How to decode route points from the JSON Output Data?

I am new in the ios field, Now i am trying to implement MKMapView Based iPhone Application. From the Google Map Web web service i Fetch the Data in JSON Output Format.

- (void)update {
 
     self.responseData=[NSMutableData data];
     NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:@"http://maps.googleapis.com/maps/api/directions/json?origin=Ernakulam&destination=Kanyakumari&mode=driving&sensor=false"]];
     [[NSURLConnection alloc] initWithRequest:request delegate:self];    
 }
 -(void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response{
     [self.responseData setLength:0];
 }
 -(void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data{
     [self.responseData appendData:data];
 }
 -(void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error{
     [connection release];
     self.responseData =nil;
 }
 -(void)connectionDidFinishLoading:(NSURLConnection *)connection{
     NSLog(@"connection established");
     [connection release];
     NSString *responseString=[[NSString alloc]initWithData:self.responseData encoding:NSUTF8StringEncoding];
     self.responseData=nil;
     NSLog(@" OUTPUT JSON DATA^^^^^^^^^^^^^^^^%@",responseString);
 
 
 }  
 

I got the out put has in the JSON Format. Now i want to draw route between this two location. sow how can i separate all the latitude and Longitude points from the JSON out put Data.

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