Question

我想测量本地时钟与运行NTP服务器的远程处理器。

我可以得到响应的tx_time，如下所示，但是更好的估计将包括网络延迟的一些估计。 NTP响应消息中还有其他字段也应使用。

import ntplib
from time import ctime,time

addr_remote = '128.128.204.207'

c = ntplib.NTPClient()
remote = c.request(addr_remote)
local = time()
print("REMOTE: " + ctime(remote.tx_time) + "   <reference clock>   ") 
print("LOCAL:  " + ctime(local)        + "   delta: " + str(local - remote.tx_time ))

如果我查看“远程”：

for attr in dir(remote):
    print("remote.%s = %r" % (attr, getattr(remote, attr)))

我知道：

remote.delay = 0.0
remote.dest_time = 1531863145.9309998
remote.dest_timestamp = 3740851945.9309998
remote.from_data = <bound method NTPPacket.from_data of <ntplib.NTPStats object at 0x000000000265B2E8>>
remote.leap = 0
remote.mode = 4
remote.offset = -1.8789582252502441
remote.orig_time = 1531863145.9309998
remote.orig_timestamp = 3740851945.9309998
remote.poll = 0
remote.precision = -7
remote.recv_time = 1531863144.0520415
remote.recv_timestamp = 3740851944.0520415
remote.ref_id = 0
remote.ref_time = 0.0
remote.ref_timestamp = 2208988800.0
remote.root_delay = 0.0
remote.root_dispersion = 0.0
remote.stratum = 9
remote.to_data = <bound method NTPPacket.to_data of <ntplib.NTPStats object at 0x000000000265B2E8>>
remote.tx_time = 1531863144.0520415
remote.tx_timestamp = 3740851944.0520415

那么，我该如何使用它们：

目的地时间
原始时间
recv_time
tx_time

消除网络延迟并更好地估计时钟差？

Answer 1

NTP客户端发送带有本地时间orig_time的数据包，NTP服务器在服务器时间recv_time收到该数据包。然后，服务器在服务器时间tx_time进行答复，客户端在本地时间dest_time收到答复。

往返行程delay计算为recv_time - orig_time + dest_time - tx_time，时钟之间的偏移量为offset = (recv_time - orig_time + tx_time - dest_time) / 2。

假设两个NTP数据包采用一致的路径，则正确的调整时间就是dest_time + offset，相当于tx_time + delay/2。

Answer 2

我在尝试将我的客户端计算机同步到 NTP 时间并检查它是否实际同步时找到了这个答案。基于@Vic，这意味着客户端时钟（与服务器 NTP 时钟相比）始终关闭：

dest_time + offset = tx_time + delay/2
dest_time - tx_time = delay/2 - offset

即

correction = delay/2 - offset

正如@Vic 所说，数据包可能会采用不同的路由来往和来自，但平均而言 correction 应该给你你的时钟偏移量（我认为）。即使通过 time.nist.gov 与 os.system('w32tm /resync/nowait') 同步，我的计算机总是以某种方式关闭 40 毫秒。欢迎评论！

这是我的代码。

import ntplib
from datetime import datetime, timezone
def get_ntp_time():
    ntp_pool = ['pool.ntp.org', 'time.nist.gov']
    def call_ntp(serverAddress):
        call = ntplib.NTPClient()
        return call.request(server, version=3)
    for server in ntp_pool:
        response = call_ntp(server)
        print(f"server: {server}")
        print(f"request packet sent (as LOCAL client time, orig_time): {datetime.fromtimestamp(response.orig_time, timezone.utc)}")
        print(f"request packet received (as NTP server time, recv_time): {datetime.fromtimestamp(response.recv_time, timezone.utc)}")
        print(f"response packet sent (as NTP server time, tx_time): {datetime.fromtimestamp(response.tx_time, timezone.utc)}")
        print(f"response packet received (as LOCAL client time, dest_time): {datetime.fromtimestamp(response.dest_time, timezone.utc)}")
        print(f'round trip duration: {response.delay} s')
        print(f'* adjusted time, tx_time + delay/2: {datetime.fromtimestamp(response.tx_time + response.delay/2, timezone.utc)}')
        print(f'* adjusted time, dest_time + offset: {datetime.fromtimestamp(response.dest_time + response.offset, timezone.utc)}')
        print(f'correction to client: {response.delay/2 - response.offset} s\n')
        # for attr in dir(response):
            # if not attr .startswith('_'):
                # print("response.%s = %r" % (attr, getattr(response, attr)))
        print('-')
get_ntp_time()

回复：

server: pool.ntp.org
request packet sent (as LOCAL client time, orig_time): 2021-04-23 16:14:46.544797+00:00
request packet received (as NTP server time, recv_time): 2021-04-23 16:14:46.535852+00:00
response packet sent (as NTP server time, tx_time): 2021-04-23 16:14:46.535862+00:00
response packet received (as LOCAL client time, dest_time): 2021-04-23 16:14:46.579710+00:00
round trip duration: 0.03490257263183594 s
* adjusted time, tx_time + delay/2: 2021-04-23 16:14:46.553314+00:00
* adjusted time, dest_time + offset: 2021-04-23 16:14:46.553314+00:00
correction to client: 0.04384756088256836 s

-
server: time.nist.gov
request packet sent (as LOCAL client time, orig_time): 2021-04-23 16:14:46.642192+00:00
request packet received (as NTP server time, recv_time): 2021-04-23 16:14:46.641157+00:00
response packet sent (as NTP server time, tx_time): 2021-04-23 16:14:46.641158+00:00
response packet received (as LOCAL client time, dest_time): 2021-04-23 16:14:46.689054+00:00
round trip duration: 0.04686117172241211 s
* adjusted time, tx_time + delay/2: 2021-04-23 16:14:46.664588+00:00
* adjusted time, dest_time + offset: 2021-04-23 16:14:46.664588+00:00
correction to client: 0.0478968620300293 s

-

Python ntplib响应中的所有字段是什么？如何使用它们？

2 个答案: