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Convergence
The Real Deal
Convergence integrated voice and data riding over one, seamless network.
The idea has been talked about for nearly two decades now. In the last few years, the concept has evolved and taken some toddler-sized steps towards reality. Now, convergence is thought of as the integration of IP (Internet-Protocol), which relies on packet or cell-based data for its features and services, with the existing circuit-switched public phone network with its traditional voice and enhanced services, such as voice mail and call forwarding. Convergence also means that these services will be supported on an array of devices ranging from the latest wireless gadgets to, quite literally, the kitchen sink.
What does that mean from a user's perspective? Today, most businesses must run their data and phone networks as separate entities. A company may have LANs (Local Area Networks), WANs (Wide Area Networks), intranets and extranets, all of which are based on IP. In most cases, however, the company phone services use voice lines and are managed by a local telecom carrier using non-IP protocols developed for the circuit-switched network.
So when a telecommuter enters her home office and starts her IP-based computer, with the proper software and security clearances, she can access the same programs and files on her company's data networks that she would if she were at company headquarters. That's because her computer is recognized by the data network as just one more IP node with which it will communicate.
Personal communication devices
However, when the telecommuter picks up the handset on her telephone, she will not have the same feature-set her colleagues back at the office do. Her telephone is part of a separate network, and its number is associated with a physical pair of wires, not the device itself. While it is theoretically possible for a carrier to provision those wires with the same features that her company's phone network offers, it would be expensive. The employer would also pay for those features even when they were not being used.
Making matters worse, the features would be associated with those wires only, not the phone or the telecommuting employee. In terms of network architecture, nothing has changed. So the features would be available to her only from that specific physical location. That's less than true service portability.
If the telecommuter instead has a wireless IP-compliant personal communication device and her company uses a wireless IP-based network to communicate with its farther-flung employees, she could use that device to send and collect voice mail, short text messages, etc., regardless of location.
New classes of equipment
At the ultimate point of convergence, devices used in the circuit-switched world will take on the characteristics of their cousins in the data world. Then the telecommuter's landline phone would indeed have its own unique IP address string, just like any other device on an IP-based network. The telecommuter would unplug it at the end of day in the office, take it home, or to a hotel, or to a friend's home, plug it in - and have the converged network recognize the phone's IP address and route her accustomed services to her, just as she can already access her employer's data networks.
Meanwhile, inside the network, new classes of equipment would make all of this possible by moving information back and forth between the circuit-switched and packet-switched networks, completely transparent to the user. Eventually, the network could be entirely packet-switched, with voice, data and all other media running over a single, fully converged network.
Here and growing
Getting to the point at which the lines blur between voice and data, computing and telephony, is going to take some time. That's because a huge volume of very important, very lucrative traffic - voice - continues to run over the highly reliable circuit switched network. This is particularly true in North America, where some vendors estimate that there is about USD 250 billion worth of equipment embedded in the circuit-switched network, virtually all of it optimized for voice connections. "That investment won't be written off overnight," says Bob Dalias, vice president, product management, for Castle Networks, in Westford, Massachusetts. "We see the need for a transition path from time division multiplexing to packet."
Packet-switched data is on the rise. Much is generated by business users, as they use the Internet and Internet-based technologies such as intranets and extranets, to conduct business with their employees, customers, suppliers and distributors all over the world. In addition, there are the ever-growing numbers of residential users browsing the web and using e- mail for work and pleasure. Much of this traffic is initiated via circuit-switched dial-up connections to Internet Service Providers (ISPs).
In fact, that's where convergence is occurring today, at the network transport layer, notes Jim Borchering, staff planner for Tellabs Inc. in Lisle, Illinois. He points out that voice and data often already ride on the same physical media, whether copper wire or fiber optic cable, to get to and from their network destinations. That makes it possible for companies and individuals to browse the web, which is packet-based, via dial-up connections.
However, this is only a very basic convergence that does not address a key issue: Running data over a circuit switched network is extremely inefficient.
Charging by the bit
A circuit-switched connection reserves an entire 64 kilobits of bandwidth per second for the duration of the call. Just as there are silences during a voice call while the participants ponder their thoughts, so there will be times during a web-browsing session in which no data is being sent or received. Yet all of that bandwidth remains dedicated throughout the session, even during the silences, so much of it goes unused.
The result? The network operator can't allocate any of the unused bandwidth to other customers for their voice or data traffic. Meanwhile, other users may be attempting to complete voice or other dial-up connections and be blocked because a circuit is taken up with what are essentially data transactions. The operator's billing for such calls may also be inappropriate. For example, if prices are based on the distance of a call, is the price of service still equitable if the call is local but the bandwidth is tied up for eight hours?
The business perspective
From the business user's perspective, running data over the circuit-switched network raises other economic and operational questions. For example, a business leasing a T1 line from a local carrier will pay for all of that bandwidth regardless of how and whether it uses all that capacity each day. The business will also rely on its carrier to provision the line - it's unlikely to be able to set up, say, 60 percent voice capacity one day and 40 percent the next, with the remainder dedicated to data, without calling up the carrier and having a carrier employee physically make the required change to a network element.
With a packet-switched network, however, carriers should be able to bill per packet or cell or even bit. The data network only uses bandwidth as it is required, effectively stuffing bits of data down a pipe. Vendors foresee carriers differentiating billing depending on what type of bits are actually in a packet or cell,
Giving business users more pricing flexibility.
In addition, in the packet world, business customers will be able to configure their own networks on a daily, even hourly basis, probably by using a web interface to instruct different nodes in the network. These IP-based virtual private networks, or VPNs, will enable businesses to integrate voice and data applications. This could include truly portable services for telecommuters, as well as enhanced customer services, such as accessing client account data simultaneously as the phone is answered.
This provides greater value to the user and is more efficient for carriers. "The customer can determine his own criteria for how to configure the network and traffic flow, and the carrier can take away a service person and bill according to how the bandwidth is used," observes Michael Welts, vice president of marketing for Castle. "That should equal lower costs for all."
So the route seems clear. Transmit all traffic, including voice, onto the emerging packet-switched data network. That won't be easy or happen quickly, however.
Voice and data are different
The technology does exist to packetize voice, a necessary first step in sending voice over the packet data network. In fact, a new group of Internet-telephony carriers already offer these services to businesses and individuals. Questions still remain, however, about whether the IP-telephony gear available today can handle traffic on the scale and with the reliability that the circuit switched network does. It is also unclear whether quality of service (QoS) of voice over IP, will be comparable to the quality offered by the circuit -switched network, which was built by and for voice.
"Voice and data are totally opposite when you look at the enhanced services of the Intelligent Network (IN), which is integrated into the circuit-switched network, to the data network. IN services and their communication protocol, Signaling System Seven (SS7), enable carriers to offer credit card calls, call forwarding, voice mail, and other enhanced services. However, the data network doesn't understand SS7, and industry analysts doubt that users will accept packet voice without the enhanced services to which they have become accustomed.
Network must work the same way
Many vendors are addressing this problem with various types of mediation devices that will work with, and possibly someday replace, the Class 5 central office switch, which is the work horse of the voice network.
However the signaling issue is solved, all vendors agree that is is essential that users should be insulated from the issue of whether their traffic is riding over a packet or circuit-switched network.
"People will want the network to work the same way," states Michael Meyers, product marketing director for Lucent Technologies Inc., headquartered in Murray Hills, New Jersey. Like many other industry insiders, he firmly believes that users connot be expected to dial different sets of numbers depending on which network their transaction will use. That eventually may mean mapping phone numbers to IP addresses so they can be read in a converged network.
Talking to your sink
As the issues of integrating the circuit and packet networks are solved, an increasingly large array of equipment, products and services should become available, some of which sound like script notes for a science fiction film.
For instance, the Internet Engineering Task Force (IETF) is creating a new schema for IP addresses to ensure an abundance of them, anticipating the day when virtually every device in the home, car, store and office will have its own unique IP address. It will be possible, in a converged network, for a user to launch a web browser-style interface customized for his home, click on an icon for "kitchen sink," and send an IP based message either over a fiber or wireless link to the sink.
In turn, the sink, with its IP chip, may signal back that it needs a new water filter.. The user might also tell an IP-based freezer to start thawing meat in a special compartment, program a videotape recorder and turn on the house lights and, with the right equipment, even look out a peephole in the front door and accept a package from a delivery person, says Mark Wilson, director for strategic planning at Ericsson Inc., in Richardson, Texas.
In addition, wireless IP-based devices will communicate with those in-home IP-compliant appliances as well as enable other services. A user might pay for lunch from an IP-equipped vending machine by aiming her PCS device at it. The cost of the food would later appear on her phone bill. If the user ordered the last soda pop and chicken sandwich, the vending machine would automatically signal its owners that it needed to be restocked.
"When everything is IP-based, you'll be able to access all kinds of data sources," predicts Wilson.
When that will be is debated. Wireless networks need to be built out to handle greater characteristics of their flow," notes Tellabs' Borchering.
For example, voice traffic is very sensitive to delay, or latency, as well as errors. It would be very difficult to carry on a phone conversation if there were long gaps between hearing the first part of a word and its final syllables, or if entire words were missing or arriving out of order. The circuit-switched network is engineered to prevent latency and errors. But the packet-switched data network is very tolerant of latency - think about waiting for a Web page to load - and if missing bits are detected, the packets simply may be retransmitted.
Another tough question is how to port the bandwidth, notes Wilson. Many vendors expect to see the circuit-switched network co-exist with the packet data network for several decades, with perhaps significant levels of convergence within 5 to 10years.
Lucent's Meyers predicts that convergence will occur first in the long distance networks, where the economies of scale are greatest; then for tandem, or toll calls; and finally, for local calls. However, several vendor sources warned that the Internet has exploded faster than many in the industry had predicted, and convergence could do the same.
Convergence seems inevitable
The last mile to the home also needs to be upgraded for converged services. While digital subscriber line services and cable modems could provide the necessary last-mile bandwidth, there are still some messy logistical issues.
"Who will run the wire from the bedroom to the cable box?" asks Meyers. "Rewiring the home is not trivial."
Another variable in the run for convergence is the impact of cable operators offering voice, video and data services over hybrid-fiber coax (HFC) architectures. While these services are not yet widespread, big names such as AT&T and Microsoft, are behind them. Fat HFC pipes enable the high-speed data access that many Internet users are craving, and cable telephony has been well accepted in many of the markets in which it is available. Greater HFC service availability might speed convergence.
Finally, wireless carriers are ramping up their network bandwidth to carry additional services. These carriers have a convergence advantage in that their equipment is already digital and moving to IP-compliance, notes Russell Levesque, vice president, product management, for Excel Switching Corp. in Hyannis, Massachusettts. Also, in many parts of the world, wireless access is nearly ubiquitous. So these carriers could be among the first to offer converged network services.
Whatever the time frame, convergence seems inevitable. AT&T recently announced it will now invest only in data switches, no longer buying Class 5 switches for its network. Sprint, with its ION network, Qwest Telecommunications International, and Level 3 Communications Inc., are building converged networks as well. The final question, this, is how carriers will approach convergence.
"It's not clear how it will all play out," says Meyers, noting that all the different types of carriers, start-ups, wireline and wireless, are developing different convergence strategies. "But it's fascinating to watch."
Sharon Watson
Sharon Watson is a Chicago-based freelancer specializing in telecommunications and information technology.
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Meeting in the Middle
One major convergence question is how to get the circuit-switched and packet-switched networks to communicate with each other.
Why bother to make them talk? The circuit-switched network is home to Intelligent Network (IN) services with such features as toll-free calls, call screening, voice mail, etc. The circuit-switched network also contains embedded Operations Support Systems (OSS) that carriers rely on to provide highly reliable, high quality networks. Carriers use a protocol called Signaling System Seven (SS7) to communicate with the IN and OSSs, but this is a protocol that the data network does not understand.
That means an IP device on the data network could not directly access the IN databases in the circuit-switched network to look up a number, forward a call, confirm a dialing card number, etc. Yet, as many vendors point out, there is about a decade's worth of research built into the IN and SS7, which work reliably and well. In the near term, at least, it makes sense to port those services into the IP world, and that will require some sort of device to bridge the networks.
"You don't want to replicate what's in the toll and tandem switches; you want to access what's in the Intelligent Network," said Jim Borchering, staff planner at Tellabs, Inc., in Lisle, Illinois.
Mediation devices, sometimes also referred to as programmable switches or VoIP gateways, appear to be the answer. These carrier-class switches will sit between the networks, often tied to a central office switch. The mediation devices may split off voice from data calls, routing data calls away from the CO switch; serve as a voice-over-IP (VoIP) gateway; and offer open Application Programming Interfaces (APIs), with the goal of enabling faster enhanced service creation in the IP world.
The devices will support call set-up and termination across both circuit and packet networks, translating and transporting SS7 and other signaling protocols between the networks as necessary. Thus carriers can offer familiar enhanced services even as voice is running over a hybrid network.
"You can't wait for the backbone to change to start offering new services," said Bob Dalias, vice president, product management, for Castle Networks, a mediation device vendor based in Westford, Massachusetts.
Industry groups are already at work to define a standard protocol for signaling devices on the data network. The Media Gateway Control Protocol, proposed by the Internet Engineering Task Force, is one. Vendors also support several others, including H.323, which is actually a videoconferencing protocol.
Most vendors say they hope the IP network platforms will be open and standardized to enable fast service creation and ease of operations, tasks which have been problematic in a highly proprietary circuit-based world. "All the layers should be open," said Russell Levesque, vice president, product management for Excel Switching Corp., a mediation device maker based in Hyannis, Massachusetts. "Close any of them, and you create the same old problems."
Quality of Service
While many of the details about convergence still are not clear, one thing is certain. Business and residential carrier customers are very used to reliable, high quality voice service, and they will demand the same as carriers move to a packet-switched network.
The rub is that a packet-switched network treats precious voice bits just like any other bits in the pipeline. That efficient but democratic approach to traffic management, a hallmark of data networks, can lead to lags and dropped words during a conversation unacceptable quality for a corporation hoping to run its data and voice over an IP-based virtual private network (VPN).
Carriers and vendors are now reviewing several technical options to ensure that VPN voice quality of service (QoS) matches the standard et by the circuit-switched world. One is to put IP-based voice inside Asynchronous Transfer Mode (ATM) cells. With its built-in control and error-correction, ATM is a highly reliable switching and transport layer. Other protocols are being defined specifically to answer the IP QoS question. One is Multiprotocol Label Switching (MPLS). Another is DiffServ, for differentiated services. The basic idea with these would be to tell devices throughout the network that they are routing voice hidden inside IP wrappers and to ensure these packets receive first-class passage through the network. That would permit carriers to offer guarantees on various classes of service and charge accordingly.
"Carriers don't make quality trade-offs; instead, they trade up," said Jim Borchering, staff planner for Tellabs, Inc., in Lisle, Illinois. That, he and other vendors agree, will be the philosophy guiding the porting of voice to the data world.
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