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Multilink Makes Sonet Flexible

Claims that its new framer chip makes it possible to adjust the size of Sonet channels on the fly

May 27, 2002

3 Min Read
Multilink Makes Sonet Flexible

Components vendor Multilink Technology Corp. (Nasdaq: MLTC) is the latest vendor to jump on the next-gen Sonet bandwagon.

Tomorrow Multilink is planning to announce the first chip in what it calls its "intelligent edge" portfolio. Part number MTC6210 is an OC192 Sonet framer chip offering a bundle of new-age Sonet features, including virtual concatenation, GFP (generic framing procedure), LAPS (link access protocol-SDH), and LCAS (link capacity adjustment scheme).

Acronym overload? In a nutshell, all these protocols aim to provide more efficient ways of transporting packet-based data over Sonet. GFP is the latest way of encapsulating Ethernet and other protocols for transportation over a Sonet-based infrastructure. LAPS does the same thing for SDH.

Virtual concatenation is a technique for "right-sizing" Sonet channels so they can carry data traffic without wasting bandwidth -- by grouping an arbitrary number of STS1 (51.8 Mbit/s) units together. (For a more detailed explanation, see PMC Pushes Sonet Silicon.)

LCAS is the really cool bit. It allows hitless switching of the virtually concatenated groups. In other words, the size of the data pipe assigned to any one customer can be changed at any time without affecting the data carried on any of the other channels. With this ability, a service provider could assign different bandwidths to the same customer at different times of day, giving them extra bandwidth for nighttime backups, for example. This is a far cry from today's Sonet networks where provisioning some types of circuit can take weeks or even months.

All this is a foray into new territory for Multilink, which previously didn't have any Sonet-specific chips in its portfolio. Its traditional product lineup includes mux/demux chips, modulator drivers, forward error correction (FEC) chips, and optical modules.

According to Tom Spencer, Multilink's senior marketing manager for intelligent edge products, the company hoped that it could leapfrog its competitors by entering the next-generation Sonet market at OC192 (10 Gbit/s). To date, the key players in this market -- including Agere Systems (NYSE: AGR), Agilent Technologies Inc. (NYSE: A), and PMC-Sierra Inc. (Nasdaq: PMCS) -- only offer OC48 (2.5 Gbit/s) products (see Agilent Boosts Ethernet-Over-Sonet).

Although Multilink appears to have fulfilled his ambition as the first company to announce an OC192 part, it will be four or five months before the product starts shipping. So it's possible that other companies, if their policy is to ship products before making announcements, could get to market first. All the vendors with OC48 parts are likely to be developing OC192.

Nevertheless, Multilink reckons that its chip will stand out in a crowd. No two virtual concatenation framers are alike, Spencer says, and customer contracts live or die by the details.

Multilink has one of the first virtual concatenation parts to support the SPI4.2 interface, which is becoming the de facto standard for interconnecting with network processors on the system side. That makes it more likely that it can form glueless connections to chips from other vendors.

It's also one of the first chips to support LCAS. The only other announced product that supports LCAS runs at OC3 (155 Mbit/s) -- that's from TranSwitch Corp. (Nasdaq: TXCC) (see TranSwitch Creates a Hybrid).

However, although LCAS sounds pretty wonderful, the standard is still immature and won't be adopted in real-world networks for some time. "Some aspects [of the standard] are ambiguous," Spencer admits. "They could be interpreted in different ways, which could end up making interoperability an issue."

The network infrastructure isn't completely ready to support LCAS, says Jim Shupenis, Agilent's strategic business development manager. It can cope with point-to-point LCAS but cannot handle situations where the signal is split and sent down different routes to the same destination. Agilent is also working on LCAS for its Sonet product line but won't say when it will be ready.

— Pauline Rigby, Senior Editor, Light Reading

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