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Symbian3/SDK/Source/GUID-8A678AE5-A133-58EA-A4DD-B5BFC94D3AEA.dita
changeset 0 89d6a7a84779 
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Symbian3/SDK/Source/GUID-8A678AE5-A133-58EA-A4DD-B5BFC94D3AEA.dita	Thu Jan 21 18:18:20 2010 +0000
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+<?xml version="1.0" encoding="utf-8"?>
+<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
+<!-- This component and the accompanying materials are made available under the terms of the License 
+"Eclipse Public License v1.0" which accompanies this distribution, 
+and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
+<!-- Initial Contributors:
+    Nokia Corporation - initial contribution.
+Contributors: 
+-->
+<!DOCTYPE concept
+  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
+<concept id="GUID-8A678AE5-A133-58EA-A4DD-B5BFC94D3AEA" xml:lang="en"><title> Variable
+TCP Receive Window</title><shortdesc>Explains how to improve performance of TCP/IP stack.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
+<p>The performance of the existing Symbian platform TCP/IP stack is improved
+by doing the following:</p>
+<ul>
+<li id="GUID-00E77774-7DC6-513E-9CC3-46B499B4C196"><p>Setting an initial TCP
+receive window size that depends on the <xref href="GUID-8A678AE5-A133-58EA-A4DD-B5BFC94D3AEA.dita#GUID-8A678AE5-A133-58EA-A4DD-B5BFC94D3AEA/GUID-CDAA0409-6ECB-5ABB-A0E5-F7C5C58E6347">bearer
+type</xref>. </p> <p> </p> </li>
+<li id="GUID-22A70B8B-AD26-5898-8505-79F5434B5971"><p>Allowing the TCP receive
+window size to dynamically resize when there is a change in modulation. For
+example, GPRS to EDGE or 2G to 3G. </p> </li>
+</ul>
+<p>Bearers provide different bandwidth for data transmission using TCP/IP.
+The connection setup between TCP hosts are through three-way handshake. The
+TCP receive window size parameter is set during the connection startup. </p>
+<p>To indicate the TCP receive window size, the TCP header contains a 16-bit
+window field. The TCP receive window size denotes the maximum number of bytes
+that a sender can send and a receiver can receive. The TCP header can have
+any value between 0 and 64KB. Use the <xref href="http://www.ietf.org/rfc/rfc1323.txt" scope="external">TCP window scaling</xref> to increase the window size beyond
+64kB. The sender and receiver must agree to the scaling factor. The scaling
+factor can be multiplied at both the ends to increase the window size. For
+example, if the scaling factor is 2 and the window size negotiated is 96KB,
+then the stored window size is 48KB. Also a scaling factor of 2 yields the
+effective size of 96KB. The TCP receive maximum window size is mentioned in <codeph>tcpip.ini</codeph> file. </p>
+<p>At ROM build time, the (NetMCPR) plug-in configures the TCP receive window.
+It is possible to enable or disable the adaptive window size based on the
+bearer type. This helps some bearers to use adaptive window size and other
+bearers to use fixed pre-defined windows. The <xref href="GUID-8A678AE5-A133-58EA-A4DD-B5BFC94D3AEA.dita#GUID-8A678AE5-A133-58EA-A4DD-B5BFC94D3AEA/GUID-E1123CF2-EA87-5F18-8F3C-3FD98DD6ABE8">lookup
+table</xref> provides the information on TCP receive window size at licensees
+specific MCPR (NetMCPR). Licensees are provided with the TCP receive window
+interface. </p>
+<p>TCP receive window must be changed due to the following reasons: </p>
+<ul>
+<li id="GUID-4E46CC4D-3CFA-5078-B801-9E0F20857CC8"><p>Change in modulation
+due to the network change - modulation value for bearer varies in different
+network. Modulation change in the network triggers the notification to change
+the TCP receive window for the connected TCP sockets. For example, change
+in network from 2.5G to 3G. </p> </li>
+<li id="GUID-41F0FC86-3E72-5372-8C43-B59F3835DD48"><p>Change in bearer - Forces
+the TCP/IP stack to supply a new TCP receive window that is specific to the
+new bearer. </p> </li>
+</ul>
+<section id="GUID-CDAA0409-6ECB-5ABB-A0E5-F7C5C58E6347"><title>Bearer types</title> <p>The
+following are the bearer types that support the TCP receive window: </p> <ul>
+<li id="GUID-302F21B4-FDBA-5052-939E-7FE309C4A7DF"><p>General Packet Radio
+Service (GPRS 2.5G) </p> </li>
+<li id="GUID-F60D6AF2-0EAA-5693-982B-B0B531E22862"><p>Enhanced Data Rate for
+GSM Evolution (EDGE 2.75G or 3G – depends on the modulation scheme) </p> </li>
+<li id="GUID-07D37BB9-2BBE-5C22-9D5C-A3477F73E766"><p>Universal Mobile Telecommunications
+System (UMTS 3G) </p> </li>
+<li id="GUID-1677511B-C52E-5E4D-8657-075468587E97"><p>High-Speed Downlink
+Packet Access (HSDPA 3G) </p> </li>
+<li id="GUID-DF4013BE-A1DE-5ECA-9124-2376924345C8"><p>WLAN </p> </li>
+</ul> </section>
+<section id="GUID-E1123CF2-EA87-5F18-8F3C-3FD98DD6ABE8"><title>Lookup table</title> <p>The
+lookup table contains the entries of TCP receive window size for each bearer
+type. To set the TCP receive window size for bearer, licensees must override
+the <xref href="GUID-5AC853D0-31FB-3944-8769-A59977F616B0.dita"><apiname>SetTcpWin()</apiname></xref> function. The licensees can define their
+own TCP window lookup table and set the TCP receive window size for a bearer. </p> <p>Symbian
+uses the following lookup table for testing purpose. The licensees can replace
+the TCP receive window size with their own values: </p> <table id="GUID-0697063E-F323-5824-9775-FE4413399697">
+<tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>
+<tbody>
+<row>
+<entry><p> <b>Bearer or Modulation</b>  </p> </entry>
+<entry><p> <b>TCP receive window size</b>  </p> </entry>
+</row>
+<row>
+<entry><p>GPRS </p> </entry>
+<entry><p>12240 – 17520 </p> </entry>
+</row>
+<row>
+<entry><p>EDGE </p> </entry>
+<entry><p>21760 – 49640 </p> </entry>
+</row>
+<row>
+<entry><p>UMTS </p> </entry>
+<entry><p>29920 – 33580 </p> </entry>
+</row>
+<row>
+<entry><p>HSDPA </p> </entry>
+<entry><p>65535 or greater </p> </entry>
+</row>
+<row>
+<entry><p>WLAN </p> </entry>
+<entry><p>65535 or greater </p> </entry>
+</row>
+<row>
+<entry><p>Ethernet </p> </entry>
+<entry><p>65335 </p> </entry>
+</row>
+</tbody>
+</tgroup>
+</table> <p> </p> </section>
+<section id="GUID-6A97BEE5-8236-40A3-899B-6A4173D51C97"><title>Handling TCP receive window in TCP/IP stack</title> <p>The
+following are the scenarios to handle the TCP receive window: </p> <ul>
+<li id="GUID-2E1E9EC2-F481-54AE-A648-D9EC50EF77C4"><p>Increase window size
+- Change in the bearer increases the window size. </p> </li>
+<li id="GUID-B6C3EC7E-E0A0-521C-8830-4FDB27B409B8"><p>Decrease window size
+- Change in the bearer decreases the window size till it reaches the appropriate
+size for the new bearer. </p> </li>
+</ul> </section>
+</conbody><related-links>
+<link href="GUID-6822E7FA-D055-5693-8872-8D0E8554A734.dita"><linktext>Configuring
+TCP Receive                 Window</linktext></link>
+</related-links></concept>
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FCL/sftools/depl/docscontent