Communication Technology  

 

 

 

BIP(Bearer Independent Protocol)

BIP stands for Bearer Independent Protocol (BIP). It is an extension of the SIM Toolkit (STK) that allows a SIM card (or USIM) to establish a data connection using the available communication bearer (e.g., GSM, GPRS, UMTS, LTE, 5G). The term "Bearer Independent" in Bearer Independent Protocol (BIP) refers to the protocol's ability to operate over various types of communication bearers (e.g., GPRS, LTE, 5G) without being tied to a specific one. This flexibility allows a SIM card or other secure elements to establish and manage data channels across different network technologies. It enables the protocol to utilize whatever data connection is available, making it adaptable to various network conditions and technologies, which is especially useful for dynamic and heterogeneous mobile environments.

Key Features of BIP

The Key Features of Bearer Independent Protocol (BIP) revolve around its ability to establish flexible communication channels between a SIM card and mobile networks. This flexibility allows the SIM card to independently manage connections over various bearers like GPRS, LTE, and 5G, making it adaptable to different network environments. BIP also supports secure data transfers, over-the-air updates, and remote management capabilities, ensuring efficient and secure communication. Its design empowers SIM-based applications to interact directly with networks, offering versatility for mobile devices and IoT deployments.

Independent Bearer Management:

As the name suggests, BIP allows the SIM card to use various bearers (network connections) independently. This means the SIM can initiate a data connection over GPRS, UMTS, LTE, or even Wi-Fi (if the device supports it).

The SIM card can select the best available bearer and establish communication without relying solely on the device's OS or user interface.

Use Cases:

  • Over-the-Air (OTA) Updates: BIP enables the SIM card to connect to the mobile network for receiving updates, configurations, or applications over the air, without requiring user intervention.
  • Remote File Management: Network operators can use BIP to manage files stored on the SIM card, such as updating roaming lists or network settings.
  • SIM-Based Applications: Some applications require the SIM card to send or receive data independently of the phone's user applications. BIP is used for such interactions, especially when the SIM card has to communicate with a remote server.
  • SIM Toolkit Extension: BIP is designed as an extension of the SIM Toolkit (STK), which is a set of commands and protocols allowing SIM cards to communicate with the device and the network. This makes BIP fundamentally tied to the SIM card's role in managing interactions between the user device and the mobile network.
  • Security and Authentication: The SIM card holds secure elements like the IMSI, Ki, and other encryption keys. Using BIP, the SIM card can manage secure communication with the mobile network or a remote server, leveraging its built-in security features.
  • Network Operator Control: BIP allows network operators to remotely manage SIM cards by sending updates or configurations over the air (OTA). The direct link to SIM-based communication is important for services like secure key exchanges, remote file management, or updating roaming lists.

How BIP Works

The operation of Bearer Independent Protocol (BIP) involves the interaction between a SIM card and the mobile network through various bearers, such as GPRS, LTE, and 5G. It allows the SIM card to initiate and control data sessions, even managing secure communication channels independently of the mobile device's operating system. BIP employs a set of commands like opening and closing channels and sending or receiving data to enable this interaction. This capability ensures efficient, secure communication, making BIP suitable for both mobile and IoT applications.

Establishing a Communication Channel:

  • Using BIP, the SIM card can request the mobile device's modem to establish a communication channel over a supported bearer.
  • The device's modem acts as a mediator, handling the low-level communication while the SIM card uses higher-level APDU commands to control the process.

Channel Types:

  • Channel with GPRS/UMTS/LTE/5G Bearers: BIP allows the SIM card to use mobile data services directly. This is common for applications that require data communication with network servers, such as secure OTA updates or authentication requests.
  • Local Connection Channel: BIP can also establish local communication between the SIM card and the mobile device itself. For example, for certain device management tasks or interactions that don't require external network access.

Security Considerations:

  • BIP ensures that communication between the SIM card and the network is secure, leveraging the SIM's secure key storage for encryption.
  • This ensures that sensitive information exchanged over the bearer is protected from potential interception.

BIP Command Structure:

BIP uses a set of STK commands for communication, such as:

  • OPEN CHANNEL: To open a communication channel using the selected bearer.
  • CLOSE CHANNEL: To close the previously opened communication channel.
  • SEND DATA: To transmit data over the established channel.
  • RECEIVE DATA: To receive incoming data on the established channel.

The mobile device's baseband processor interprets these commands and facilitates the data exchange between the SIM card and the network.

Communication between SIM and UE Modem

The communication between the SIM card and the modem within a User Equipment (UE) follows a structured protocol stack that integrates physical, data, and command layers. At the base, the ISO/IEC 7816 standard defines the physical interface, specifying the electrical connections and data transmission between the SIM and the modem. Building on this, BIP (Bearer Independent Protocol) allows the SIM card to initiate and manage data connections over cellular bearers. The exchange of commands and data between the SIM and modem uses APDUs (Application Protocol Data Units), which structure the messages for operations like authentication, data transfer, and bearer management. Together, these layers ensure secure and efficient communication between the SIM card and the mobile network through the UE modem.

Physical Interface: ISO/IEC 7816 Standard

The SIM card and the mobile device communicate over a physical interface, usually following the ISO/IEC 7816 standard. This standard specifies the electrical characteristics, signal protocols, and data exchange formats.

The physical connection is typically a set of contact points that connect the SIM card to the SIM card reader in the phone. These contacts include:

  • VCC (Power Supply)
  • GND (Ground)
  • CLK (Clock signal)
  • RST (Reset signal)
  • I/O (Data line)

The SIM card is powered by the phone and can communicate with the baseband processor using these pins.

Communication Protocol: BIP/APDU Commands

The communication between the SIM card and the modem baseband processor relies on APDU (Application Protocol Data Units) commands, as outlined in the ISO 7816-4 standard. APDUs facilitate data exchange by defining a structured message format, consisting of Command APDUs (sent from the modem to the SIM for tasks like data access or authentication) and Response APDUs (sent back from the SIM, providing status or requested data). These interactions enable functions such as PIN verification, SMS management, and network-specific information retrieval, forming a core part of SIM-modem communication.

  • Data exchange between the SIM card and the modem baseband processor is achieved using APDU (Application Protocol Data Units) commands. APDUs are defined as part of the ISO 7816-4 standard.
  • APDUs consist of command messages (from the phone to the SIM) and response messages (from the SIM to the phone):
  • Command APDU: Sent from the modem to the SIM card, it contains instructions like reading or writing data, authentication requests, etc.
  • Response APDU: Sent from the SIM card to the modem, containing status information or requested data.
  • Example APDU interactions include PIN verification, reading/writing SMS, or retrieving network-specific information.

Data Transfer: Protocol Layer (Layer 2 - Layer 4):

The data transfer between the SIM and the baseband processor involves several protocol layers:

  • Layer 2: T=0 or T=1 Protocols: These protocols are used for the communication over the I/O line. T=0 is a byte-oriented protocol, while T=1 is block-oriented.
  • Higher-Level Protocols: Above the physical and link layers, higher-level protocols like GSM 11.11, 3GPP TS 31.102 (for USIM), or 3GPP TS 31.101 provide details about file structures, authentication procedures, and other functionalities.
  • These protocols help manage files like SMS, contacts, and various parameters that are crucial for network operations (e.g., PLMN lists, Roaming configurations, etc.).

Authentication and Key Exchange

One of the key interactions is authentication between the SIM card and the network via the modem baseband. This involves:

  • The SIM card contains unique identifiers like the IMSI (International Mobile Subscriber Identity) and Ki (a secret key).
  • When a phone tries to connect to the network, the modem sends the IMSI to the network. The network then sends a random challenge (RAND) back to the phone.
  • The SIM card uses the Ki and the RAND to generate a response (SRES) and session keys (Kc or CK/IK).
  • The modem sends the SRES to the network, which verifies it to authenticate the user.
  • The session keys are used for encrypting the communication between the phone and the network.

Overview of Flow:

  • The modem powers the SIM card and establishes communication using a physical interface.
  • APDU commands are exchanged for reading data, authentication, and performing network-specific functions.
  • The SIM card generates responses and session keys for secure communication.
  • The baseband uses this information to establish a secure connection to the cellular network.

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