Huawei AR150 Series Configuration Manual page 103

Huawei AR150&200&1200&2200&3200 Series Enterprise
Routers
Configuration Guide - Device Management
Figure 5-6 Multicast mode
Multicast server
Manycast Mode
Manycast mode is applied to a small set of servers scattered over the network. Clients can
discover and synchronize to the closest manycast server. Manycast can especially be used where
the identity of the server is not fixed and a change of server does not require reconfiguration of
all the clients in the network.
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To prevent the client from constantly sending NTP request packets to the manycast server and
reduce the load of the server, the NTP protocol defines a minimum number of connections. In
manycast mode, the client records the number of connections established every time it
synchronizes clock with the server. The minimum number of connections is the minimum
number of connections called during a synchronization process. If the number of connections
called by the client reaches the minimum number during subsequent synchronization processes
and the synchronization is completed, the client considers that the synchronization is completed.
After that, the client sends a packet every time a timeout period expires to maintain the
connection. The NTP protocol uses the time to live (TTL) mechanism to ensure that the client
can successfully synchronize with the server. Every time the client sends an NTP packet, the
TTL of the packet increases (the initial value as 1) until the minimum number of connections is
reached or the TTL value reaches the upper limit. If the TTL reaches the upper limit or the
number of connections called by the client reaches the minimum number, but connections called
by the client still cannot complete the synchronizing process, the client stops data transmission
in a timeout period to eliminate all connections. Then the client repeats the preceding process.
Issue 05 (2014-01-16)
P e r i o d i c m u l t i c a s t c l o c k
synchronization packets (mode5)
Interaction of clock synchronization
packets (mode3 and mode4)
P e r i o d i c m u l t i c a s t c l o c k
synchronization packets (mode5)
Manycast server: The manycast server continuously listens to the packets. If a server can
be synchronized, the server returns a packet (the Mode field is set to 4) by using the unicast
address of the client as the destination address.
Manycast client: The client in manycast mode periodically sends request packets (the Mode
field is set to 3) to an IPv4/IPv6 multicast address. After receiving a reply packet, the client
filters and selects clock signals, and synchronizes its clock with the server that provides
the optimal clock.
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Multicast client
Initiate a server/client request
a f t e r r e c e i v i n g t h e f i r s t
multicast packet
Obtain a network delay , and
enter multicast client mode
Receive the multicast packets,
and synchronize the local clock
to that of the multicast server
5 NTP Configuration
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