E.164

E.164 is the ITU-T international public telecommunication numbering plan, defining the structure of telephone numbers up to 15 digits comprising a country code and a national subscriber number. It is the format used by MSISDNs in mobile networks, by SIP URIs that carry phone numbers, and by SS7 signalling. STIR/SHAKEN attestation operates on E.164 numbers in SIP INVITEs.

Categories: SignalingIdentity and SubscriberProtocols and Standards

E.164 in context

Signaling protocols carry the control-plane messages that set up calls, register subscribers and route SMS. SS7, Diameter, GTP-C and SIP are the four dominant families, and interconnect exposure of any of them is treated by GSMA as top-tier telecom risk.

Subscriber identifiers (IMSI, SUPI, MSISDN, IMEI) anchor authentication, charging and lawful interception. Any protocol that leaks a permanent identifier is treated as a privacy defect, which is why 5G introduced SUCI concealment on the air interface.

To place E.164 in the wider telecom-security picture, review OCS, P-Asserted-Identity, AAA, ADSL, Any-Time Interrogation (ATI) and Attack Surface Mapping — each entry cross-references back to this page so you can walk the topic in either direction.

Related terms

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