3Com CoreBuilder 3500, Implementation Manual

Page: 56 / 592

56 C
HAPTER
3: S
YSTEM
P
ARAMETERS
Simple Network
Time Protocol
(SNTP)
This section covers:
■
SNTP Overview
■
Implementing SNTP
SNTP Overview SNTP is an adaptation of the Network Time Protocol (NTP), which is used
to synchronize computer clocks in the global Internet. NTP provides
comprehensive mechanisms to access national time and frequency
dissemination services, organize the time-synchronization subnetwork,
and adjust the local clock in each participating subnetwork peer.
SNTP is a simplified access strategy for servers and clients using NTP
version 3. The access paradigm is identical to the User Datagram Protocol
(UDP)/TIME protocol, so it is relatively easy to adapt a UDP/TIME client
implementation to operate using SNTP. SNTP is designed to operate in a
dedicated server configuration with existing NTP and other SNTP clients
and servers.
SNTP can operate in either unicast mode (point-to-point), multicast mode
(point-to-multipoint), or anycast mode (multipoint-to-point):
■
A unicast client — Sends a request to a designated server at its
unicast address and expects a reply within a specified time frame.
From the reply, the unicast client can determine the time and
(optional) the round-trip delay and local clock offset relative to the
responding server
■
A multicast server — Periodically sends a unsolicited message to a
designated IP local broadcast address or multicast group address and
expects no requests from clients.
■
An anycast client
— Sends a request to a designated IP local
broadcast address or multicast group address. One or more anycast
servers reply with their individual unicast addresses. The anycast client
binds to the first reply that it receives and then continues the
operation in unicast mode.