Marconi Modifies SDH Stance
Marconi's presentation of the MLS (multilayer switch), still in development, emphasized future support of Synchronous Digital Hierarchy (SDH), the predominant mode of optical networking used in telecom networks worldwide. But telecom carriers in the U.S. and Canada rely on Sonet (Synchronous Optical Network) technology, and most telecom equipment makers support both Sonet (Synchronous Optical NETwork) and SDH (Synchronous Digital Hierarchy).
Last week, at least one Marconi spokesman indicated that the company was stopping development of Sonet products in favor of SDH. Presentations at the company's press conference focused on SDH data rates, and press materials specified SDH capabilities, rather than Sonet ones (see Tutorial on Grooming Switches, page 4, for an explanation of the distinctions between the two). This week, Marconi folk say they should have known better.
"We should have clarified what we meant by stopping Sonet development," says spokesman Jim Blew. "We tried to highlight SDH and may have done so to the detriment of Sonet functionality."
Specifically, Blew says Marconi has closed a facility in Montreal dedicated to the production of discrete Sonet add/drop multiplexers and crossconnects -- that did not simultaneously support SDH.
So what Marconi meant to say was that it was stopping development of discrete Sonet products made in Canada, Blew says, like the MCN-7000, which Marconi claimed in 2000 "combines the functionality of an optical cross-connect, add-drop multiplexer and data switch/router into one advanced, high-density SONET access and transport edge device with support for DWDM (Dense Wave Division Multiplexing)." Interestingly, the company has also discontinued the MAS (Multiservice Access System), which in May 2002 Marconi said also supported SDH.
In contrast, products like Marconi's BXR-48000 multiservice switch and the developing MLS will support both Sonet and SDH interfaces equally, Blew says.
The MLS will have grooming of both Sonet and SDH channels, according to Glenn Wellbrock, VP of product engineering. It will compete with the CoreDirector from Ciena Corp. (Nasdaq: CIEN), according to Wellbrock, offering grooming at the STS1 level, Sonet parlance for a 51.84-Mbit/s channel. Marconi's press material says the MLS will groom at the "ODU and VC4 level," ODU standing for "optical data unit" and VC4 being an SDH 139.26-Mbit/s channel. No mention is made of STS1 grooming.
— Mary Jander, Senior Editor, Light Reading