Technology for Innovators
Telephony software: the hidden glue in an HLOS-based smartphone
HLOS: The most
effective 3G applications
The early generation mobile phones were designed with closed, proprietary
or off-the-shelf Real Time Operating Systems (RTOS). The applications
environment had minimal functionality resulting from moderate user
expectations (voice and SMS being the primary applications), limited
network bandwidth and meager phone processing power. With the
deployment of 3G networks and the availability of powerful applications
processors for mobile phones, High-Level Operating Systems (HLOS)
represent the most effective way to meet increased user expectations while
providing an efficient management of the application lifecycle. In this paper
we will refer to an HLOS-based phone as a “smartphone.”
W H I T E
By Alessandro Araldi
HLOS Modem Software
P A P E R
HLOS allow faster and more cost-efficient applications development
while providing a large developer network that effectively meets operators’
and end-users’ requirements. HLOS, including Symbian OS™/Series 60
Platform, Microsoft® Windows Mobile™ and Linux®, provide several
advantages over other applications environments:
• Standard APIs allow developers to more efficiently develop applications,
reducing development time and costs. These APIs also allow OEMs and
operators to easily port the same applications across different platforms.
• Stable User Interface (UI) and development tools allow developers to
lower pre-sale applications development and test costs and operators to
lower post-sale maintenance and support costs across devices.
• A large developers’ network provides a large pool of applications from
which to choose, creating economies of scale for the operators and
making 3G more compelling for end-users.
HLOS telephony architecture
HLOS telephony: Definition
Logical Channel Layer API
(ex. GSM 07.10)
(PC or PDA)
Physical Channel Driver
Current smartphone mobile phone architectures strive to separate the
application execution environment from the modem module. With continually
increasing processing demands of the communications software protocol
stack, this isolation is often accomplished using a dedicated application
processing unit (APU) and a modem processing unit (MPU). Regardless
of whether the application and modem environments execute on separate
processors or are integrated onto a single processor, there remains a
challenging task of interfacing these domains to manage the complex call
control features of a mobile phone.
HLOS telephony is the software layer that interfaces the application to
the modem environment. It provides a command interface to regulate the
exchange of information between the HLOS and the protocol stack and to
control the various modem functions.
Generic HLOS telephony is composed of three major interfaces: telephony
and sockets API, telephony modem and external. The telephony API is the
application interface to access the telephony functionality. The telephony
API is unique for each operating environment and covers functions such as
SMS, voice call setup and control and data call setup. A telephony engine is
responsible for translating the telephony API into modem commands and is
specific to the modem. The sockets API are the platforms standard network
API to interface the network IP layers to the modem hardware.
The telephony modem interface is located between the applications and the
modem. It provides a set of logical channels, a channel multiplexer, and a
physical channel driver.
The external interface includes not only the interfaces between the mobile
phone and external controllers, but also the accessory manager and
debug/trace functions. The accessory manager tracks the state of attached
devices and assigns communication channels to the accessories. The
debug/trace interface enables the other modem components to run on a
PC emulation environment to which the modem can be directly interfaced.
The challenges of
Developing HLOS telephony is one of the most complex tasks in the overall
development of a 3G smartphone. There are several challenges associated
with developing HLOS telephony, including the need to choose any
combination of HLOS/UI and modem, the need to support HLOS across
different market segments with different architecture requirements, a long
development and validation cycle, the need for a robust network of
specialized third parties as well as many technical challenges.
OEMs want to choose any combination of HLOS/UI and modem without
being forced into a proprietary one-vendor only solution. This in turn poses
a great challenge for chipset vendors, who are required to support multiple
HLOS/UI solutions across multiple modem technologies. To successfully
handle this complexity, chipset vendors need to create a telephony
architecture that abstracts the underlying modem hardware architecture
and can easily be ported to multiple HLOS/UI. This result can be achieved
through a standard modem interface that is independent of the modem
technology (GSM/GPRS, EDGE, UMTS) or architecture (single or multiple
cores) and a consistent set of APIs exposed to the HLOS. This allows the
same telephony to be ported across multiple modems and HLOS/UI.
While HLOS started as a high-end applications environment, it is now
moving to the mainstream market. This requires more cost-effective
architectures where HLOS might run on the same core as the protocol stack.
Making HLOS coexist with protocol stack on the same core poses
additional challenges for the overall software architecture of the system and,
particularly, for the HLOS telephony. A scalable and flexible HLOS telephony
architecture is required to handle these challenges and the different
architecture requirements of the different market segments.
HLOS telephony involves a long development and validation cycle. In
addition to architecting and developing the telephony, chipset vendors are
required to validate it through FTA and IOT. This lengthy and expensive
process requires deep wireless system knowledge. In order to successfully
develop a 3G smartphone, OEMs need to partner with a chipset vendor
that has extensive expertise in HLOS porting, protocol stack and telephony
development and validation, and wireless system integration. A proven and
stable protocol stack and telephony pre-validated through FTA and IOT and
an experienced chipset partner allow OEMs to reduce development risks
and ultimately time-to-market and development costs.
The need to scale support to multiple HLOS/UIs and modems requires
chipset vendors to establish a robust network of specialized third parties.
While the chipset vendor provides the protocol stack and generic telephony
architecture, APIs and telephony commands, third parties specializing in
Symbian OS™/Series 60 Platform, Microsoft® Windows Mobile™ and Linux®
are key to accelerate the integration and validation of the telephony with the
HLOS and to help OEMs get to market quickly.
Finally, there are several technical challenges associated with the
development, integration and validation of HLOS telephony:
Native packet vs. PPP: A new architecture has to be developed to
support a native packet interface instead of PPP as a new standard for
communication between HLOS and the modem, enabling longer battery life,
better system response time and less software overhead.
Large telephony command set: Special test procedures must be created
to develop and validate a large set of commands; not only ETSI commands
but also custom commands developed in cooperation with major HLOS
PC connectivity: To allow users to connect their phone to a PC and use the
phone to transfer data, a special software interface is required and must
be taken into account when developing the telephony.
Multiple data contexts: Support for multiple data contexts with low
latency allows support of multiple connections to the network at the same
time. For example, a user can download e-mails while watching a movie.
This in turn requires specialized software architecture and an inter-domain
HLOS telephony solution
Texas Instruments (TI) was the first chipset vendor to port all major HLOS/UIs
to a mobile phone. In addition, TI offers multiple modem technologies and
architectures. As a result, TI has accumulated unmatched experience
in the development, integration and validation of HLOS telephony. TI has
developed close relationships with multiple HLOS/UI vendors, including
Symbian®, Nokia, Microsoft®, ChinaMobileSoft, PalmSource, Trolltech and
Savaje. Many of these vendors now use TI reference designs and telephony
as their standard development environment. TI has also built an extensive
network of specialized partners, including Atelier, Digia, Teleca, Elektrobit
and Hampex, with expertise in all aspects of HLOS and telephony
development, integration and validation.
TI cellular systems roadmap
TI OMAP-Vox™ Solutions
TI Provides Easy Migration Across Standards and Market Segments
HLOS telephony solutions
TI’s HLOS telephony has been architected to be compatible and easily
portable across different HLOS/UIs and multiple modems. TI also works
closely with HLOS vendors to maintain a stable and backward-compatible
TI’s HLOS telephony is also scalable across different market segments, from
the high-end to the mainstream. Its architecture is compatible with different
phone architectures, allowing HLOS to run either on a dedicated core or on a
core that is shared with the protocol stack.
TI HLOS telephony is based on standard native packet communication
protocol and standard telephony commands. The adoption of a native packet
interface allows the applications processor to view the modem like a network
card, minimizing software complexity and power consumption by removing
one layer of software necessary with PPP-based solutions. The use of
standard telephony commands reduces development and validation time
as well as costs while enabling efficient reuse across multiple HLOS/UIs
TI HLOS telephony provides a unique and comprehensive set of features:
Application control interface (ACI): TI’s ACI is the portion of the telephony
software that interprets the telephony commands and maintains an internal
state through a complex state machine. The ACI supports all telephony
commands in a consistent and predictable way with one interface across
different modem technologies.
Support for all telephony command formats: TI’s HLOS telephony supports
all telephony command formats, both function-based, which allows low
overhead binary interface, and text-based telephony commands.
Inter-domain communication: This is a software module complementary
to the ACI that abstracts the modem hardware architecture, allowing
portability of telephony across different modem technologies and
SIM toolkit: The SIM toolkit is an ETSI functionality enabled by TI HLOS
telephony to allow the operators to customize the phone. In order to fully
support SIM toolkit with all HLOS, TI has added several custom commands.
Native packet-based telephony: TI’s HLOS telephony is based on a native
packet interface communication protocol that reduces software overhead
and improves response time and “always on” user experience. TI supports
HLOS on all OMAP™ applications processors and OMAP-Vox™ chipsets.
As operators deploy 3G networks, HLOS represents the most efficient way to
meet users’ expectations for compelling applications while leveraging
increased handset processing power. Standard, stable HLOS APIs, UIs,
development tools and a large developers’ network enable reduced
time-to-market and development costs, while creating economies of scale
for operators in the development and deployment of applications.
One of the key challenges in the development of a 3G smartphone is the
development, integration and validation of the telephony. To minimize the
risks, costs and time associated with the development of HLOS telephony,
OEMs need to partner with a chipset vendor that has extensive expertise in
HLOS porting, protocol stack and telephony development and validation, and
wireless system integration.
TI was the first chipset vendor to offer all major HLOS (Symbian OS/Series
60 Platform, Microsoft Windows Mobile and Linux) on a mobile phone. As
a result, TI has accumulated the most expertise in this market. In addition,
TI has developed close relationships with all HLOS vendors and built an
extensive network of specialized system integrators skilled in all aspects of
HLOS porting and integration, including telephony adaptation and validation.
Finally, TI has developed a telephony architecture that allows efficient
support for multiple HLOS/UIs and modem technologies/architectures.
TI OMAP™ applications processors and OMAP-Vox™ chipsets bring the
benefits of HLOS to 3G wireless phones, enabling operators to increase
ARPU and lower applications-related costs and for users to experience
new compelling services and usage models.
For more information
Statements contained in this white paper regarding the growth of the 3G handset market, TI market penetration and qualification of TI products and other statements of
management's beliefs, goals and expectations may be considered forward-looking statements as that term is defined in the Private Securities Litigation Reform Act of 1995, and are
subject to risks and uncertainties that could cause actual results to differ materially from those expressed or implied by these statements. The following factors and the factors discussed
in TI's most recent Form 10-K could cause actual results to differ materially from the statements contained in this white paper: actual market demand for 3G products in general and TI
semiconductor products specifically, and actual certification test results relating to TI products. TI disclaims any intention or obligation to update any forward-looking statements
as a result of developments occurring after the date of this white paper.
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© 2005 Texas Instruments Incorporated