IOS Gatekeeper counts twice the layer seven payload of each call in it's CAC decision. For example, a 64kbps G.711 call is deducted as 128kbps. Most importantly though, it does *not* account for any of the Layer 2-5 overhead (Ethernet/MLPP, IPv4, UDP, RTP respectively). You will need to calculate how many calls fit under the 2Mbps (MB and Mb are not the same thing!), then decide what to set the zone bandwidth for based on that.
For example, if your calls are G.711 with RTCP over Ethernet then each call is 99.2Kbps. The 2000kbps link will support 20 concurrent calls assuming it is dedicated 100% to RTP traffic. In reality, that's untrue though (e.g. SIP/H.323, routing protocols, etc) and Cisco recommends that the LLQ priority queue not exceed 33% of the link anyway. So, how many calls would fit into the 33% or 667Kbps LLQ queue? That's a total of six. Finally, what value do you put in IOS GK to represent those six calls? That's 768Kbps, or (64*2)*6.
