Resources
eSIM and telecom glossary
Plain definitions of the eSIM, telecom and VoIP terms developers meet when integrating mobile data: IMSI, ICCID, eUICC, SM-DP+, LPA, SIP, SBC and more.
Telecom
- MNOMobile Network Operator
A company that owns licensed radio spectrum and operates its own mobile radio access network. It issues IMSIs and provides mobile services (voice, SMS, data) to end users.
- MVNOMobile Virtual Network Operator
An operator that provides mobile services to end users without owning licensed radio spectrum or a full radio access network. An MVNO leases network capacity from one or more MNOs.
- eSIMembedded Subscriber Identity Module
A SIM built into the device as a secure chip (the eUICC) rather than a removable card. It stores one or more eSIM profiles, each representing a mobile subscription.
- eSIM profile
A provisioned subscription stored on an eSIM, typically issued by an MNO or MVNO. Every eSIM the Firsty API provisions is one profile; the states it moves through are covered in eSIM lifecycle.
- ICCIDIntegrated Circuit Card Identifier
A unique 19 to 22 digit number (typically 19 or 20) identifying a SIM card. Printed on a physical card or shown in device settings, it acts as the SIM's primary account number.
- IMSIInternational Mobile Subscriber Identity
The subscriber identity within an MNO's network. An eSIM profile can carry several IMSIs, but only one is active at a time.
- MSISDNMobile Station International Subscriber Directory Number
The number assigned to an IMSI, which is usually the subscriber's phone number.
eSIM provisioning
- eUICCEmbedded Universal Integrated Circuit Card
The secure chip built into a device that stores eSIM profiles and switches between them. It replaces the removable SIM card and is what makes remote provisioning possible.
- EIDeUICC Identifier
A unique 32-digit number identifying the eUICC chip itself, separate from the ICCID of any profile installed on it. It is how a specific device is targeted when a profile is provisioned remotely.
- RSPRemote SIM Provisioning
The GSMA-defined system for downloading, installing, enabling and deleting eSIM profiles over the air, with no physical SIM swap. In practice it is the SM-DP+, SM-DS and LPA working together.
- LPALocal Profile Assistant
The software on the device, in the operating system or on the eUICC, that talks to the SM-DP+ to download a profile and lets the user manage the profiles installed. It is what reads an activation code or QR code and starts the install.
- Activation codeLPA string
The string an SM-DP+ issues to point a device at a specific profile, in the form
LPA:1$smdp.address$matchingId. Encoded as a QR code or entered by hand, it is what you hand a user once a profile is released.- Matching ID
The token inside an activation code that tells the SM-DP+ which prepared profile to release to the requesting device. It is tied to one profile download.
- Confirmation code
An optional extra code, separate from the activation code, that an SM-DP+ can require before releasing a profile. Operators use it when they want a second factor before an install.
VoIP
- VoIPVoice over IP
Voice communication carried over IP networks instead of circuit-switched networks. A circuit-switched network sets up a fixed path (circuit) between two endpoints for the whole duration of a call. On a packet-switched (IP) network the voice is broken into packets that share network links with other traffic, so network resources are only used while packets are being sent.
- OTT voiceOver-The-Top voice
Voice services delivered over the internet without direct control of the underlying access network (for example WhatsApp, Skype or Signal).
- SIPSession Initiation Protocol
A signalling protocol used to establish, modify and terminate real-time communication sessions such as voice and video calls.
- RTPReal-time Transport Protocol
The protocol used to carry voice and video media streams in real time.
- CDRCall Detail Record
A record generated by VoIP servers containing metadata about a call or session (caller, callee, duration, timestamps), used for billing, analytics and compliance.
- SIP registrar
Receives register requests from SIP clients and maintains a dynamic mapping between a user's SIP address (URI) and their current IP address and location. In other words, it knows where to reach each SIP user.
- Media server
A server that processes media streams (RTP) for functions such as announcements, IVR, conferencing, call recording and transcoding.
- SBCSession Border Controller
A specialised network device placed at the edge (border) of a VoIP network to control, secure and manage real-time communication sessions such as SIP calls, WebRTC sessions and media streams.
- NATNetwork Address Translation
A method of remapping IP addresses that hides internal addresses by translating them to public ones. VoIP traffic commonly needs an SBC or the STUN, TURN and ICE mechanisms below to cross it.
- STUNSession Traversal Utilities for NAT
Lets a device discover its public-facing IP address and port. A client behind NAT sends a request to a STUN server, the server replies with the public address and port it sees, and the client shares that with a peer for direct communication.
- TURNTraversal Using Relays around NAT
Acts as a relay when direct peer-to-peer communication fails: instead of flowing directly, all media and data pass through the TURN server. The downsides are added latency, server bandwidth and the cost of operating the relay.
- ICEInteractive Connectivity Establishment
A framework that coordinates STUN and TURN to find the best path between two devices. ICE gathers connection options called candidates: host candidates (local IP addresses), STUN candidates and TURN candidates, in that order of preference.
It does not try them one by one. Both peers gather every candidate at once, assign each a priority, run connectivity checks in parallel and select the first working pair with the highest priority.