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[manjunath455]

[quote author=ChittiNaidu link=topic=141351.msg1602939#msg1602939 date=1294524754]
[size=12pt][color=red][b]Voice over ATM: Integrating voice and data transmission in DSL - Technology Information[/b][/color][/size]

Sometimes, advance publicity doesn't always measure up to the fact. Just ask the folk who still have 500 gallons of bottled water in their basements meant for the Y2K catastrophe. Or those who thought super-cheap telephone service using voice over Internet protocol (VoIP) would replace traditional telephony. Or even those who expected digital subscriber line (DSL) in its initial roll-outs to answer all their voice and data needs over a single copper local loop. They've since discovered that, while ADSL combines voice and broadband data services on a single twisted pair, the technology provides only one voice channel. If another voice line is needed, the phone company still has to come out and install it the old-fashioned way. That isn't to say that VoIP isn't improving or that DSL isn't a tremendous boost to our ability to utilize the existing copper plant. On the contrary, VoIP definitely has applications for which it is well suited. But it's the combination of asynchronous transfer mode (ATM) technology and DSL that really delivers on the promise of fully integrated voice and data services.

[b]CONTEMPORARIES, NOT COMBATANTS[/b]

Voice over ATM (VoATM) and VoIP are often portrayed as competing technologies, slugging it out for dominance in the era of voice/data convergence. In fact, these technologies address the needs of different market segments and will coexist for some time as viable alternatives for transmitting voice and data together.

Voice Over IP

VoIP is a reasonable solution for two kinds of network users: 1) those who seek long-distance cost savings and can accept connections that are of less than traditional toll-quality, and 2) companies with private networks that interconnect the PBX systems of two or more offices.

To reduce their phone bills, some residential users are willing to put up with the signal loss and echo that can be caused by network delay and jitter, which results from IP's large, variable-length transmission packets. Designed for data transmission, which is unaffected by small fits and starts, IP is less than ideal for voice traffic. Because most IP networks still don't address quality of service (QoS), you're never guaranteed you'll hear the second syllable immediately alter the first, if at all.

Some corporations with significant resources to invest have compensated by implementing VoIP over relatively expensive, private high-speed IP networks. For them, VoIP provides an excellent way to make the best use of IP networks already in place for data services. But these solutions often require the same hardware and software at both ends of the connection, limiting their usefulness on the public network where uniform standards are still a long way off.

Between the Internet hobbyists and the large corporations lies a large group of users for whom VoIP is simply not the best answer. These are the small-to-midsized businesses and the residential users who want access to high-quality voice and broadband data services, but don't have the resources--or the need--to build a private network. For them, VoATM plus DSL is the logical choice.

[b][size=18pt]Voice Over ATM[/size][/b]

The local loop has traditionally been a serious bottleneck for data communications. Trying to deliver broadband services via dial-up modem has been like trying to channel Niagara Falls through the kitchen faucet.

DSL has changed all that. By making it possible for smaller organizations to use existing copper links to connect with high-speed services, DSL offers a seemingly ideal solution. However, most asymmetric DSL solutions use a splitter on the telephone line to separate the signal into its voice and data components which means, the voice element can't take advantage of the bandwidthsharing benefits of DSL technology.

Voice over ATM is the logical solution, especially since ATM is already in use as the standard Layer 2 transport protocol for DSL. With its small, fixed-length data packets, ATM is an ideal vehicle for voice. Because the small packets travel the wires at a fast, even clip, users don't have to put up with delays or distortions when talking on the phone. And, since ATM was designed from the ground up to integrate multiple services on one infrastructure, it allows bandwidth to be used efficiently for voice as well as data.

[size=12pt][b]THE ADVANTAGES OF VoATM[/b][/size]

This ability to dynamically allocate bandwidth to different types of traffic is an ATM forte, thanks to the ATM adaptation layer (AAL). An AAL defines how traffic is converted into ATM cells and translates higher layer services, such as TCP/IP, into a format ATM can use. The latest incarnation of the adaptation layer, AAL 2, supports both constant bit rate (CBR) and variable bit rate (VBR) statistical multiplexing, and it delivers multiple voice calls simultaneously on a single permanent virtual circuit (PVC). When a phone line is not in use--or even when there is a brief lull in a conversation--the unused capacity can be occupied by data traffic. When voice traffic expands, data throughput is scaled back.

In addition, because AAL 2 includes content information inside each data packet, traffic can be easily prioritized. This is the key to guaranteeing a crystalline voice connection, since voice traffic is always given greater priority than data traffic. It also ensures that bandwidth is used as efficiently as possible for all traffic types.

Another major advantage of VoATM is that the technology does not require existing equipment to be retrofitted. Its implementation consists simply of installing a next-generation integrated access device (NG-IAD) at the customer premises and a voice gateway at the central office. The NG-IAD interfaces DSL service with both telephony equipment and data equipment, allowing them to seamlessly merge their traffic.

EVERYBODY WINS

The benefits of VoATM technology are obvious, from the carrier's point of view as well as from the customer's.

Advantages for Carriers

With VoATM, incumbent and competitive local exchange carriers (ILECs and CLECs) can provide up to 24 voice lines, in addition to data services, using the same twisted-pair that used to support only one voice connection. Of course, VoATM voice service is generally offered with broadband data service as well, meaning that carriers can offer bundled voice and data services at a per-line price far less than customers are used to paying. By bundling voice and data services, carriers are also able to take a multipronged approach to building strong relationships with their customers.

In short, with VoATM, communications providers can earn more per copper line, support more customers with less capital investment, and attract more customers who are eager to take advantage of converged services at a reasonable price.

Advantages for Customers

As for customers, they can continue to use the same computer and telephony equipment they always have, with the simple addition of an NG-IAD. They can add more voice lines simply by making a phone call or visiting a carrier's Web site. And they have only one provider to contact for all their data and voice service needs, which makes it easier to set up or modify their service choices. Customers benefit most, however, from the wide array of services they can now access through a single copper line, typically at a far lower cost than before.

[size=18pt][b]VoATM: MAKING GOOD ON ITS PROMISE[/b][/size]

For the foreseeable future, VoIP will continue to make sense in the low and high end of the telecommunications market. But for the mass of network users in the middle--residential users with intensive communications needs and small-to-midsized businesses--VoATM is living up to its billing as the most practical solution for delivering high quality voice and data over the last copper mile.

Bibliography for: "Voice over ATM: Integrating voice and data transmission in DSL - Technology Information"

Greg Langdon "Voice over ATM: Integrating voice and data transmission in DSL - Technology Information". Communications News. FindArticles.com. 08 Jan, 2011. [url=http://findarticles.com/p/articles/mi_m0CMN/is_4_37/ai_62051124/]http://findarticles.com/p/articles/mi_m0CMN/is_4_37/ai_62051124/[/url]
COPYRIGHT 2000 Nelson Publishing
COPYRIGHT 2000 Gale Group
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[manjunath455]

[quote author=Pilla Zamindar link=topic=141351.msg1602980#msg1602980 date=1294525110]
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[Pilla Zamindar]

[quote author=my luv is gone link=topic=141351.msg1603032#msg1603032 date=1294525705]
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