NAC/NAS Address Resolution

When dialing a number from a telephone attached to the local Passport 4400 unit, the destination address is resolved in one of the following three ways:

• Local number, locally resolved. If the number appears in the local Egress Table, it is a local number. No network address resolution is required, and the address is resolved within the voice application of the local Passport 4400 unit. If that number is not busy, a connection will be established when the local number answers.
• Remote number, locally resolved. If the number does not appear in the local Egress Table, it is referred to the local cache, a table that stores network addresses (DNAs) that have been previously resolved. This network address is then used by the voice application of the Passport 4400 unit to contact the remote Passport 4400 unit where the called number is located. If that number is not busy, a connection will be established when the called number answers.
• Remote number, resolved by Network Address Server (NAS). If the number does not appear in either the local Egress Table or the local cache, the local 4400 unit contacts its previously designated NAS for address resolution. In turn, the NAS accesses its table where all valid network addresses are stored. If the called number appears within that table, the called number's DNA is returned to the local cache, and forwarded to the local voice application. Ultimately, the voice application contacts the remote Passport 4400 unit where the called number is located. If that number is not busy, a connection will be established when the called number answers.

All future calls to this number will then be resolved locally without accessing the server. The following figure highlights the sequence of events involved in resolving network addresses.