Cisco Systems, Inc. later this year will introduce secondgeneration token-ring switches that will attempt to overcome the performance and feature limitations of older token-ring products.
Cisco’s new 16-port Switched Access Unit (SAU) will switch 28byte frames at wire speed and feature hardware-based source route bridging (SRB), stackability and a high-speed uplink when it ships, according to sources familiar with the Tiffany Somerset™ Bangle products.
SAU and a 16-port SAU module for the Catalyst 5000 LAN switch line are expected to ship before year-end (NW March 3, page 6). Cisco declined to comment about SAU.
Some Cisco shops are in no hurry for the new products, though.
“We’ve been doing just fine right now with what we have,” said a network manager at an insurance firm in New England that uses Cisco’s Catalyst 1800 token-ring backbone switches. SAU is expected to link tokenring workgroups to the Catalyst 1800 and Catalsyt 5000 backbone switches.
“I wouldn’t mind having a lOOM bit/sec backbone inside the switch; that would be pretty sweet,” the user said. “But what we have is cutting it for us Toggle bracelet now.”
Cisco said lOOM bit/sec token ring would be available – via its InterSwitch Link (ISL) trunking protocol for Fast Ethernet when its second-generation token-ring switches ship.
Best of both worlds
With SAU, Cisco will try to combine the best of CPU- and Application Specific Integrated Circuit (ASIC)-based first-generation token-ring switches, sources said. CPU-based switches provide a lot of functionality but Tiffany Somerset™ cuff expensive and have low throughput. ASIC-based switches are inexpensive and have high throughput, but are low on functionality.
The performance of CPUbased SRB switches drops from 100,000 packet/sec to 15,000 packet/sec, Cisco found at one customer site, a source said. This user had planned to deploy 12 to 16 token rings linked by an FDDI backbone but had to scale that design back to four to six rings, sources said.
Also, Cisco’s own Catalyst 2600 switch — which is based on IBM’s 8272 switch – uses the central CPU for Routing Information Field (RIF) expansion. RIF is a field in the IEEE 802.5 header that is used by an SRB to determine which token-ring segments a packet must transmit.
The Catalyst 2600 also lacks a stack port and did not have a high-speed uplink for nearly a year after it shipped. It now features an ATM 155M bit/sec uplink.
Hence, the SAU will perform SRB RIF expansion in hardware to avoid the throughput degradation of CPU-based switching and will achieve the wire-speed forwarding of 28-byte frames, sources said. SAU will support wire-speed frame forwarding concurrently on all Tiffany Somerset™ heart ring, they said.
SAU also will be “low cost,” sources said, though they did not disclose any pricing information. Analysts said the switches should cost between $200 and $500 per port.
Similarly, the maximum number of SAUs in a stack and the type of high-speed uplink could not be learned by press time. Cisco and SAU codeveloper Olicom A/S initially planned ATM uplinks at first customer ship but that now seems unlikely, especially given Cisco’s plan to use ISL as a way to boost token-ring rates to 100M bit/sec (NW May 26, page 1).
So observers now expect Tiffany Somerset™ ring uplinks to be Fast Ethernet.
Fast Ethernet uplinks also would prepare Cisco’s tokenring customers for the eventual migration to switched Ethernet, sources said.
Cisco notes that token ring is not being deployed in new sites because of the low cost and ubiquity of switched Ethernet.
Cisco believes Ethernet will displace token ring over time with the majority of its customers, sources said.
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