Verifying the distributed real-time network protocol RTnet using Uppaal

RTnet is a distributed real-time network protocol for fully-connected local area networks with a broadcast capability. It supports streaming real-time and non-realtime traffic and on-the-fly addition and removal of network nodes. This paper presents a formal analysis of RTnet using the model checker Uppaal. Besides normal protocol behaviour, the analysis focuses on the fault-handling properties of RTnet, in particular recovery after packet loss. Both qualitative and quantitative properties are presented, together with the verification results and conclusions about the robustness of RTnet

Scheduling of Early Quantum Tasks

An Early Quantum Task (EQT) is a Quantum EDF task that has shrunk its first period into one quantum time slot. Its purpose is to be executed as soon as possible, without causing deadline overflow of other tasks. We will derive the conditions under which an EQT can be admitted and can have an immediate start. The advantage of scheduling EQTs is shown by its use in a buffered multi-media server. The EQT is associated with a multimedia stream and it will use its first invocation to fill the buffer, such that a client can start receiving data immediately

RTnet: a real-time protocol for broadcast-capable networks

This paper presents an overview of a real-time network protocol, meant to be used on fully-connected local area networks with a broadcast capability. The intended use of this protocol is an in-home digital network, with support for on-the-fly addition and removal of network nodes, for resource-lavish and resource-lean devices, and for multimedia, command and control and regular data traffic. Both the design and the operation are presented, together with results from measurements on a prototype of the protocol on top of Ethernet

Benchmarking for RTN, a real-time variation on IEEE802.11

RTN is a network access protocol that uses a token scheduling mechanism to enable real-time multimedia streaming on Ethernet-like networks. Unlike other token based protocols, RTNs token mechanism is based on pre-emptive earliest deadline first (PEDF) scheduling. PEDF has interesting characteristics, such as one hundred percent bandwidth utilization and a uncomplicated feasibility analysis. RTN is simulated and implemented on Ethernet and IEEE802.11. The latter implementation is not straightforward, because some for RTN important details are not defined in the standard. As a consequence the standard had to be evaluated before adaptation and implementation of RTN could start. This paper briefly describes the RTN protocol. The focus, however, is on benchmarking the IEEE802.11 standard

A real-time multimedia streaming protocol for wireless networks

This paper describes a new token-based medium access protocol for real-time networks and its implementation on a wireless network. Originally, the protocol is developed for use in low cost domestic or home networks that are based on Ethernet hardware. In contrast to existing protocols the token is assigned to network nodes on basis of a pre-emptive earliest deadline first (PEDF) schedule of the multimedia streams. The scheduler is distributed over all active nodes in the network. Although other schedulers could be used, PEDF is chosen because it has a theoretical bandwidth utilization of one hundred percent and feasibility analysis is very simple, so even simple devices can participate in such a network. This is confirmed by simulation experiments and a prototype based on Ethernet hardware. The protocol is successfully adapted to and implemented on an IEEE 802.11b wireless LAN, even though this type of network has some unpredictable properties, such as bandwidth switching

Experimental implementation of a real-time token-based network protocol on a microcontroller

The real-time token-based RTnet network protocol has been implemented on a standard Ethernet network to investigate the possibility to use cheap components with strict resource limitations while preserving Quality of Service guarantees. It will be shown that the proposed implementation is feasible on a small network. For larger networks a different approach is necessary, using delegation by means of proxies. A delegation proposal will be discussed. For small networks it is possible to use a PIC microcontroller in combination with a standard Ethernet controller to run the RTnet network protocol. As more systems are added to the network the performance of this combination becomes insufficient. When this happens it is necessary for the microcontroller to delegate some tasks to a more powerful master and to organize a low-level communication protocol between master and slave

ClockWork: a Real-Time Feasibility Analysis Tool

ClockWork shows that we can improve the flexibility and efficiency of real-time kernels. We do this by proposing methods for scheduling based on so-called Real-Time Transactions. ClockWork uses Real-Time Transactions which allow scheduling decisions to be taken by the system. A programmer does not need to be aware of synchronisation due to the sharing of resources and may have the illusion of a run-to-completion semantics even under pre-emptive scheduling protocols. The ClockWork tool presented here analyses the schedulability of a set of RT Transactions for a variety of protocols and visualises the result in a graphical form

A case against periodic jukebox scheduling

This paper presents the jukebox early quantum scheduler (JEQS). JEQS is a periodic jukebox scheduler for a Video-on-Demand system. JEQS uses the jukebox robots in a cyclic way and the time is divided in constant units called quanta. A quantum is the maximum time needed to unload and load all the drives. An RSM is loaded in a drive for a fixed period of time, corresponding to the time needed to switch the media on the other drives. During this time the drive can read data from it. JEQS is based on the scheduling theory on early quantum tasks (EQT). An early quantum task executes its first instance in the next quantum after its arrival and the rest of the instances are scheduled in a normal periodic way with the release time immediately after the first execution. Although JEQS is an efficient periodic scheduler, that can guarantee the execution of most tasks in the next cycle after the requests arrive, we show that using JEQS results in much longer response times than using a-periodic schedulers. Furthermore, we show that the bad performance of JEQS is intrinsic to any periodic jukebox scheduler. The only advantage of using a periodic scheduler is that the scheduling algorithms are less complex. However, the simplicity of the algorithms clearly does not outweigh the unacceptably long response times

Time synchronization for an Ethernet-based real-time token network

We present a distributed clock synchronization algorithm. It performs clock synchronization on an Ethernet-based real-time token local area network, without the use of an external clock source. It is used to enable the token schedulers in each node to agree upon a common time. Its intended use is in resource-lean systems, where heavyweight protocols like NTP cannot be used. We present a short overview of the working of the protocol, as well as experimental results

RTnet, a new approach to in-home real-time multimedia communication

streams, but variable-bit-rate streams can be mapped using several techniques [3]. The EDF scheduler is distributed over the nodes and the token is the place where the schedule is kept; nodes will keep backups of the schedule though. If a node has the token and it wants to add or remove a stream, it calculates a new schedule and acts upon it. Before a new stream may be added the node does an EDF feasibility test to determine if the newly added real-time stream will meet its deadlines without making other streams miss theirs. The EDF feasibility test is simple [4]: the total of bandwidth utilizations by all streams may not exceed 100%. However, only 80% of network bandwidth is dedicated to real-time (multimedia) communications, the rest is used for non-real-time purposes. Actually, the maximum bandwidth is slightly less because of the token transmission and Ethernet packet overhead. When the scheduler at the active node decides that another node must become active it stores the global