Browse Prior Art Database

One to One Network Synchronization Algorithm

IP.com Disclosure Number: IPCOM000020755D
Original Publication Date: 2004-Jan-25
Included in the Prior Art Database: 2004-Jan-25
Document File: 2 page(s) / 55K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

In modern Computer networks time synchronization is often desirable. The most commonly used method for this is the Network Time Protocol (NTP). When there is a client machine wanting to synchronize with a server machine it sends an NTP packet to the server. This packet has a timestamp t1 in the field "transmit timestamp" that represents the time when the packet was sent. As soon as the server receives the packet it moves t1 from "transmit timestamp" to the field "originate timestamp", puts t2 in "receive timestamp" and finally writes t3 into the field "transmit timestamp". Then the packet is sent back to the client, which at time t4 repeats the process the server made and resends the packet to the server, and so on. This process is shown in Figure 1. Now the two machines are able to determine the roundtrip delay d of the network between them by using:

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© SIEMENS AG 2003 file: 2003J15951.doc page: 1

One to One Network Synchronization Algorithm

Idea: Elvino Rodrigues, PT-Lisbon; Nuno Silva, PT-Lisbon

In modern Computer networks time synchronization is often desirable. The most commonly used method for this is the Network Time Protocol (NTP). When there is a client machine wanting to synchronize with a server machine it sends an NTP packet to the server. This packet has a timestamp t1 in the field "transmit timestamp" that represents the time when the packet was sent. As soon as the server receives the packet it moves t1 from "transmit timestamp" to the field "originate timestamp", puts t2 in "receive timestamp" and finally writes t3 into the field "transmit timestamp". Then the packet is sent back to the client, which at time t4 repeats the process the server made and resends the packet to the server, and so on. This process is shown in Figure 1. Now the two machines are able to determine the roundtrip delay d of the network between them by using:

d = (t4-t1)-(t3-t2).

The offset c between the machines can be determined by:

c = (t2-t1+t3-t4)/2,

assuming the delay between the server and the client is the same as the delay between the client and the server, for example when the network is symmetric.

The problem of this algorithm is that it may be very good when there are many machines used for synchronizing the client but if there is only one machine to synchronize another one it lacks precision. Another problem is the measuring of the error taking into account the asymmetrical characteristics of a network.

It is herewith propose...