Telecom glossary: A2P, eSIM & IoT

Short definitions from across the site. Each term links on to the product or tool page where it applies.

Unicom Americas – Mobile Business team

Definitions only — a term explained here is not a service we sell.

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2G and 3G retirement: Network retirement is an operator closing a 2G or 3G network, which stops any device that relies on that bearer.

A

A2P SMS: Application-to-person SMS is traffic an application sends to a handset, such as a verification code or a transaction alert, via a registered sender.
APN: An access point name selects the gateway a mobile data session uses, from the public internet to a private enterprise network.
AS number: An autonomous system number identifies the network that announces an address prefix, and the AS path shows which networks the route crosses.

B

Beamforming: Steering an antenna array's energy toward a device.
BGP: BGP is how autonomous systems announce address reachability, and the AS path shows the networks a route crosses.

C

Carrier aggregation: Combining multiple carriers to increase the effective bandwidth.
CDR: A call detail record (CDR) is the billable line for one network event, used to reconcile invoices against records.
Cell: One radio coverage area served by a base-station sector.

D

Data residency: Data residency is where data is stored and processed, and the jurisdiction whose rules apply to it.
DIA: Dedicated internet access gives one site committed internet capacity, a static address block and a demarcation point, distinct from IP transit.
DLR: A delivery receipt reports the mobile network's status for a sent SMS, such as delivered, expired, rejected or unknown.
DNS: The domain name system turns a hostname into an address, and a slow or filtered lookup can make a healthy server look slow.

E

EARFCN: The E-UTRA absolute radio frequency channel number names one LTE carrier: a band and an exact frequency encoded in one integer.
eSIM: An eSIM is a downloadable operator profile stored on an embedded chip, not a plastic card. Consumer devices use SGP.22 and IoT devices use SGP.32.
eUICC: The eUICC is the secure chip that stores eSIM profiles; one chip holds several, usually with one active, and SGP.22 v3 adds multiple enabled profiles.
eUICC identifier (EID): The eUICC identifier, separate from the subscription.

F

Frequency band: A frequency band is a named slice of radio spectrum with an uplink and a downlink range, such as B3 or n78.

G

GDPR: The EU General Data Protection Regulation requires a lawful basis and purpose limits for personal data, and sets out people's rights over it.
gNodeB: The 5G base station; eNodeB is the 4G equivalent.
GSM-7: GSM-7 is the 7-bit alphabet for basic Latin text in SMS: 160 characters per segment, or 70 once the message switches to UCS-2.

H

HLR: The home location register records where a subscriber attaches and whether the line can receive. An SMS route can query it before delivery.
Home subscriber server (HSS): The LTE (4G) subscriber database; in the 5G core the UDM and UDR take this role, and the HSS remains for EPC and IMS interworking.

I

ICCID: The ICCID is the serial number on a SIM or eSIM profile. It names the card, rather than the subscription.
ICP filing: ICP filing records a website and its operator with China's authorities before content is served from mainland China.
IEPL: An international Ethernet private line gives two sites private Ethernet capacity between countries, with committed bandwidth and a handoff.
IMEI: The IMEI is the 15-digit identity of a handset or module. It names the device, not the SIM inside it.
IMSI: The IMSI is the subscription identifier on a SIM: up to 15 digits of MCC, MNC and MSIN that the network uses to authenticate and locate a device.
IP transit: IP transit rents full-table reachability from an upstream, so a network can announce its prefixes and reach the whole internet.
IPLC: An international private leased circuit is a dedicated TDM private line between countries, still installed where legacy interfaces remain in service.

J

Jitter: The variation in latency from packet to packet.

L

Latency: Delay between two points, measured one-way or round-trip, set by distance, hops and queues, and measured along a path rather than a link.
LGPD: Brazil's LGPD governs personal data with legal bases, data-subject rights, ANPD supervision and extra safeguards for children's data.
Local profile assistant (LPA): The device component that downloads, enables and manages eSIM profiles.
LTE-M: LTE-M is a low-power LTE bearer for machines, with handover and optional voice that NB-IoT lacks, plus more throughput.

M

M2M: M2M links meters, trackers and sensors that report without a person, so the traffic profile decides the bearer, the power budget and the monitoring.
MCC: Mobile country code: the three digits in an IMSI and a PLMN identity that name the country of a network.
Message concatenation: How a long SMS splits into segments, why most routes bill each one, and how encoding changes the count.
MIIT: MIIT is China's ministry for industry and information technology, and it sets the rules for telecom networks, spectrum, numbering and filings.
MNC: Mobile network code: the two- or three-digit code after the MCC that names one operator network in a country.
MNO: Mobile network operator: the company that holds spectrum licenses and runs the radio access and core network that carry traffic.
Mobile number portability: Mobile number portability lets a subscriber keep a number across operators, which breaks prefix-based routing and requires a portability check.
MSIN: The subscriber part of an IMSI after the MCC and MNC.
MSISDN: The diallable phone number in international E.164 format, which identifies a subscription and can move to another network.
Multi-IMSI: Several IMSIs on one SIM let a device present a local identity per country, but they remain one subscription.
MVNO: Mobile virtual network operator: a brand that buys wholesale network access and sells subscriptions without owning spectrum.

N

NB-IoT: NB-IoT is a narrowband low-power bearer for small, infrequent device messages, with deep indoor reach and long battery but no handover or voice.

O

One-time password: A single-use code sent by SMS to check who controls a phone number, with a short expiry and attempt limits.
Opt-in: Opt-in is provable prior consent to receive messages: the wording, timestamp, source and scope a sender records and can produce.
Opt-out: An opt-out is the working exit from a message stream: a reply such as STOP that is recorded and reaches every system able to send.

P

P2P: Person-to-person SMS is traffic one person sends another. It has no sender registration or template approval, so it is not for application messages.
Packet gateway (PGW): The core node that assigns the device IP address and exits data to the internet or a private network.
Packet loss: The share of packets that never arrive.
PDU: A protocol data unit is one SMPP command on the wire, such as submit_sm: a fixed header, then a body set by the command.
Ping: Ping shows whether a host answers and how long a round trip takes on one path at one moment.
PIPL: China's PIPL governs personal information with consent and necessity rules, plus defined routes for cross-border transfers.
PLMN: A public land mobile network is one operator network identified by an MCC and MNC pair, broadcast by its cells and stored in the IMSI.
PoP: Point of presence: a city or facility where a network hands traffic to another network on the path to the user.
Private APN: A private APN routes fleet traffic to a dedicated gateway and into a corporate network, keeping it off the public internet.

R

Radio access network (RAN): The base stations, antennas and radio controllers that connect devices over radio to the core.
RCS: Rich Communication Services is carrier messaging with media, branding and read receipts where operators and handsets support it.
Refarming: Reassigning spectrum from an older generation to a newer one.
Roaming: Roaming lets a subscription use visited networks outside its home market under inter-operator agreements, while the home network keeps control.
RSRP: Reference signal received power is the LTE signal-strength measurement in dBm that field teams compare, unlike the bars a device shows.
RTT: Round-trip time is the measured form of latency between two endpoints, covering both directions of the path.

S

Sender ID: The sender identity a message appears to come from, alphanumeric, numeric or a short code, and how markets register it.
Sender registration: Sender registration records who may send, from which identity and for what content, before traffic flows.
SGP.02: The legacy M2M eSIM provisioning generation, managed through subscription-manager servers, with no over-the-air path to SGP.32.
SGP.22: The consumer eSIM specification: the user starts a profile download with a QR code or an app.
SGP.32: SGP.32 is the GSMA eSIM specification for IoT fleets: an eIM orders profile downloads and enables or deletes profiles without a person at the device.
Short code: A short code is a short numeric sender allocated within one country, often separately registered, for high-volume two-way application messaging.
SIM: The subscriber identity module holds a subscription's identity and authentication keys, and its form factor is packaging.
SMPP: SMPP is the binary protocol applications use to submit SMS to a message center and receive receipts on a transceiver or a receiver bind.
SMS signature: An SMS signature is the bracketed sender name at the start of a China-bound template and part of the approved content.
SMS template: Message text approved in advance for destinations that regulate content as well as the sender, including the variable rules and the re-approval step.
SMSC: A short message service center stores and forwards each submitted SMS to the destination network and, on request, returns a final status report.
Spectrum: The radio frequencies a regulator assigns to mobile networks.

T

TAC: The type allocation code is the first eight IMEI digits. It names the device model, not the individual unit.
Throughput: The rate data actually moves, not the link's headline rate.
TTFB: Time to first byte measures how fast a server starts answering: DNS, connection setup, server processing and the first byte back.

U

UCS-2: The 16-bit SMS encoding used for most emoji and non-Latin scripts: 70 characters per segment, 67 once concatenated.

V

VoLTE: Voice over LTE carries calls as IP packets on the LTE bearer, so a device needs VoLTE support once older networks retire.

W

Webhook: An event post to an HTTPS endpoint: receipts, inbound messages and status changes that the receiver must verify, acknowledge fast and queue.