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TitleTelecommunications Essentials
File Size6.4 MB
Total Pages507
Document Text Contents
Page 2


Introduction 3
About the Author 5
Acknowledgments 6

Part I Telecommunications Fundamentals

Chapter 1 Understanding the Telecommunications Revolution 7

Changes in Telecommunications 8
Incorporating Human Senses in Telecommunications 8
The Emergente of Wearables 9
Moving Toward Pervasive Computing 10
Moving Toward Machina-to-Machine Communications 11
Adapting to New Traffic Patterns 11
Handling New Types of Applications 12
Increasing Backbone Bandwidth 12
Responding to Political and Regulatory Forces 13
The New Public Network 16
Convergence 18

Chapter 2 Telecommunications Technology Fundamentals 19

Transmision Lines 19
Circuits 19
Channels 21
Lines and Trunks 22
Virtual Circuits 23
Types of Network Connections 24
The Electromagnetic Spectrum and Bandwidth 24
The Electromagnetic Spectrum 24
Bandwidth 28
Analog and Digital Transmission 29
Analog Transmission 29
Digital Transmission 30
Analog Versus Digital Transmission 31
Conversion: Codecs and Modems 32
Multiplexing 33
FDM 35
TDM 36
Intelligent Multiplexing 37
Inverse Multiplexing 38
Standars Organizations 40


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and by the fact that it offers improved performance and management. These VPNs are characterized
as having excellent performance and security, but the negative is that a single vendor offers both
reach and breadth in terms of service offerings.

Figure 11.6 shows what the equipment would like look at a customer premise in support of a Frame
Relay- or an ATM-based VPN. The customer would have an IAD that would allow voice and data to
be converged at the customer premise. The IAD would feed into the data communications
equipment, over which a circuit would go to the service provider's POP. At the service provider's
POP would be a multiservice access device that enables multiple protocols and interfaces to be
supported and that provides access into the service provider's core network, which would be based
on the use of Frame Relay or ATM. To differentiate Frame Relay- and ATM-based VPNs from
Internet-based VPNs, service providers stress that multiple protocols are supported and that they rely
on the use of virtual circuits or MPLS labels to facilitate the proper path, thereby ensuring better
performance and providing traffic management capabilities.

Figure 11.6. A Frame Relay- or ATM-based provisioned VPN

To further differentiate Frame Relay- or ATM-based VPNs from regular Frame Relay or ATM
services, additional functions—such as packet classification and traffic isolation, the capability to
handle multiple separate packet-forwarding tables and instances of routing protocols for each
customer—reside at the edge.

VPN Applications

A VPN is an architecture, a series of products and software functions that are tied together and
tightly calibrated. Managing a VPN entails dealing primarily with two issues: security policies and
parameters and making sure that applications function within the latency requirements.

VPN applications provide maximum opportunities to save money and to make money—by
substituting leased lines with Internet connectivity, by reducing costs of dialup remote access, and by
stimulating new applications, using extranets. These savings can be substantial. According to
TeleChoice (, in the realm of remote access, savings over customer-owned and
maintained systems can range from 30% to 70%; savings over traditional Frame Relay services can
range from 20% to 60%; savings over leased lines or private lines can range from 50% to 70%; and
savings over international private lines can be up to 90%.

It is important to be able to effectively and easily manage the VPN environment. You need to
consider the capability to track the tunnel traffic, the support for policy management, the capability
to track QoS, the capability to track security infractions, and the support for public key certificate
authorities (CAs).


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The one-stop-shopping approach to VPNs—managed VPN services—is designed to lock in users
and to reduce costly customer churn, but with this approach, interoperability is very restricted.
Managed VPNs provide capabilities such as IP connection and transport services, routers, firewalls,
and a VPN box at the customer site. Benefits of this approach include the fact that it involves a
single service vendor, SLAs, guaranteed latency and bandwidth, and the security of traffic being
confined to one network. Approximately one-third of VPN users opt for such a managed service.

There are three major applications of VPNs—intranets (that is, site-to-site VPNs) remote access, and
extranets—which are examined in the following sections.

Intranet VPNs

Intranet VPNs are site-to-site connections (see Figure 11.7). The key objective of an intranet VPN is
to replace or reduce the use of leased-line networks, traditional routers, and Frame Relay services.
The cost savings in moving from private networks to Internet-based VPNs can be very high, in the
neighborhood of 50% to 80% per year. Remember that Internet-based VPNs allow less control over
the quality and performance of applications than do provisioned VPNs; this is a bit of a deterrent,
and many clients still want to consider the Frame Relay- or ATM-based ATMs, which would
provide better QoS. The savings might drop a bit, but the cost of a provisioned VPN would be
substantially less than the cost of using leased lines.

Figure 11.7. An intranet-based VPN

There are a few key barriers to building out more intranets based on VPNs:

• No standardized approach to encryption

• Variance between vendors' products, which leads to interoperability problems

• Lack of standards regarding public key management

• Inability of today's Internet to provide end-to-end QoS

Remote Access VPNs

The most interesting and immediate VPN solution for most customers is the replacement of remote


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An ITU-T numbering plan, E.164, that divides the world into nine zones. Each zone is allocated a number
that forms the first digit of the country code for every country in that zone. The zones are follows: (1)
North America (including Hawaii and Caribbean islands, except Cuba), (2) Africa, (3 and 4) Europe, (5)
South America and Cuba, (6) South Pacific (Australasia), (7) Russia, (8) North Pacific (Eastern Asia), and
(9) Asia and the Middle East. There is also a spare code (0), which is available for future use.

WWW (World Wide Web)

An Internet application that uses hypertext links between remote network servers for accessing and
displaying multimedia information.



An ITU-T standard that defines the basic functionality of an asynchronous PAD usually used in
conjunction with ITU-T standards X.28 and X.29.


An ITU-T recommendation that defines a general purpose physical interface between a DTE and DCE for
full duplex synchronous operation on circuit switched or packet-switched data networks.


A standard that defines the interface between DTE and DCE for equipment operating in the packet mode
on public data networks. It also defines a link control protocol.


A standard for connecting X.25 networks, developed by the ITU-T


The ITU-T standard for the addressing plan used with X.25 PDNs.


A standard for electronic mail exchange; developed by the ITU-T.



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The family of protocols that define the operation of the ITU-T/ISO directory service.


The ITU-T/OSI recommendation for a directory authentication framework.


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