Download Full Article TUNABLE_LASERS

In a wavelength-division multiplexed (WDM) network carrying 128 wavelengths of information, we have 128 different lasers giving out these wavelengths of light. Each laser is designed differently in order to give the exact wavelength needed. Even though the lasers are expensive, in case of a breakdown, we should be able to replace it at a moment’s notice so that we don’t lose any of the capacity that we have invested so much money in. So we keep in stock 128 spare lasers or maybe even 256, just to be prepared for double failures.

What if we have a multifunctional laser for the optical network that could be adapted to replace one of a number of lasers out of the total 128 wavelengths? Think of the money that could be saved, as well as the storage space for the spares. What is needed for this is a “tunable laser,”

                Tunable lasers are still a relatively young technology, but as the number of wavelengths in networks increases so will their importance. Each different wavelength in an optical network will be separated by a multiple of 0.8 nanometers (sometimes referred to as 100GHz spacing. Current commercial products can cover maybe four of these wavelengths at a time. While not the ideal solution, this still cuts your required number of spare lasers down. More advanced solutions hope to be able to cover larger number of wavelengths, and should cut the cost of spares even further.

                The devices themselves are still semiconductor-based lasers that operate on similar principles to the basic non-tunable versions. Most designs incorporate some form of grating like those in a distributed feedback laser. These gratings can be altered in order to change the wavelengths they reflect in the laser cavity, usually by running electric current through them, thereby altering their refractive index. The tuning range of such devices can be as high as 40nm, which would cover any of 50 different wavelengths in a 0.8nm wavelength spaced system. Technologies based on vertical cavity surface emitting lasers (VCSELs) incorporate moveable cavity ends that change the length of the cavity and hence the wavelength emitted. Current designs of tunable VCSELs have similar tuning ranges.

LASERS

                Lasers are devices giving out intense light at one specific color. The kinds of lasers used in optical networks are tiny devices — usually about the size of a grain of salt. They are little pieces of semiconductor material, specially engineered to give out very precise and intense light. Within the semiconductor material are lots of electrons — negatively charged particles. Not just one or two electrons, but billions and billions of them. Some of these electrons can be in what is known as an “excited” state, meaning that they have more energy than regular electrons. An electron in an excited state can just spontaneously fall down to the regular “ground” state. The ground state has less energy, and so the excited-state electron must give out its extra energy before it can enter the ground state. It gives this energy out in the form of a “photon” — a single particle of light.

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Download Full Article Voice User Interface

Definition

In its most generic sense a voice portal can be defined as “speech enabled access to Web based information”. In other words, a voice portal provides telephone users with a natural language interface to access and retrieve Web content. An Internet browser can provide Web access from a computer but not from a telephone. A voice portal is a way to do that.

Overview

The voice portal market is exploding with enormous opportunities for service providers to grow business and revenues. Voice based internet access uses rapidly advancing speech recognition technology to give users any time, anywhere communication and access-the Human Voice- over an office, wireless, or home phone. Here we would describe the various technology factors that are making voice portal the next big opportunity on the web, as well as the various approaches service providers and developers of voice portal solutions can follow to maximize this exciting new market opportunity.

Why Voice?

Natural speech is modality used when communicating with other people. This makes it easier for a user to learn the operation of voice-activate services. As an output modality, speech has several advantages. First, auditory input does not interfere with visual tasks, such as driving a car. Second, it allows for easy incorporation of sound-based media, such as radio broadcasts, music, and voice-mail messages. Third, advances in TTS (Text To Speech) technology mean text information can be transferred easily to the user. Natural speech also has an advantage as an input modality, allowing for hands-free and eyes-free use. With proper design, voice commands can be created that are easy for a user to remember .These commands do not have to compete for screen space. In addition unlike keyboard-based macros (e.g., ctrl-F7), voice commands can be inherently mnemonic (“call United Airlines”), obviating the necessity for hint cards. Speech can be used to create an interface that is easy to use and requires a minimum of user attention.

VUI (Voice User Interface)

 For a voice portal to function, one of the most important technology we have to include is a good VUI (Voice User Interface).There has been a great deal of development in the field of interaction between human voice and the system. And there are many other fields they have started to get implemented. Like insurance has turned to interactive voice response (IVR) systems to provide telephonic customer self-service, reduce the load on call-center staff, and cut overall service costs. The promise is certainly there, but how well these systems perform-and, ultimately, whether customers leave the system satisfied or frustrated-depends in large part on the user interface.

Many IVR applications use Touch-Tone interfaces-known as DTMF (dual-tone multi-frequency)-in which customers are limited to making selections from a menu. As transactions become more complex, the effectiveness of DTMF systems decreases.

In fact, IVR and speech recognition consultancy Enterprise Integration Group (EIG) reports that customer utilization rates of available DTMF systems in financial services, where transactions are primarily numeric, are as high as 90 percent; in contrast, customers’ use of insurers’ DTMF systems is less than 40 percent.
Enter some more acronyms. Automated speech recognition (ASR) is the engine that drives today’s voice user interface (VUI) systems. These let customers break the ‘menu barrier’ and perform more complex transactions over the phone. “In many cases the increase in self-service when moving from DTMF to speech can be dramatic,” said EIG president Rex Stringham.

The best VUI systems are “speaker independent”-they understand naturally spoken dialog regardless of the speaker.  And that means not only local accents, but regional dialects, local phrases such as “pop” versus “soda,” people who talk fast (you know who you are), and all the various nuances of speech. Those nuances are good for human beings; they allow us to recognize each other by voice. For computers, however, they make the process much more difficult. That’s why a handheld or pocket computer still needs a stylus, and why the ‘voice dialing’ offered by some cell-phone companies still seems high-tech.

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Download Full Article Voice Over Internet Protocol

I N T R O D U C T I O N

Using an ordinary phone for most people is a common daily occurrence as is listening to your favorite CD containing the digitally recorded music. It is only a small extension to these technologies in having your voice transmitted in data packets. The transmission of voice in the phone network was done originally using an analog signal but this has been replaced in much of the world by digital networks. Although many of our phones are still analog, the network that carries that voice has become digital.

In todays phone networks, the analog voice going into our analog phones is digitized as it enters the phone network. This digitization process, shown in Figure 1 below, records a sample of the loudness (voltage) of the signal at fixed intervals of time. These digital voice samples travel through the network one byte at a time.

At the destination phone line, the byte is put into a device that takes the voltage number and produces that voltage for the destination phone. Since the output signal is the same as the input signal, we can understand what was originally spoken.
The evolution of that technology is to take numbers that represent the voltage and group them together in a data packet similar to the way computers send and receive information to the Internet. Voice over IP is the technology of taking units of sampled speech data .

So at its most basic level, the concept of VoIP is straightforward. The complexity of VoIP comes in the many ways to represent the data, setting up the connection between the initiator of the call and the receiver of the call, and the types of networks that carry the call.

Using data packets to carry voice is not just done using IP packets. Although it won’t be discussed, there is also voice over Frame Relay (VoFR) and Voice over ATM (VoATM) technologies. Many of the issues VoIP being discussed also apply to the other packetized voice technologies.

The increasing multimedia contents in Internet have reduced drastically the objections to putting voice on data networks. Basically, the Internet objections to putting voice on data networks. Basically, the Internet Telephony is to transmit multimedia information in discrete packets like voice or video over Internet or any other IP-based Local Area Network (LAN) or Wide Area Network (WAN). The commercial Voice Over IP (Internet Protocol) was introduced in early 1995 when VocalTec introduced its Internet telephone software. Because the technologies and the market have gradually reached their maturity, many industry leading companies have developed their products for Voice Over IP applications since 1995.

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Download Full Article  Virtual LAN

                        In today’s networked backbone, there are certain hardware devices that connect other networks to the backbone. These are special purpose devices and computers that just transfer messages from one network to another. Before we look deep into the topic Virtual LAN’s, let us see the basic devices used in the network backbone. They are

1. Bridges.

                                           2. Switches.

3. Routers.

4. Gateways.

5. Hubs.

BRIDGES-Bridges operate at the data link layer.  They connect two LAN segments that use the same data link and network protocol.  They may use the same or different types of cables.  Bridges “learn” whether to forward packets, and only forward those messages that need to go to other network segments.

                        If a bridge receives a packet with a destination address that is not in the address table, it forwards the packet to all networks or network segments except the one on which it was received. Bridges are a combination of both hardware and software, typically a “black box” that sits between the two networks, but can also be a computer with two NICs and special software.

SWITCHES-Like bridges, switches operate at the data link layer. Switches connect two or more computers or network segments that use the same data link and network protocol. They may connect the same or different types of cable. The switch is a device that connects a material coming in with an appropriate outlet. They require more processing power. Switches operate at the same layers as bridges but differ from them in two ways:

1. First, most switches enable all ports to be in use simultaneously, making them faster than bridges.

2. Second, unlike bridges, switches don’t learn addresses, and need to have addresses defined.

There are two types of switches:

1. Cut-through switches examine the destination of the incoming packet and immediately connect the port with the incoming message to the correct outgoing port. It is hardware-based.

2. Store-and-forward switches copy the incoming packet into memory before processing the destination address.

ROUTERS-Routers operate at the network layer.  Routers connect two or more LANs that use the same or different data link protocols, but the same network protocol.  Routers may be “black boxes,” computers with several NICs, or special network modules in computers.

In general they perform more processing on each message than bridges and therefore operate more slowly.

                        Routers can choose the best route when compared with bridges .They only process messages specifically addressed to it. Routers can connect networks using different data link layer protocols. Therefore, routers are able to change data link layer packets. Routers may split a message into several smaller messages for better transmission.

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Download Full Article Computer Viruses

What are computer viruses ?

                A computer virus is a self-replicating program containing code that explicitly copies itself and that can “infect” other programs by modifying them or their environment such that a call to an infected program implies a call to a possibly evolved copy of the virus.

                These software “pranks” are very serious; they are spreading faster than they are being stopped, and even the least harmful of viruses could be life-threatening.  For example, in the context of a hospital life-support system, a virus that “simply” stops a computer and displays a message until a key is pressed, could be fatal.  Further, those who create viruses can not halt their spread, even if they wanted to.  It requires a concerted effort from computer users to be “virus-aware”, rather than continuing the ambivalence that has allowed computer viruses to become such a problem.

                Computer viruses are actually a special case of something known as “malicious logic” or “malware”.

COHEN’S theoretical definition of Computer Viruses

                Consider the set of programs which produce one or more programs as output.  For any pair of programs p and q, p eventually produces  q if and only if p produces q either directly or through a series of steps (the “eventually produces” relation is the transitive closure of the “produces” relation.)  A viral set  is a maximal set of programs V such that for every pair of programs p and q in V, p eventually produces q, and q eventually produces p.  (”Maximal” here means that there is no program r not in the set that could be added to the set and have the set still satisfy the conditions.)  For the purposes of this paper, a computer virus is a viral set; a program p is said to be an instance of, or to be infected with, a virus V precisely when p is a member of the viral set V.  A program is said to be infected  simpliciter when there is some viral set V of which it is a member.  A program which is an instance of some virus is said to spread  whenever it produces another instance of that virus.  The simplest virus is a viral set that contains exactly one program, where that program simply produces itself.  Larger sets represent polymorphic viruses, which have a number of different possible forms, all of which eventually produce all the others. 

 Detecting a Virus

                For the purposes of this paper, an algorithm A detects a virus V if and only if for every program p, A(p) terminates, and returns “true” if and only if p is infected with V.  Similarly, an algorithm A detects a set of viruses S  if and only if for every program p, A(p) terminates, and returns “true” if and only if p is infected with some virus V which is a member of S.  This is essentially Cohen’s definition in [1], and it is the only formal definition of detection that has proven theoretically fruitful.  It also captures (at least to a first approximation) our intuitive notion of computer virus detection. 

 What is a Worm?

A computer WORM is a self-contained program (or set of programs), that is able to spread functional copies of itself or its segments to other computer systems (usually via network connections). Note that unlike viruses, worms do not need to attach themselves to a host program.  There are two types of worms–host computer worms and network worms.

What is a Trojan Horse?

                A TROJAN HORSE is a program that does something undocumented that the programmer intended, but that some users would not approve of if they knew about it.  According to some people, a virus is a particular case of a Trojan Horse, namely one which is able to spread to other programs(i.e., it turns them into Trojans too). 

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