If metro network technologies were soap powders, Next-Generation Sonet would be a leading brand. But that’s part of the problem for carriers trying to figure out how next-gen Sonet fits into their metro plans – it’s just a brand, not a single technology or standard.
To help get a fix on where next-gen Sonet is today, this report reviews the technologies and industry drivers behind the brand and samples some of the products on the market under the Next-Generation Sonet banner.
Pretty well all Sonet vendors have, or will soon release, products they describe as next-generation Sonet in some sense. But it's a terminological nightmare (and a marketeer’s delight) because no one can quite agree on what it is exactly – though it hardly seems to worry the brochure writers, as the marketing usually emphasizes the packet and client services (which, admittedly, generate the revenues), not the underlying transport mechanism. This might be OK, but for the fact that the transport mechanism does matter, because it determines some of the ultimate capabilities of the carriers’ network and service offerings. Powder X may indeed not wash as clean as Powder Y in the long term.
Wavelength Division Multiplexing (WDM) makes things even more complicated, as most multiservice provisioning platforms (MSPPs – prime users of next-gen Sonet) are now going over to DWDM, and it is very unclear whether wavelength-aware digital wrapping schemes such as G.709 can be usefully regarded as descendants of Sonet or not – even though they incorporate various Sonet ideas (check out our Beginners' Guide for more on Digital Wrappers and Forward Error Correction (FEC)).
But take a look at Sonet’s fundamentals, and some clues emerge to what next-generation Sonet might mean at a technical minimum. Traditional Sonet does four basic things:
- It creates a synchronous, framed bitstream that can be interpreted and used by higher-layer communications protocols.
- It imposes a specific circuit-oriented TDM (time-division multiplex) scheme onto that bitstream for the mapping of a limited range of client services.
- It provides managed end-to-end paths through a network for service creation and management.
- It offers service and network resilience through automatic monitoring and protection switching – together with a range of essential OAM (operations, administration, and maintenance) functions.
“I am simply stunned how fast the market in the metro shifted from ATM to Ethernet. Two years ago every little startup out there was doing an ATM-over-Sonet box, and now it’s almost nobody. Ethernet is really the dominant one, and it makes sense because it’s inexpensive, it’s ubiquitous, and enterprises understand it,” says Richard Goode, senior manager of the Optical Networking Group at Lucent Technologies Inc. (NYSE: LU).
What’s needed are ways to manage data-service bandwidth dynamically in small increments, to provide a range of service guarantees, and to engineer traffic flows more efficiently. So to improve Sonet into a new generation, while keeping its essential virtues, the main technological focus is on devising new client-service encapsulations and scrapping the traditional multiplexing/mapping scheme, replacing it with a more flexible alternative within the basic Sonet framing.
Bigger Picture – Costs and Densities
But, of course, there is a bigger industry picture behind next-gen Sonet than just new encapsulations and mappings. Classical Sonet has had the stigma of being expensive, difficult, and complex, with time-consuming service provisioning, although its solid OAM has been appreciated by incumbents.
The collapse in telecom finances has left the surviving carriers desperate to cut costs and to raise revenues – but in an environment where bandwidth growth has slowed, as has the premium that enterprise customers are prepared to pay for connectivity. Since the survivors tend to be big incumbents that have already invested heavily in Sonet, vendors of Sonet equipment naturally see next-generation Sonet in this light, too.
“It really takes existing Sonet – which is a standards-based technology – and makes it better through increasing the densities, reducing the footprint, and reducing the costs,” says Goode. “Currently, the carriers’ message to us is they are not asking how many technologies you can integrate into one box, but rather how can you help me save money. So they really have to do more with less. So they are still looking for the benefits of MSPPs, but those functions that the MSPP box does have to be done well.”
Continual improvements in semiconductor technology have increased densities by up to 50 percent in some cases – say, being able to support 80 OC48s in four chassis instead of 40 in three. And higher densities mean smaller footprints. Power consumption is falling, too. So reduced space leads to lower real-estate costs, and reduced power consumption leads to lower power costs – both leading to reduced operational expenses (opex).
And the savings from next-generation Sonet have to be big – and include functional and architectural gains as well. So says Joe Padgett, director of the Metro Optical Group at Nortel Networks Corp. (NYSE/Toronto: NT): “It has got to set a new benchmark in economics. So you are consolidating nodes, you are consolidating some of the rings. If you are not getting a 25 percent to 35 percent capex/opex savings, then you are definitely not next-generation Sonet.”
Evolution and Legacy Support
Evolution is another key attribute of the next-generation Sonet brand. Carriers have to be able to do new things, such as extending enterprise broadband service capabilities into a shared point-to-multipoint environment, while keeping their revenue-generating traditional services.
“The real key of next-generation Sonet is that it has got to support the legacy protocols and the legacy services,” says Padgett. "If you don’t do that, then to me you are not meeting the definition of next-generation Sonet as an evolution. Next-generation Sonet is not a forklifting. This is basically taking what you’ve got and gaining some efficiencies out of it."
Even newer carriers are having to take account of legacy considerations. Says Nazik Andonian, director of Integrated Network Design at the European carrier Interoute Telecommunications: “Our approach is to align the service requirements of our customers with the solutions offered, so we are currently studying the capabilities of next-generation SDH platforms. Interoute is penetrating the metropolitan area; and providing an efficient last-mile access solution for carrying both Ethernet and voice traffic is a significant step. Interworking with any installed-base metro platform is obviously a major concern.”
There are also some specific challenges that next-gen Sonet equipment must meet. These include:
- Getting up to 10 Gbit/s to converge Sonet and packet
Ten gigabits per second is increasingly looking like the sweet spot in future metro architectures on the access and aggregation sides, since it is where 10-Gigabit Ethernet and OC192 Sonet meet; it is also a level of the new G.709 OTN (Optical Transport Network) hierarchy. This would be a natural point at which to converge packet-oriented services and architectures with Sonet-oriented ones before handing them to the metro/regional cores. So metro equipment vendors will have to design their systems to handle 10-Gigabit Ethernet LAN PHY and WAN PHY interfaces while supporting Sonet OC192 and legacy services.
- Simple card upgrades
There is big pressure on carriers to reuse as much equipment as they can and to migrate gently to Ethernet metro services. This means doing card upgrades if possible and keeping the existing chassis. This is one of the big drivers for increased density of cards – the ability to provide for multiple rates on a card and the ability to provide for multiple services on a card.