An implicit numbering plan is one in which the numbers are not accompanied by an indication to which numbering plan they apply.
The type of number (private, public, local, national, international) passed between the servers must be deduced entirely from the digit string itself. In an implicit numbering network, the number type is often signaled in the form of prefix digits (for example, 9 for local 91 for national, 9011 for international, 8 for private). The signaling between originating phone and the originating switch and server is always “implicit.”
An explicit numbering plan is one in which each number is accompanied by an indication as to which numbering plan it applies.
The type of number (private, public, local, national, international) is passed explicitly between the servers in the form of separate signaling parameters. In an explicit numbering network, the call setup message typically carries NPI (number plan identifier) and TON (type of number) parameters, which guide the receiving switch in interpreting the dialed digit string. In the administration interfaces, the administrator will see NPI and TON referred to as NOA (nature of address).
The SIP protocol used in most switch-to-switch communication currently does not support explicit numbering (it does not support passing of the NPI and TON parameters). For IP connections of Lotus Sametime Unified Telephony and to other Lotus Sametime Unified Telephony systems SIP-Q supports explicit numbering and is the required signaling protocol.
Block dialing is a variation of dialing where the originating endpoint transmits all of the digits for the destination at one time, in single message or command, to the originating switch. The alternative is digit-by-digit dialing, which is customary in most public wireline networks. In digit-by-digit operation, each digit is transmitted to the originating switch as the user dials it. DTMF and rotary phones operate in this fashion. Newer networks, such as the public cellular networks and VoIP networks use block dialing.
Historically, in an open numbering plan and open dialing plan arrangement, the originating switch (where the caller is connected) might not know how many digits are needed to reach a given destination, so the system may rely on interdigit timeouts or use of a terminator digit (#) to detect the end of dialing by the caller. Lotus Sametime Unified Telephony and its endpoints support interdigit timing and the use of a terminating digit, but because SIP endpoints are block dialing devices, use of these special mechanisms is not required in most cases.
Overlapped sending is the practice by which one switch begins sending digits to the next switch before the user has completed dialing. SIP does not support overlapped sending. Likewise, Lotus Sametime Unified Telephony does not support overlapped sending.
Parent topic: Numbering Plan