Convergence of Voice,
Video, and Data
Objectives
In this chapter, you will learn to:









Identify terminology used to describe applications and other
aspects of converged networks
Describe several different applications available on converged
networks
Outline possible VoIP implementations and examine the costs
and
benefits of VoIP
Explain methods for encoding analog voice or video signals as
digital signals for transmission over a packet-switched network
Identify the key signaling and transport protocols that may be
used with VoIP
Understand Quality of Service (QoS) challenges on converged
net-works and discuss techniques that can improve QoS
Terminology

Voice over IP (VoIP) - the use of any network (either public or
private) to carry voice signals using TCP/IP.

Voice over frame relay (VoFR) - the use of a frame-relay
network to transport packetized voice signals

Voice over DSL (VoDSL) - the use of a DSL connection to
carry packetized voice signals

Fax over IP (FoIP) - uses packet-switched networks to transmit
faxes from one node on the network to another.
Voice Over IP (VoIP)
The use of packet-switched networks and the
TCP/IP protocol suite to transmit voice
conversations.
Reasons for implementing VoIP may include:
 To improve business efficiency and competitiveness
 To supply new or enhanced features and applications
 To centralize voice and data network management
 To improve employee productivity
 To save money
VoIP and Traditional Telephones
Techniques for converting a telephone signal from
digital form include:

Using an adapter card within a computer workstation.

Connecting the traditional telephone to a switch capable of
accepting traditional voice signals, converting them into
packets, then issuing the packets to a data network.

Connecting the traditional telephone to an analog PBX,
which then connects to a voice-data gateway to convert the
signals.
VoIP and Traditional Telephones
VoIP and IP Telephones
VoIP and IP Telephones
Popular features unique to IP telephones include:

Screens on IP telephones can act as Web browsers,
allowing a user to open HTTP-encoded pages and, for
example, click a telephone number link to complete a call to
that number.

IP telephones may connect to a user’s personal digital
assistant (PDA) through an infrared port, enabling the user
to, for example, view his phone directory and touch a
number on the IP telephone’s LCD screen to call that
number.

If a line is busy, an IP telephone can offer the caller the
option to leave an instant message on the called party’s IP
telephone screen.
VoIP and IP Telephones
VoIP and Softphones
VoIP and Softphones
Fax over IP (FoIP)
Fax over IP (FoIP)
Fax over IP (FoIP)
Vidoeconferencing
The real-time transmission of images and audio
between two locations.

Video streaming - the process of issuing real-time video
signals from a server to a client.

Video terminals - devices that enable users to watch,
listen, speak, and capture their image.

Multipoint control unit (MCU) - also known as a video
bridge, provides a common connection to several clients.
Call Centers
Call Centers
Unified Messaging
A service that makes several forms of
communication available from a single user
interface.

The goal of unified messaging is to improve a
user’s productivity by minimizing the number of
devices and different methods she needs to
communicate with colleagues and customers.
VoIP Over Private Networks
VoIP Over Private Networks cont’d

Characteristics that make a business particularly wellsuited to running VoIP over a private network include:

A high number of telephone lines (for example, more than 100)

Several locations that are geographically dispersed across long
distances (for example, over a continent or across the globe)

A high volume of long-distance call traffic between locations within
the organization

Sufficient capital for upgrading or purchasing new CPE,
connectivity equipment, LAN transmission media, and WAN links

Goals for continued network and business expansion
VoIP Over Public Networks
To carry packet-based traffic, common carrier networks
incorporate the following:






Access service - provides endpoints for multiple types of incoming
connections.
Media gateway service - Translates between different Layer 2
protocols and interfaces.
Packet-based signaling - Provides control and call routing.
Signaling gateway service - Translates packet-based signaling
protocols into SS7 signaling protocol and vice versa.
Accounting service - Collects connection information, such as
time and duration of calls, for billing purposes.
Application service - Provides traditional telephony features to
end-users.
VoIP Over Public Networks
VoIP Over Public Networks

Softswitch - is a
computer or group of
computers that
manages packetbased traffic routing
and control.
VoIP Over Public Networks
VoIP Over Public Networks
Cost-Benefit Analysis

The major costs involved in migrating to and supporting a
converged network include:

Cost of purchasing or upgrading CPE, connectivity devices and
transmission media for each location

Cost of installation services and vendor maintenance

Cost of training technical employees and other staff

Recurring cost of new or expanded connections

Cost of transmitting voice and data, if part of the connection fees
are usage-based
Cost-Benefit Analysis

Potential economic gains of converged network can
be estimated by taking into account the following:

Bypassing common carriers to make long-distance calls,
thus avoiding tolls

Consolidating traffic over the same connections, which
leads to reducing or canceling PSTN or leased-line
connections

Providing employees with more efficient tools and means of
communication

Increased productivity for mobile employees
Waveform Codecs

G.711 - known as a waveform codec because it obtains
information from the analog waveform, and then uses this
information to reassemble the waveform as accurately as
possible at the receiving end.

G.723 - uses a form of PCM known as differential pulse code
modulation (DPCM). In DPCM, the codec samples the actual
voice signal at regular intervals.
Waveform Codecs

DPCM codecs - work well with human speech because,
within very short time spans, our speech patterns are
predictable.

Adaptive differential pulse code modulation (ADPCM)
- in this codec, not only do the nodes base predictions on
previously-transmitted bits, but they also factor in human
speech characteristics to recreate wave-forms.
Vocoders
Apply sophisticated mathematical models to
voice samples, which take into account the
ways in which humans generate speech.

G.729 - reduces its throughput requirements by
suppressing the transmission of signals during silences.
 Can operate over an 8-Kbps channel.
 Requires only moderate DSP resources and results in
only moderate delays.
Hybrid Codecs

Incorporate intelligence about the physics of
human speech to regenerate a signal.

Hybrid codecs use lower bandwidth than
waveform codecs, but provide better sound
quality than vocoders.

One example of a hybrid codec is specified in
the ITU standard G.728.
Hybrid Codecs
H.323
An ITU standard that describes not one
protocol, but an entire architecture for
implementing multiservice packet-based
networks.

H.225 - the H.323 protocol that handles call
signaling.

H.245 - ensures that the type of information,
whether voice or video, issued to an H.323
terminal is formatted in a way that the H.323
terminal can interpret.
Session Initiation Protocol (SIP)

SIP was codified by the IETF (in RFC 2543) as a set
of Session-layer signaling and control protocols for
multiservice, packet-based networks.

Because it requires fewer instructions to control a
call, SIP consumes fewer processing and port
resources than H.323.

SIP and H.323 regulate call signaling and control on
a VoIP network. However, they do not account for
communication between media gateways.
Media Gateway Control Protocol
(MGCP) and MEGACO (H.248)
Resource Reservation Protocol
(RSVP)
A QoS technique that attempts to reserve a
specific amount of network resources for a
transmission before the transmission occurs.

Allows for two service types: Guaranteed service and
Controlled-load service.

As a result of emulating a circuit-switched path, RSVP provides
excellent QoS.

Because it requires a series of message exchanges before data
transmission can occur, RSVP consumes more network
resources than some other QoS techniques.
Differentiated Service (Diffserv)
A technique that addresses QoS issues by
prioritizing traffic.

DiffServ defines two types of forwarding:
 Expedited Forwarding (EF)
 Assured Forwarding (AF)
Multiprotocol Label Switching
Offers a different way for routers to determine
the next hop a packet should take in its route.

To indicate where data should be forwarded, MPLS
replaces the IP datagram header with a label at the first
router a data stream encounters.

The MPLS label contains information about where the
router should forward the packet next.
Multiprotocol Label Switching
Summary

VoIP can improve efficiency and competitiveness,
supply new or enhanced features and applications,
and centralize voice and data network management.

Fax over IP (FoIP) is commonly implemented
according to either the ITU T.37 or T.38 standard.

Call centers are good candidates for converged
networks.

Codecs convert analog voice signals into digital form.