Posted 03/2001
Network Solutions
In Sync
Startups Often Overlook Network
Synchronization
By Pat Blake
The widening breadth of broadband services is a tantalizing elixir that lures data-hungry clientele. It's brewed with a mix of IP and ATM, and sprinkled with a dash of SONET for mass appeal.
This may whet the appetite for capacity, but to truly satiate customer demands, carriers must also meet specified service guarantees. To fill that tall order, service providers will need the essential, yet often-overlooked, secret ingredient: network synchronization.
"Synchronization is an incredibly important backbone for lots of systems, including telecom," says Marc Weiss, mathematician with the National Institute of Standards and Technology (NIST, www.nist.gov). NIST provides time and frequency standards that are used by manufacturers--among others--to precisely sync equipment.
"Synchronization is generally not noticed until something fails. But it is one of the core technologies that allows traffic to flow," says Weiss. "The better the synchronization, the more you can utilize the bandwidth in the fibers; the more reliable and robust a network is, the faster you can heal errors and failures. All that stuff is strongly aided by synchronization."
One of Weiss' concerns and the concern of others in the industry is that CLECs, because they are relative newcomers, don't hear about synchronization for a while. "They see that there's an opportunity and they build a system," he says. "It works fine when the system isn't stressed out. But as soon as they try to use a significant fraction of their bandwidth, things start falling about."
A network left to flounder without adequate sync generates frame slips and lost packets, among many other service-degrading troubles. For voice, bad sync will cause an auditory click or pop. But for data, it is particularly more odious.
"If you're trying to send lots and lots of data," Weiss explains, "poor synchronization is a problem because you have to resend that data. If you're working with secure systems where the customer is sending a key, that key has to be resent. That degrades the security of the system, which is a very big problem for some, such as government agencies, that use secure communication systems."
New entrants to the telco scene that bank all their fortunes on a voice-only scenario today are an anachronism. ICPs are following the market demand for data by emphasizing high-speed services such as DSL, or building data-centric platforms based on IP where voice is sometimes an add-on service.
ICPs are increasingly data-centric. Their customers are increasingly quality-of-service-oriented. And never the twain shall meet without filling the need for sync.
A Taste For Sync
Options abound on the synchronization menu. Typically, service providers build a sync strategy based on the level of accuracy--with Stratum 1 being the premium--and on the source of the signal, such as GPS, CDMA or cesium atomic clocks.
The question, though, is not only how to build a strategy, but when to deploy it.
"Our approach from a synchronization perspective is a strong appreciation for why it is mission critical to have a solid sync plan, and to map it out and implement it on the front end," says Joe Calzone, Choice One Communications (www.choiceonecom.com) senior vice president of engineering. "This vs. the putting the cart before the horse and installing a network architecture first and later finding out that it is not properly synched. With data, poor synchronization is unbelievably disruptive in terms of getting proper throughput and handshakes. Without proper synchronization, your data network has very little chance of succeeding."
Heavily vested in both data and voice services, Choice One is in markets primarily within the Verizon Communications (www.verizon.com) and Ameritech Corp. (www.ameritech.com) territories. They blend DSL, voice and a suite of web services for small and medium-sized businesses in those areas.
The source of the sync signal can be confounding for ICPs. Pressured to quickly generate a steady revenue stream, new service providers may be tempted to derive a signal from their incumbent rivals. Borrowing timing may work in the short term, but it proves to be a half-baked solution as a network grows.
"The most common misconception about synchronization is, 'I can get it from the network,'" says Dave Figge, vice president of product marketing for Datum-Austin (www.datum.com), an equipment manufacturer that specializes in timing and synchronization products. Datum's telecommunications division is based in Austin, Texas.
"While a CLEC can enter a new market area and initially derive synchronization from the incumbent's network, as that CLEC grows, they no longer have a place from which to derive that signal," Figge says.
A sync signal from an incumbent is viable for only a limited number of POPs. As the new carrier adds nodes and extends the network, that borrowed signal cannot be maintained. In other words, it loses its strength and cannot live up to the requirements of today's optical networks.
Up the Stratum Staircase
A Stratum 1 clocking level is the de facto standard for carriers whose customers demand a guaranteed quality of service. When carriers borrow a sync signal from an incumbent (also known as line timing), they may expect to receive a Stratum 1 level. However, there is no guarantee that a borrowed Stratum 1 level will be maintained across their network. It generally will degrade to Stratum 2 or Stratum 3 without any warning or immediate indication. Some competitive service providers may feel pressure to make that quality trade-off simply to cut costs.
"Newcomers focused on voice that are small and may not be as properly capitalized as they would like may lean toward a Stratum 2 or Stratum 3," Calzone says. "There's little degradation for voice service, and perhaps their clients won't notice.
Diagram: Accuracy & Stability Concepts
"For the true ICP that has any plans for provisioning high-speed Internet service, the absolute lion's share has stepped up to the plate and said, 'I need a Stratum 1.' Data and fiber-optic MUXes are just hypersensitive to proper synchronization."
Traditionally, atomic clocks, such as rubidium, delivered the accuracy and reliability carriers crave. These clocks are still prevalent in many long-haul and incumbent networks. The arrival of GPS (global positioning system) heralded a less expensive alternative.
By placing a GPS antenna on a rooftop or using one of the new breed of CDMA antennaless options, carriers can derive a Stratum 1 signal from one of the 24 satellites that continuously orbit the Earth. Theoretically, at any given time from any given point in the world, a carrier can access at least four satellites from which it can retrieve a signal for synchronization. The other option is to buy newly affordable standalone cesium atomic clocks that do not require antennas and place them at various locations within a network.
"To purchase an atomic clock when we got started two years ago would not have been the most cost-effective way," says Calzone, referring to the first generation of atomic clocks. "We thought it was more important to gain market entry as early as we can and with as robust a coverage in a given market as quickly as we can.
"We started off with independent islands. Our Albany and Buffalo sites had their collocation cages attending them, but they weren't necessarily connected to one another. It was important to have access to Stratum 1. With GPS, it worked out very well to put an antenna on each one of our ultimately 29 regional switching centers. We like GPS because it gives us direct access to Stratum 1 and it is one of the most secure timing devices."
Stratum 1 may be Choice One's first line of defense, but it is not, by far, its only one. The Datum-Austin system that Choice One uses allows for 30 days of holdover; meaning that the signal would be maintained for that length of time should the Stratum 1 system be compromised. And the last fail-safe measure is the internal clocks embedded in many switches, which are best left as a last resort and not as the centerpiece to a strategic sync plan.
Multifaceted Mayhem
To hold the mantle of competitive providers, carriers generally support a wide swath of platforms. Their diversity is quickly making them all things to most, if not all, data customers. However, if a service provider relies solely on the internal clocks placed in each network element, they are building a plan based on Stratum 2 or 3 at best. Furthermore, the faulty design will lack any cohesive element to tie each piece of equipment together in an operationally unified manner. So, while they may offer a plethora of platforms, they will not be able to guarantee a specified level of performance across the network.
"The fact that we chose to do both voice and data and the fact that the origination and termination of traffic onto the network means that traffic can come in many different flavors and with many different types of synchronization," Calzone explains. "I can have traditional voice traffic from the telephone company coming to and from the axis tandem. For my DSL and Internet connections, I have to connect the various routers and ATM switches. So there's a whole host of different networks that we have to interface with."
"Stratum 1 really maximizes the opportunity for seamless transitions," he adds.
An exasperating situation that arises from these multiple networks and multiple platforms is the difficulty in identifying the source of a problem.
Diagram: Level of Sync Accuracy
"Diagnosing problems becomes very, very awkward," Figge says. "The fact that these multitudes of service types--conventional voice, IP, ATM--may be coming from a variety of different backbone providers. Carriers need to ensure that their network is in tight and accurate synchronization. It becomes critical in identifying where the problems are coming from and going to.
"The other side of the coin is that while you try to meld service offerings--for example, two-way voice over IP or packing IP services onto an ATM network--synchronization has repeatedly proven to be a crucial, but often overlooked, element in ensuring the highest possible bandwidth intervals for accurate delivery of data."
A prime benefit for ICPs is that most are entering their markets with new equipment and can incorporate new sync management tools from the ground up. They can now remotely manage their network, validating the synchronization of specific elements and fine-tuning their performance while at arm's length. The latest generation of Cesium atomic clocks is also available as an affordable option to GPS.
The challenge is to offensively address synchronization before it puts a system in a defensive mode.
Pat Blake is a free-lance writer based in Cedar Rapids, Iowa, who wrote this article on behalf of Datum Inc. (www.datum.com). Pat can be contacted at B814@aol.com.
