Soft-Tunable Access
from "Closing The Gap At The Optical Edge"
bcr.com
ADVA Optical Networking Inc., plus start-ups Appian Communications, LuxN, Inc., and Quantum Bridge Communications all offer products for the very edge of the public network. Of these, ADVA, LuxN, and Quantum Bridge focus primarily on extending optics to the customer premises while Appian seeks to make optical access more cost-effective.
Appian's Optical Service Access Platform (OSAP), which is scheduled to begin beta testing in June, is targeted for deployment in office buildings and controlled-environment vaults (CEVs?telco field units). On the user side, the OSAP supports Ethernet-based data services at speeds up to 1 Gbps and TDM-based legacy services up to OC-12.
On the network side, OSAP delivers data streams in PPP, frame relay, ATM or Ethernet over standard SONET/DWDM pipes. By translating between Ethernet and standard WAN protocols, the OSAP lets access providers replace all the devices in a TDM tail circuit without changing anything at the POP or CO.
The whole idea behind the OSAP is to increase bandwidth and operational efficiencies. According to Anand Parikh, Appian's vice president of marketing and business development, OSAP's data services, called Etherband,
are "soft-tunable"?i.e., access providers can assign each service a guaranteed bit rate (GBR) and a maximum burst rate (MBR) in 64-Kbps increments at speeds ranging from 1 Mbps to 1 Gbps. Over a 100-Mbps Ethernet interface, for example, an Internet access service could start at a GBR of 10 Mbps and an MBR of 40 Mbps.
If the customer needed more bandwidth, the provider would adjust the parameters to the desired level?no truck rolls, no circuit provisioning and no arbitrary hierarchy.
The OSAP lets multiple services share SONET channels (Figure 2). IP-aware traffic prioritization enforces bit rate guarantees, manages delay for real-time services like voice and video and lets providers exploit over-subscription.
Services can also share interfaces at the user end. Rather than having to provision a separate TDM line for each service, a provider can, for example, deliver Internet access, virtual private network (VPN) access and transparent LAN service simultaneously over a single Ethernet link.
Lighting the Last Mile
Still, improved SONET utilization may not be enough for everyone. "An explosion in the use of Fibre Channel and Gigabit Ethernet will create demand for access bandwidth that SONET can't meet," predicts Paul Strudwick, vice president of marketing at LuxN, Inc.
The solution: Light up some dark fibers and give each enterprise its own gigabit wavelengths. According to LuxN, 60 percent of today's fiber infrastructure is still unlit, and 70 percent of that unlit fiber is in local or metro-area networks.
Strudwick describes LuxN's approach as the optical counterpart to DSL. At a capital cost of about $20,000 per connection, users plug their Gigabit Ethernet, Fibre Channel, SONET or T1 and 100Base-T links into LuxN's WavPortal and WavFarer "optical DSUs."
At the CO, a WavStation "optical DSLAM" passes each link through to the carrier network sans aggregation. All three products, which began shipping in February, support wavelengths at speeds up to OC-48. LuxN's first customer, a large high-tech enterprise, uses the products to provide Gigabit Ethernet links between routers on several of its campuses.
This sort of enterprise application is just what ADVA Optical Networking Inc. is looking for. With both ring and point-to-point topologies, its Fiber Service Platforms (FSPs) resemble an inter-CO solution.
But according to Brian McCann, ADVA's president, "We are working with carriers to provide wavelength services between enterprise sites," not between COs.
By lighting dark fibers, carriers can offer transparent carriage of anything optical?SONET, Fibre Channel, ESCON or Gigabit Ethernet?for high-volume applications like data center disaster recovery.
ADVA's FSP-I and FSP-II have been shipping since mid-1999 to large enterprise customers and metro-area carriers. Prices start at $8,800 per link. In Q2 of this year, ADVA will add the FSP-300, designed for deployment in central offices. It will list at $25,000 per DWDM channnel.
Bridging the First Mile
While LuxN and ADVA dedicate whole fibers to high-volume customers, Quantum Bridge Communications has a scheme for sharing fiber among several small to medium-size businesses.
Using passive optical splitters?a technology common in cable TV networks?Quantum Bridge creates up to 32 branches off a single dark fiber. At the end of each branch, a QB100 Intelligent Optical Terminal accepts 10/100 Ethernet and T1 traffic. At the service provider's central office, a QB5000 Optical Access Switch concentrates input from up to seven shared fibers into an OC-12 or OC-48 network interface.
Since the branching devices are passive, all the QB100s on a fiber see the same 600-Mbps optical signal. Quantum Bridge's proprietary Dynamic Wavelength Slicing (DWS), a form of time-division multiplexing, divides the signal into fixed portions for each end point.
Each QB100 can be provisioned at a different speed and the speeds can be adjusted dynamically?in 1-Mbps increments?from a central point. Quantum Bridge began beta tests at cable TV provider Comcast Corp. in January and promises product availability for June 2000.
ADMs, The Next Generation
Faster, more manageable access loops are key to opening up the optical infrastructure, but what about the inter-office facilities that sit between access loops and the network core?
Doug Faber, director of product planning and management at Ciena Communications maintains that ATM is the solution, at least for the next two to three years.
Ciena's MultiWave EdgeDirector 500 concentrates private lines, analog voice and 10/100-Mbps Ethernet into OC-3 and OC-12 ATM pipes. "Today the ED500 is used mostly in point-to-point configurations in CO's," says Faber, "but it can also sit in mesh and ring-based topologies."
Ciena also has another product in development that will be optimized for premises deployment at less than $10,000 per box.
Fujitsu Network Communications also advocates ATM for improved MANs. Like traditional add/drop multiplexers (ADMs), Fujitsu's FLASH ADX sits on a dual fiber-optic ring and manages SONET channels. Unlike traditional ADMs, however, the ADX can use several channels as an ATM pipe and exploit the efficiency of statistical multiplexing.
Imagine a metro-area ring carrying traffic from 48 DSL access multiplexers (DSLAMs). Typically, each DSLAM attaches to the ring at T3 with an average bandwidth utilization of only 16 percent. With traditional ADMs, each DSLAM is assigned an STS-1 SONET channel and the 48 DSLAMs exhaust a 2.4-Gbps ring.
With the ADX, however, the DSLAMs share an ATM pipe comprising just 8 STS-1s and leave 2 Gbps free for other applications. According to Fujitsu, increased bandwidth efficiency alone saves the carrier nearly $700,000 per year.
If the savings are so impressive, why not carry everything as ATM? "A lot of telcos are comfortable dealing with SONET," says Bob Laurent, manager of product marketing for Fujitsu access products. "You can put this box into traditional environments, but with a path to ATM."
A MAN for All Seasons
Still, not everyone is impressed. "ATM makes SONET more efficient," says Doug Green, vice president of marketing at Chromatis Networks, "but tripling MAN capacity only buys nine months."
For increased scalability, Chromatis and fellow start-up Alidian Networks Inc. incorporate DWDM in their next-generation ADMs.
To date, DWDM hasn't really caught on in MANs. Over short distances, it can cost less to pull another fiber-optic cable than to add a layer of DWDM multiplexers. The Chromatis Metropolis product family addresses the cost issue by delivering a SONET ADM and a 32-wavelength DWDM mux, plus IP and ATM switching, in a single chassis for under $50,000.
Chromatis' products became commercially available in early March, are in trials by multiple customers, including Cogent Communications.
Chromatis eases the migration to DWDM with its proprietary Selective Wave Division Multiplexing (SWDM). As shown in Figure 3, SWDM creates a single-wavelength ring and a multi-wavelength ring side-by-side on the same fiber.
Low-bandwidth sites use only the single wavelength and avoid the expense of DWDM optics. High-bandwidth sites plug into multiple wavelengths for increased scalability. Within each wavelength, SONET carries circuit-oriented traffic while ATM and IP transport the data.
Like Chromatis, Alidian offers incremental migration to DWDM. Alidian's Optical Service Network (OSN) nodes sit on a single-wavelength OC-48 ring, and the nodes can be upgraded to handle multiple wavelengths.
Alidian has chosen to emphasize service flexibility over scalability. Within each wavelength, Alidian's proprietary WavePack technology allocates bandwidth to separate services: ATM DSLAM aggregation, packet-over-SONET router links, transparent LAN service and so on.
Each service gets only the bandwidth it needs and bandwidth allocation is controlled from a central point.
Within each service flow, packets, frames, cells and circuits remain in their native format, and Alidian OSN nodes maintain performance guarantees as required by MPLS, DiffServ or ATM QOS.
A WaveSwitch matrix in each node provides add/drop of individual services and cross-connect between wavelengths. The WaveDirect feature allows carriers to dedicate whole wavelengths to gigabit-speed protocols like Fibre Channel, ESCON and Gigabit Ethernet.
Alidian's Optical Service Network products began beta testing in April, with full availability promised for October. Pricing for the OSN family begins around $35,000.
Beyond ADMs
While Ciena, Fujitsu, Chromatis and Alidian compete to deliver next-generation ADMs, Cisco and Astral Point Communications are trying to make ADMs obsolete.
Cisco's Dynamic Packet Transport (DPT) products, for example, replace standalone ADMs with packet-based add/drop capability on a card.
DPT passes packets between Cisco routers over two counter-rotating OC-12 fiber rings. Cisco's Spatial Reuse Protocol manages the add/drop process and ensures a fair distribution of network resources among the nodes.
Unlike SONET, which keeps one fiber on standby for outages, DPT uses both fibers concurrently. Coupled with the statistical gain of packet multiplexing, DPT much more than doubles the throughput of SONET over the same facilities. DPT modules are available for the GSR 12000, Cisco 7500 and uBR7200 product families at prices ranging from $10,000 to $30,000.
Rather than build rings with routers, Astral Point wants to eliminate rings altogether. It offers a mesh topology with direct DWDM links between nodes. Some wavelengths carry multiplexed ATM traffic while others provide direct transport for Gigabit Ethernet, Fibre Channel or ESCON.
Built-in cross-connect capability switches TDM circuits over the same mesh.
Astral Point promotes both the scalability and the manageability of its solution. "Instead of multiple rings, we can build a single mesh with several hundred nodes," says Bill Mitchell, vp of marketing. "And like an ATM or IP network, the mesh builds its routing tables dynamically. To provision a new service, the operator picks two endpoints and sets up the connection in one step."
Integrated communications provider Advanced TelCom Group, Inc., began beta testing Astral Point's ON 5000 Optical Services Node in March. General availability begins in Q200 with prices starting at $30,000.
Access Unification
MAYAN Networks has an altogether different take on the access gap. According to Drew Lanza, senior vice president of marketing, "The problem isn't a lack of bandwidth; there's plenty in both the premises and the WAN. The problem is linking them together."
MAYAN's UNIFIER product takes in pretty much anything and spits out pretty much anything: Ethernet, IP, ATM or TDM. It is most likely to go into co-location sites or POPs where, says Lanza, "It can replace a SONET ADM, a digital cross-connect, an M1/3 mux, a FRAD, a DSLAM, an IP router, a frame relay switch, an ATM switch and a remote access server.
Operators don't have to learn and operate all those different boxes." In a typical installation, the UNIFIER will replace three to five devices and MAYAN is pricing the product accordingly. The UNIFIER began beta testing in February, and general availability is targeted for the end of Q200.
Mind the Gap
The wide-area access gap is closing rapidly. Fiber optics and DWDM are increasing the raw capacity of MANs and tail circuits by orders of magnitude. Data networking techniques like statistical multiplexing and distributed routing are boosting network efficiency while slashing the time and effort required to provision new services.
The result will be radically lower costs, and a new generation of access services that actually fit customer requirements.
However, it's still unclear what the new access networks will look like, because of the considerable overlap between product categories?all of the emerging MAN solutions include low-end devices designed to sit in large office buildings, while many of the access solutions can be configured as MAN-like rings.
Incumbent carriers may maintain the current hierarchy in some form, upgrading just one tier at a time, but new carriers are free to build simpler, more direct infrastructures.
Will it really happen? Some analysts say users don't want more than T1 or T3, but if you could buy Ethernet-speed access at T1 prices, why wouldn't you do so? Others say that incumbent carriers are reluctant to undercut existing access services with cheap broadband. But if they don't, the competitive carriers will do it for them. It's only a matter of time until new products close the gap at the optical edge. |
