Hello Sunny,
for firewalls we can measure the performance in terms of max sessions and max session rate served (sessions/sec) that can be handled because a firewall inspects each TCP session that attempts to go through and has to build a stateful entry for it (if stateful).
For a C7600 acting as a router the number of TCP sessions that are going through is not really important: traffic is switched at OSI L3 and the router does not suffer from the number of TCP sessions but it is more important the traffic volume and the potential for oversubscription in each linecard.
The only aspect where the number of distinct flows counts is in the netflow accounting: there are limits in the netflow local table size and the more flows are seen the more accounting packets should be exported.
Depending on the supervisor in use you can face scenarios where the system is able to foward a given level of traffic with no problems but traffic variety (n. of traffic flows) is so big that the system is not able to account for all flows and there misses in the netflow accounting.
With this kind of device, aa multilayer switch, this is a possible scenario.
So from a performance point of view the number of connections on a router is not a parameter used to characterize it: you can use packet per second and traffic rate.
You should use the datasheets for supervisor and linecards to understand if you are near any limit or beyond.
Hope to help
Giuseppe
