June 2003
Increasing Value Using Standards-Based IP
Telephony Solutions
BY MIKE WERNING
Designers of embedded systems have many choices to make when choosing a
platform for their embedded design. Choosing an off-the-shelf solution is
good for both time to market and compatibility with third-party content.
This article details the advantages of using standards-based platforms based
on the more popular embedded system platforms in the industry. In addition,
an application in the IP telephony segment is examined.
IDENTIFYING VALUE
A key decision that a designer must make is whether to design a proprietary
system in house or to purchase a more general solution from a third party.
Every company has core competencies that differentiate it in the
marketplace. Designers must focus on where this core competency lies and
leverage that in the development of their overall solutions. This allows a
company to dedicate resources to their core business where their added value
is. A company who buys products in the embedded system marketplace is
generally one whose core competency or value proposition lies somewhere
else. Even though a telecom company knows how to design and manufacturer
computer boards, it doesn�t make sense for them to do so if what they need
is available on the open market. Their value-add is in the software and in
the integration of the pieces that make up the end solution. These companies
benefit from not having to re-invent the wheel. They can have their
engineers concentrate on their market niche and focus on gaining market
share through time to market and functionality enhancements that can be
realized through the use of commodity computing components. There are
situations where a company must design their own platforms. For example, a
telecom company may not be able to procure a wide-band digital modem
off-the-shelf or at least not one that can give them a competitive advantage
in their marketplace. Similarly an imaging company may not be able to buy a
signal amplifier board or sequencer board due to the unique nature of the
application. In these cases it makes perfect sense to design and manufacture
the product in house.
LEVERAGING SYSTEMS & STANDARDS
Systems designed to industry standards can meet the needs of many market
segments. This is achievable due to the ecosystem of compatible products
that are created based upon the common specifications. Interoperability with
third-party content, time to market, and reduced cost are all benefits that
are achieved through the use of industry standards. Bodies such as The PCI
Industrial Computer Manufacturers Group (PICMG), Institute of Electrical and
Electronics Engineers (IEEE), Internet Engineering Task Force (IETF), and
the International Telecommunications Union (ITU) govern these standards.
These organizations are made up of representatives from various
manufacturers in the industry who work together to create standards based on
the input of not one company, but of the industry as a whole. This ensures
that standards represent a general list of requirements that apply to the
market and not just one company. It also ensures that manufacturers that
make products based on these standards will interoperate on some level. This
opens up the options available to a designer who chooses an open platform
rather than designing a closed proprietary one.
VoIP MEDIA GATEWAYS
A highly scalable VoIP media gateway can be put together using off-the-shelf
hardware based on industry standard components. These platforms are largely
based upon PICMG 2.x standards. CompactPCI (PICMG 2.0) is based on the PCI
specification. It uses industry standard mechanical components and
high-performance connector technologies. Since it is based upon the PCI
spec, the vast amount of low-cost PCI components can be utilized. The goal
is to provide an optimized system intended for rugged applications. In a
media gateway system the CompactPCI bus is used for internal control of
system elements rather than for bearer traffic. Bearer traffic is typically
routed on the computer telephony bus (PICMG 2.5). The goal of this
specification is to extend the capabilities and utility of the CompactPCI
based system architecture to support the application needs of the computer
telephony industry. It essentially adds the H.110 TDM bus by a standard
implementation. This allows interoperability between CompactPCI system
vendors and computer telephony board vendors thereby allowing an ecosystem
of compatible products to develop in the market. Smaller media gateway
systems utilize the H.110 bus by interfacing line cards to it and switching
voice traffic internally within the chassis.
Using PICMG 2.5 for bearer traffic allows for 2,048 simultaneous full
duplex voice calls per chassis. Applications that require higher call
density utilize the Packet Switching Backplane (PICMG 2.16) to carry the
bearer traffic. This specification defines an IEEE 802.3�2000, Ethernet
packet switching backplane in addition to the existing suite of PICMG 2.x
specifications. High availability is also provided through the use of
redundant interconnections and switching components. Use of IEEE 802.3-2000
provides an industry standard framework for network communication within the
chassis. Larger gateway systems can be created utilizing the backplane IP
network to switch voice and data calls between boards within a chassis. The
number of simultaneous voice/data streams scales by the number of slots in
the system and by the call capacity for each board.
Required Interfaces
A VoIP media gateway typically has three types of interfaces to the outside
world. The media gateway controller (MGC) interface provides a data path
between the call agent located on the MGC, sometimes called a softswitch,
and the media gateway located in the data path. The media gateway controller
uses Megaco/H.248 to set up endpoint connections in the media gateway. This
provides an industry standard protocol connection between the gateway and
controller. A circuit switch interface is also required to communicate
directly with the PSTN. Typically T1/E1, T3/E3 interfaces must be provided.
Since a media gateway provides a bridge between the TDM streams and
packet-based data, a packet network interface is required. The packet
network interface is typically 100/1000Mbit Ethernet.
System Implementation
A scalable system that encompasses all of these interfaces can be built
using off-the-shelf hardware and software. There are a number of vendors
that provide scalable PICMG 2.x systems that can accommodate a variety of
different telephony resource boards. These systems include TDM and packet
switching interconnects embedded into the backplane for simple
interconnection between payload cards. In addition to the chassis
infrastructure, switch cards are also available to provide a redundant data
path between the packet network elements and the payload cards. For media
gateway applications, the conversion between circuit switched voice and data
to packet switched voice and data is accomplished on payload cards called
packet voice resource boards (PVRB). These boards contain DSP resources that
provide transcoding functionality. In addition a packet processor and
control path processor are also provided to interface to the packet network
via the 2.16 backplane interconnections (Figure 3). These types of boards
are also capable of taking TDM data in on the H.110 bus embedded in the
backplane. This interface could be used for TDM switching between PVRBs,
voice channel tandem applications, or for taking TDM streams in from H.110
line interface cards located elsewhere in the system. Scalable call capacity
is achieved through the use of multiple boards in the system.
Software
Media gateways utilize a number of different processor technologies to
provide the overall solution. DSP resources are required for transcoding,
network processors are required for packetization, and general purpose
processors for control. Having the correct software framework to make each
part work together is absolutely essential in order to focus the software
effort on the top-level application rather that the integration of each of
these components.
THE BOTTOM LINE
The utilization of standards-based, off-the-shelf systems, boards, and
software is vital in accelerating the development of media gateway
solutions. This allows a company to focus on the value added parts of the
solution rather than on the development of the commodity parts. Years ago,
companies were forced to develop proprietary systems solutions. Today the
situation has changed dramatically. There are many hardware, software, and
system vendors who make this equipment and products are extremely flexible.
Companies that leverage off-the-shelf technology are able to focus on where
they add the most value and outsource products outside of their core
competency. This enables them to work more efficiently and ultimately to be
more profitable.
Mike Werning is principal staff engineer at Motorola Computer Group, a
leader in the innovation of intelligent building blocks for standards-based
embedded computing. These building blocks include open-architecture
hardware, rich software, and application-ready platforms that enable
equipment manufacturers to quickly and cost-effectively embed leading-edge
functionality into their next-generation systems. More information can be
found at
www.motorola.com/computer.
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