Cisco virtual switching technology vs. Nortel split multi link trunking

Phil Edholm, Nortel enterprise CTO has posted his take on Cisco's upgrade last month to the Cisco Catalyst 6500 that improves the product's ability to support real-time enterprise communication and collaboration. The Virtual Switching System feature effectively allows users to combine multiple 6500 switches into one, thereby pooling switch bandwidth to increase performance.

Edholm, in his blog post, gives the following comparison between Cisco VSS and Nortel's Split Multi Link Trunking (SMLT) technology, which has been available for a number of years.

The following are Edholm's observations taken from his blog, in his own words:

* It would appear that Virtual Switching System (VSS) is only available on the top-of-the-range, fully-loaded Catalyst 6500 Switch. Fitted with the Supervisor 720-10GE module; the Virtual Switch Link (VSL) must be made with 10G Ethernet connections, using either the 10G ports on the Sup720 or those on the X6708-10GE with DFC3/CXL Interface module.

* In order for the system to work, it appears all interfaces in the chassis must have the latest DFC functionality installed, potentially causing an expensive upgrade for any older modules. SMLT, on the other hand, works across all the modules in a Nortel 8600 and does not require card level upgrades or specialized interfaces.

* The Cisco VSS seems to essentially turn two switches into a single chassis by connecting the control processors together across the VSL. While in some cases this may have limited advantages in configuration and management, it would appear to have serious implementation drawbacks. Between two switches operating as a VSS pair, there can only be 2 Sup720 modules. This means that when there is a failure or other reason to take one of the chassis down (for re-configuration for example), the remaining chassis will only have a single processor, exposing it to failure issues. In the Nortel implementation, each chassis can have both a primary and secondary processor, essentially doubling the overall redundancy at minimal cost.

* It is not clear if or how the VSS can interoperate with open MLT access devices such as wiring closet switches and server NICs. A critical strength of the SMLT solution is seamless integration with standards based MLT devices.

* Nortel SMLT has been identified by VMWare as the optimal solution for multi-connections in a VMWare virtualization environment. While it appears that the VSS uses software in the access devices for some levels of functionality, it is not clear whether or how it performs in an open multi-vendor environment and how this limits functionality when the devices are not Cisco.

Does Nortel have a point or is Nortel SMLT past its prime?

See also: Nortel: Get out of the Cisco rut

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