 as being "chatty". Examples of "chatty" messages in protocols include "are you ready?" and "did you get those packets?" Error messaging dialogues create delays because documents aren't downloaded until both ends of the transmis- sion respond to these and other control messages. Certeon's software improves transmissions by substituting a proxy that emulates these error messages at the receiving end. The sending end removes most of the error messages. At the receiving end, the proxy performs the error control locally SO that transmissions are not delayed by control messages. This technique works effectively on high-quality links such as those made up of fiber-optic cabling. Because most WAN traffic is identical to previous transactions, Certeon's patent- pending de-duplication (a type of compression) sends only changes in data exchanges, not the entire file each time. As an example, when two offices collaborate on a Micro- soft PowerPoint presentation, the software learns what is in the file the first time it is sent. When a person resends the file with edits, only the changes are transmitted, thus decreasing the file size from perhaps 5 megabytes to 10 kilobytes. The software at the receiving end reassembles the file with the changes included. In addition to latency elimination and compression, some WAN optimization soft- ware can prioritize certain types of data traffic. For example, for a financial institution, it can give priority to customer web transactions over internal communications. This speeds up money transfers to the institution. Streamlining protocols and using compression increases throughput on enterprise data links and creates more capacity for current and future applications. An important capability makes it possible to utilize an organization's data links to electronically back up corporate data to other sites. If the main data center is destroyed by fire or a natural disaster, the organization's data is preserved. This is possible because WAN acceleration software and compression technology fre