I am interested to know if that if two network cables are to be joined together,can we use a pair of rj-45 to connect them?
Two RJ-45s can't be connected together. They're both "male" connectors.
Something like this product (http://www.newegg.com/Product/Product.aspx?Item=N82E16812999142&Tpk=cat5%20coupler) would work. Unfortunately, it's not much cheaper than just buying a longer patch cable. (I have no affiliation with Newegg.)