<?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-18C39927-625C-5B24-919F-469FCBCD501D" xml:lang="en"><title>BCA2
API Overview</title><shortdesc>Explains the second Baseband Channel Abstraction design (BCA2). </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<section id="GUID-8EA6D7A7-26A8-5B96-ADD7-E01E86B05329"><title>Required background</title> <p>You
should be familiar with the following areas: </p> <ul>
<li id="GUID-CCE01846-276A-5EB9-9876-DBBC90BD31A7"><p>architecture of device
drivers in Symbian platform (see <xref href="GUID-8D80AA51-5108-5D4B-B6B9-7FA47570AB89.dita">Device
Drivers Concepts</xref>) </p> </li>
<li id="GUID-8DAA8E32-B216-5279-A4AE-4435596F5517"><p>general principles of
a telephony stack (see <xref href="GUID-FA5A24BE-F4AF-5EC3-8969-6184A5A5BBFA.dita">Cellular
Baseband Services</xref>) </p> </li>
<li id="GUID-01DF1F36-5E88-5365-82E3-6601FBFE5F48"><p>networking and telephony
components. </p> </li>
</ul> </section>
<section id="GUID-679587F9-CD73-51C2-8D7E-AE5817533660"><title>Key concepts
and terms</title> <p> </p> <dl>
<dlentry>
<dt>BCA</dt>
<dd><p>Baseband Channel Adapter </p> </dd>
</dlentry>
<dlentry>
<dt>LDD</dt>
<dd><p>Logical device driver (see <xref href="GUID-8D80AA51-5108-5D4B-B6B9-7FA47570AB89.dita">Device
Drivers Concepts</xref>) </p> </dd>
</dlentry>
<dlentry>
<dt>PPP</dt>
<dd><p>Point-to-Point Protocol (see <xref href="GUID-E18F402A-6478-5B24-8DC0-33989FC5FD43.dita">What
is PPP?</xref>) </p> </dd>
</dlentry>
<dlentry>
<dt>HDLC</dt>
<dd><p>High-level Data Link Control </p> </dd>
</dlentry>
<dlentry>
<dt>ISDN</dt>
<dd><p>Integrated Services Digital Network </p> </dd>
</dlentry>
<dlentry>
<dt>ECUART</dt>
<dd><p>Serial RS232 driver for Symbian platform. UART means Universal Asynchronous
Receiver/Transmitter. </p> </dd>
</dlentry>
<dlentry>
<dt>C32</dt>
<dd><p>Serial Communications Server in Symbian platform (see <xref href="GUID-9B83CDD4-FC94-51A0-AC67-CD04BCAFEF08.dita">Serial Communications Server</xref>) </p> </dd>
</dlentry>
</dl> </section>
<section id="GUID-FEB0738E-8AB9-48DD-8648-493AC70258A0"><title>Introduction</title> <p>The
Baseband Channel Adapter (BCA) provides a telephony-specific abstraction of
the baseband driver. </p> <p>You implement your BCA components depending on
the level of abstraction you require, providing a standard interface to the
component above it in the Communications stack. You can also stack BCA components
for more flexibility. </p> <p>Performance is a critical requirement for the
Comms Data Plane. To improve throughput, update your BCA components and your
link layer protocol plugins to use the <xref href="GUID-55442FD0-FD97-3FA3-A61A-C1288C4D5670.dita"><apiname>MBca2</apiname></xref> interface. </p> </section>
<section id="GUID-5D32EEFF-FFF5-51DE-AF53-F182A4E49F9D"><title>Architecture</title> <p>This
topic focuses on a general case where there is one BCA component between the
driver and the lower layer of the Data Plane. In the case of a stack of BCA
components, the same design is repeated between each BCA layer. </p> <p>In
a "pull" communication model, the destination requests data from the source.
Data transfer happens when the destination is ready. In a "push" model, the
source provides data to the destination : data transfer happens when the source
is ready. </p> <p>BCA2 is based on a "push" architecture. The link layer component
registers with the BCA component. The BCA component provides the data to its
registered clients as soon as the data becomes available. </p> <p>The API
is split into five classes to separate control flow and data flow methods. </p> <fig id="GUID-699CB340-3DBB-50F5-8555-D4E2609BDECC">
<title>              MBca2 design            </title>
<image href="GUID-0B45D491-F88A-5036-A51C-9BFD6DB574D5_d0e65333_href.png" placement="inline"/>
</fig> <p>Moreover, the <xref href="GUID-55442FD0-FD97-3FA3-A61A-C1288C4D5670.dita"><apiname>MBca2</apiname></xref> interface
relies on shared buffers instead of regular buffers. Using shared buffers
avoids data copies between different layers of the stack. For more information,
see <xref href="GUID-A248C2C0-5F64-5484-85B2-57C86E3499E1.dita">Memory Management
in the Communications Framework</xref>. </p> </section>
<section id="GUID-5826984F-EAFA-5EDC-9C39-3966C89373A2"><title>APIs</title> <p><b>BCA component</b> </p> <table id="GUID-049AA111-6F8D-52F3-9681-0746FD0E4E9B">
<tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>
<thead>
<row>
<entry>API</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><p> <xref href="GUID-55442FD0-FD97-3FA3-A61A-C1288C4D5670.dita"><apiname>MBca2</apiname></xref>  </p> </entry>
<entry><p>Provides startup and shutdown methods. </p> </entry>
</row>
<row>
<entry><p> <xref href="GUID-55442FD0-FD97-3FA3-A61A-C1288C4D5670.dita"><apiname>MLowerDataSender</apiname></xref>  </p> </entry>
<entry><p>Provides the <codeph>Send()</codeph> method, which takes a <xref href="GUID-55442FD0-FD97-3FA3-A61A-C1288C4D5670.dita"><apiname>RCommsBufChain</apiname></xref> as its parameter
and is called by the link layer component whenever it needs to send data to
the baseband (through the BCA component). </p> </entry>
</row>
<row>
<entry><p> <xref href="GUID-55442FD0-FD97-3FA3-A61A-C1288C4D5670.dita"><apiname>MLowerControl</apiname></xref>  </p> </entry>
<entry><p>Provides methods for downwards flow control and control options.
The control options depend on your implementations of the BCA, the driver
and the link layer component. For examples of control options, see the <xref href="GUID-E054E7F6-3918-5F76-8489-D5CFC9EE257A.dita">BCA2 Control Options</xref> reference
page. </p> </entry>
</row>
</tbody>
</tgroup>
</table> <p><b>Link
layer component</b> </p> <table id="GUID-D33F08E6-3192-56C8-9989-82B82F7024AC">
<tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>
<thead>
<row>
<entry>API</entry>
<entry>Description</entry>
</row>
</thead>
<tbody>
<row>
<entry><p> <xref href="GUID-55442FD0-FD97-3FA3-A61A-C1288C4D5670.dita"><apiname>MUpperDataReceiver</apiname></xref>  </p> </entry>
<entry><p>Provides the <codeph>Process()</codeph> method, which takes a <xref href="GUID-55442FD0-FD97-3FA3-A61A-C1288C4D5670.dita"><apiname>RCommsBufChain</apiname></xref> as its parameter
and is called by the lower BCA component whenever data is available, in order
to push the data to the upper layer. </p> </entry>
</row>
<row>
<entry><p> <xref href="GUID-55442FD0-FD97-3FA3-A61A-C1288C4D5670.dita"><apiname>MUpperDataControl</apiname></xref>  </p> </entry>
<entry><p>Provides methods for error management and upwards flow control. </p> </entry>
</row>
</tbody>
</tgroup>
</table> <p>In the case of stacked BCA components, these APIs are implemented
by the upper BCA component. </p> </section>
<section id="GUID-71B6234B-470C-5241-A899-679709B91AE0"><title>Typical uses</title> <p>Device
driver developers implement the BCA2 design in the Networking stack (BCA components
and link layer protocol plugins). </p> <p>The following three diagrams show
common BCA components and illustrate how they integrate with the Communications
Framework. For definition of the abbreviations used in the diagrams, see the <xref href="GUID-18C39927-625C-5B24-919F-469FCBCD501D.dita#GUID-18C39927-625C-5B24-919F-469FCBCD501D/GUID-679587F9-CD73-51C2-8D7E-AE5817533660">Key
concepts and terms</xref> section. </p> <fig id="GUID-4B18CDAD-FDF3-5AF2-8B7C-85DC77C3E5FE">
<title>              Use case for BCA: IP communication through the serial
port            </title>
<image href="GUID-0F5C8DA1-EF91-588B-A917-350793DA03A5_d0e65531_href.png" placement="inline"/>
</fig> <fig id="GUID-1297D10A-59C2-5C15-877D-7CF94B667878">
<title>              Use case for BCA: PPP communication through the serial
port            </title>
<image href="GUID-760222AA-59F0-58E6-A494-F9CB6D739960_d0e65539_href.png" placement="inline"/>
</fig> <fig id="GUID-4A636F57-AF70-5646-A957-4B4F4AD5EA70">
<title>              Use case for BCA: PPP communication over Ethernet   
        </title>
<image href="GUID-96F5CB06-F1C2-5F37-B5B8-DA8C086B73AA_d0e65547_href.png" placement="inline"/>
</fig> </section>
</conbody><related-links>
<link href="GUID-E054E7F6-3918-5F76-8489-D5CFC9EE257A.dita"><linktext>BCA2 Control
Options</linktext></link>
</related-links></concept>