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5.6 Segmentation and Reassembly (SAR)
Some of the Series 30 phones support Segmentation and Reassembly (SAR) functionality, which is an
optional feature in the Wireless Transport Protocol (WTP) layer defined by the WAP Forum. SAR is used
to split large WTP messages into a number of smaller datagrams and selectively retransmit failed
datagrams. The use of SAR improves over-the-air efficiency for downloading large messages to the
phone and makes content download (e.g., Java MIDlet download) and MMS transfer faster and more
reliable.
The use of SAR enables the transmission of large data files through WAP to the mobile phone. To use
SAR, it must be supported by both of the communicating parties, typically the WAP gateway and the
WAP browser. WAP service developers do not need to take any actions to enable SAR in their service
development. Even though phones supporting SAR allows downloading of large files, it should be
noted that other elements in the network (WAP gateways) might restrict the downloadable file sizes.
Nokia WAP gateways let through files up to 100 KB but the limit might be smaller than that in some
gateways. Another factor to keep in mind is that SAR can only be used in connection-oriented
(permanent) mode.
Further information about SAR functionality can be found in the "Segmentation and Reassembly in the
Wireless Transaction Protocol" document, which is available at the Forum Nokia Web site,
http://forum.nokia.com.
WAP Service Developer's Guide for Nokia Series 30 Phones with WML Browser
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