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April 2003 Issue

Point 2 Point

ATM, SONET Make the Connection

by Gene White, Advance Newhouse, Tampa Bay Division

Advance Newhouse Tampa Bay deploys a SONET and ATM architecture to meet its ever-evolving point-to-point communications needs.

The Tampa Bay Division of Advance Newhouse consists of 18,000 miles of hybrid fiber/coax (HFC) plant serving 79 hubs spread over seven counties. This network is engaged daily in point-to-point communications throughout its expanding Internet protocol (IP) network.

The origins of the IP network started in 1997 when the Tampa Bay Division deployed the cable modem service "Linerunner," the predecessor of today's Road Runner service. The Linerunner point of presence (POP) was geography centered in the division and was the first service that not only went to all hubs but had identical connection requirements and service as well. The physical size of the division presented network design challenges along with unique opportunities for the division to leverage the capabilities of a flexible network design. The network contained 1,327 strand miles of county-to-county and hub-to-hub transport fiber. In fact, one segment was over 40 miles long between hubs. With a good deal of due diligence, our engineering team chose the network architecture discussed below to provide a flexible transport network that would serve the future needs of the division.

SONET backbone

For backbone transport, we selected synchronous optical network (SONET) for a variety of reasons. SONET was a proven technology with standards that provided us various optical carrier (OC) level drops at all hub locations. SONET transport allows interoperability among transmission products from multiple vendors. It is an off-the-shelf item, which is expandable by ring or interface, and provides the flexibility needed to transport many different digital signals. In 1997, it also had the long-range cards we needed for county-to-county connectivity.

ATM aids traffic management

ATM offers traffic engineering via private network-to-network interface (PNNI) protocol and routed smart virtual circuits (SPVCs), which incorporate complete traffic management and self-healing capabilities for all traffic types across a large backbone network. ATM also offers high-speed, low-delay, connection-oriented, packet-like switching and multiplexing techniques, and interfaces well with SONET. It also allocates bandwidth on the fly making it the ideal choice for high-speed connection of broadband IP networks.

With the launch of cable modem services, the Tampa division made a significant leap forward; we moved from subscription-based broadcast services to a transaction-based, interactive subscription service. Not only had we forever changed our business, we would continue the evolution by leveraging the existing network for all digital services. We began using the network for internal functions like operation support systems (OSS), business local area networks (LANs), digital ad insertion, internal phone traffic, inventory management, converter control, analog pay-per-view return, and carrying customer voice from remote PBXs to distant call centers.

To complement the SONET/ATM network and to add ports for the additional services, we added a switch router in each hub location, which allowed us to route IP / layer 3 / 4 at the edge and switch in the core. (See Figure 1.) This places intelligence at the edge and switching at the core where switching can take advantage of the layer 2 transport protocols. The IP intelligence provided by the routers at specific points in the network increases network performance and efficiencies in handling all traffic types while adding very little delay or latency to the IP traffic, which is inherent with core-only routing.

Support for digital TV

In 1998, Tampa Bay launched digital TV and other digital video services that leveraged the existing fiber network and once again made a major impact on our business. The digital TV platform supplied by Scientific-Atlanta required the transport of data and video, both of which would be supported via a single backbone network. We were able to use the existing SONET/ATM network because ATM networks are independent of the IP addressing, IP data payload, or the IP domains. This independence allows the ability to support multiple IP addressing schemes within the same backbone network without experiencing addressing and IP conflicts or packet loss.

Following digital video, in 1999 we launched video-on-demand (VOD), and our first venture was movies-on-demand (MOD). With MOD, we moved from subscription-based broadcast services to a transaction-based service. We began delivering video in the form of multi-megabits from a single point to a single point on a transaction basis. This again changed the nature of our business and offered up a new set of technical challenges.

We needed a way to load 70 hours of content (200 gigabytes) onto 78 remote servers or 15,600 GB weekly. Again the SONET/ATM network was the vehicle of choice. (See Figure 2.) With capacity expansion in the SONET core and ATM rings, we could "burst" large traffic through the network as needed. To avoid network congestion and negative impacts on other network services, we established contracts and rate shaping for the circuits that carry the MOD content propagation traffic to limit the amount of data to 30 megabits per second (Mbps) per hub.

After MOD, we launched HBO On Demand (HOD) in 2002, which is soon to be followed by Showtime On Demand, Cinemax On Demand, Movie Channel on Demand, and Free Content on Demand. These launches require loading 200 plus hours of content per week into 78 hubs. It was apparent that a network change would be needed, because passing 31,200 GBps weekly would require a massive network upgrade. The solution may be to leverage the SONET/ATM network for gigabit Ethernet to 10 remote storage devices and stream content through the ATM network from remote storage out to the subscriber. Once again we will be able to leverage the existing backbone network for advanced business needs.

Business data addressed next

The ability to add/drop traffic at any hub combined with the fact that IP traffic is not being regulated, led to the logical extension of the cable modem service into the business community. Our first venture was cable modems for Internet access for smaller businesses, followed by work-at-home applications, which generally required a fiber connection to the business with the security of private data being a major deciding factor when a business selects the product. The answer to the business needs came from the ATM network with is ability to create virtual private networks (VPNs).

Without a high degree of data security, we would not be able to compete in this segment of the market. A key feature of the ATM transport is the ability to create virtual paths and virtual circuits. These virtual circuits are known as SPVCs; they provide the ability to create new connections without installing new equipment, optics or fiber. The creation of the SPVCs is configured once and maintained automatically via ATM transport protocols. Each virtual circuit can be assigned a contract that controls the key transport characteristics of the circuit. For example, business customers are provided with an OC-3 port, but they may only purchase 20 Mbps, which is automatically controlled via the virtual circuit contract. This virtual circuit capability became critical as the network and services expanded.

What started out as SONET OC-12 (622 Mbps) rings and ATM OC-3 (155 Mbps) rings supporting a single service, has now grown to multiple services and backbone data rates of SONET OC-192 (9.95 Gbps) rings and ATM OC-12 and OC-48 (2.48 Gbps). When I step back and look at the network, it becomes apparent that the network is designed to move traffic in the form of Mbps point-to-point.

Basically, we are moving services like digital video (3.2 Mbps), MOD (3.75 Mbps), HOD (3.75 Mbps), data (10 baseT to OC-48), fax, and voice over IP (VoIP)--all in one network from point of origin to point of destination. Despite the network complexity, our division has constructed a simple, reliable, redundant network that moves bytes of data from point-to-point, no more or no less.

Running on the Tampa network today are 455,000 digital converters (S-A Explorer) with access to both MOD and HOD; 250,000 cable modem subscribers with a choice of five Internet service providers; and over 20,000 IP business customers on services levels from 1 megabit to 2.5 gigabit services and multi in-house networks, all sharing one network with no problems, bottlenecks or traffic issues. Since 1997, the network has only been down twice, and only in ATM feeder rings; both times the errors were with the operators and not the network equipment.

Gene White is vice president of engineering for Advance Newhouse's Tampa Bay Division in Clearwater, Fla. Email him at .

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BOTTOMLINE

SONET/ATM Delivers Flexible Network

Time Warner Tampa Bay deployed a SONET and ATM architecture to meet its evolving point-to-point communications needs. The network supported the launch of digital TV services, initial VOD rollouts, VOD expansion plans and business data services offerings. Plus, Tampa Bay is using the network for internal functions like operation support systems (OSS), business LAN services, digital ad insertion, internal phone traffic, inventory management, converter control, analog pay-per-view return, and carrying customer voice from remote PBXs to distant call centers.

Running on the Tampa network today are 455,000 digital converters with access to both movies on demand (MOD) and HBO On Demand; 250,000 cable modem subscribers with a choice of five Internet service providers; and over 20,000 IP business customers on service levels from 1 megabit to 2.5 Gigabits, all sharing one network with no problems, bottlenecks or traffic issues.

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