dissemination of time using network time protocol and its
TRANSCRIPT
Dissemination of time using
Network Time Protocol and
its application
R. C. Jha, A. Shukla, A. Agarwal, P. Thorat, T. Bharadwaj, N. Sharma*
, and V. N. Ojha
Pranalee Thorat/ATFW/2017
Role of CSIR-NPL
CSIR_NPL - NMI of India -
Maintains Primary standard of
Time by the act of Parliament
- responsible for
the highest level of time and
frequency measurements in
India and its traceability to
BIPM using ultra precise
satellite links.
In simple words, we maintain
the Indian Standard Time (IST)
based on a bank of Cesium (Cs)
atomic clocks and a Hydrogen
maser
CSIR-NPL
PRECISE TIMING SYSTEM AT CSIR-NPL
Name of NMIs Long Wave Radio Telephone NTP
NPL, India
UTC(NPLI)
__ “Teleclock” +11 45608687
+11 45608688
Accuracy:10 ms–1 s
Accuracy: 100 ms
NIST, USA
UTC(NIST)
WWV Broadcast
(60 KHz)
Station: Fort Collins, Colorado
“ACTS” +1-303-499 7111
Accuracy: 30 ms
20 servers (free)
3 servers (restricted)
Accuracy: 50 ms
NPL, UK
UTC(NPL)
MSF Radio Time signal
(60 KHz)
Station: Anthorn
Accuracy: within 1 ms
“Phoneclock” +44-020-8943 6333
Accuracy: 30 ms
02 NTP servers (within NPL)
2 NTP servers (Public services)
Accuracy: 20 ms
PTB, Germany
UTC(PTB)
DCF77 (77.5 kHz)
Station: Mailflingen
(South-East of Frankfurt)
Accuracy: ms
+49-0531- 512038
Accuracy: few ms
3 servers
NRC, Canada
UTC(NRC)
3330, 7850, 14670 kHz
Station: near NRC
Accuracy: 0.1 ms
+1-613-745 1576
and
+1-613-745 9426
Accuracy: 1 ms
2 servers
NICT, Japan
UTC (Japan)
40 kHz, 60 kHz
Station: Ohtakadoya-yama and Hagane-yama
+81-42-327 7592
ntp.nict.jp
NIM, China
UTC (China)
BPC (68.5 KHz)
Station: Shangqiu
Telephone Time Service
+8610 6422 9086
Accuracy: 300 ms
Australia
UTC (Aus)
__ +02 8467 3727 NTP multiple servers
Accuracy: better than 10 ms
LNE-SYRTE, France
UTC(OP)
TDF (162 kHz)
Station:
Allouis (150 Km south of paris)
Accuracy: 1 ms
(Speaking clock)
Method: one array of four speaking
clocks
Accuracy: 20 ms
Stratum-1 time server: ntp-
p1.obspm.fr (restricted access)
Stratum-2 time server:
ntp.obspm.fr (free access)
SU, Russia
UTC(Russia)
RBU: 66.66 kHz, Moscow/Russia Speaking clock
Dial 100 or 060
(08 servers in stratum1 and 01
in stratum 2)
Accuracy: few tens of ms
Various NMI time Dissemination Methods
• There are various way of time dissemination but time
synchronization protocols working on the IP networks are mainly
• Windows W32 Time service (using SNTP) Protocol, Network
Time Protocol (NTP) and Precision Time Protocol (PTP) etc.
• NTP is the most effective and robust method for time
synchronization using Internet.
• NTP is a hierarchical protocol partitioned into stratums which
defines the distance of the Server from the reference clock,
which can be Atomic clock, GNSS time etc.
NTP- Network Time Protocol
• NTP stands for Network Time Protocol.
• It is an Internet time synchronization protocol.
• Used to synchronize computer clocks to a time reference using the
internet.
• This protocol was designed by Prof David L. Mills at University of
Delaware.
• Protocol to sync clocks of computer systems over packet-switched,
variable –latency data networks
– Uses UDP port 123
– Designed to resist effects of variable latency (jitter buffer)
– Designed in 1985 by Dave Mills at U. Delaware
– Can achieve accuracy of 200 µsec
– Based on Marzullo Algorithm
Introduction
• NTP is intended to synchronize within a
few milliseconds of Coordinated Universal Time (UTC).
• Uses a modified version of Marzullo's algorithm & is designed to
mitigate the effects of variable network latency
• NTP can usually maintain time within tens of milliseconds over
the public Internet & can achieve better than one millisecond
accuracy in LANs under ideal conditions.
• Asymmetric routes and network congestion can cause errors of 100
ms or more
• The protocol is usually described client-server model, but can as
easily be used in peer-to-peer relationships where both peers
consider the other to be a potential time source.
• Implementations send and receive timestamps using the User
Datagram Protocol (UDP) on port number 123
Introduction continues
• They can also use broadcasting or multicasting, where clients passively listen to time updates after an initial round-trip calibrating exchange.
• The current protocol is version 4 (NTPv4), which is a proposed standard as documented in RFC 5905. It is backward compatible with version 3, specified in RFC 1305
History Of NTP • 1979- First public demonstration of Network time synchronization.
• 1981- Protocol was developed and documented n RFC 778
• 1985 – NTPv0 was implemented in Fuzzball and Unix: documented in RFC 958
• 1988- NTPv1 much more complete specification with associated algorithms: RFC 1059
• 1989- NTPv2 :state machines and pseudocodes, management protocol, cryptographic authentication scheme: RFC 1119
• 1992- Included analysis of all sources of error, broadcast mode introduced : RFC 1305
• 2010- Proposed new specifications: RFC5905
• 2014- Updated RFC is being processed which is yet to publish.
Basic features of NTP • NTP needs some reference clock that defines
TRUE TIME to operate.(Usually UTC is reference time for NTP service)
• NTP is a fault tolerant protocol.
• NTP is highly scalable.
• Protocol is highly accurate
• In temporary absence of internet connectivity, NTP can use measurement from past to estimate current time and error.[x]
• NTP also maintain estimates for the accuracy of local time.
NTP Clock Stratum Structure
• NTP uses hierarchical system of
“clock strata” • Stratum levels define distance
from reference clock and exist to
prevent cycles in hierarchy
– Stratum 0
• devices are atomic clocks, GPS
clocks, radio clocks
– Stratum1
• computers attached to stratum0
devices
• Act as servers for timing requests
from Stratum 2 servers via NTP
– Stratum2
• Similar to Stratum1, but they also
have peering relation to other
stratum2 servers
Plan of Time Synchronization throughout INDIA
Enormous applications of NTP Time
synchronization • Web Time Display
• Voice over IP
Web time display
Disseminates time over internet through http or https
Web time display Objective: Disseminates time from CSIR-NPL NTP Server to Web
Browser
NTP Server
Browser
Web Time Display : Challenge
• Browser cannot send NTP request to NTP Server
Request
NTP Time
Response
NTP Data NTP Server
Browser
Web Time Display : Solution – Web
NTP CLIENT
Request
NTP
Time
Response
NTP Data
Request
HTTP
Time
Response
HTTP
Data Browser
Web NTP Client
NTP Server
Web NTP Client mediates between web browser and NTP Server.
It also logs all time request from the user.
Log data: User IP Address, Timestamps of each node (User, NTP Client, NTP Server)
Web Time Display : MACROS
Initiating Time
(𝑡𝑖)
Receive Time
(𝑡 )
NTP Client Receive Time
(𝑡𝑛 )
NTP Client Transmit Time (𝑡𝑛 )
NTP Serv
(𝑡𝑛 )
NTP Serv
(𝑡𝑛 )
Web Time Display : Calculation-Time
Calibration
Round Trip Time (𝑡 )
Clock Difference (𝑡 𝑖𝑓𝑓)
Receive Time (𝑡 ) - Initiating Time
(𝑡𝑖) NTP Server transmit Time (𝑡𝑛 ) – (Receive Time ( 𝑟) + Initiating Time ( 𝑖)2
NTP Client
Round Trip Time
User
Round Trip Time
NTP
SERVER
Processing
Time
Statistical Data Analysis of CSIR-NPLNTP
servers
Currently NPLI having 2 NTP servers and from statistical data
analysis of NTP users, we found that NTP Service is used in
diversified sectors. These are
• Telecom Sector
• Cable TV Communication
• Electronic Device Manufacturing
• Internet Service
• Cloud Computing Service
• Research and Education
• IT services
but we found that more than 50% of our NTP service is utilized by
VoIP Server Providers
UTM data analysis of NTP servers of NPLI
(TOP_HITS) (26/05/2017-13/06/2017)
IP ADDRESS NO OF
HITS
NAME OF ORGANIZATION COUNTRY
110.172.171.194 249813 World Phone Internet Service Pvt. Ltd. India
14.139.47.4 58368 National Institute of Science Communication and In India
182.71.216.178 29123 Bharti Airtel limited India
24.15.80.185 21742 comcast cable communication LLC United States
69.20.5.68 11547 BACKSPACE HOSTING United States
131.193.178.43 10172 University of Illinois at Chicago United States
192.11.130.225 10160 Alcatel Lucent United States
73.14.95.143 10111 Comcast Cable Communications LLC United States
132.163.136.80 7928 National Institute of Standards and Technology United States
218.248.28.20 6110 Bharat Sanchar Nigam Limited India
121.241.246.150 6066 Tata Communications Limited India
192.11.69.21 5155 Alcatel Lucent United States
115.111.15.170 4432 Tata Communications Limited India
196.1.113.248 3374 Centre for Development of Advanced Computing India
203.101.52.55 3019 BHARTI AIRTEL India
UTM data analysis country-wise of NTP servers of
NPLI (01/01/2017-01/02/2017)
COUNTRY Number of HITS
INDIA 4,06,124
USA 77,397
CHINA 13
RUSSIAN
FEDERATION
24
IRAN 8
UKRAINE 4
ROMANIA 2
CANADA 7
GERMANY 14
FRANCE 8
UNITED KINGDOM 110
OTHERS 16,707
Country Hit Ratio
INDIA 406,124(81.1%)
UNITED
STATES
77,397(15.5%)
RESERVED 16,707(3.3%)
Other (1.1%)
UTM data analysis Date wise of NTP servers of NPLI
(26/01/2017-13/06/2017)
DATE HITS (in
thousand
)
26-05-2017 12
27-05-2017 142
28-05-2017 134
29-05-2017 22
30-05-2017 21
31-05-2017 27
01-06-2017 26
02-06-2017 16
03-06-2017 28
04-06-2017 42
05-06-2017 30
06-06-2017 24
07-06-2017 36
08-06-2017 21
09-06-2017 19
10-06-2017 24
Holi
days
Top NTP Users Hits per Day of NTP servers of NPLI
(01/01/2017 - 01/02/2017) IP
ADDRESS
NO OF
HITS
DATE SERVER NAME OF
ORGANIZATION
182.71.216.178
135879
1/17/2017 14.139.60.106 Bharti Airtel, New Delhi,
110008
182.71.216.178 79955 1/16/2017 14.139.60.106 Bharti Airtel, New Delhi,
110008
182.71.216.178 61585 1/18/2017 14.139.60.106
Bharti Airtel, New Delhi,
110008
182.71.216.178 53971 1/27/2017 14.139.60.106 Bharti Airtel, New Delhi,
110008
182.71.216.178 85836 1/28/2017 14.139.60.106 Bharti Airtel, New Delhi,
110008
110.172.171.194 36917 1/14/2017 14.139.60.106
World Phone Internet Services
Pvt Ltd. New delhi,india,
110001
110.172.171.194 33233 1/15/2017 14.139.60.106
World Phone Internet Services
Pvt Ltd. New delhi,india,
110001
110.172.171.294 12803 1/13/2017 12803
World Phone Internet Services
Pvt Ltd. New delhi,india,
110001
What is VoIP
• VoIP (voice over IP) is the transmission of voice and multimedia content over Internet Protocol (IP) networks. VoIP is enabled by a group of technologies and methodologies used to deliver voice communications over the internet, enterprise local area network or wide area network.
• VoIP encapsulates audio via a codec into data packets, transmits them across an IP network and unencapsulates them back into audio at the other end of the connection. VoIP endpoints include dedicated desktop VoIP phones, softphone applications running on PCs and mobile devices, and WebRTC - enabled browsers.
It is also possible to bypass a VOIP Service Providers and directly connect to another VOIP user.
(first user)IP Phone----- Ethernet ----- Router ---- Internet ---- Router ----Ethernet ---- IP Phone(end user)
Dependence Of VoIP on NTP Time Stamping Time synchronization plays a key role in VoIP or Internet telephony services in several
areas, such as:
• SLA measurements :- The service level agreement (SLA) is a contract between a
service provider and a customer that guarantees a certain quality and availability.
SLAs are therefore a critical part of any VoIP service. Recently, service providers have
started providing end-to-end SLAs guaranteeing VoIP QoS.
• Fault analysis
• Call Data Record (CDR) generation and billing :- Billing is also a core function in
telecom. CDRs are the primary source of billing information in VoIP. They provide
information about call origination, destination, and duration. CDR duration includes
the timestamp indicating when the call was initiated and either the call duration or the
time the call was terminated
• Security
• Network fault diagnostics and recovery
Loss of connection
Buffer overflow
Missing packets
Crashes
Denial of service attacks
NTP Server provides the timestamp with holding
accuracy of microseconds and disseminating
accuracy of milliseconds. So, quality of service and
security in VoIP Service could be achieved by
synchronizing time from NTP Server.
Any user across the world can uses NTP service if
their system is having Internet connection and NTP
provide time to user at stratum 3 to 15 level and it is
free in INDIA.
So it is very cheaper way to uses NTP services for
Business like VOIP etc.
Conclusion
Thank You