Standardisation - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 247

into smart card operating systems that are already available, in particular dual interface
smart cards, as simple as possible. The protocol defined in ISO 14443-4 is therefore
often called T = CL .
The entire data transmission to an ISO 14443 card can also be represented in accor-
dance with the OSI layer model , as Figure 9.27 shows. In this model, every layer
independently takes on specific tasks and is thus transparent to the level above it.
Layer 1, the physical layer, describes the transmission medium and the coding of the
data at byte level. ISO 14443-2 provides two equivalent procedures here, Type A and
Type B. Layer 2, the transport layer, controls the transmission of data between reader
and smart card. Layer 2 automatically looks after the correct addressing of the data
blocks (CID), the sequential transmission of excessively sized data blocks (chaining),
the monitoring of the time procedure (FWT, WTX), and the handling of transmission
errors. Layer 7, the application layer, contains the application data, i.e. the command
to the smart card or the response to a command. In contactless smart cards the data
structures used in the application layer are generally fully identical to those used in
contact smart cards. This procedure is very worthwhile for dual interface smart cards
in particular, because it means that the application layer is independent of the com-
munications interface that is currently being used (contact, contactless). Layers 3 to 6
are used in complex networks for the determination and forwarding of data packets.
In smart cards these layers of the OSI layer model are not used.
After the smart card has been activated (e.g. Type A after the transmission of the
ATS and possibly a PPS) it waits for the first command from the reader. The sequence
that now follows always corresponds with the master-slave principle, with the reader
as master and the card as slave. The reader always sends a command to the smart
card first, which executes the command and sends a response back to the reader. This
pattern may never be broken; a smart card thus cannot initiate any communication with
the reader.
Thebasicstructureofa data block (frame) from the transport layer is shown in
Figure 9.28. We differentiate between three types of blocks according to the method
of functioning:

• Iblock (information block): Transmission of data from the application layer (APDU)

• Rblock (recovery block): Handling of transmission errors

• Sblock (supervisory block): Higher control of the protocol.

ISO 7816-4
ISO 7816-7
proprietary

Layer 7
Application layer

Layer 2
Transport layer

ISO 14443-4
(ISO 7816-3 contact card)

ISO 14443-2, Type-A, -B, ...
(ISO 7816-2 contact card)

Layer 1
Physical layer

Figure 9.27 The ISO/OSI layer model in a smart card