The new products show Cisco continues to invest in silicon and proprietary software to gain an edge over competitors, even as it embraces standard interfaces such as OpenFlow that aim to level the playing field.
Cisco’s Nexus 6000 will pack up to 384 10G or 96 40G Ethernet ports with a port-to-port latency of one microsecond. The company claims it has three times as many ports and a fraction of the latency of switches from Arista Networks, Juniper and others in high-end data center and service provider markets.
At the heart of the switch are two ASICs that form a three-stage Clos network. In an effort to lower the latency of the existing Nexus 5000, engineers took the radical approach of throwing out the scheduler block in the fabric ASIC.
“A packet goes across the fabric and sometimes collides with another packet and you sort out the collision--its going back to [the roots of] Ethernet,” said Peter Newman, a principal engineer who worked on the chips. “The trick to making this work is making sure there’s enough bandwidth in the fabric so there aren’t too many collisions,” he said.
Cisco packed into the fabric chip 192 input and 384 output serdes each running at 14 Gbits/s. They are linked on a crossbar switch with an arbiter but no buffer or storage.
“It’s not a lot of logic, just I/O,” said Newman.
The port chip is more complex, making up the first and last stages of the Clos network. It supports cut-through forwarding, can queue up to 320 Gbits of egress traffic, includes forwarding tables supporting layer-3 look ups and a large memory switch.
The switch is in some ways ahead of the market. Server chips supporting 40G Ethernet are just starting to ship, and none have yet arrived for the Fibre Channel over Ethernet variant that handles both networking and storage. Cisco’s server group has such a chip, but it