Bill,
Techprefix is a prefix used for routing by the gatekeeper. If there are multiple gateways in a zone and when gatekeeper needs to the route the call, the gatekeeper checks the techprefix that was received in the call to route it to the appropriate gateway. If a techprefix was not found in the incoming call setup, and a default tech prefix is configured, calls will route to the gateway associated with the default tech prefix. Kind of like a gateway of last resort in the routing and switching world.
Bandwidth is controlled per zone, between zones or within a zone using bandwidth total commands. This has nothing to do with tech prefixes.
HTH
Sankar
PS: please remember to rate posts!
Sankar Nair
UC Solutions Architect
Pacific Northwest | CDW
CCIE Collaboration #17135 Emeritus