Silicon Laboratories SI2494/39, SI2493/57/34/15/04 manual Appendix A-EPOS Applications, Modulation

AN93

APPENDIX A—EPOS APPLICATIONS

EPOS applications generally require nearly flawless call connection reliability and a very short overall transaction time. The message length of a typical EPOS terminal is between 120 to 260 bytes of information. Due to the relatively small message length, the need for reliable connections under all line conditions, and short connection times, the preferred modulations have traditionally been variations of V.22 (1200 bps) or Bell 212 (1200 bps). EPOS servers do not strictly follow ITU standards. Despite the informal use of the term “V.22 fast connect”, there is no ITU “fast connect” standard. De-facto standards with modifications of ITU standards, such as V.22 Fast Connect, have been adopted to reduce the transaction time. Some server manufacturers make changes to the modem with the intent of making it difficult for competing terminals to connect. Many EPOS servers have out-of- specification clocks and use reduced handshake timing. V.22bis (2400 bps) is occasionally used in EPOS terminals as well. The primary method by which V.22bis terminals achieve a shorter connection time has been through the use of a shorter answer tone. V.29 FastPOS is a Hypercom proprietary protocol based on the V.29 Fax standard. For these reasons, EPOS applications often require some amount of reverse engineering and fine tuning of the ISOmodem performance, typically with a patch.

Recently, improvements to the overall user experience have necessitated the storage of transaction information within the EPOS terminal based on some predefined criteria. These stored transactions are typically sent as part of a larger transaction at a later time. This effectively increases the message length to over 2 kB, necessitating the use of higher-speed modulations, such as V.29 FastPOS or V.32bis.

The choice of either V.29 FastPOS versus V.32bis is a tradeoff between transaction message length and connection times. It is common for a terminal to support both of these modulations.

Modulation		Typical Connect Time (Sec)*
V.90		25
V.34		10.7
V.32b		7.8
V.22b		5.0
V.22		3.0
V.22	FastConnect	0.6
V.29	FastPOS	0.5

*Note: Does not include dial delay.

VISA II (7E1)

Terminal		Host
Dials host		ENQ (0x05)
	STX <data>ETX, LRC

ACK (0x06)

STX <data>ETX, LRC

ACK (0x06)

Disconnects

EOT (0x04)

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