This glossary defines the terms you will meet when buying, integrating, or operating a bulk SMS gateway. Each entry is one practical sentence, enough to follow a spec sheet, a contract, or a support conversation, and the deeper articles in this series link back here as their terminology hub.
How to Use This Glossary
Start with the terms that appear on your spec sheet: ports, SIM slots, network generation, protocols, and DLR. If a vendor page uses a term you do not recognize, look it up here before comparing products, because most buying mistakes start with a misunderstood specification. The glossary is organized alphabetically so it also works as a quick reference during procurement discussions.
The glossary also helps you read the documents that come with a purchase: a quotation, a firmware release note, a carrier agreement, and a support ticket all use the same vocabulary, and a shared vocabulary shortens every conversation. When a support engineer asks about a DLR status or a routing rule, knowing the term lets you answer precisely instead of describing the problem from memory.
Two distinctions are worth internalizing early. Ports and SIM slots are different numbers on many models, with active channels setting parallel capacity and SIM slots setting how many cards the device can hold or rotate. Messages and segments are different billing units, with long or Unicode text splitting into multiple paid segments. Keeping these two pairs separate will prevent most of the confusion that appears in procurement emails.
A to W Term Groups
A2P (Application-to-Person) messages are sent from an application to a phone, such as OTP codes and notifications. An aggregator buys SMS capacity from multiple carriers and resells it to businesses, while an API (Application Programming Interface) is the interface software uses to submit SMS, commonly HTTP or SMPP. An AT command is a text instruction such as AT+CMGS used to control GSM modems and gateway modules.
Bulk SMS is the practice of sending a large volume of messages in one campaign or operation. A bind is the SMPP session role a client takes, either transmitter, receiver, or transceiver.
Carrier refers to the mobile network operator that delivers messages to handsets. Concatenated SMS splits a long message into multiple segments that the phone reassembles. Consent is a recipient's permission to receive messages and is the foundation of compliant sending. CSQ is the signal-quality indicator reported by GSM modules.
Deduplication (duplicate protection) prevents the same message from being submitted twice by retries or double submissions. A DLR (Delivery Receipt) is the carrier's report on whether a message was delivered, expired, rejected, or undeliverable. DND (Do Not Disturb) is a national registry of numbers that must not receive marketing SMS.
E.164 is the ITU standard format for international phone numbers. An eSIM is an embedded SIM provisioned remotely instead of using a physical card.
Gateway refers to hardware or software that connects applications to mobile networks for SMS. GSM is the 2G mobile standard that many gateways and modems use, and GSM-7 is the 7-bit alphabet behind the standard 160-character SMS segment. A GSM module is the radio component inside a gateway or modem that sends and receives SMS. A grey route moves SMS traffic through unapproved channels and is high-risk and usually non-compliant.
HLR (Home Location Register) is the carrier database that tracks where subscribers are located. An HTTP API is a web-based interface for submitting SMS from applications.
IMEI is the unique identifier of a mobile device or module. An IP pool is the set of IP addresses a proxy gateway exposes for traffic.
Latency is the delay between message submission and delivery. LCR (Least Cost Routing) chooses the cheapest acceptable route for traffic.
Message ID is the unique identifier returned on submission, used to match delivery reports. MMS is multimedia messaging, a different service from SMS. MO (Mobile Originated) is a message sent from a phone, such as a reply or opt-out, while MT (Mobile Terminated) is a message sent to a phone. MNP (Mobile Number Portability) lets a number move between carriers. A modem is a hardware device that uses a SIM to send and receive SMS.
Operator is another word for carrier. Opt-in is explicit recipient consent, and opt-out is a recipient's request to stop receiving messages, often triggered by replying STOP. OTP (One-Time Password) is a verification code delivered by SMS.
P2P (Person-to-Person) messages are exchanged between individuals and generally carry higher trust than A2P. PDU mode is the hex-encoded SMS format that supports Unicode and long messages. A port is one GSM module and SIM channel in a gateway, and a port sends one message at a time. A prepaid SIM is paid in advance and commonly used in bulk operations. A protocol defines the rules for exchanging messages, such as SMPP or HTTP.
Retry resends a failed message according to configured rules and backoff. Roaming uses a SIM on a foreign network. A route is a delivery path to a destination network, and a routing table contains the rules a gateway uses to choose SIMs and routes.
Segment is one part of an SMS; long messages split into 160-character (GSM-7) or 70-character (UCS-2) segments. A sender ID is the name or number shown as the sender. A short code is a five-to-six-digit number used for two-way SMS services. SIM is the subscriber identity module that connects a device to a carrier; a SIM bank is a centralized chassis for managing many SIMs; a SIM pool is a set of SIMs used for rotation and load spreading. SMPP is the protocol for high-volume SMS integration, and an SMSC is the carrier system that stores and forwards SMS. SMS is the Short Message Service, and an SMS modem is a device with a SIM slot for sending and receiving SMS. A softswitch switches voice traffic in software, and submit_sm is the SMPP command used to submit a message. A status report is another name for a delivery receipt.
Throughput is the number of messages sent per unit of time. Transactional SMS is tied to a user action such as OTP and account alerts. Two-way SMS sends and receives on the same number.
UCS-2 is the 16-bit encoding used for Unicode SMS, limited to 70 characters per segment.
VoIP is voice over IP, relevant when a business runs SMS and voice on related hardware. Voice termination routes voice calls into mobile networks.
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Which Terms Matter on a Spec Sheet
Four terms decide most purchase decisions: ports and SIM slots set capacity, network generation sets where the device works, protocols set how it integrates, and DLR handling sets how you will know delivery worked. A spec sheet that does not separate active channels from SIM-slot capacity, or that lists "up to" figures without conditions, deserves a direct question before you compare prices.
| Spec-sheet term | What it decides |
|---|---|
| Ports / active channels | Parallel sending capacity |
| SIM slots | How many SIMs the device holds or rotates |
| Network generation | Where the device works and how long it stays usable |
| Protocols (SMPP / HTTP API) | How the device integrates with your stack |
| DLR handling | How you confirm delivery per message |
A practical reading order for a spec sheet: confirm the exact model name and configuration, check active channels and SIM-slot capacity separately, confirm the network generations and bands for the countries you send to, verify SMPP and HTTP API support on the specific model, and check whether DLRs are captured per message and exposed through the interface or API.
Anything the spec sheet leaves vague should become a written question in your RFQ.
Related Reading
The SMS gateway solution guide and the SMS modem product line use the same terminology, so this glossary stays consistent across the site. Deeper definitions live in the series articles on message flow, DLR semantics, throughput, and SIM management.
Telarvo Expert Views
Most spec confusion in support calls comes from three terms: ports, SIM slots, and segments. Buyers assume ports equal SIMs and messages equal segments, and both assumptions fail at scale. Read the spec with those three separations in mind and the rest of the evaluation gets easier.
— Messaging Solutions Engineer, Telarvo Store
Conclusion
Terminology is the first filter in any SMS gateway purchase: it lets you read a spec sheet, ask better questions, and avoid the mistakes that start with a misunderstood definition.
Key Takeaways for B2B Buyers
Distinguish active channels from SIM-slot capacity, count segments rather than logical messages, map DLR labels to your provider's definitions, and treat consent and sender registration as delivery factors rather than paperwork.
Questions to Ask Before Committing
Ask which terms the vendor's spec sheet leaves undefined, how ports, SIM slots, and concurrent SIMs relate on the exact model, how segments are billed, and how DLR statuses are defined by the provider.
FAQs
What is the difference between MO and MT?
MO is mobile-originated traffic, such as replies and opt-outs; MT is mobile-terminated traffic sent to phones, such as marketing and OTP.
Why do long messages cost more?
Messages over 160 characters (GSM-7) or 70 characters (Unicode) split into multiple segments, and carriers bill per segment.
Is a grey route ever acceptable?
No. Grey routes carry high delivery, compliance, and reputation risk; build on registered, authorized routes instead.
Where can I learn more about a specific term?
Use this glossary as the hub and follow the internal links in each related article for deeper explanations.