whats the difference between two sketch arduino nano ethernet

Hello,
i upload the default Ethernet/WebServer example, but it never takes ip. then i changed the library and upload UIPEthernet then it works fine. here is the codes for UIPEthernet and see attached UIPEthernet_library.zip

whats the gap in the default ethernet webserver sketch? How can we modify the default webserver.ino?

// UIP is a proper library for Arduino Nano Ethernet shield
// NOTE: UIPEthernet library is not needed if you are using Arduino UNO/Duemilanove/Mega/etc.
// UIPEthernet library is used for Arduino Nano Ethernet Shield

#include <UIPEthernet.h> // Used for Ethernet

// **** ETHERNET SETTING ****
byte mac = { 0x90, 0xA2, 0xDA, 0x0D, 0x78, 0xEE };
IPAddress ip(192, 168, 1, 115);
EthernetServer server(80);

void setup() {
Serial.begin(9600);

// start the Ethernet connection and the server:
Ethernet.begin(mac, ip);
server.begin();

Serial.print("IP Address: ");
Serial.println(Ethernet.localIP());
}

void loop() {
// listen for incoming clients
EthernetClient client = server.available();

if (client)
{
Serial.println("-> New Connection");

// an http request ends with a blank line
boolean currentLineIsBlank = true;

while (client.connected())
{
if (client.available())
{
char c = client.read();

// if you’ve gotten to the end of the line (received a newline
// character) and the line is blank, the http request has ended,
// so you can send a reply
if (c == ‘\n’ && currentLineIsBlank)
{
client.println(“Hello World!

Hello World!

”);
break;
}

if (c == ‘\n’) {
// you’re starting a new line
currentLineIsBlank = true;
}
else if (c != ‘\r’)
{
// you’ve gotten a character on the current line
currentLineIsBlank = false;
}
}
}

// give the web browser time to receive the data
delay(10);

// close the connection:
client.stop();
Serial.println(" Disconnected\n");
}
}

UIPEthernet_library.zip (101 KB)