ATM & How it Works

An automated teller machine (ATM) is an electronic banking outlet that allows customers to complete basic transactions without the aid of a branch representative or teller. Anyone with a card can access cash at most ATMs.

ATMs are convenient, allowing consumers to perform quick self-service transactions such as deposits, cash withdrawals, bill payments, and transfers between accounts. Fees are commonly charged for cash withdrawals by the bank where the account is located, by the operator of the ATM, or by both. Some or all of these fees can be avoided by using an ATM operated directly by the bank that holds the account.

ATMs are known in different parts of the world as automated bank machines (ABM) or cash machines.

There are two primary types of ATMs. Basic units only allow customers to withdraw cash and receive updated account balances. The more complex machines accept deposits, facilitate line-of-credit payments and transfers, and access account information.

Whenever you enter your Card (Mag/EMV), ATM will read the following information.

1. Your Track2 (Contains Card number, CVV, Expiry Date)
2. Transaction Type (Whiter is Cash withdrawal/Balance Enquiry/ Pin Change/Mini Statement)
3. You Enter the Transaction Amount (In case of Cash Withdrawal Transaction)
4. EMV tags (In case of EMV trx. e.g. Application Counter, AID, Unpred Number, Application cryptogram, etc.)
5. You enter your 4 or 6-digit card PIN.
6. All This data is collected by ATM and Sent to Switch in ATM-supported format (Could NDC+/Diebold/ Wincor).
7. Host “switch” after recovering the message check if the transaction is

• If it is of the same bank (On-Us) then the message is forwarded to the same bank's transaction processing engine (core banking) after PIN block validation.
• If it is of a different bank (Off-Us) then the message is forwarded to ATM switch/gateway, from where it will be routed to the specific bank, based on the card's details. ATM switch has a record of card number schemes of all issuer banks connected to that switch. Routing is normally done on the bases of the first (left) 6 digits of the card number, also called BIN (bank identification number)

1. The host (switch) will parse this data and identify what type of transaction it is (based on Operational Code).

• This is a financial transaction. So, DE-0 “MTI” will be fixed (0200)
• PAN number is extracted from Track2 So, DE-2 will be formed.
• Processing Code based on transaction type selection.
• You have entered Amount So, DE-4 “Amount Transaction”, DE-19 “Acquiring institution country code”, and DE-49 “Currency Code Transaction” is formed.
• The host has its own date as well as GMT date So, DE-7 “Transmission Date & Time (MMDDhhmmss)”, DE-12 “Time, local transaction (hhmmss)”, DE-13 “Date, local transaction (MMDD)”, DE-14 “Date, expiration”, DE-17 “Date, capture” is formed.
• There are unique sequence numbers assigned to every transaction. DE-11 “System trace audit number (STAN)”, and DE-37 “Retrieval Reference Number (RRN)” are formed.
• Based on your terminal Capabilities, DE-22 “Point of service entry mode” will be formed.
• The host has a unique acquirer ID, which will be populated in DE-32 “Acquiring institution identification code”, DE-33 “Forwarding institution identification code”, Track in DE35 “Track 2 data”, Terminal & Merchant Details in DE-40 “Service Restriction Code”, DE-41 “Card Acceptor Terminal Identification”, DE-42 “Card Acceptor Identification Code”, DE-43 “Card acceptor name/location (1-23 address 24-36 city 37-38 state 39-40 country)”.
• You have entered your PIN, which is encrypted under TMK to give you a 16-digit pin block. This forms DE-52. Based on the PIN Block ISO method it follows there are various pin block formation methods (for eg. Visa).
• This all info is collected and sent to NPCI.
• NPCI will base on PAN number, will decide which is the correct issuer to this bin and routes the transaction to that particular issuer.
• The issuer will check all the preliminary checks (like Card is hot-listed or not, CVV is proper, Pin is correct) and Send the transaction to Core Banking (or approve in Stand-in).
• Issuer Host will generate a Transaction Response and send it back to NPCI and NPCI will forward it to Acquirer Switch.
• Based on DE-39 “Response Code”, Acquirer Host will give a function command to dispense the cash and you get the cash

*PIN block can be of any format ISO-0, ISO-1, etc. depending upon the switch's implementation.

What is NDC/NDC+/DCC??

NDC/NDC+ are NCR proprietary formats, and DDC is Diebold's proprietary format. Most ATMs try to emulate NCR/Diebold formats as they are the most used protocols

What is NDC+?

NDC+ is the terminal control application from NCR. It is table-driven and can be customized to meet your own requirements. NDC+ is the 4th generation version of NDC and has been developed for NCR’s 4th generation SSTs and Account Services Terminals. It allows you to run 4th generation and Personas terminals in your network, in either Diebold Emulation or Native mode.

NDC+ Software System

The NDC+ software system is made up of two parts:

• Terminal Application: The terminal application gathers transaction details from the cardholder and sends these details in a transaction request message to the Central When a terminal receives a transaction reply from the central, it completes the transaction. The terminal application responds to terminal commands from the central, such as go-in-service or go-out-of-service, and requests for information, such as tallies, by sending solicited status messages to the central. An unexpected event can be reported to central using an unsolicited status message.
• Central Application: The central application receives transaction request messages from the terminal, and determines whether the transaction should be approved or declined. It controls the terminal by sending terminal commands to it and acting on responses received. The central application must be able to decode and act on the messages it receives from the terminal. The central application must also be able to code the messages in the form that the NDC+ software in the terminal understands.

?Customization Data

STATE TABLES: States control the information-gathering part of cardholder transactions. NDC+ includes a set of standard states. The state table is made up of the state number, state type, and state data. Most state includes a screen number and a next state number as part of the table data. In the following table, we list each of the standard state table types that control transaction processing.

SCREEN DATA: A screen is a string of characters that defines what is to be displayed and where to display it. There are two types of screens:

• Customized – screens that you create

§?A customized screen is a screen that you create. You decide on the text to be included, and any pictures or logos to be used. The data is downloaded to the terminal in a screen data load message. All the screens that are accessed by the state tables are stored in the screen table. Each screen in the table has a unique number from 000 to 999. It is this number that is referenced by parameters in the state tables during transaction processing.

• Reserved -- screens that are already defined within the terminal software.

§?A reserved screen is a screen that is already defined within the terminal software. Reserved screens have four fixed functions, such as display supervisor prompts and menus, and are only displayed at pre-defined?times, such as when the terminal is in out-of-service or off-line mode

KEYBOARD DATA: The keyboard is an interface between the cardholder and the terminal.?NDC+ supports full touch screen keyboards and four/eight FDKs. It may be customized to suit customers’ requirements.

PRINTER DATA: The NDC+ SST software supports printing on five different devices:

o??Receipt

o??Journal

o??Statement

o??Programmable printing depository

o??DPM

The data to be printed on a particular printer, or printers, must be placed in a printer data field contained in a Transaction Reply Command Message. The length of the printer data field is variable and depends on the amount of data and data compression performed, the printer characters, and the overall message length limitation. There are 13 printer data?fields. On the receipt and journal printers, the uncompressed data length is restricted to 500 characters per printer data field.

SUPERVISOR MESSAGES: The supervisor messages are output to CRT, VEROP, basic/enhanced operator interfaces, and the receipt and journal printers. These supervisor messages are rules as follows:

o??Character set

o??Control codes

o??Screen size limitations

o??CRT layout

o??Printer layout

o??Automatic screen editing

o??Media status messages

o??Test cash report

o??Check the CDM report

o??Note: It is not supported by the YDC.