How to Request the Time from NTP Server using ESP8266

IOT projects are driven by very precise triggers and calculations based on timing and synchronization. But how can we get the perfect time without manual adjusting? One way to accomplish that is by asking an Network Time Protocol (NTP) Server. On the ESP8266, all you need is an Internet connection: you can just ask a time server what time it is. To do this, the NTP is used.


NTP is based on UDP. UDP doesn’t use a connection, a client can just send a message to the server directly, and the server can just send a response message back to the client when it has finished processing. There is, however, no guarantee that the messages will arrive at their destination, and there’s no way to know whether they arrived or not (without sending an acknowledgment, of course). This means that we can’t halt the program to wait for a response because the request or response packet could have been lost on the Internet, and the ESP8266 will enter an infinite loop.

Instead of waiting for a response, we just send multiple requests, with a fixed interval between two requests, and just regularly check if a response has been received.

Getting the time

Let’s take a look at an example that uses UDP to request the time from an NTP server.

Libraries, constants, and globals

#include <ESP8266WiFi.h> 

#include <ESP8266WiFiMulti.h>

#include <WiFiUdp.h>

ESP8266WiFiMulti wifiMulti; // Create an instance of the ESP8266WiFiMulti class, called 'wifiMulti' 

WiFiUDP UDP;                     // Create an instance of the WiFiUDP class to send and receive 

IPAddress timeServerIP;          // NTP server address const char* NTPServerName = ""; 
const int NTP_PACKET_SIZE = 48;  // NTP time stamp is in the first 48 bytes of the message 
byte NTPBuffer[NTP_PACKET_SIZE]; // buffer to hold incoming and outgoing packets
To use UDP, we have to include the WiFiUdp library and create a UDP object. We’ll also need to allocate memory for a buffer to store the UDP packets. For NTP, we need a buffer of 48 bytes long. To know where to send the UDP packets to, we need the hostname of the NTP server, this is


void setup()


Serial.begin(115200);          // Start the Serial communication to send messages to the computer  



startWiFi();                   // Try to connect to some given access points. Then wait for a connection  


 if(!WiFi.hostByName(NTPServerName, timeServerIP))

{ // Get the IP address of the NTP server    

Serial.println("DNS lookup failed. Rebooting.");    




Serial.print("Time server IP:\t");  


Serial.println("\r\nSending NTP request ...");  


In the setup, we just start our Serial and Wi-Fi, as usual, and we start UDP as well.
We need the IP address of the NTP server, so we perform a DNS lookup with the server’s hostname. There’s not much we can do without the IP address of the time server, so if the lookup fails, reboot the ESP.
If we do get an IP, send the first NTP request, and enter the loop.


unsigned long intervalNTP = 60000; // Request NTP time every minute unsigned long 

prevNTP = 0; 

unsigned long lastNTPResponse = millis(); 

uint32_t timeUNIX = 0; 

unsigned long prevActualTime = 0; 

void loop() 


unsigned long currentMillis = millis();  

if (currentMillis - prevNTP > intervalNTP) { // If a minute has passed since last NTP request    

prevNTP = currentMillis;    

Serial.println("\r\nSending NTP request ...");    

sendNTPpacket(timeServerIP);  // Send an NTP request  }  

uint32_t time = getTime();  // Check if an NTP response has arrived and get the (UNIX) time  

if (time) {   // If a new timestamp has been received    timeUNIX = time;    Serial.print("NTP response:\t");    


lastNTPResponse = currentMillis; 


else if ((currentMillis - lastNTPResponse) > 3600000) 

Serial.println("More than 1 hour since last NTP response. Rebooting.");    


uint32_t actualTime = timeUNIX + (currentMillis - lastNTPResponse)/1000;
 if (actualTime != prevActualTime && timeUNIX != 0) { // If a second has passed since last print   prevActualTime = actualTime;    

Serial.printf("\rUTC time:\t%d:%d:%d   ", getHours(actualTime), getMinutes(actualTime), getSeconds(actualTime));  

}   }
The first part of the loop sends a new NTP request to the time server every minute. This is based on Blink Without Delay.
Then we call the getTime function to check if we’ve got a new response from the server. If this is the case, we update the timeUNIX variable with the new timestamp from the server.
If we don’t get any responses for an hour, then there’s something wrong, so we reboot the ESP.
The last part prints the actual time. The actual time is just the last NTP time plus the time since we received that NTP message.

Setup functions

Nothing special here, just a function to connect to Wi-Fi, and a new function to start listening for UDP messages on port 123.
void startWiFi() { // Try to connect to some given access points. Then wait for a connection  

wifiMulti.addAP("ssid_from_AP_1", "your_password_for_AP_1");   // add Wi-Fi networks you want to connect to  

wifiMulti.addAP("ssid_from_AP_2", "your_password_for_AP_2"); wifiMulti.addAP("ssid_from_AP_3", "your_password_for_AP_3"); Serial.println("Connecting");  

while ( != WL_CONNECTED) {  // Wait for the Wi-Fi to connect   


Serial.print('.');  }  


Serial.print("Connected to ");  

Serial.println(WiFi.SSID());  // Tell us what network we're connected to 

Serial.print("IP address:\t");  

Serial.print(WiFi.localIP()); // Send the IP address of the ESP8266 to the computer Serial.println("\r\n"); } 

void startUDP() 


Serial.println("Starting UDP");  

UDP.begin(123); // Start listening for UDP messages on port 123  

Serial.print("Local port:\t");  




Helper functions

uint32_t getTime()


if (UDP.parsePacket() == 0)

{ // If there's no response (yet)    return 0;  }, NTP_PACKET_SIZE); // read the packet into the buffer  // Combine the 4 timestamp bytes into one 32-bit number

uint32_t NTPTime = (NTPBuffer[40] << 24) | (NTPBuffer[41] << 16) | (NTPBuffer[42] << 8) | NTPBuffer[43];  // Convert NTP time to a UNIX timestamp:  // Unix time starts on Jan 1 1970. That's 2208988800 seconds in NTP time:

const uint32_t seventyYears = 2208988800UL;  // subtract seventy years:  uint32_t UNIXTime = NTPTime - seventyYears;  return UNIXTime; }

void sendNTPpacket(IPAddress& address)


memset(NTPBuffer, 0, NTP_PACKET_SIZE);  // set all bytes in the buffer to 0  // Initialize values needed to form NTP request

NTPBuffer[0] = 0b11100011;   // LI, Version, Mode  // send a packet requesting a timestamp:

UDP.beginPacket(address, 123); // NTP requests are to port 123




inline int getSeconds(uint32_t UNIXTime)


return UNIXTime % 60;


inline int getMinutes(uint32_t UNIXTime)


return UNIXTime / 60 % 60;


inline int getHours(uint32_t UNIXTime)


return UNIXTime / 3600 % 24;

In the getTime function, we first try to parse the UDP packet. If there’s no packet available, the function just returns 0. If there is a UDP packet available, however, read it into the buffer. The NTP timestamp is 32 bits or 4 bytes wide, so we combine these bytes into one long number. This number is the number of seconds since Jan 1, 1900, 00:00:00, but most applications use UNIX time, the number of seconds since Jan 1, 1970, 00:00:00 (UNIX epoch). To convert from NTP time to UNIX time, we just subtract 70 years worth of seconds.
To request the time from the NTP server, you have to send a certain sequence of 48 bytes. We don’t need any fancy features, so just set the first byte to request the time, and leave all other 47 bytes zero.
To actually send the packet, you have to start the packet, specifying the IP address of the server, and the NTP port number, port 123. Then just write the buffer to the packet, and send it with endPacket.

sarah ali

sarah ali

Sarah is a passionate writer and blogger. As an early adopter, she enjoys trying out new social media and Internet tools along with WordPress plugins and Web apps.
sarah ali

Leave a Reply

Your email address will not be published.