Python ntplib 响应中的所有字段是什么？如何使用它们？

Question

我想测量本地时钟和一个远程处理器运行一个 NTP 服务器。

我可以获得响应的 tx_time，如下所示，但更好的估计应该包括一些网络延迟估计。 NTP 响应消息中还有其他字段也应该使用。

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 ))

如果我看"remote"：

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

我明白了：

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，我该如何使用这些：

dest_time
orig_time
recv_time
tx_time

消除网络延迟，并更好地估计时钟差异？

Answer 1

NTP 客户端发送一个带有本地时间 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 回复，客户端在当地时间 dest_time.

收到回复

往返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数据包走的路径一致，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）总是关闭：

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

即

correction = delay/2 - offset

正如@Vic 所说，数据包可能采用不同的路由进出，但平均而言 correction 应该给你你的时钟偏移（我认为）。即使通过 time.nist.gov 与 os.system('w32tm /resync/nowait') 同步，我的计算机也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

-

Answer 3

我发现前面的回答对dealy或offset（延迟的一半）计算有点迷惑。我想指出这一点。

原来，ntplib.py源，dest_timestamp（接收时间），orig_timestamp（发送时间）是本地（客户端）时间。 tx_timestamp（服务器发送时间）和recv_timestamp（服务器接收时间）是服务器时间。所以以下代码中的第一项表示数据包发送和接收差异，第二项表示服务器处理时间。

无论如何，调整后的时间可以这样计算 adjusted_time = response.tx_time + response.delay*0.5

@property
def delay(self):
    """round-trip delay"""
    return ((self.dest_timestamp - self.orig_timestamp) -
            (self.tx_timestamp - self.recv_timestamp))

Python ntplib 响应中的所有字段是什么？如何使用它们？

What are all the fields in a Python ntplib response, and how are they used?

python

ntp