CCITT, IEEE and ISO are organizations which define standards which are used for working of hardare or software together. These standards define how to communicate through messages between these hardwares. So the two harwares from different vendors works, this is the magic of these standards. The competition between hardware companies become high so the cost of these hardware automatically decreases. As the companies have more competition so they tend to give more and more features to their hardware and give efficient result. For example you can take the example of memory card of mobiles. In earlier days the memory card comes in low capacity of space and low speed also. Nowadays the momory card of mobile comes with high speed and more space with even low price.
CCITT stands for Consultative Committee on International Telegraph and Telephone. CCITT is United Nation Agency. This organization defines standards for telegraph, telephone and data communication. X25 is one the standard of this organization. X25 is used for wide area network communication. The new name of CCITT is International Telecommunication Union(ITU).
IEEE is short of Institute of Electrical and Electronics Engineers. IEEE is also used for defining communication protocols. These protocols are used for LAN communication. Example of these protocols are Ethernet, Token bus and token ring.
ISO is short of International Standard Organization. It is also used for defining different standards. ISO started in 1926 and it was named as ISO in 1946.