Cut & pasted from the Frank Coluccio New Tech message board. Surprising how many of these 10 OT's MRVC is active in/with.
Ten Optical Technologies that Rock!
Sam Masud / March 2005
telecoms-mag.com.
With the network equipment spending depression officially over according to the Telecommunications Industry Association (TIA), service providers are starting to refocus on fast-emerging optical technologies that promise to simplify operation and deepen long-shallow revenue streams.
Though it doesn’t always require industry tenure to identify promising technologies, it does require a solid understanding of equipment trends to explain how and where they’re most likely to be used. You needn’t have 20-20 vision to see the allure of optical technologies. But with an eye toward future network planning, determining how to introduce products based on hot optical technologies painlessly is of paramount importance.
With this in mind, we’ve drawn critical information from the industry’s best and brightest minds to guide you in this make or break undertaking. It’s much more than 10 optical technologies that rock. It’s a sorely-needed survival guide for service providers, as network equipment spending climbs and the need for optical products comes into focus. So, rock on!
SFP
A key demand of service providers is flexibility in network equipment. For example, they want to be able to upgrade a port from short-reach multimode fiber to long-reach single-mode fiber. SFP (small form-factor pluggable) transceivers enable this—and much more.
Larger pluggable transceivers called GBICs (gigabit interface converters) have been common for Ethernet and Fibre Channel for some time. What’s new are SFPs for SONET. “With the convergence of data communications and telecom, there now are SFPs for SANs, LANs and the telecom network, so you’re seeing economies of scale,” notes Dennis Karst, product line director for JDS Uniphase.
Until recently, optical transceivers for SONET required the leads to be soldered to the line card. This practice didn’t allow for changing a port in the field. It also required service providers to buy transceivers quickly for all ports of a line card, even if the intention was only to use half of them.
SFPs are a result of an MSA (multisource agreement) among component vendors such as Agilent, Finisar, Hitachi, JDSU and Lucent. The challenge ahead for SFP suppliers is to support wider temperature ranges as increasingly more transceivers with higher data rates are crammed onto a board. Although the market in the past has favored SFPs for copper-based networking due to the success of Gigabit Ethernet, Tom Fawcett, Agilent’s marketing manager for fiber optics product, says the bulk of the market for Agilent is now in fiber-based SFPs.
OTN
It’s easy to confuse the term Optical Transport Network with SONET or WDM. Leaving aside the original intent and various ITU-T recommendations for the OTN, the notion behind the OTN is to provide a reliable, interoperable high-speed optical network.
If the confusion with SONET occurs, it’s because a key standard for the OTN—G.709—borrows many SONET concepts such as monitoring and protection, but adds the concept of the management of optical channels in the optical domain as well as the benefit of stronger FEC (forward error correction). This would allow optical signals to be managed end-to-end without expensive OEO (optical/electrical/optical) conversions.
Because the OTN includes FEC and also provides for the OAM (operations, administration and management) of the optical network, the line rates for the OTN are about 7 percent higher than SONET to accommodate the overhead. However, G.709 is protocol agnostic. This allows protocols other than SONET to be mapped to the payload of a G.709 frame. On the down side, the OTN requires new hardware and management systems.
Companies from large chip vendors such as Intel, to test equipment manufacturers like Ixia, are helping network equipment vendors deliver OTN wares. “Vendors are offering OTN-compliant products, but service providers are implementing OTN in a more evolutionary way,” says Neal Neslusan, marketing director of Applied Micro Circuits Corp.’s transport product group. Still, he believes OTN will level the playing field by enabling service providers to buy multivendor solutions for optical networks.
Widely Tunable Lasers
Service providers long for a crystal ball to tell them where to fire up individual wavelengths. Widely tunable lasers obviate the need for such foresight. These devices from vendors such as Agility, Iolon and Santur are starting to make life much easier for carriers because a single tunable laser, unlike traditional DFB (distributed feedback) lasers used in DWDMs can deliver any wavelength across the popular C and L bands. As a result, tunable lasers not only make it easier for carriers to keep spare lasers on hand, they also reduce a carrier’s inventory headaches. They also make network equipment vendors happy.
The knock on tunable lasers was that they were unreliable and more expensive than DFB lasers. That is not the case when measured against the total cost of a circuit pack, says Kevin Affolter, Agility’s vice president of sales. Moreover, the reliability of tunable lasers is on par with DFB lasers, which have to meet Telcordia specifications, he says.
And whereas tunable lasers previously often required an external modulator—or came with one—the trend appears to be shifting to tunable transponders. They offer a tunable laser and an integrated modulator, as well as a transponder for OEO conversion: ROADMs (reconfigurable optical add/drop multiplexers).
These devices are drawing much attention from carriers as they incorporate either tunable lasers or tunable filters, according to Affolter. Of the two, tunable laser technology is more mature and cost effective. So will tunable lasers that work across both the C and L bands be next?
Wavelength Selective Switch
It’s a king-size carrier headache: Predicting where services might be needed and which sites will need to connect to others. Wavelength selective switches claim to be the Rx for this problem, which is why this technology is being incorporated in ROADMs. In a nutshell, ROADMs enable carriers to easily add/drop a wavelength at any node in the network, in contrast to traditional DWDMs that make manual provisioning of channels a time-consuming and error-prone task.
Several established equipment vendors such as Alcatel, Cisco, Fujitsu, Marconi and Nortel, as well as newcomers like Mahi Networks, Tropic Networks and Movaz, say they have—or soon will have—ROADMs.
Wavelength selective switches and wavelength blockers are viewed as the key technology choices for building ROADMs. And though the wavelength selective switch is the newer technology, some would argue that it is also the more complex technology. The hopes of ROADM vendors are high because the unpredictability of traffic, combined with increased penetration of broadband and emerging IPTV services, is expected to make ROADMs the technology that will give carriers flexibility and scalability in the metro network. Movaz CTO Zouhair Mansourati says the company has a more ambitious ROADM in mind, one capable of handling traffic in four directions, not just east-west traffic supported by single-ring ROADMs.
EPON
Given all the buzz about fiber to the premises from the ILECs, many are betting that higher bandwidth than that offered by current c able modem and DSL technologies will be delivered via EPONs (Ethernet passive optical networks). If ILECs decide to deploy EPONs as a last-mile technology, they’ll likely be trailing their counterparts in the Asia/Pacific countries. Passave, a start-up EPON silicon supplier, already claims to have shipped more than 2 million EPON ports, mostly to the Far East. NTT and Softbank have deployed EPONs in Japan. According to Sal’ee, they’re even replacing DSL with EPON in some places.
EPONs are attractive to service providers because they don’t require active electronics at any intermediate point between the CO and subscriber. This fact simplifies network operation and maintenance, thus reducing costs. A single shared fiber goes from the optical line terminal in the CO to an optical splitter, at which point separate strands fan to optical network units located at or near individual subscribers. Ratified as an IEEE standard 802.3ah in mid-2004, EPONs provide a Layer 2 network with usable bandwidth of 1.2 Gbps.
There is a built-in comfort factor with an EPON because it uses Ethernet with all services—voice, data and video—delivered via IP. But it may get plenty of competition from a rival technology, GPON (Gigabit PON), which proponents say supports more services, such as TDM-based voice, ATM, leased lines and Ethernet. Defined by the ITU-T G.984 group, a GPON operates at line speeds of up to 2.5 Gbps. GPON, however, has a higher overhead than EPON. Alcatel, which supplies both Ethernet and the more mature APON (ATM-based PON) solutions, believes that if the success of DSL is an indicator, the ITU approved GPON technology may have an edge. In the end, carriers voting with their wallets will decide.
Storage Over SONET
Led by the financial sector, enterprise customers have until now taken a do-it-yourself approach when it comes to extending a SAN (storage area network), typically over their own short-distance DWDM networks. The need to have continuous access to information, even in the face of a power failure or natural disaster, has raised the consciousness of businesses and is leading them to place data centers at greater distances from each other. Because of this, carriers like AT&T, Verizon and AboveNet see an emerging market for SAN extension services.
Whereas previously TDM-based SAN extension solutions were made for low-speed lines (T-1/T-3), equipment vendors such as Cisco, Ciena and Nortel, as well as service providers, see a small but growing market for extending corporate SANs in a way that leverages the installed SONET infrastructure.
Indeed, the ubiquity of the SONET infrastructure makes it more suitable for asynchronous replication of data over long distances than the synchronous mirroring for high data availability since the latter is less tolerant of distance delays. SONET vendors that play in the SAN extension place have a method to map Fibre Channel to SONET and to use SONET bandwidth in a more granular fashion. They have also implemented a buffer-to-buffer credit management scheme (a concept analogous to the TCP window) to ensure there is no loss of data as it goes from one SAN to another across the SONET infrastructure.
Managed CWDM
Until recently, CWDM (coarse wavelength division multiplexing) has been the much overlooked metro optical technology. But this may be starting to change. Initially deployed by enterprises in a private fiber network, service providers are now starting to look to CWDM to offer protocol-agnostic managed optical services. CWDM vendors Adva Optical Networking and Ciena both say that CWDM has found early traction in Europe.
“Now carriers in North America are interested because CWDM offers a 30-percent-to-50-percent cost savings over DWDM,” says Per Hansen, Adva Optical Networking’s director of infrastructure business development. “Carriers also have a success-based business model [for offering managed CWDM], where they have a verified customer even before they deploy the equipment, which gives them a quick payback.”
The prospect of managed CWDM services taking off has raised expectations of optical equipment vendors such as Adva (which has OEM agreements with Fujitsu and Siemens), Alcatel, Ciena, Cisco and Nortel.
Perhaps one reason carriers in North America have been slow to offer managed CWDM services is because of the large deployment of DWDM systems, initially in the long-haul but increasingly in the metro, notes Glenn Thurston, vice president of marketing for start-up BTI Photonics. Although the wide channel spacing means CWDM systems support fewer channels than DWDM, lower-cost optics and lower-power consumption makes CWDM extremely price competitive.
CWDM may also be getting a boost because of a mid-2002 ITU-T standard that supports 16 channels whereas formerly CWDM channel spacing was propriety. Additionally, amplification is being added for CWDM to operate over greater distances. And though 2.5-Gbps channel is still the norm, some CWDM also supports 10-Gbps channels. Moreover, it’s no longer an issue of one or the other because many vendors offer both CWDM and DWDM in one platform. For these reasons, vendors are optimistic about CWDM having increasing importance as a last-mile technology and as a metro access technology for various types of traffic.
Ethernet Over SONET
At first blush, Ethernet over SONET may sound incongruous, since data-oriented Ethernet is supposed to show voice-centric SONET a thing or two about bandwidth and cost. In fact the early adopters built Ethernet networks for LAN-to-LAN connectivity and/or Internet access.
Although going pure Ethernet is a valid strategy, advances in next-gen SONET gear have made for a happy marriage between Ethernet and SONET. These systems use generic frame protocol for encapsulating Ethernet as well as other data traffic to SONET; virtual concatenation to make more efficient use of SONET bandwidth; and link capacity adjustment schemes for increasing or decreasing SONET bandwidth allocated for the data traffic.
Still, these technologies only serve as a foundation for efficiently handling Ethernet across a SONET infrastructure, not for reducing the cost per bit, according to Rajiv Ramaswami, vice president and general manager of Cisco’s optical transporting group. “If you sell a 10-Mbps Ethernet pipe, the cost per bit would be no different than if you sold a T-1 or T-3,” he says. The real reduction in per-bit transport comes from taking advantage of statistical multiplexing offered by packet technologies.
In other words, statistical multiplexing must occur not just at edges where Ethernet switches reside but at all SONET nodes in the network to maximize the SONET infrastructure. For example, the benefit here is that if 10 subscribers each have a 1 Mbps Ethernet connection, the service provider might only perhaps need to reserve 3 Mbps of bandwidth within the SONET. Additionally, this will also enable service providers to offer differentiated services, from best effort to offerings with SLAs.
Gigabit Ethernet
It says much about Ethernet that 30 years after its advent it’s still attracting so much attention. The reasons for this are its ubiquity in the LAN and downward spiraling prices even as line rates go up. Aside from the fact that it’s been shipping in 1 Gbps and 10 Gbps versions, another testament to its maturity and scalability is that Ethernet is fast positioning itself as a carrier technology.
ILECs are using GigE to backhaul traffic from IP DSLAMs and cable operators to do the same for traffic from CMTSs, in both instances replacing what were ATM/SONET connections. If both ILEC and cable operators can install fiber close enough to customers, Ethernet will be the preferred means for delivering a triple-play to residential subscribers and high-speed LAN connections to businesses.
Through the efforts of the Metro Ethernet Forum, Ethernet has been groomed to enable service providers to offer E-Line (point-to-point) and E-LAN (multipoint-to-multipoint) services so that dispersed subscriber locations appear as if they were on the same LAN. The group has also joined hands with the IETF to extend E-LAN Ethernet connectivity across an IP multiprotocol label-switched network. Such efforts could make Ethernet the VPN of choice for business customers of all sizes.
Additionally, a new standard in development by the IEEE 802.1ah working group for “backbone provider bridges” aims to address the scalability and security issues that arise when multiple services are delivered to an increasing number of subscribers over a single link.
SOAs
Though hot and promising, SOAs (semiconductor optical amplifiers) have not gained traction in the equipment component maker community but likely will in the not-too-distance future, according to industry visionaries. The allure of SOAs is that they are expected to go a long way toward shrinking the size of network elements, which should be quite appealing to cost-crunching equipment vendors.
SOAs present a wait-and-see situation for the optical networking segment of the telecom industry. Hot optical technologies like SOA certainly need to gain traction with major equipment vendors, but it often takes this group some time to make a business case for a specific product segment with potential. That process could get a much-needed boost according to Dana Cooperson, optical network group director at RHK. “SOAs may also help push new applications that rely less on optical line amplifier-based systems.”
It remains to be seen, however, what the interest level in SOAs is from vendors such as Nortel. The largest optical equipment makers, in turn, are waiting to see if and when component suppliers show commitment to SOAs, analysts say.
The less-than-rapid emergence of SOAs may be attributed in part to the priorities of the industry leading component vendors, which is understandable. While SOAs do promise benefits, at least in concept, industry kingpins such as JDSU have been hard at work over the last several months on TOSAs (transmitter optical sub-assemblies). In fact, several leading players signed a multisource agreement in the TOSA space..
Sam Masud is a contributor for Telecommunications® magazine (sam7861@hotmail.com). |
