okay, be just careful that an int can be different that 4 bytes on somes machines and langages. (for instance an integer can be 16 or 32 bits long...)
Did you receive Pongs?

I don't think your Payload_type field is right. You have:
char Payload_Type;
...
and:
p_head->Payload_Type = '0';


but the char '0' as you write has as ASCII Code 0x30 and not 0x00
so code instead:
p_head->Payload_Type = 0x00;

Concerning the non responding hosts and clients, i have exactly the same problem with the client I develop. Nearly all the servents are busy, and it's a real problem