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July 1998 By Peter Heywood Product Leaders: Packet Over Sonet A Switch in Plans CSR's Coreswitch80 solves the capacity crunch at the core of router nets by running packets over Sonet Gigabit ethernet or ATM? Central System Research (CSR) has another answer for network architects looking to cure the congestion at the core of routed IP backbones. Its Coreswitch80 is the first implementation of Mapos—a new packet-over-Sonet scheme from Nippon Telegraph and Telephone Corp. (NTT, Tokyo). Mapos handles IP at ATM speeds—155 or 622 Mbit/s—without the latter's complexity. Unlike ATM, it's a connectionless protocol: There's no need for a Mapos switch to set up and tear down thousands of circuits a second. According to its creators, that translates into greater reliability and simpler management. What's more, Mapos (Multiple Access Protocol over Sonet/SDH) doesn't suffer from gigabit Ethernet's distance limitations: It can be extended globally over carrier services. MORE INFO Prouct Summary But it's not all smooth switching. Mapos is strictly proprietary. Until it becomes a standard, router vendors are unlikely to write software drivers that let their gear work with the Coreswitch80. What's more, the protocol can't prioritize traffic. Swifter Switch The Coreswitch80 from CSR Corp. (Tokyo) boasts an 87-Gbit/s backplane and 16 module slots. The vendor also sells 155/622-Mbit/s adapters that can link servers or power-user desktops directly to the switch. CSR says that 2.4-Gbit/s adapters are in the works and claims there's no reason the switch can't scale to 10 Gbit/s. The most likely configuration for a Coreswitch80 would be connected directly to backbone routers ( see the figure ). The box can deliver high-speed traffic over copper (to 100 meters) or fiber (to 40 kilometers). Longer-haul connections can be made over Sonet (synchronous optical network) or SDH (synchronous digital hierarchy). Multiple Coreswitch80s also could be deployed in a ring, star, or mesh. At The Core of routed Nets CSR switches exchange control packets to determine the best path through the network and use spanning-tree to prevent broadcast storms. Mapos subnets should be separated by routers and should connect no more than 200 IP hosts, says Ken Ichiro Murakami, senior research scientist at NTT Laboratories and principal inventor of Mapos. As indicated, Mapos creates a connectionless LAN—a good match for connectionless IP traffic. Further, according to NTT, Mapos is a self-discovering protocol: New devices can be added to a network without registering them in a database. ATM (asynchronous transfer mode), in contrast, forces net managers to manually reconfigure their networks each time they're changed. Finally, NTT indicates that Mapos can deal with 64-kbyte frames, so there's no overhead associated with dicing and slicing frames into cells. NTT also says that Mapos finishes out in front of gigabit Ethernet. It can carry t raffic over virtually unlimited distances and has the potential to operate at much higher speeds. And since it runs over Sonet or SDH—both of which reroute traffic around failures—it can deliver more resilient connections. Other Schemes Mapos isn't the only packet-over-Sonet (POS) scheme out there. Both Cisco Systems Inc. (San Jose, Calif.) and Ascend Communications Inc. (Alameda, Calif.) already sell point-to-point POS software for their routers. However, Mapos alone can be used on mesh networks. Still, it's not clear when—or if—Mapos will make it onto the enterprise. For that to happen, router vendors will have to rally behind the protocol and write software drivers for it. CSR claims it has sold 50 cards and software developers kits to U.S. router manufacturers. NTT is promoting the protocol as a global standard and has published details in IETF RFCs 2171 through 2176. It also has set up a Mapos Alliance, whose members include Cisco. (For more informati on visit http://www.MAPOS.org) But Cisco see Mapos differently. "It's not a commercial option, and we don't think it will become one," says Edward R. Kozel, senior vice president at Cisco. The router vendor worked with NTT to create Mapos drivers for its Cisco 12000 but says that was for demonstration purposes only. Whether or not Cisco is right remains to be seen. It's still early days, and NTT is building an experimental Mapos MAN (metropolitan-area network) in Tokyo. It's not going to come cheap, though. The Coreswitch80 chassis costs $111,000; modules run roughly $15,000; adapters, about $6,000 each. Still, the Coreswitch80 delivers more for the money than high-end ATM switches like the ASX-4000 from Fore Systems Inc. (Warrendale, Pa.). Fore's switch costs roughly the same but has about half the backplane capacity. [ Home ] [ Registration | Subscriptions ] [ Contact Us | E-Mail ] Home Contact Editors Lab Tests Registration Tech Tutorials Buyer's Guide Global Networks Opinion / Columns FAQs Subscriptions