A two-tiered architecture splits the Instant Messaging server deployment into two layers: an access layer and a data layer. In a simplified two-tiered deployment, you might add one or more multiplexors and servers to the access layer. The multiplexor acts as a proxy for users, and relays messages to the Instant Messaging server. The data layer holds the Instant Messaging server database and Directory servers. Figure 20–1 shows a simplified two-tiered Instant Messaging architecture.
Are easier to maintain than one-tiered architectures
Enable the offloading of load-intensive processes like SSL, message reprocessing
Are easier for growth management and you can upgrade your system with limited overall downtime
When you size your multiplexor, the calculation is based on your system load, particularly the number of concurrent connections the multiplexor needs to handle.
In addition, you must:
Add CPU or a hardware accelerator for SSL if appropriate.
Add memory to the machine if the multiplexor is being configured on it.
One or more of each type of machine should still handle peak load without a substantial impact to throughput or response time when you plan for redundancy in your deployment.