VoIP Numbering schemes

The most common addressing systems are:

  • E.164: The ITU-T recommendation used in PSTN
  • URI: Universal resource identifier, used in internet
  • ENUM: E.164 addressing plan based NUMber
  • GDS: Global Dialling Scheme
  • DUNDi: Distributed Universal Number Discovery


ENUM is a protocol defined by IETF that facilities resolving of  E.164 telephone numbers into other resources or services on the Internet.
E.g.:%204689761234 3:


GDS, Global Dialing Scheme, is a dialling scheme for enabling global number recognition for H323. the structure of GDS is:

  • < IAC>
  • The International Access Code (IAC)
  • Country Code (CC)
  • Organisational Prefix (OP)
  • Endpoint Number (EN)
  • E.g.: 00(IAC) 1(CC) 189(OP) 7201234(EN): 0011897201234


Opposed to ENUM and GDS which are based on servers for resolving addresses the DUNDi is a p2p standard (one can say p2p version of ENUM). DUNDi is not a numbering standard but an implementation standard. Instead of DNS server registration a client has a record of all nodes connected to it. When a client needs to look up for a number it will contact all connected nodes to find the address, they in turn ask the nodes they are connected to for finally to find the destination.

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