GFP: Good For Positioning

Circuit-switched shortcomings

Circuit-switched networks: Will they last forever? Or are they ready to give way to a new ecology of communications networks based on datagrams and packets? These are the questions that nobody seems to be able to answer these days.

Current telecom transport networks, built with pieces ranging from add/drop multiplexers (ADMs) to digital crossconnects and optical switching systems, are almost entirely comprised of Sonet or SDH systems. They are well standardized (though not terribly interoperable), as reliable as Swiss watches, and familiar to telecom engineers worldwide.

Their shortcomings, however, have gotten a great deal of attention in the past four years, as entrepreneurs have looked to engineer a New World Order based on Internet and Internet Protocol (IP) technology. Sonet is, after all, ill-adapted to bursty data traffic, while the Internet grooves on Ethernet-based interface rates of 10 Mbit/s, 100 Mbit/s, and 1 Gbit/s, adapting to shifting traffic patterns and logical topologies. Sonet is about nailing up pipes, leaving them for eternity, and charging a decent fee to make certain they never go down for more than an imperceptible 50 milliseconds. This has served a network of voice callers well, but IP found itself either uncomfortably constrained by narrow pipes, or equipped with overprovisioned connections it could never possibly fill. (Think of a 51-Mbit/s STS1 provisioned for a 10-Mbit/s Ethernet interface. No matter how hard you drive it, 41 Mbit/s will always go unused, on both working and protect paths.)

Many startups tried to evolve the trusty Sonet ADM by integrating packet and cell switch fabrics, circuit switch fabrics, and even DWDM uplinks. But most if not all of this new equipment employed proprietary bandwidth management, mapping and framing techniques, so the large incumbent service providers did not bite. At one time, an ample supply of greenfield carriers embraced these developments, but there aren’t many of those folk left. So, it became clear that if Sonet and SDH were to survive, they needed to do it in incumbent networks – and that means they needed standards.

Enter GFP

Along came Nortel Networks Corp. (NYSE/Toronto: NT) and Lucent Technologies Inc. (NYSE: LU), with a proposition to save Sonet for future generations: Generic Framing Procedure. In short, GFP is a traffic adaptation protocol, designed to support variable and fixed-packet transport over a general-purpose, high-speed communications channel. In other words, it’s flexible, and it can deal in both worlds – whether it’s bursty IP data traffic or the more steady stream of voice or storage interconnect.

GFP has a few key strengths. For Ethernet services, compared to packet-over-Sonet (POS), Frame Relay, or other framing procedures that employ HDLC (High-Level Data Link Control), GFP is a much more elegant mapper, with a very low, deterministic overhead and low processing requirements, making chips much cheaper to create. Additionally, GFP preserves the relevant MAC layer information for Ethernet, from destination address through Frame Check Sequence (FCS), supporting a true Ethernet private line that matches the operations requirements of a traditional TDM private line. For storage services, GFP can operate in what’s called Transparent Mode, mapping Fibre Channel, Escon, Ficon, or even digital video into fixed GFP frames. Thus, on the same system, GFP can support a mix of traditional services and emerging ones, managed as transport connections just as Sonet/SDH circuits are today. Operators love that kind of thing.

GFP represents a key element of next-gen Sonet/SDH. It’s well standardized in American National Standards Institute (ANSI) T1X1.5 and the International Telecommunication Union, Standardization Sector (ITU-T) and could be an agreeable method for incumbent providers to extend the useful life of Sonet/SDH networks while opening the door for multiprotocol transport over OTN (optical transport network, once called digital wrapper).

But it gets even better! Bringing the whole next-gen Sonet/SDH family together are virtual concatenation and LCAS, the Link Capacity Adjustment Scheme. Virtual concatenation supports much finer granularity circuit provisioning (groups of STS1 circuits or even VT1.5 circuits), without requiring the service provider to upgrade existing Sonet/SDH gear. This allows for “right-sized” pipes for packet services. A customer could take what it has in place already, such as a 10/100-Ethernet port on an enterprise switch, and allocate Sonet bandwidth as needed, boosting up the bandwidth in time. This effectively creates an Ethernet private line that scales cost-effectively, without the need for new customer equipment.

LCAS, which does not have as many supporters, is designed to provide operators with greater flexibility in provisioning virtual concatenation groups (VCGs). This helps adjust bandwidth in service and provide protection options. Someday, LCAS could be used to dynamically adjust bandwidth based on signaling from attached devices, such as switches or routers, but that may take a while (lest it suffer the fate of ATM switched virtual circuits). In the meantime, LCAS will likely be used for scenarios when a customer requests more bandwidth on an Ethernet private line.

At the OFC conference last year, a representative from SBC Communications Inc. (NYSE: SBC) said he hoped to manage their edge network as a single logical element, via a common management system. This multiservice edge would support just about any network protocol imaginable, including things such as TDM, Ethernet, storage traffic, and digital video. All of this would be transported over their Sonet-based network via well accepted standards. GFP, along with virtual concatenation and LCAS, is making this vision possible.

Today, most vendors are working on adding GFP interfaces to their Sonet ADMs, while a few router vendors are adding GFP to their POS interface cards to support virtual concatenation of POS links directly from the router. You’ll even see some Ethernet switch vendors implementing GFP interfaces as an alternative to POS.

Looking at vendor developments today, there are two main classes of GFP product:
    1) Multiprotocol Metro Switch: An OC48 or OC192 Sonet system with ports for TDM, Ethernet, and in some cases storage or RPR using GFP to provide a standardized method of mapping and framing. As this model evolves, look for new visions of a “GFP Switch,” a sort of black box with GFP on the outside, circuit and packet switching on the inside, providing a true multiservice edge platform.

    2) Multiprotocol CPE/CLE: This comes in the form of a pizza box or an even smaller, cheaper wall unit that sits in a wiring closet and provides direct access from a subscriber to a carrier's transport network, supporting a mix of Ethernet and TDM on the client side and an OCx port on the network side. Fiber is still required to the building, but these are the key customers an out-of-region ILEC intends to poach. The multiprotocol CPE is under development today, but not much is shipping. Look for lots of announcements later this year.
Ready for takeoff

So are the customers really biting? So far, the answer seems emphatically yes, and this applies to worldwide markets. In North America, the incumbent local exchange carriers (ILECs) are planning to attack their competitors out of region using GFP to take services from subscribers (T1s, Ethernet, and even storage, in some cases) and backhaul them over leased circuits to their metro POPs. The invading LEC can buy a private line from the incumbent that connects directly from the customer to the invader’s POP, so no network equipment need be collocated in the incumbent’s central office, avoiding the associated access charges and crossconnect charges. The ILECs may find themselves freed of CLECs, but now they must face each other, and it will certainly get ugly. GFP gives them an interesting tool, if they choose to go that route.

This backhaul model is interesting – it creates the need for a very scaleable aggregation platform for GFP-based transport services. It may come as small surprise that Lucent, Nortel and Tellabs Inc. (Nasdaq: TLAB; Frankfurt: BTLA) have devoted significant resources to the Lambda Unite, OPTera Connect, and 5500 NGX, respectively; this must certainly fuel the hopes of startups in this space, such as Mahi Networks Inc. and Polaris Networks.

But the open question remains: Is all this talk of next-generation Sonet/SDH just forestalling the inevitable, throwing good money after obsolescence? If your plan really is to head out of region and snatch customers away from rivals, why not look to a next-gen pure-packet solution? Putting multiple services over a shared packet infrastructure certainly appears to be more efficient than working with Sonet, even if GFP and virtual concatenation give you greater control over circuit provisioning. But let’s remember that these are ILECs we’re talking about – and that includes ILEC sales people, support personnel, and back-office managers. They’re used to dealing with rock-solid transport systems. The new money is still in basic connectivity services such as Ethernet private line, storage transport, and virtual RPR rings among multiple corporate locations. The ILECs know how to do transport, and that’s where I would put my bet. GFP is a good card to play in this market.

In 2003 you’ll start seeing GFP show up in marketing material, product brochures, and grand visions of a unified transport network architecture. GFP makes for good positioning, though someone needs to come up with a better name: Future Sonet? The Next Next Sonet? Not Your Father’s Sonet? Brave New Sonet? Well... It obviously won’t be me.

— Scott Clavenna, Director of Research, Light Reading
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straight shooter 12/5/2012 | 12:39:30 AM
re: GFP: Good For Positioning Scott,

Good article. But... I would encourage you to dig deeper into parallel activities in out-of-region competitive situations in the EU and Asia and how this might apply back to the U.S. and hopefully translate into smarter domestic ILEC behavior/initiatives.

When you do this analysis, it becomes obvious that the true way to success for an incumbent carrier (again, look at out-of-region initiatives in China and Western Europe) is to build the lowest cost, highest scale local infrastructure and get their costs (capital and operations) down to 1/10th the embedded competitive network. I can guarantee this doesn't happen with a GFP/LCAS "band aid" to SONET/SDH! It comes with next generation packet based infrastructure. If U.S. ILECs don't recognize this soon, I guarantee they will be "taught" by Asian and European competitors that are proving in competitive initiatives close to home (for now) and are ready (soon) to leapfrog the slow-moving domestic ILECs on their home turf.

In the end, this is why GFP will be, as you say, "Good For Positioning" versus "Good For Deployment" or, maybe should I say, GFD, "Good For Dinosaurs".
zettabit 12/5/2012 | 12:39:29 AM
re: GFP: Good For Positioning Scott,

You do a major service to SONET/SDH transport networks in positioning them as purely circuit-based "pipes" without GFP.

You are right to say that the traditional (ie: pre-RPR)SONET/SDH systems are not adapted to carrying burtsy data traffic.

But over 5 years ago Cisco introduced DPT, Nortel introduced iPT, and the two were merged along with contributions from others (ie: Luminous) into the RPR protocols, that are available today as a standard blade off nearly all SONET/SDH vendor's boxes. RPR specifically addresses the issue of "efficient" packing of bursty data traffic into SONET payloads through the use of spatial protocol re-use that enables statistical muxing of multiple data demands, highly flexible and variable bandwidth allocation, and different classes of service while still retaining the current levels of network availability through SONET protection protocols.

GFP on the other hand is primarily a "packaging" protocol for traffic types other than DS-1/3, VC-4 etc... It delivers on SONET/SDH's 15-year old promise to enable any protocol to be "packaged" into a SONET/SDH payload, and is being enabled to allow GbE, FC etc... transport over an existing installed base of SONET/SDH transport systems. A big benefit is that by using GFP existing SONET/SDH overhead can be used for performance monitoring to guarantee an end-end performance of the data signals, which cannot be done when these are mapped directly to a wavelength via a transponder.

From a bandwidth efficiency standpoint, which from the introduction of your article seems to be the main point of your article, RPR does a lot more to enable more efficient TDM bandwidth use than does GFP.
straight shooter 12/5/2012 | 12:39:27 AM
re: GFP: Good For Positioning Zettabit,

In the end though, whether RPR or GFP, both are just "blade" enhancements and are constrained by SONET/SDH envelopes. Try to create a 20K endpoint VPN/TLS offering as are currently demanded and/or in deployment in Asia and the SONET/SDH solution breaks. For a carrier to create a successful business model in an increasingly data-dominated service mix you must make these economics work, i.e., break this barrier.
Scott Clavenna 12/5/2012 | 12:39:26 AM
re: GFP: Good For Positioning Very good point. GFP does little for bandwidth efficiency on its own, other than providing lower overhead than other mapping schemes. Combined with virtual concatenation, particularly lower order VCAT, it does a better job. RPR can improve further on that efficiency by supporting statistical multiplexing on the ring and spatial reuse of ring capacity. That comes at a cost of service provisioning complexity, but some carriers seem willing to take the plunge as of late, though few incumbent operators.

RPR's fate within incumbent operators in many ways seems tied to the success of GFP, which provides a standardized method of mapping the RPR MAC to SONET/SDH, enabling these carriers to deploy virtual RPR rings over their existing SONET/SDH infrastructure. And, of course, RPR's success is tied to vendor's ability to provide a solution that is much easier to install, provision and manage than what is shipping today.

Scott Clavenna 12/5/2012 | 12:39:25 AM
re: GFP: Good For Positioning In many ways I agree with you. I think many carriers are already finding that the customers most aggressively demanding Ethernet services are asking for rates over 100 Mbps, which at some point does not make economic sense to put over SONET/SDH infrasturcture, even if it is better at adapting Ethernet traffic to SONET payloads.

But, it's important to recognize that when an ILEC looks out of region, they must weigh the supposed economic benefits of new pure-packet infrastructure relative to service pricing, against the costs of training, management, new backoffice systems, lack of true private line support, etc.

My feeling is that the GFP-based solutions will give ILECs the confidence to move quickly and tactically out of region (cheap IAD with Ethernet and T1s). If they wait to get comfortable with pure-packet solutions, it could take years. That time may come, but I think GFP/next-gen SONET will dominate their thinking (for good reason) for years. Overseas is a differnet story, particularly in Asia. In Western Europe GFP is doing quite well.

shadowandlight 12/5/2012 | 12:39:24 AM
re: GFP: Good For Positioning http://www.mangrovesystems.com...

Look out! Someone's been drinking Jonathan Reeves kool-aide...

mordecai 12/5/2012 | 12:39:23 AM
re: GFP: Good For Positioning What you RPR advocates are forgetting is that service providers who HAVE infrastructure are not likely to spend to get a NEW ONE. SONET is out there already, and paid for. (PS this goes for you metro DWDM/CWDM guys as well...)

GFP outflanks RPR any time on this front. GFP can simply sit on the edge of the network and use those dumb old pipes to make nice crisp new dollars.

What else matters these days?

Who would seriously deploy a new network technology broadly just to enable new (cheap) services, when they can use what they already have to get the same revenue dollars?

Challenge to RPR people--tell us all how you can make incremental revenue on a carrier's network via RPR? How can you couple the first dollar spent on equipment to the first revenue dollar?

Please don't say I have to deploy RPR all over the network just to sell some stat-muxed packet service so my web surfing is a bit less expensive. You have to do better than that mkay?

gea 12/5/2012 | 12:39:21 AM
re: GFP: Good For Positioning Scott:
I didn't see any reference to G.709, the so called "digital wrapper". Though not a super-believer in it myself, G.709 plus GFP is supposed to form a complete zoo of transport kritters for pretty much any protocol. (Of course, GFP can/will operate over SONET too, but G.709 seems to have some special 'hooks' built in for GFP.)
Care to comment?
zettabit 12/5/2012 | 12:39:21 AM
re: GFP: Good For Positioning Mordecai,

In answer to your post, the real beauty of RPR is that it can be deployed as a blade into an existing vendors' (Nortel, Alcatel, etc...) box. Obviously the SONET/SDH ring has to have unused capacity (if it didn't then you'd be in the "overbuild" scenario you say is not the case), and you would then add an RPR blade for any data traffic you wanted to carry IN PARALLEL with your existing TDM traffic. This is exactly what Nortel is offering off their successful Metro 3500 box.

The only vendors that get screwed by the "installed base" argument are the ones that are positioning the need for a NEW box to do RPR. That is what Luminous is doing, and their long-term prospects are bleak given that RPR is now a standard and blades will be available from all the incumbent SONET/SDH vendors for their legacy transport boxes.
Scott Clavenna 12/5/2012 | 12:39:13 AM
re: GFP: Good For Positioning I guess what might be interesting in regard to digital wrapper is the ability to pack multiple traffic types into a single wavelength using GFP. An edge "GFP switch" could be designed in such a way as to "pack" wavelengths as efficiently as possible, using an OTN mapper that encapsulates packets using GFP and aggregates them into OPU-n payloads.

This would require that the carrier support digital wrapper end to end, I think, which would be a non-starter here. I don't think any do in North America. There are a few overseas, mostly Lucent customers, that do.

Might be an interesting way to kick start wave services, though. Deploy digital-wrapper-enhanced wavelengths to customers and let them use GFP-based edge switches to put all their traffic onto a managed wavelength. Each of the services the customer puts on the wave can be managed independently using GFP, while the wave itself can be managed and protected via digital wrapper.

Again, the drawback here seems to be tge need to deploy digital wrapper all through the network. When using GFP-over-SONET/SDH, the core network remains untouched. A big plus in this market.

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