Firewalls

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I spent some time talking about the HTTP infrastructure because XML can be transferred through the same port. Most modern companies have a way for their employees to access Web pages. Since most public Web services listen to port 80, most firewalls allow data to flow freely through this port. Firewall software doesn't generally check for the type of data going through this port, because information providers add new data types all the time—keeping up would be an administrative nightmare. Using port 80 for getting information between businesses, then, is a no-brainer, because it doesn't involve complex administrative issues for network administrators.

The POST method provides an elegant way to ship data between clients and servers through the Web infrastructure. Because XML is based on the same encoding standards as HTML, you can easily use XML to pass information between two servers.