consume webservice when you just have url without adding ref

Question

i have web service url as

 

string url="http://192.168.1.155:8078/WebService1.asmx?op=Write & a="+stringValue;

where stringValue is string which is passed to webservice

write is function in webservice

 

i have just this information.

how can i call this in my client page

i cannot add reference of the webservice

 

how to do this . how to call webservice when you just have the information as the URL only

kindly suggest