Clock synchronization in computer networks with quality of service

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

The Network Time Protocol (NTP), a protocol that synchronizes clocks from networked computers, has nearly two decades of existence and is continuously evolving. Due to its robust treatment of phase and frequency, an algorithm that disciplines the local machine clock, implementations available for a great deal of platforms and operating systems, it became a âde factoâ standard. However, this protocol still has some drawbacks that need to be addressed to make it operationally more efficient, since its performance depends on good network conditions for a proper exchange of synchronization information and it suffers from any level of network congestion. Due to such limitations, in many countries (including Brazil) NTP is considered inadequate to provide time information in a trustable way, considering without legal value any time registries in systems that use it. Furthermore, many applications need a trustable clock control system to work correctly (for example, banking systems and geographically distributed database servers). This requires many companies to use traditional and more expensive legacy systems for a correct and legal functioning of their computer clocks. With the use of Quality of Service in computer networks, this problem can be elegantly approached and solved. Many Quality of Service architectures were recently proposed, but the Differentiated Services architecture, due to its low implementation complexity and to the fact that it was the most studied and implemented architecture, is the strongest candidate to worldwide use in the coming years. This architecture fits the problem of clock synchronization very well, but the solution is not trivial, as is showing this work. This dissertation suggests a framework to deal with clock synchronization using NTP in DiffServ domains with or without the use of bandwidth brokers. Using Well Defined Services (WDS) and based on the idea that applications should be aware of the type of treatment required by their traffic, this framework consists of the adoption of policies to treat NTP traffic at network nodes and the adoption of a policy to mark packets by the application. The proposal is validated with a case study performed with real measurement of the application performance over an environment based on network emulation

ASSUNTO(S)

ciencia da computacao synchronization networks quality of service

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