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...sly mentioned there have been minor modifications to TCP but not to its overall functionality - one of these modifications was the inclusionsChapter 1 Introduction 3 of a congestion control algorithm =-=[Jac88]-=-. The congestion control algorithm attempts to make TCP “network friendly” and to encourage it to reduce the output of packets when it believes the network is congested. TCP assumes the network to be ...

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...acket was delivered without errors and this is optional on many implementations of UDP. Like TCP, UDP normally runs over IP, as shown in Figure 2-7. 2.3.1.3 RTP The Real-time Transport Protocol (RTP) =-=[Sch96]-=- is a protocol designed to provide functionality required by distributed real-time applications. RTP itself does not guarantee quality-of-service for the transport connection nor does it enforce QoS f...

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...f studies that the performance of high-speed communication protocols have been limited by their implementations. New concepts such as Application Level Framing (ALF), Integrated Layer Processing (ILP)=-=[Cla90]-=-, header prediction, and Protocol Layer Bypass (PLB) [Woo90] are aimed at overcoming these limitations in networking software implementations. Applying these optimisation techniques to protocol implem...

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...Chapter 4 Mobile Computing Environments 92 4.2.1 I-TCP Normal TCP Corresponding Host Base Station TCP Indirect TCP Corresponding Host Base Station TCP TCP Figure 4-9 Indirect TCP Indirect TCP (I-TCP) =-=[Bak95]-=- was developed at the Department of Computer Science at Rutgers University. Indirect TCP separates the TCP connection over two sections - the wired network section and the wireless network connection ...

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...see that the functionality provided by TCP is unsuitable for this networking environment. As mentioned, these traditional protocols were designed for the networks and applications present at the time =-=[Cla88]-=-. As the characteristics of modern networks and the requirements of modern applications deviate from their traditional counterparts, the performances of these traditional protocols will suffer. Theref...

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... service. [Fox96] suggests the use of an intermediate system that can modify the quality of the incoming data to better suit the mobile computers requirements. This follows the active network concept =-=[Ten96]-=-[Zen96] where the aim is to place more of the application within the network rather than on the end system. Such an approach can be used in conjunction with an I-TCP indirection service, where an inte...

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... Computing Environments 94 OSI model are supposed to provide end-to-end services. By introducing intermediate processing of TCP packets, we break the end-to-end significance of TCP. 4.2.2 Snoop Snoop =-=[Bal95]-=- was developed at the University of California, Berkeley. Like I-TCP, Snoop attempts to separate the connection into a wired link and a wireless link. Unlike ITCP, however, this is not achieved by exp...

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...er a packet is lost, and although this is true for fixed network technologies where errors are generally a result of congestion rather than bit-errors, this assumption fails in a wireless environment =-=[Cac94]-=-. Wireless networks are naturally error prone particularly when the transmitter and receiver are spread far a part or the signal is being interfered [Rey92]. The result of TCP’s congestion control in ...

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...e higher application-oriented protocols and the lower network-dependent layers. The transport protocol has been considered the “keystone of the whole concept of a computer communication architecture” =-=[Sta89]-=- and “the heart of the whole protocol hierarchy” [Tan88]. The importance of the transport protocol is that in the case of protocols like TCP and TP4 they provide guaranteed error free services indepen...

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... a delay, of between 1.0 - 1.5 seconds that is the result of TCP's congestion control mechanisms: the exponential back-off and slow start algorithms.sChapter 4 Mobile Computing Environments 89 In TCP =-=[Ste94]-=-, each packet has to be acknowledged to guarantee reliability. If after a certain period an acknowledgement has not been received, the packet is retransmitted. The Retransmission Time Out (RTO) value ...

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...each of the connection sections. Another strength of the I-TCP model is that it has the potential to be combined with other intermediate functionality - like filtering and compression as discussed in =-=[Fox96]-=-. An arguable limitation of the I-TCP model is that it modifies the end-to-end significance of protocols above the network layer. Transport protocols, like TCP, according to thesChapter 4 Mobile Compu...

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...a network without a physical connection thus enabling the computer to be moved. Wireless technologies are dependent on the science of electromagnetic and radio technology for the transferring of data =-=[And95]-=-. Radio propagation is mainly determined by three factors - reflection, diffraction and scattering. Reflection occurs when an electromagnetic wave hits an object that has a size much greater than the ...

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...ls, with the exception of DaCapo, are based within the kernel. Given the compilation approach it is not realistic to generate kernel level protocols for each application. It has been shown by Thekkah =-=[The93]-=- that user level protocols can provide a high level of performance. Most of the runtime approaches are based on a modular approach where the basic protocol framework exists within the kernel and funct...

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...ol behaviour. 47sChapter 3 Automated Communication Protocol Generation 48 This can be seen in a number of variants of TCP - Vegas, Reno and Boston - designed for different network environments [Bes97]=-=[Jon95]-=-[Moo95]. • Application of New Protocol Concepts : it has been highlighted by a number of studies that the performance of high-speed communication protocols have been limited by their implementations. ...

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...col developed for one environment can not expect to provide the same level of performance in a second network environment. Furthermore, with the development of mobile routing protocols like Mobile IP =-=[Per96]-=-, portable computers are able to maintain their network connectivity as they move between different network environments. Thus in such an environment, the characteristics of the underlying network can...

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...ions given the application's requirements and the underlying network. There is no discussion of implementation optimisations like ALF or ILP. 3.3.2 F-CSS F-CSS (Function-Based Communication Subsystem)=-=[Zit93]-=- was developed at the Institute of Telematics, University of Karlsruhe. Again, this model uses a similar threelayer approach (application, end-to-end layer and the underlying network services). Modula...

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... assumption fails in a wireless environment [Cac94]. Wireless networks are naturally error prone particularly when the transmitter and receiver are spread far a part or the signal is being interfered =-=[Rey92]-=-. The result of TCP’s congestion control in a wireless network is that TCP will continue to drastically reduce throughput as errors occur although the errors are not created by congestion. Thereby the...

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...to JPEG format and transmits it to the client. The client then displays the picture. The JPEG image is transferred from the server to the client using the standard JPEG File Interchange Format (JFIF) =-=[Ham92]-=-, thus allowing the exchange of compressed JPEG pictures over a large set of platforms. JFIF is entirely compatible with the JPEG format and requires the exchange of specification tables at the beginn...

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...e. [Fox96] suggests the use of an intermediate system that can modify the quality of the incoming data to better suit the mobile computers requirements. This follows the active network concept [Ten96]=-=[Zen96]-=- where the aim is to place more of the application within the network rather than on the end system. Such an approach can be used in conjunction with an I-TCP indirection service, where an intermediar...

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...DAPTIVE system will try to take advantage of this by creating an appropriate communication protocol. 3.3.4 Highly Layered Architecture The Highly Layered Architecture for High Speed Networks (HLAHSN) =-=[Oma91]-=- was developed at the Department of Computer Sciences, University of Texas at Austin. HLAHSN uses micro protocols that subdivide protocol functionality to build the communication layer. It has explici...

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... Description Language (FPDL).sChapter 3 Automated Communication Protocol Generation 58 3.3.3 ADAPTIVE ADAPTIVE (A Dynamically Assembled Protocol Transformation, Integration and Validation Environment)=-=[Sch92]-=- was developed at the Department of Information and Computer Science, University of California. ADAPTIVE like the other models discussed so far uses a three-layer model. The main difference between AD...

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...o being done by the research community. The section discusses other models used to support the automated generation of communication protocols. 3.3.1 DaCapo DaCapo (Dynamic Configuration of Protocols)=-=[Vog93]-=- was developed at ETH Zurich, and follows the three layer communication model consisting of an application, an end-toend communications layer and a transport infrastructure. The DaCapo project has mai...

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...e for Linux andsChapter 7 Implementation of PNUT Prototypes 151 produced better results when switching between different threads of execution when compared to a kernel-level thread package from INRIA =-=[Ler97]-=-. The need for a multithread package support was to provide multiple threads of execution. This was necessary because the protocol should run independently from the application. Therefore although the...

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...orms. An interesting result is the Byte-swap + PES ILP loop on the i486 which shows negative performance which shows that ILP used incorrectly can result in a reduction of performance. Experiments by =-=[Ahl96]-=- and [Bra95] showed that although ILP performance well with simple functionality, the performance gains were significantly lower when used with more realistic complex functionality like an encryption ...

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...rotocols have been limited by their implementations. New concepts such as Application Level Framing (ALF), Integrated Layer Processing (ILP)[Cla90], header prediction, and Protocol Layer Bypass (PLB) =-=[Woo90]-=- are aimed at overcoming these limitations in networking software implementations. Applying these optimisation techniques to protocol implementations require the talents of highly skilled network prog...

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...e to the similar situation where multimedia applications require a sequencing service that exists in between reliable and unreliable transfer mechanisms. Such concepts are discussed in more detail in =-=[Dia94]-=-. None of the protocols studied in this section support partial ordering partial reliability functionality. 2.3.2.8 Time stamping RTP packets contain a 32-bit time stamp field that allows transmitters...

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...ocol Figure 3-3 UTS ACPG Model Protocol Functions Library Implementation Techniques (eg.ILP)sChapter 3 Automated Communication Protocol Generation 60 3.3.6 Inria Stub Compiler The Inria Stub Compiler =-=[Dio95]-=- was developed at INRIA (Institut National de la Recherche en Informatique et Automatique), France and is shown in Figure 3-4. Unlike the other modules discussed in this section, the stub compiler is ...

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...ny details of how it deals with issues concerning ILP (refer to Chapter 5).sChapter 3 Automated Communication Protocol Generation 59 3.3.5 UTS Runtime Adaptive Process UTS (Universal Transport System)=-=[Ric95]-=- was developed at the University of Technology, Sydney. Modularity is defined as protocol functions like error control and flow control. The main aim of the work was to consider if dynamic adaptation ...

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...ng a connection from entity B who would acknowledge the connection from A if it was accepting it. On receiving the connection acknowledgement from B, A would acknowledge the opening of the connection =-=[Bag92a]-=-. The main difference in the connection establishment mechanism used by TCP and TP4 are that TCP uses a single packet format using flags within the packet to indicate different functions. Conversely, ...

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...s used by the protocol to recover from errors. The types of errors that can occur can be divided into damaged Transport Protocol Data Units (TPDUs), lost TPDUs and duplicated or out-of-sequence TPDUs =-=[Bag92b]-=-. 3 The XTP transmitter does not have to wait for the acknowledgement of the implicit open before it can send the END packet.sChapter 2 Background 37 Detection of Damaged Transport Protocol Data Units...

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... protocol behaviour. 47sChapter 3 Automated Communication Protocol Generation 48 This can be seen in a number of variants of TCP - Vegas, Reno and Boston - designed for different network environments =-=[Bes97]-=-[Jon95][Moo95]. • Application of New Protocol Concepts : it has been highlighted by a number of studies that the performance of high-speed communication protocols have been limited by their implementa...

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...g two possible methods. The first is the Mach 3.0 UX server that provides a kernel level implementation of TCP/IP within the Unix Server while the second is a user level library implementation of TCP =-=[Mae92]-=-. Figure 3-6 illustrates the different configurations in which the resulted protocols were implemented. UTS is currently based on the Mach 3.0 user level library implementation of TCP. Therefore, resu...

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...ted without errors. Although TCP normally runs over IP, experimental systems have been carried out where TCP has been run over different network layers, including over ATM (Asynchronous Transfer Mode)=-=[Rom93]-=-. The TCP/IP stack is illustrated in Figure 2-7. A number of different protocols can sit above the TCP stack. At the time of designing TCP, applications normally sat directly over TCP and in many case...

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... receive. Again UDP and RTP being unreliable protocols do not support flow control [Bag92b, Saw93, Sch96]. XTP allows flow control to be disabled using the NOFLOW flag in XTP header of outgoing flags =-=[Wea91]-=-. A summary of the flow control functionality supported by the protocols is given in Table 2-4. 2.3.2.4 Expedited Data The expedited data service generally allows the user to send data that is not res...

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...ironment as shown in Figure 4-5. The PCs (486s and Pentiums) used for these tests were running Linux (version 2.0.30) and the Mobile IP v1.0 developed at the State University of New York, Binghampton =-=[Dix96]-=-. We have chosen this implementation as it complies with the IETF Mobile IP draft (revision 16). Tcpdump was used to observe the data transmission during the Mobile IP handoff.sChapter 4 Mobile Comput...

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...chnologies. Technology Typical 2.1.5 The Internet Downstream Rate Hybrid Fiber Coax 45 Mbps Shared Typical Upstream Rate 1.5 Mbps Shared Maximum Distance N/A 500 Table 2-1 Residential Access Networks =-=[Jai97]-=- Homes Per Fiber To The Curb 25-50 Mbps 25-50 Mbps 100 m 10-50 Optical Unit Fiber To The Home 155 Mbps 155 Mbps N/A 10-200 Asymmetric Digital Subscriber Line Very High-Speed Digital Subscriber Line 6 ...

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...viour. 47sChapter 3 Automated Communication Protocol Generation 48 This can be seen in a number of variants of TCP - Vegas, Reno and Boston - designed for different network environments [Bes97][Jon95]=-=[Moo95]-=-. • Application of New Protocol Concepts : it has been highlighted by a number of studies that the performance of high-speed communication protocols have been limited by their implementations. New con...

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...s is graceful connection release, which is not supported by TP4 but rather by the session layer. Figure 2-6 illustrates how TP4 fits into the OSI model. 2.3.1.6 AAL5 The ATM Adaptation Layer 5 (AAL5) =-=[Saw93]-=- sits above the ATM layer which provides network layer functionality and data link functionality as shown in Figure 2-9. AAL5 is a lightweight protocol version of AAL3/4. Application ATM Adaption Laye...

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...ructure, the Internet II intends to provide a more intelligent network that will allow users to get access to high bandwidth connections that will allow the development of future network applications =-=[Was96]-=-. 2.1.5.2 Next Generation Internet The Next Generation Internet, is a US government initiative to study the future of the Internet. The US government has recognised the need to be at the leading edge ...

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..., the results are at least 2Mb under those of Ultrix. This can be explained by the user level location of the transport protocols and the better implementation of the Ethernet device driver in Ultrix =-=[Wit94]-=-. TCP STRL Mach 3.0 SC 5607 5507 Mach 3.0 UX 5192 3681 Ultrix 4.3 8972 8714 Table 3-3 Cross-Platform Throughput 3.5.6 Performance under Erroneous Conditions The selective retransmission and the ALF ar...