Unfortunately, because vendors have not yet implemented a common set of codecs, you will face interoperability problems with large-scale deployments. But G.711 requires 64 Kbps of continuous bandwidth for every network end point. The H.323 standard also specifies a laundry list of more efficient codecs that may be used. G.729, which uses 8 Kbps at each end. To complicate matters, some first-generation products support G.723.1 while others support G.729.
Security is another major consideration.
In version 2 of H.323, encryption and authentication are optional, though most implementations include no security protections at all. As a result, an H.323-aware network analyzer becomes an effortless wiretap. If you're on a shared-media network, anyone can monitor any conversation without ever leaving his or her desk. Another problem is network congestion, an inevitable result of the high-utilization levels engendered by widespread deployment of G.711. To deal effectively with the congestion, you need to implement prioritization services at the physical, data-link and network layers of your enterprise network.