What is the required prefix for routing calls across a Master Bridge with 3-digit extensions to a Slave Bridge with 4-digit extensions?

When routing calls across a Master Bridge with 3-digit extensions to a Slave Bridge with 4-digit extensions, it is essential to use a mandatory prefix. This requirement is in place to differentiate between the extension lengths of the calling and receiving systems. Because the two bridges handle extensions of different lengths, a prefix serves as a clear identifier to ensure that the call is routed correctly to the intended destination.

The prefix acts as a mechanism for the system to recognize that it is dealing with an extension on a different bridge, making the necessary adjustments in processing the call. Without a mandatory prefix, there would be ambiguity in the routing process, leading to possible call failures or misrouted calls. Therefore, using a specific prefix is crucial for maintaining clarity and accuracy in inter-bridge communications.

In contrast, while calling rules can sometimes allow for optional prefixes, this particular scenario mandates their use to ensure successful communication between the distinct extension formats of the Master and Slave Bridges. The other options do not adequately address the routing requirements needed to maintain proper call connectivity, especially when dealing with extension discrepancies.