Implementing network protocols at user level

Traditionally, network software has been structured in a monolithic fashion with all protocol stacks executing either within the kernel or in a single trusted user-level server. This organization is motivated by performance and security concerns. However, considerations of code maintenance, ease of debugging, customization, and the simultaneous existence of multiple protocols argue for separating the implementations into more manageable user-level libraries of protocols. The present paper describes the design and implementation of transport protocols as user-level libraries. The authors begin by motivating the need for protocol implementations as user-level libraries and placing their approach in the context of previous work. They then describe their alternative to monolithic protocol organization, which has been implemented on Mach workstations connected not only to traditional Ethernet, but also to a more modern network, the DEC SRC AN1. Based on the authors' experience, they discuss the implications for host-network interface design and for overall system structure to support efficient user-level implementations of network protocols     

Increasing the portability and re-usability of protocol code

Deploying protocols is an expensive and time-consuming process today. One reason is the high cost of developing, testing, and installing protocol implementations. To reduce this difficulty, protocols are developed and executed within environments called protocol subsystems, and protocol software is often ported instead of being coded from scratch. Unfortunately, today a variety of protocol subsystems offer a plethora of features, functionality, and drawbacks; the differences among them often reduce the portability and reusability of protocol code, and therefore present barriers to the deployment of new protocols. In this paper, we consider differences in subsystems and their effect on the portability and reusability of protocols and protocol implementations. We then propose two different approaches, each optimized for a different situation, that allow protocol code implemented in one subsystem to be used without modification within other subsystems, and thus reduce the barriers to protocol deployment. We relate our experiences designing, implementing, and measuring the performance of each approach using, as a baseline, an AppleTalk protocol stack we have developed     

An object-oriented analysis of a BISDN control system with a focus on the UNI protocol object

The control system of a BISDN network will undoubtedly be very complex to design, implement and maintain. Its complexity has led researchers to look for ways of breaking down the problem into smaller and manageable parts. This has motivated the use of an object-oriented approach to analyse and comprehend the BISDN control system. This paper thus presents an object-oriented analysis (OOA) of a BISDN control system. This analysis is based on a method introduced by Coad and Yourdon and comprises five steps. All five steps, namely identifying subjects, identifying objects, identifying structures, defining attributes, and defining operations, will be worked out in detail with an emphasis on the user network interface (UNI) signalling protocol object. Four subjects, nine objects, and three structures are identified in the problem space at hand. This structuring offers a framework to analyse in detail the three aspects, data, structure and dynamic behaviour, of the UNI signalling protocol. A parallel between this approach and the well known approach used by the International Telecommunication Union (ITU) for specifying signalling protocols and contained in Recommendation I.130 is drawn. The Coad and Yourdon OOA approach applied to a BISDN control system can be used for the analysis of different aspects of such systems. This paper focuses on the UNI signalling protocol object which leads to a complete specification. Any protocol resulting from such analysis can be claimed to be object-oriented protocol. This approach offers modularity and thus offers a way of structuring the problem space into identifiable objects and data. Full benefits of object orientation can be gained only in the consistent use of object orientation throughout all steps in the development process. The proposed approach allows one to create libraries of generic procedures which can be reused in specific implementations.     

The λMAC framework: redefining MAC protocols for wireless sensor networks

Most current WSN MAC protocol implementations have multiple tasks to perform—deciding on correct timing, sending of packets, sending of acknowledgements, etc. However, as much of this is common to all MAC protocols, there is duplication of functionality, which leads to larger MAC protocol code size and therefore increasing numbers of bugs. Additionally, extensions to the basic functionality must be separately implemented in each MAC protocol. In this paper, we look at a different way to design a MAC protocol, focusing on the providing of interfaces which can be used to implement the common functionality separately. This leaves the core of the MAC protocol, determining only when to send, which is substantially different for each protocol. We also look at some examples of MAC extensions that this approach enables. We demonstrate a working implementation of these principles as an implementation of B-MAC for TinyOS, and compare it with the standard TinyOS B-MAC implementation. We show a 35% smaller code size, with the same overall functionality but increased extensibility, and while maintaining similar performance. We also present results and experiences from using the same framework to implement T-MAC, LMAC, and Crankshaft. All are demonstrated with data from real-world experience using our 24 node testbed.     

网络协议中的时间约束测试

对协议实现的时间约束进行测试,是验证协议实现的实时特性的重要方法.本文考查了当前实时系统测试方面的进展,结合路由协议测试的实践,修正了现有方法几个不符合实际情况的假设,扩展了时间自动机的理论和思路,将时间约束下的状态机转换成非确定性有限状态自动机,运用Wp方法生成抽象测试集,讨论将抽象测试集参数化的方法.以路由协议RIP的时间约束为例说明了生成基于TTCN测试例的过程.     

A programmable transport architecture with QoS guarantees

The emergence of distributed multimedia applications exhibiting significantly more stringent quality of service requirements than conventional data-oriented applications calls for new transport protocols with different characteristics to coexist and be integrated within single applications. The different delivery requirements posed by these diverse multimedia applications often imply the need for highly customized protocol implementations. Hence, application developers are faced with the threat of code obsolescence caused by the development of even newer delivery techniques. We present an object-oriented transport architecture that allows for dynamically binding a variety of protocol stacks on a per-call basis. By binding protocol stacks together, the special needs of the application can be met without the need to rewrite the code. This differs significantly from the traditional transport architecture which assumes preinstalled transport protocol stacks that cannot be customized. To illustrate some of the advantages provided by the architecture, we describe the transport component of the first reference implementation of the 150 MPEG-4 Delivery Multimedia Integration Framework and demonstrate how quickly it was implemented in our framework     

Design and Performance of PRAN: A System for Physical Implementation of Ad Hoc Network Routing Protocols

Simulation and physical implementation are both valuable tools in evaluating ad hoc network routing protocols, but neither alone is sufficient. In this paper, we present the design and performance of PRAN, a new system for the physical implementation of ad hoc network routing protocols that unifies these two types of evaluation methodologies. PRAN (physical realization of ad hoc networks) allows existing simulation models of ad hoc network routing protocols to be used - without modification - to create a physical implementation of the same protocol. We have evaluated the simplicity and portability of our approach across multiple protocols and multiple operating systems through example implementations in PRAN of the DSR and AODV routing protocols in FreeBSD and Linux using the standard existing, unmodified ns-2 simulation model of each. We illustrate the ability of the resulting protocol implementations to handle real, demanding applications by describing a demonstration with this DSR implementation transmitting real-time video streams over a multihop mobile ad hoc network; the demonstration features mobile robots being remotely operated based on the real-time video stream transmitted from the robot over the network. We also present a detailed performance evaluation of PRAN to show the feasibility of our architecture     

Multiprotocol management agents: a look at an implementation andthe issues to consider

This paper discusses the implementation of a multiprotocol management agent. While there are numerous implementations of agents that allow for management of objects using one protocol or the other, few implementations provide for management of the same set of objects over multiple protocols. To be manageable over multiple protocols, the managed objects have to be modeled according to the different management models as well as resolve the management protocol related differences. Additional requirements may be imposed on the multiprotocol management agent to render the subagents and the protocol entities independent of the multiple protocols and management models. The differences between the multiple management mechanisms involved and the need to support future mechanisms imply that efficient implementations of management agents must converge the multiple management mechanisms into a generic local mechanism. The management agent described in this paper allows for the management of a generic network device such as a gateway. The network device operates at the transport-layer level of several communication protocol stacks and therefore, has several modules to be managed, corresponding to the lower layers of each protocol stack     

A dynamic reconfigurable routing framework for wireless sensor networks

Sensornet deployments of the future are expected to deliver a multitude of services, ranging from reliable sensing, real time streams, mission critical support, network reprogramming and so on. Naturally, no one routing protocol can sufficiently cater to the network layer functionalities expected. Severe resource constraints further limit the possibility of multiple routing protocols to be implemented. Further, vertically integrated designs of present protocols hinder synergy and code-reuse among implementations. In this paper, we present an architecture that allows applications to send different types of flows, often with conflicting communication requirements. A flow’s requirements are made visible to our framework by using just 3 bits in the packet header. The core architecture is a collection of highly composable modules that allows rapid protocol development and deployment. We show that our framework can provide: (i) flow based network functionality that ensures each flow gets an application specific network layer which is dynamically knit as per the flow’s needs, (ii) modular organization that promotes code-reuse, run time sharing, synergy and rapid protocol development and (iii) pull processing that allows flows to dictate their traffic rate in the network, and implement flexible scheduling policies. This creates a framework for developing, testing, integrating, and validating protocols that are highly portable from one deployment to another. Using our framework, we show that virtually any communication pattern can be described to the framework. We validate this by gathering requirements for one real world application scenario: predictive maintenance (PdM). The requirements are used to generate a fairly complete and realistic traffic workload to drive our evaluation. Using simulations and 40 node MicaZ testbed experiments, we show that our framework can meet the deployments demands at granularities not seen before in sensornets. We measure the costs of using this framework in terms of code size, memory footprints and forwarding costs on MicaZ motes.