Difficulty connecting to a time server in vb.net

[thehoten]

I am trying to use the following piece of code to connect to a time server and attain the time but have had no luck:

Dim ntpServer As String = "time.windows.com"
Dim ntpData(47) As Byte

Dim addresses = Dns.GetHostEntry(ntpServer).AddressList

Dim EndP As IPEndPoint = New IPEndPoint(addresses(0), 123)

Dim soc As Socket = New Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp)


soc.Connect(EndP)

soc.Send(ntpData)


soc.Receive(ntpData)


soc.Close()

Stepping through the program I can't get past the following line of code soc.Receive(ntpData). What am I doing wrong?

Thanks

[techgnome]

A couple things... I'm no expert on this so, take it for what it's worth...

1) ntpData is empty when you send it... don't you need to send something?
2 )I notice in the examples online for the Send and Recieve methods, they return an integer representing the number of bytes sent....
if you change your code similarly:

Dim ntpServer As String = "time.windows.com"
Dim ntpData(47) As Byte
Dim addresses = Dns.GetHostEntry(ntpServer).AddressList
Dim EndP As IPEndPoint = New IPEndPoint(addresses(0), 123)
Dim soc As Socket = New Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp)

soc.Connect(EndP)

Dim i as integer = soc.Send(ntpData)
'If you check i here... I bet it's zero because the array was empty.

'Since nothing was sent, the server doesn't know to send anything back... so the receive hangs...
i = soc.Receive(ntpData)

soc.Close()

As to what to send to the server in the first place? That I do not know.
Documentation & example: http://msdn.microsoft.com/en-us/library/w93yy28a.aspx


-tg

[thehoten]

Hi and thanks for your reply. I kind of figured this was the issue. I am essentially trying to translate some c code into vb.net but am unsure of what to do with the following:

ntpData[0] = 0x1B; //LI = 0 (no warning), VN = 3 (IPv4 only), Mode = 3 (Client Mode)

Do you know what 0x1B is in vb.net?

[thehoten]

Also i attains a value of 48 (ntpData is an array of length 48 containing zeros)

[techgnome]

Basically you sent 48 bytes of nothing... so it's not going to respond...

0x1B is hex... translates to 27 in decimal... Hex is represented in VB by using &H ... so &H1B is the equivalent... you can also just use 27, it's the samething.

        data(0) = &H1B
        data(1) = 27

So it looks like you need to sent byte 27 in order to provoke a response back from the server.


-tg

[dbasnett]

Take a look at

http://tools.ietf.org/html/rfc1059