DistOS-2011W NTP

Introduction

1. Introduction:

1.1 Context/Background

Network Time Protocol (NTP) synchronizes clocks of hosts and routers. According to NIST estimates there are 10-20 million NTP servers and clients deployed in the internet and its tributaries all over the world. NTP software has been ported to almost every workstation and server platform available today – from PCs to Cray’s – UNIX, Windows, VMS and embedded systems, even home routers and battery backup systems.

NTP provides nominal accuracies of low tens of milliseconds on WANs, sub milliseconds on LANs and sub microseconds using a precision time source such as cesium oscillator or GPS receiver. Our time protocol was designed over the LAN and our goal was to achieve sub milliseconds of accuracy.

1.2 Importance

Precision of time is very important in the computer world. Following are some example why it is so important to maintain a precise and accurate time.

Network monitoring, measurement and control, Distributed database transaction journaling and logging, Secure document timestamps with cryptographic certification, Radio and TV programming lunch and monitoring, Stock market buy and sell orders, Distributed network gaming and training, etc.

1.3 Definition of the problem

My goal was to acquire time accuracy in the Linux lab assuming that all the computers do not have internet connection. To time synchronize all the computers I had to build our own hierarchy of NTP servers and clients.

1.4 Summary of the result

An efficient hierarchy of NTP server and client has been implemented. Precision of Sub milliseconds were achieved.

1.5 Outline of the report Detailed background information and the structure of our time protocol are provided in Section 2. The development setup and code explanation is reviewed in Section 3. Details of which server/client contains which files are given in section 4. My contributions in this implementation are described in Section 5.

2. Detailed context/background information

In this section the background information of Network Time protocol and the hierarchical model and the comparison with the original NTP designed by Dave Mills is reviewed. For unambiguity I will call the protocol as Linux lab time protocol (LLTP) and the original Network time protocol as NTP.

2.1 NTP timestamps

The 64-bit timestamps used by NTP consist of a 32-bit second part and a 32-bit fractional second part. I followed the same time structure for our LLTP which gives us a time scale of 232 seconds (136 years) and a theoretical resolution of 2-32 seconds (233 picoseconds).

2.2 Structure

NTP uses a hierarchical, semi-layered system of levels of clock sources; each level of this hierarchy is termed a stratum and assigned a layer number starting with 0 at the top. The stratum level defines its distance from the reference clock and exists to prevent cyclical dependencies in hierarchy.

My target is to develop a time synchronizing software for a small office or lab with a large number of computer where a very few computer has internet connectivity but all the computers are connected together in a local network. As a result not all the computer is able to connect to internet for time accuracy. LLTP uses similar hierarchical, semi-layered sources as NTP. Each layer of this hierarchy is termed as level and assigned a layer number starting with 1.

2.3 Level 1 server

Computers with internet connectivity are the level 1 server for our LLTP

Level 1 server

synchronizes its system clock with the NTP servers on the internet. In this hierarchy, only a fixed (5) number of level 1 servers are used. Unlike NTP we don’t have the privilege to use a 10 of thousands of level 1 and level 2 servers, and unlike NTP our LLTP has only 3 level structures.

Picture below shows the connectivity and the hierarchy of LLTP

File:Z:\LTTPHireachy.jpg

2.4 Level 2 server and client

Level 2 servers run two different programs. A client program to synchronize its system clock with the level1 servers and a server program that waits for any level 3 client for time request. Upon the request it sends its synchronized system time to the client. Level 2 servers also synchronize its system clock with the other level2 servers.

Each level2 server is connected to 4 level1 servers. It polls time from each level1 server and chooses the best time and synchronizes its system clock. How the best time is achieved is described in the section 3 below with code explanation. There are maximum 5 level2 servers with our LLTP model. Each level2 server is connected to 4 different level1 servers. None of the level2 server has the same level1 server set.

2.5 Level 3 client

Bottom of the LLTP hierarchy is level3 client. It only runs a client program that polls time from the level2 servers. It can only connect/request time from one of our level2 servers at a time. It also requires the knowledge of the IP address of the level2 server. For the load management purpose level 3 clients are not able to connect to a Level1 servers.

Evaluated Systems/Programs

Describe the systems individually here - their key properties, etc. Use subsections to describe different implementations if you wish. Briefly explain why you made the selections you did.

Experiences/Comparison (multiple sections)

In multiple sections, describe what you learned.

Discussion

What was interesting? What was surprising? Here you can go out on tangents relating to your work

Conclusion

Summarize the report, point to future work.

References

Give references in proper form (not just URLs if possible, give dates of access).