XML Protocol in Wireless Mobile Environments
          Jaakko Kangasharju
  Helsinki Institute for Information Technology
        jaakko.kangasharju@hiit.fi

SOAP is rapidly gaining popularity as a generic messaging protocol.
If SOAP is to be used even in mobile environments, any weaknesses it
may have need to be evaluated and addressed.  The messaging model used
for the messaging service implementation supposes that smallish SOAP
messages are sent intermittently between two applications, of which at
least one may be mobile.  The connectivity model supposes a persistent
connection for messaging that is separate from the actual transport
layer connections used to carry the messages.

The first concern to address is the high bandwidth requirement caused
by the use of XML.  Measurements indicate that, for the typically
small SOAP messages, the payoff of generic compressors is quite small,
and a binary representation of XML fares much better.  The persistence
of connections permits caching of XML items and elements from one
message to another.  The intent is to keep the basic binary format
very simple and specify ways to extend it for application-specific
needs.

Protocol concerns are not SOAP-specific as such, but apply to any
one-way messaging system.  The protocol used for messaging keeps
connections persistent and supports continuing the same connection
from a new network address.  Connection characteristics are measured
to permit adaptive applications to react to access technology changes.
Sending of non-application data, such as message headers, is minimized
by reusing existing connections and bundling messages together.