The Cisco CCIE Service Provider (CCIE SP) certification validates expert level skills required of a Network Engineer to configure, build, troubleshoot, and optimize a complex highly available Service Provider IP NGN core infrastructure.
Dialed Number Identification Service. Dialed Number Identification Service (DNIS) is a service sold by telecommunications companies to corporate clients that lets them determine which telephone number was dialed by a customer. This is useful in determining how to answer an inbound call. The telephone company sends a DNIS number to the client phone system during the call setup. The DNIS number is typically 4 to 10 digits in length. Any DID (Direct inward dial) number will have a DNIS. This is the number sent from the central office to the PBX (Private branch exchange) or key system, telling the telephone system which number was dialed.
Those extensions are defined on the listed-directory screen the extensions are incoming DID or DNIS digits sent from the trunk provider for incoming calls and are directly related to 800 numbers or 10 digit numbers being called from the outside world.