TPDU and ATR - Practices

Transmission Protocol Data Units (TPDUs): these protocols are used for the transmission of APDUs and the data structure that is exchanged by the host and a card suing the transport protocol are called as TPDUs.

Mainly two types of protocols are in common use for this purpose:

1. T = 0: the smallest unit processed and transmitted by the protocol is single byte, in other words it is byte oriented.
2. T = 1: this consists of sequence of bytes, in other words it is block oriented.

ATR

ATR is used for conveying parameters that are required by the card to establish a data communication pathway. This message is conveyed as soon as the power in the smart card is set to on and stands for answer to reset (ATR).

It is usually up to 33 bytes, contains the transmission parameters such as T = 0 and T = 1, which are supported by the card. It also carries all the necessary information that is required to be known by the host such as:

• Data transmission rate
• Card hardware parameters
• Chip serial number
• Mask version number