Packet Telephony: Call of the Future

Voice
over ATM. Voice over Frame Relay. Voice over IP. Now IP
telephony! These terms are being used to describe a paradigm
shift occurring in the telecom industry–the shift from circuit
switching and Time Division Multiplexing (TDM) to innovative
packet-based networks designed for data but optimized for voice.
These services are the industry’s response to a fast-growing
problem: Circuit-switched networks that were designed to carry
voice are over-stressed trying

to keep pace as data traffic exceeds voice on public networks.
The introduction of these pioneering technologies has given the
industry valuable insights into the challenges and solutions of
real-life deployment of voice-over-packet technologies. These
efforts have also given rise to new voice-over-packet
technologies that have found their way to the world’s premier
packet-switched network, the Internet.

Yet
none of the above terms succinctly defines this change that is
taking place. A new word called "packet telephony" has
been coined to reflect the convergence of telephony services and
the packet infrastructure–the logical network transformation
for service providers.

Packet
Telephony Vis-à-vis Voice-over-Packet

Packet
telephony is much more than a voice-over-technology. It is the
integral combination of the following elements:

Transport and Access

The network infrastructure
enables communications among people regardless of distance and
time. The primary focus is on providing reliable, scalable,
high-speed/low-latency connections that seamlessly span multiple
networks. Today, the network infrastructure employed for
telephony comprises predominantly circuit switches, wiring
plants, and TDM Wide Area Networks (WANs).

Connection Control

This is the basic
intelligence in the network required to manage connections
between end points desiring to communicate. This includes
establishing, monitoring, maintaining, and terminating
connections. This is the functionality required to provide
telephony services over a packet infrastructure. Network and Client Services

Network and client
services are designed to enrich the communications experience
and enhance productivity. Network services such as calling card,
single-stage and multi-stage dialling, automatic route
selection, called number screening, called number digit
manipulation, flexible dialing plans, call detail records and
billing, and interactive voice response address the requirement
to provide network-based functionality beyond basic connection
control.

From an end-user
perspective, client services are manifested in the form of
terminals (for example, phones and multimedia devices) with
intuitive user interfaces and call management capabilities for
flexible and intuitive interpersonal communications.

In a business environment,
this would be extended to include business-critical
applications. These applications enhance personal productivity
within an enterprise and allow the enterprise to build strong
relationships with the external audience (for example, customers
and suppliers) regardless of distance and time. Custom Local
Area Signalling Services (CLASS), call centres, multimedia
conferencing, Interactive Voice Response (IVR) applications,
speech-activated applications, and unified messaging are just a
few of the examples of business-critical telephony applications.
Today, these services are closely coupled with circuit switches
(PBX, key systems, and central office equipment), as they
typically form the heart of the network infrastructure.

Network Management

Network management is the
ability to configure, monitor, manage, and report on the
network, including all network elements and services. Beyond
configuration, fault, performance, accounting, and security
management, it must address customer-related items like service
provisioning, delivery, and billing. It must also be able to
deal with the complexity and scale of very large service
provider networks with continuous churn of customer service
requirements.

The Basic
Packet Telephony Components

Media Gateway

The media gateway function
implements bi-directional interfaces between a circuit-switched
network and various media-related elements in a packet network.
Typical associated packet elements are either end-user devices
or other media gateways. The key responsibilities of the media
gateway are to allow media of various types–including voice,
fax, video, and modem data–to be transported as packets in the
packet network and analog or digital streams in the
circuit-switched network without loss of integrity or
degradation of quality. These gateways will be available in
several forms to fit various price/performance and deployment
requirement such as the following:

• Packet-enabled
  voice switching devicesconsist of gateways that are
  tightly integrated with central office switches, PBXs, or
  key systems. These gateways are closely coupled with the
  call routing, trunk selection, and telephony
  class-of-service capabilities inherent in the parent voice
  switching devices. They also inherit the reliability and
  scalability characteristics of the parent voice switching
  devices. Telephony-enabled
  network devicesconsist of gateways that are tightly
  integrated with networking devices such as routers, Frame
  Relay Access Devices (FRADs), concentrators, and switches.
  These gateways are closely coupled with the network routing,
  bandwidth management, and traffic-management characteristics
  of the parent network devices. They also inherit the
  reliability and scalability characteristics of the parent
  networking devices.
  
  
  
  

• Standalone
  gatewaysare translation devices whose sole purpose
  is to provide the gateway functions. These are optimized for
  high-density applications typically found in service
  provider networks and very large enterprises.

Signalling Gateway

The signalling gateway
function implements bi-directional interfaces between an SS7
network and various call control-related elements in a packet
network. The associated packet network elements typically
implement either media controller functions or database query
functions. The key responsibilities of the signalling gateway
are to repackage SS7 information into formats understood by
elements in each network and to present a reliable view of the
elements in the packet network to the SS7 network.

Controller

The controller function
issues instructions to various media, signalling, and
service-related elements in a packet network. Typical associated
packet elements are media gateways, signalling gateways, service
modules, or sophisticated end-user devices. The key
responsibilities of the controller are to make decisions based
on flow related information and to provide associated
instructions on the interconnecting of two or more interested
parties wishing to exchange information. This includes call
signal processing, call establishment and related management,
resource management, service delivery, and admissions control in
a packet network environment.

Controllers typically
maintain current status information of all information exchanges
and generate administrative records necessary for activities
including billing. Today vendors like Nortel are offering two
types of controllers that are optimized for different deployment
scenarios and are designed to interwork with each other: Server-based
controllersconsist of software implemented on server
platforms and can be replicated for redundancy and
availability.

End-User Devices

End-user devices are
usually IP-enabled telephony clients that enable personal
communications, which include:

• IP-enabled
  phones

• Adapters to
  adapt and extend the life of analog and digital phones
  intended for use with circuit-switched voice systems

• Virtual
  phones based on software running on a workstation or
  personal computer, enabling multimedia communications and
  telecommuting

• Universal
  Serial Bus (USB)-based phones to work with personal
  computers.

Service Modules

These provide value-added
capabilities beyond plain telephone communications. This
includes network services, including calling card, single stage
and multi-stage dialing, automatic route selection, called
number screening, called number digit manipulation, flexible
dialing plans, call detail records and billing, and IVR.

• CLASS
  services, including caller ID, calling name ID, repeat
  dialling, call return, selective call
  rejection/forwarding/acceptance, VIP alert, do not disturb

• Advanced
  business services, including call waiting, call transfer,
  three-way calling, call hold, speed dialling

• Centrex
  services, including private numbering plans and closed user
  groups

• Multimedia
  conferencing services

• Desktop
  services, including unified messaging applications that
  integrate voice mail, e-mail, and fax mail

• E-commerce
  services, including call centres

• Remote user
  services, including roaming support and virtual second line

• Speech-activated
  services

  

  Value of
  Packet Telephony to Service Providers

  The
  technological innovations associated with the information age
  have brought an unparalleled freedom in the ways people
  communicate. Personal computers, portable phones, and Personal
  Digital Assistants (PDAs) with user-friendly graphical
  interfaces, fibre optics, the growth of Internet, and the
  associated IP applications have all given rise to an evolving
  user that demands:

  • Mobility–any
    service delivered anytime, anywhere

  • Bandwidth–highly
    interactive, bandwidth-hungry graphical interfaces

  • Real-time–support
    for delay-sensitive traffic, such as voice

  • Integration–the
    ability to access all types of messages, such as voice,
    e-mail, and fax, through a common interface

  • Ease of use–an
    easy-to-understand interface that encourages use

  With any disruptive
  technology, the full impact of the paradigm shift cannot be
  totally quantified at first, yet the fear sometimes is, "If
  you stand still you will be trampled!" Though the services
  and the way services are delivered are changing, the way service
  providers make money remains fundamentally the same with local,
  national, international, and wholesale services. Service
  providers are still in the business of satisfying end-user needs
  to communicate and share ideas and information.
  

  What
  Is Packet Telephony?

  To
  understand the term "packet telephony" one must
  first define it. The word "packet" focuses on
  the transport mechanism. It is an all-encompassing term
  that can be used to describe the gamut of packet-based
  technologies, including IP, ATM, Frame Relay, wireless
  packet, and others. Traditionally, the word
  "telephony" focused on voice-based
  communications. It is much more than voice transport. It
  encompasses the full set of high quality communications
  services provided by today’s Public Switched Telephone
  Network (PSTN).

  Thus, conceptually,
  "packet telephony" means today’s telephony
  services delivered over a packet network. In reality,
  packet telephony is much more than that. It is a means to
  an end–a service-enabling solution that allows the
  creation of integrated services and networks.

  Telephony networks have
  been focused on people–where advancements have been
  directed at improving personal networking and human
  efficiency through new and advanced services.

  Packet networks,
  particularly IP and Internet-based networks, have been
  focused on computers–where advancements have been
  directed at improving speed, automation, and user
  interface.

  Integrating telephony
  services with packet networking, therefore, gives us
  powerful ways of improving the way humans communicate,
  such as allowing users to travel and receive calls and
  other telephony features at their temporary locations.
  Voice and data can be combined in innovative ways for
  improved user interface to access voice mail, e-mail, and
  fax mail.

  Also, the convergence of
  packet and telephony will allow the unification of the
  network infrastructure, including directories, network
  management, and policies.

  
  

  Packet
  Telephony Definition

  Packet
  telephony is a packet-based communications solution that
  has the following characteristics:
  • Reliably supports today’s
    complete portfolio of high-quality telephony services
    with no need to change customer behavior
  • Enables the transport of
    both telephony and data on a common packet-based
    infrastructure
  • Transparently
    interoperates with the existing circuit-switched
    networks
  • Provides efficiencies in
    both transport and infrastructure
  • Facilitates the
    decoupling of services from transport
  • Enables the development
    of new services and new ways of communicating and
    doing business that leverage voice/data convergence

  	Circuit Networks	Packet Networks
  Transport	TDM	Packet
  Media	Dedicated	Shared

  
  

  Topology

  Hierarchical

  Flat, meshed

  Bandwidth

  Narrowband

  Broadband

  Networks

  Multiple, specialized

  Single, multiservice

  Architecture

  Centralized

  Distributed

  Design Point

  Voice

  Data

  Service Location

  Switch-based

  Server-based

  Revenue Growth

  The
  enterprise market is driving the introduction of converged
  telephony and data telecom solutions, which capture the
  efficiencies of multi-service networks and meet the exploding
  demand for data and multimedia communications. Service providers
  must compete aggressively for this business by offering Virtual
  Private Networking (VPN) solutions for voice and data.

  New applications such as
  unified messaging, which links e-mail, fax, and voicemail will
  become standard offerings. In addition, new broadband services,
  such as videoconferencing, will expand rapidly in the enterprise
  market. A multi-service packet network will enable service
  providers to address these opportunities.

  Cost Optimization

  WANs are increasingly
  dominated by data traffic. Therefore, WANs of tomorrow
  (optimized to carry data and telephony) will naturally have to
  be adapted to coexist in a packet-dominated WAN. Using a
  packet-optimized WAN for telephony transport significantly
  reduces costs by sharing expensive WAN bandwidth with data. In
  addition, data and telephony network administration can be
  significantly simplified by collapsing voice onto the data
  network.

  Enterprise LANs are
  dominated by Ethernet at Layers 1 and 2 and IP at Layer 3.
  Connecting end-user telephony clients over such LAN
  infrastructures allows sharing of campus infrastructure
  equipment between telephony and data networks and results in
  reduction of in-building (and campus) equipment and
  administration required for wiring infrastructures. In addition,
  moves, adds, and changes can be simplified by employing the
  plug-and-play advantages of Ethernet and IP.

  Flexibility and Responsiveness

  With the continuous
  acceleration of change in technology, it is difficult to
  maintain a leading-edge position in offering competitive telecom
  services. New packet-based network solutions are built on a
  distributed architecture, with open interfaces that support the
  rapid introduction of new services.

  Packet
  Telephony Solutions for Service Providers

  There
  is no single packet telephony solution that fits all service
  providers. Rather, each service provider must implement a
  network strategy that is aligned with its unique business
  strategy. For the existing service providers, this could involve
  migrating to packet networks to reduce costs and provide new
  revenue opportunities while protecting their current revenue
  stream. For the new service providers, packet telephony provides
  them the opportunity to create a unified network. For many
  incumbent service providers, the need is to rapidly transform
  their existing TDM networks into multi-service packet networks.
  Other incumbent service providers will choose to build entirely
  new overlay networks. Many new service providers will build new
  IP-optimized networks. And that is the reason why the market
  leaders like Lucent Technologies, Nortel Networks, and Cisco
  Systems, amongst others, all have a considerable
  "packet-telephony" strategy, which may be adopted in
  part or in full.