TCP (Transmission Control Protocol) is a transport protocol designed for the wired Internet. In wireless networks packet losses occur more frequently due to the unreliability of the physical link. The main problem is that TCP treats all losses as congestion, which leads to a lower throughput. Ad hoc networks are multihop wireless networks of mobile nodes, where each node can allow other packets to pass through it. Topology changes often occur and may lead to packet losses and delays, which TCP misinterprets as congestion. We want to modify TCP to recognize the differences between link failure and congestion to improve the capacity. In our model we have built a connection in an ad hoc network where packet losses and partitions can be made. Simulation experiments show that we didn't get the problems we expected. This can be explained by low delays and because we buffered the packets during link failure. A simple modification of TCP was made and simulated, and showed that an improvement of performance is possible. More research should be done to make a modification of TCP that would further affect the throughput.

Detta examensarbete behandlar problemet med att testa inbyggda system i kontorsmiljö. För att göra detta och därigenom kunna göra anrop på det inbyggda systemets API, måste detta anrop skickas som ett seriellt datapaket över en seriell kommunikationslänk som TCP/IP. Detta möjliggjordes genom att först upprätta en kommunikationslänk med protokollet TCP/IP, där användningen av POSIX-sockets tillämpades. För att packa ner och packa upp funktionsanropen till seriell data implementerades ett protokoll som följdes när detta utfördes. Hantering av data i samband med överföring över TCP/IP sköttes av ett protokoll vid namn BGSFP, ett protokoll som bygger på det tidigare protokollet TSFP.

HMS Networks AB develops, produces and sells communication technology for industrial automation. The product handles communication between a variety of protocols. The product treated in this project is an Anybus X-gateway Modbus-TCP Master/Client and this module is currently configured from a web-based interface. In doing so, the flexibility for handling protocols is limited to what the company chooses to add to the interface. Therefore the company had a request that the flexibility should be extended using a script language. The project has mainly consisted of two parts. The first part deals with the implementation of the script language Lua and the second part is about measurement and evaluation of the time required for the script. A prototype was developed with an operational implementation and successful results for data transmission. Although it was a successful project some optimizations are required if this solution is to replace the existing one, because script languages are not as fast as C. Some knowledge in programming and network is required to obtain an adequate understanding of the report.

Partial Reconfigurable FPGA provides ability of reconfigure the FPGA duringrun-time. But the reconfigurable part is disabled while performing reconfiguration. In order to maintain the functionality of system, data stream should be hold for RP during that time. Due to this feature, the reconfiguration time becomes critical to designed system. Therefore this thesis aims to build a functional partial reconfigurable system and figure out how much time the reconfiguration takes. A XILINX ML605 evaluation board is used for implementing the system, which has one static part and two partial reconfigurable modules, ICMP and HTTP. A Web Client sends different packets to the system requesting different services. These packets’ type information are analyzed and the requests are held by a MicroBlaze core, which also triggers the system’s self-reconfiguration. The reconfiguration swaps the system between ICMP and HTTP modules to handle the requests. Therefore, the reconfiguration time is defined between detection of packet type and completion of reconfiguration. A counter is built in SP for measuring the reconfiguration time. Verification shows that this system works correctly. Analyze of test results indicates that reconfiguration takes 231ms and consumes 9274KB of storage, which saves 93% of time and 50% of storage compared with static FPGA configuration.

Web browsing via Wi-Fi wireless access networks has become a basic function on a variety of consumer mobile electronic devices, such as smart phones, PDAs, and the Apple iPad. It has been found that in terms of energy consumption, wireless communications/networking plays an important role in mobile devices. Since the power-saving mode (PSM) of the IEEE 802.11 a/b/g standard is not tailored for the HTTP protocol, we propose a novel power saving scheme that exploits the characteristics of web applications. After sending HTTP requests, the proposed power saving scheme updates the estimated value of RTT based on the information contained in the TCP timestamp header field. Next, the proposed scheme adjusts the value of the listening period based on the estimated value of RTT. When all TCP connections have been closed, the wireless network card could enter the deep-sleeping mode. In this case, the value of the listening period could be larger than one second, since the user is reading the webpage and is unlikely to send another HTTP request within one second. The usage of the deep-sleeping mode can significantly reduce the power consumption of mobile devices.

Due to the rapid development of the Internet and the fast expansion of the bandwidth, the requirement of the real-time service for the Internet is necessary. In this way, the problem of the real-time service for the Internet becomes an important issue. Most of the applications still use TCP as the protocol, but due to the reliable property of TCP, TCP can¡¦t fit the requirement of the real-time transfer. So, we need to implement a protocol which we can use on the real-time transfer service. According to the requirement, we find an open source application layer protocol ¡V UDT (UDP-based Data Transfer). We can implement the application of real-time transfer by using the partial reliable messaging property of the protocol. In addition, user can adjust the parameters or settings of the protocol to make their application get into better performance by using the composable property of the protocol. In our research, we¡¦ll compare with RTP (Real-time Transport Protocol) and UDT, and also explain the reason why we don¡¦t choose RTP in our research. The assumption environment of our research is financial real-time service, and the protocol of such applications is TCP. In this way, we¡¦ll analyze and compare the result of the tests between TCP and UDT. We¡¦ll also adjust the parameters of the protocol to test the performance of the UDT under the environment of the real-time transfer, such as data lose rate, etc.. These results can supply the reference for the users when using UDT as their protocol to implement their real-time applications.

This thesis demonstrates the performance of Probabilistic Early Response TCP (PERT), a new TCP congestion control, for video streaming. As a delay based protocol, it measures the delay at the end host and adjusts the congestion window accordingly. Our experiments show that PERT improves video delivery performance by decreasing the fraction of packets delivered late. Furthermore, our Linux live streaming test indicates that PERT is able to reduce the playback glitches, when high resolution video is delivered over a link with non-zero packet loss. In order to operate PERT at higher thoughputs, we design PERT to work with Acknowledgement (ACK) coalescing at the receiver. ACK coalescing makes data transfers burstier and makes it hard to estimate delays accurately. We apply TCP pacing to fix this issue, and validate its effectiveness in the aspects of throughput, packet loss and fairness. Our experiment results also show that PERT with Delayed ACK and Pacing is more friendly, and therefore more suitable when multiple traffic flows are competing for limited bottleneck bandwidth or sharing the same router buffer.

In recent years, the requirement for embedded controllers has been steadily on the increase due to the development of computers, communication ,WWW and consumers¡¦ products. Consequently, integration and application of the embedded system and the World-Wide Web become more and more important. The Web-based embedded system developed in this paper tends build a service of micro web server. By this service, users can not only receive the information from the system via the browser, but also design particular processes for themselves. Besides, the system developer can use the most popular tools to edit the page for the Web-based embedded system. This Web service technology offers an operational interface, which is user-friendly, and cost effective with the capability of cross-platform and TCP/IP transmission. The presented achievement is applied to temperature control system for performance evaluation of remote control.

Multi-Protocol Label Switching (MPLS), a label swapping and forwarding technology proposed by IETF, is very suitable for the backbone of the next-generation Internet. MPLS has the advantages in improving the performance of network-layer routing and increasing network scalability as well. To provide more reliable delivery in MPLS networks, it is necessary for every label switch router (LSR) to perform a fast recovery mechanism after link failures. It is also required for an LSR to support the functions of failure detection, failure notification, and protection mechanisms in each label switched path (LSP). Therefore, different kinds of recovery schemes in previous literatures have been proposed to enhance the reliability of MPLS networks when a link failure occurs in the primary LSP. In this thesis, we focus on the comparisons of three famous recovery mechanisms, Makam, Haskin, and Hundessa approach. By investigating different locations of link failure, the influences of the three approaches individually on the TCP performance are our major concerns, especially under different TCP versions. Finally, we use the MPLS Network Simulator (MNS) to verify our observations. Four different TCP versions, including TCP-Tahoe, TCP-Reno, TCP-NewReno, and TCP-SACK, are employed in our simulator. From the simulation results, the characteristics of congestion control when using different TCP versions are discussed. Without applying fast retransmission and fast recovery, the average throughput of TCP-Tahoe is the smallest, as compared to that of other TCP versions. In addition, multiple packet losses in the period of link failures would largely downgrade the performance of average throughput, no matter which TCP version (TCP-NewReno or TCP-Reno) is employed. Using Makam approach, we found out that the average throughput becomes better when the location of link failures is close to the ingress node.

In this thesis, a modified routing protocol, MAODV (Modified Ad Hoc On-Demand Distance Vector), is proposed for wireless Ad Hoc networks. MAODV uses ACK paths for rerouting data traffic whenever there is a route failure. We create new flags in the routing information of AODV to timely notify TCP layer the network status. After a route failure, the source node monitors ACK packets from the destination node. Every ACK packet when it is received from the destination node, its carried information is used to update the routing tables. Thus, without any interruption, TCP can take the reverse route of the ACK forwarding paths to continue to transmit the rest of data packets. In our proposed scheme, without decreasing the size of TCP congestion window (CWND), a lost packet can be immediately retransmitted as soon as the first duplicate ACK is received. We use NS-2 to simulate the proposed MAODV. From our simulation results, we have shown that when the position of route failures is near the source node, it may take more time to find new data paths. Hence, MAODV has the advantages by taking the reverse ACK paths to transmit data packets before new routing paths are found. Finally, we have demonstrated that MAODV performs better than TCP-BuS (BUffering capability and Sequence information) and the original TCP, when there are many hops between the source node and the destination node. On the other hand, when the position of route failures is near the destination node, the advantages of MAODV become not so significant because there exists some local repair mechanisms to be applied.