MPLS.and.Next.Generation.Networks

Understand the business case for deploying MPLS-based services and solutions

Provides network managers and architects a precise MPLS primer
Defines MPLS service problems and their associated solutions
Includes ROI models for MPLS-based solutions
Discusses pros and cons of various options for each MPLS service
Network managers often question the value that MPLS brings to their business environment. This book provides them with a precise guide for evaluating the benefits of MPLS-based applications and solutions. The book guides the network manager through the business case for MPLS by exploring other technology alternatives, including their applications, benefits, and deficiencies. Understanding the service creation process as the basis for MPLS-based solutions is pivotal when describing the benefits that MPLS offers. Furthermore, the book explores MPLS technology and its components, providing an overview of the architecture necessary to reap the true advantages that MPLS brings to a service provider or enterprise network. These advantages include new revenue opportunities and a total cost of ownership reduction that positively impacts a company’s bottom-line. ROI models and case study examples further confirm the business impact and help decision-makers create a blueprint for MPLS service creation. Specific aspects such as security, network management, advanced services and the future of the technology complete the book, helping decision makers assess MPLS as a candidate for implementation. In short, you can use this comprehensive guide to understand and build a business case for the inclusion of MPLS in your network.

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OFDM and OFDMA: The Difference

I was curious as to why IEEE 802.16d (fixed service) uses Orthogonal Frequency Division Multiplexing (OFDM). IEEE 802.16e (mobile) uses Orthogonal Frequency Division Multiple Access (OFDMA). So, what’s the difference between the two, and why is there a difference?

Lets first look at FDM:

In FDM system, signals from multiple transmitters are transmitted simultaneously (at the same time slot) over multiple frequencies. Each frequency range (sub-carrier) is modulated separately by different data stream and a spacing (guard band) is placed between sub-carriers to avoid signal overlap.

OFDM is sometimes referred to as discrete multi-tone modulation because, instead of a single carrier being modulated, a large number of evenly spaced subcarriers are modulated using some m-ary of QAM. This is a spread-spectrum technique that increases the efficiency of data communications by increasing data throughput because there are more carriers to modulate. In addition, problems with multi-path signal cancellation and spectral interference are greatly reduced by selectively modulating the “clear” carriers or ignoring carriers with high bit-rate errors.

Like FDM, OFDM also uses multiple sub-carriers but the sub-carriers are closely spaced to each other without causing interference, removing guard bands between adjacent sub-carriers. This is possible because the frequencies (sub-carriers) are orthogonal, meaning the peak of one sub-carrier coincides with the null of an adjacent sub-carrier.

In an OFDM system, a very high rate data stream is divided into multiple parallel low rate data streams. Each smaller data stream is then mapped to individual data sub-carrier and modulated using some sorts of PSK (Phase Shift Keying) or QAM (Quadrature Amplitude Modulation). i.e. BPSK, QPSK, 16-QAM, 64-QAM.

OFDM needs less bandwidth than FDM to carry the same amount of information which translates to higher spectral efficiency. Besides a high spectral efficiency, an OFDM system such as WiMAX is more resilient in NLOS environment. It can efficiently overcome interference and frequency-selective fading caused by multipath because equalizing is done on a subset of sub-carriers instead of a single broader carrier. The effect of ISI (Inter Symbol Interference) is suppressed by virtue of a longer symbol period of the parallel OFDM sub-carriers than a single carrier system and the use of a cyclic prefix (CP).

The OFDM spread-spectrum scheme is used for many broadly used applications, including digital TV broadcasting in Australia, Japan and Europe; digital audio broadcasting in Europe; Asynchronous Digital Subscriber Line (ADSL) modems and wireless networking worldwide (IEEE 802.11a/g).

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VoIP 2nd Edition

A systematic approach to understanding the basics of voice over IP

Understand the basics of enterprise and public telephony networking, IP networking, and how voice is transported over IP networks
Learn the various caveats of converging voice and data networks
Examine the basic VoIP signaling protocols (H.323, MGCP/H.248, SIP) and primary legacy voice signaling protocols (ISDN, C7/SS7)
Explore how VoIP can run the same applications as the existing telephony system but in a more cost-efficient and scalable manner
Delve into such VoIP topics as jitter, latency, packet loss, codecs, QoS tools, and security

Voice over IP (VoIP) has become an important factor in network communications, promising lower operational costs, greater flexibility, and a variety of enhanced applications. To help you understand VoIP networks, Voice over IP Fundamentals provides a thorough introduction to the basics of VoIP.