Fixed-point models have already been successfully used to analytically study networks consisting of persistent TCP flows only, or mixed TCP/UDP flows with a single queue per link and differentiated buffer management for these two types of flows. In the current study, we propose a nested fixed-point analytical method to obtain the throughput of persistent TCP and UDP flows in a network of routers supporting class-based weighted fair queuing allowing the use of separate queues for each class. In particular, we study the case of two classes where one of the classes uses drop-tail queue management and is intended for only UDP traffic. The other class targeting TCP, but also allowing UDP traffic for the purpose of generality, is assumed to employ active queue management. The effectiveness of the proposed analytical method is validated in terms of accuracy using ns-3 simulations and the required computational effort.
Open Access
Performance modeling and analysis of the interplay among Tcp, active queue management and wireless link adaptation
(2015-09) Öztürk, Onur
We propose a novel workload-dependent queuing model of a wireless router link which employs active queue management and is offered with a number of persistent TCP flows. As opposed to existing work that focus only on the average queue occupancy as the performance metric of interest, the proposed analytical method obtains the more informative steady-state queue occupancy distribution of the wireless link. With the intention of maximizing TCP throughput, this analytical method is used to study traffic agnostic link adaptation schemes with and without hybrid ARQ. Moreover, a novel cross-layer queue-aware link adaptation scheme is proposed to improve the TCP throughput relative to the case where adaptive modulation and coding decisions are made based solely on the physical layer parameters. A fixed-point analytical model is proposed to obtain the aggregate TCP throughput attained at wireless links employing active queue management and queue-aware link adaptation. Allowing packet retransmissions and generalizing the scope from a single link to a network of such links, we propose an energy efficient queue-aware link adaptation scheme with hybrid ARQ which jointly adapts the transmission power and rate of the wireless links based on the queue occupancy levels and the channel conditions. Furthermore, we provide a fixed-point analytical method for such networks.
Open Access
Performance modeling of communication networks offered with a mixture of persistent TCP and UDP flows
(2013) Çalış, Gökhan
A damped fixed-point approximation is proposed to characterize the throughput of persistent TCP and UDP flows in a network of router links supporting per-class queuing and Deficit Round Robin (DRR) scheduling among classes. In particular, we study the case of two classes where one of the classes uses drop-tail queue management and is intended for UDP traffic. The other class targeting TCP traffic is assumed to use Active Queue Management (AQM). The effectiveness of the proposed analysis method in this scenario is validated by extensive NS3 simulations. Moreover, we study, using the proposed fixed-point algorithm, the potential gain of employing the many-to-one communications paradigm with respect to the conventional one-to-one communications in which a client downloads a specific content from one server only.
Open Access
A simulation study on HTTP performance analysis in terms of its interaction with TCP
(1998) Gürkan, Deniz
In this thesis, we have performed a. simulation study on performance analysis of HTTP (HyperTrext Transfer Protocol) in terms of its interaction with TCP ('Transmission Control Protocol). The latency through internet connections can he reduced by making modicifations on the application and transport layer protocols. For the simulations, we have built models of HTTP/l.O and HTTP/1.1 using a simulation package Network Simula.- tor. Pour different connection mechanisms have been realized. They are serial, parallel, pipelined and segment-filled connections. Serial and parallel connections are simulated for comparison purposes. These are connection mechanisms of HTTP/I.O. The modification proposed in in HTTP /1.1 is pipelined connection. VVe have obtained segment-filled connection by modifying pipelined case. We have examined the performance of each modification and compared their simulation results with HTTP/I.O connections. For the traffic conditions used in the simulations, segment-filled and pipelined connections performed better in terms of effective web page retrieval rate. In addition, a,s a modification to the TCP, we have increased the initial window size and compared vvith the one segment initial window size case. Changing initial window size' from I l.o 2 and .‘1 has increased the performance of each connection case individually.
Open Access
Workload-dependent queuing model of an AQM-controlled wireless router with TCP traffic and its application to PER-based link adaptation
(SpringerOpen, 2014 -04) Ozturk, O.; Akar, N.
We propose a novel workload-dependent queuing model for a wireless router link which employs active queue management (AQM) and is offered with a number of persistent Transmission Control Protocol (TCP) flows. As opposed to existing work that focus only on the average queue occupancy as the performance metric of interest, the proposed analytical method obtains the more information-bearing steady-state queue occupancy distribution of the wireless AQM link. Simulations are performed to demonstrate the accuracy of the proposed model in both wireline and wireless scenarios. With the intention of maximizing TCP throughput, this analytical method is used to obtain guidelines for setting the target wireless packet error rate (PER) for a PER-based traffic-agnostic link adaptation scheme.