BCA2 +API Overview

Required background

You +should be familiar with the following areas:

architecture of device +drivers in Symbian platform (see Device +Drivers Concepts)
general principles of +a telephony stack (see Cellular +Baseband Services)
networking and telephony +components.

Key concepts +and terms

BCA: Baseband Channel Adapter
LDD: Logical device driver (see Device +Drivers Concepts)
PPP: Point-to-Point Protocol (see What +is PPP?)
HDLC: High-level Data Link Control
ISDN: Integrated Services Digital Network
ECUART: Serial RS232 driver for Symbian OS. UART means Universal Asynchronous +Receiver/Transmitter.
C32: Serial Communications Server in Symbian OS (see Serial +Communications Server)

Introduction

The Baseband Channel Adapter (BCA) +provides a telephony-specific abstraction of the baseband driver.

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.

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 MBca2 interface.

Architecture

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.

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.

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.

The API +is split into five classes to separate control flow and data flow methods.

+ MBca2 design + +

Moreover, the MBca2 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 Memory Management +in the Communications Framework.

APIs

BCA component

+ + + +API +Description + + + + +

MBca2

Provides startup and shutdown methods.

+ + +

MLowerDataSender

Provides the Send() method, which takes a RCommsBufChain as its parameter +and is called by the link layer component whenever it needs to send data to +the baseband (through the BCA component).

+ + +

MLowerControl

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 BCA2 Control Options reference +page.

+ + + +

Link +layer component

+ + + +API +Description + + + + +

MUpperDataReceiver

Provides the Process() method, which takes a RCommsBufChain 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.

+ + +

MUpperDataControl

Provides methods for error management and upwards flow control.

+ + + +

In the case of stacked BCA components, these APIs are implemented +by the upper BCA component.

Typical uses

Device +driver developers implement the BCA2 design in the Networking stack (BCA components +and link layer protocol plugins).

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 Key +concepts and terms section.

+ Use case for BCA: IP communication through the serial +port + + + Use case for BCA: PPP communication through the serial +port + + + Use case for BCA: PPP communication over Ethernet + + +