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Stacking capacity is how much traffic can be sent via backplane through stacking cable. Catalyst 3750-x has 32 Gbps per stacking cable which is 64 Gbps in each direction or 128 Gbps in marketing speak.http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps5023/prod_white_paper09186a00801b096a.html
My understanding of the StackWise Plus, it offers just 64 Gbps across both stack ports. Cisco's "marketing speak" usually describes StackWise as having 32 Gbps and StackWise Plus 64 Gbps. Also from your reference:
Technology Overview
Cisco StackWise technology provides an innovative new method for collectively utilizing the capabilities of a stack of switches. Individual switches intelligently join to create a single switching unit with a 32-Gbps switching stack interconnect. Configuration and routing information is shared by every switch in the stack, creating a single switching unit. Switches can be added to and deleted from a working stack without affecting performance.
Bidirectional Flow
To efficiently load balance the traffic, packets are allocated between two logical counter-rotating paths. Each counter-rotating path supports 16 Gbps in both directions, yielding a traffic total of 32 Gbps bidirectionally. The egress queues calculate path usage to help ensure that the traffic load is equally partitioned.
StackWise Plus
StackWise Plus is an evolution of StackWise. StackWise Plus is only supported on the Cisco Catalyst 3750-E and Catalyst 3750-X switch families. The two main differences between StackWise Plus and StackWise are as follows:
1. For unicast packets, StackWise Plus supports destination striping, unlike StackWise support of source stripping. Figure 9 shows a packet is being sent from Switch 1 to Switch 2. StackWise uses source stripping and StackWise Plus uses destination stripping. Source stripping means that when a packet is sent on the ring, it is passed to the destination, which copies the packet, and then lets it pass all the way around the ring. Once the packet has traveled all the way around the ring and returns to the source, it is stripped off of the ring. This means bandwidth is used up all the way around the ring, even if the packet is destined for a directly attached neighbor. Destination stripping means that when the packet reaches its destination, it is removed from the ring and continues no further. This leaves the rest of the ring bandwidth free to be used. Thus, the throughput performance of the stack is multiplied to a minimum value of 64 Gbps bidirectionally. This ability to free up bandwidth is sometimes referred to as spatial reuse. Note: even in StackWise Plus broadcast and multicast packets must use source stripping, because the packet may have multiple targets on the stack.
This I've taken to mean, the bidirectional bandwidth of the pair of StackWise Pluse stack cables is 32 Gbps, duplex, and that each stack port is 16 Gbps, duplex.
Regarding the "minimum value", this is in reference to StackWise Plus's "spatial reuse", which allows a stack ring, of more than two members, to increase its aggregate bandwidth. More details of this can be found in (Cisco's) RFC 2892.
