SWP

Protocol

Single Wire Protocol -- a high-speed serial interface defined by ETSI TS 102 613 linking a SIM card to an NFC controller over a single wire.

Aussi connu sous le nom de: Single Wire Protocol

What Is SWP?

Single Wire Protocol (SWPSWPProtocolSingle-wire link between SIMSIMApplicationSmart card for mobile network authentication.Click to view → and NFC controller.Click to view →) is a high-speed, full-duplex serial interface defined by ETSI TS 102 613 that links a SIM card to an NFC controller inside a mobile device over a single electrical wire -- specifically the C6 contact pin of the standard ISO 7816 interface. SWP enables the SIM's secure element to participate directly in NFC transactions, powering use cases like mobile payment, transit ticketing, and access control.

How SWP Works

In a conventional smart card interface, the C6 pin is reserved or unused. SWP repurposes this pin as a bidirectional communication channel between the UICC/SIM and the NFC controller (CLF -- Contactless Front-end). The protocol uses voltage-level signaling in one direction and load-modulation signaling in the other, achieving full-duplex communication at up to 1.7 Mbps.

The signaling layers of SWP are:

  • Physical layer (S1) -- electrical signaling on C6, including activation and power management.
  • Data link layer (S2) -- HDLC-like framing with error detection and flow control.
  • Transport layer -- carries APDU exchanges between the NFC controller and the SIM's card applets.

SWP in the NFC Architecture

The NFC ecosystem inside a smartphone typically includes three components:

Component Role
NFC controller (CLF) Manages the RF field and ISO 14443ISO 14443StandardStandard for contactless smart cards.Click to view → communication
SIM / UICC Hosts payment and transit applets on its secure element
Application processor Runs the host application (wallet, transit app)

SWP connects the SIM to the CLF, enabling the SIM-hosted applets to communicate directly with external contactless readers. This is the foundation of SIM-based NFC payments, where the payment applet (e.g., EMV contactless) runs inside the SIM rather than in the device's embedded secure elementsecure elementSecurityTamper-resistant hardware for secure operations.Click to view →.

Relationship to HCI

SWP is the physical transport, while HCI (Host Controller Interface, ETSI TS 102 622) is the logical protocol that runs on top of SWP. HCI defines gates, pipes, and registries that allow multiple host applications to share the NFC controller. Together, SWP and HCI form the standard communication stack between a UICC-based secure element and an NFC controller in mobile devices.

Questions fréquemment posées

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