Frontline Test Equipment, Inc. |
| Glossary |
While FTS is used primarily to passively monitor data as it travels over a link, several FTS products have the ability to actively transmit data, generally for the purpose of substituting for one of the devices in a circuit. A user might, for example, want to send commands to a device to see if the responses it receives from the device are correct.
Alignment Error
An Alignment Error occurs in a data frame in cases where both the number of bits received is not a multiple of 8 and the frame has a Frame Check Sequence Error. Alignment Errors often result from MAC layer packet formation problems, cabling problems that cause corrupted or lost data, or packets that pass through more than two cascaded multiport transceivers.
Asynchronous (async)
Serial data is transmitted in one of two ways, synchronous (sync) or asynchronous (async). Async communications involve the use of a start bit to signal the beginning of a character and a stop bit to signal the end of the character.
A commonly used term for a standard set of commands for modems. All the commands start with the prefix "AT" (for ATtention), followed by a number or a combination of numbers and symbols. For example, if you use a terminal program ( the terminal window in Frontline's SerialBERT products), type in the command "AT" and press enter, the modem should respond "OK". If the modem is plugged into a standard telephone line, typing "ATDT" should get you a dial tone, "ATDT" followed by a telephone number will dial that number etc. The online Help in Frontline's SerialBERT products outlines several useful AT commands.
Baud is often erroneously thought to be synonymous with bits per second, but baud is actually a measure of the frequency of a carrier signal on a phone line. At one time, a single bit was sent with each modulation, but modern modems transmit more than one bit per change so bps numbers are generally multiples of the baud rate.
An acronym for Bit Error Rate Testing. Bit Error Rate Testers (such as Frontline's SerialBERT Async and SerialBERT ComProbe) are typically used to test modems and/or telephone lines by sending a known data pattern over the circuit and then testing to see that the pattern arrived intact at it's destination. Traditionally, Bit error Rate Testers were large, bulky and expensive pieces of hardware; with SerialBERT the tester only needs a notebook PC and the SerialBERT software.
A form of synchronous communication that uses sync characters to frame the data. Monosync uses a single sync character at the start and end of each frame, bisync uses two.
Short for Binary digIT, a bit is the smallest unit of data communication. Computers speak in base 2 numbers where a digit can be only 1 or 0.
Serialtest can look at data either Least Significant Bit first (normal) or Most Significant Bit first (reversed). For example, if FTS is monitoring data in LSB mode and sees 0000 0001 on the circuit, it will display this as hex 01. In MSB mode, FTS will reverse the order of the bits as they come in and display this byte as 1000 0000, or hex 80. Bit reversal occurs both when monitoring data and when transmitting data.
In a Bit Error Rate Test, bits are sent out in groups called blocks, pre-defined groups of bits of fixed length. In SerialBERT Async or SerialBERT ComProbe, the block size can be selected (1K, 10K, 100K, 100M bits). If SerialBERT detects an error in a single bit, the block containing that bit is considered to be an errored block.
See Block, above.
A traditional breakout box is a device that can be placed in a circuit and uses LED's to show when a line in the circuit is active. Serialtest contains a software breakout box that shows a graphical display of the control signal changes in real time. Serialtest also retains a history of those changes that can be reviewed in the Signal Display Window.
In most computer systems, a byte is a unit of information that is eight bits long (see Word Length). A byte is the unit most computers use to represent a character such as a letter, number, or typographic symbol (for example, "g", "5", or "?"). A byte can also hold a string of bits that need to be used in some larger unit for application purposes
CD (Carrier Detect)
A control signal from a DCE device (a modem, for example) indicating that the DCE has recognized another device and that the carrier connection is established. This signal stays on during the entire conversation between the two. (See also TD, RD, RTS, CTS, DSR, DTR, RI)
The set of symbols used to display data. Most of us are familiar with the ASCII character set, it's what you're looking at right now. FTS can show you your data in ASCII as well as EBCDIC or BAUDOT, two other character sets sometimes used in data communications.
When using an FTS product that includes sync capability (Serialtest ComProbe or SerialBERT ComProbe) you must select the communication mode that matches the circuit under test. Communication Mode specifies the basic physical layer operation for the circuit. You can select asynchronous (Async), synchronous (Sync) or isochronous operation. Synchronous choices include NRZ (Non-Return to Zero) or NRZI (Non-Return to Zero Inverted) data encoding, and external or internal clock.
RS-232 communications involve the use of control signals to manage the communication between devices. The control signals are: TD (Transmit Data), RD (Receive Data), RTS (Ready To Send), CTS (Clear To Send), DSR (Data Set Ready), DTR (Data Terminal Ready), RI (Ring Indicator) and CD (Carrier Detect). These signals are used by the devices involved to keep each other informed as to when they are ready to send data etc.
CRC stands for Cyclical Redundancy Check. CRC is a mathematical technique to check for data transmission errors. A check is performed on a block of data as it is received to insure that it has arrived intact.
CTS (Clear To Send)
A Control Signal from the DCE that alerts the DTE device that the DCE is ready to receive data. (See also TD, RD, RTS, CD, DSR, DTR, RI)
Frontline's Serialtest Async and AsyncExpress come with a custom cable set to tap an asynchronous serial link. It consists of three parts, a routing cable, a monitor head and a source head. Two ends of the routing cable (marked DTE and DCE) are connected to the two serial ports on the PC. Serialtest Async or AsyncExpress are connected to either the monitor head or the source head, depending on the application. As their names imply, the monitor head is used to "T" into a link for the purpose of passively monitoring the link, or the source head to inject data into the circuit.
Data Circuit terminating Equipment. An example would be a modem. In a typical RS-232 link a DTE (Data Terminal Equipment) device, such as a PC, talks to a DCE device, such as a modem. DTE and DCE are complimentary interfaces. A DTE device always transmits on pin 2 and receives on pin 3 of a DB25 connector, a DCE device does the opposite.
Traditionally, a Data Protocol Analyzer was a large, bulky and expensive piece of hardware that a technician would lug around to test data circuits and to perform analyses on a data link. Using FTS, a technician can now carry a notebook computer, with FTS software installed, to capture data and analyze it right on the spot.
Literally, to decode means to translate a code into plain English. FTS takes the raw data that it captures and decodes it into it's native protocol. Data, as transmitted is a continuous stream of numbers. The meaning of these numbers may be very difficult to determine when looking at your data in it's crude form, but, when decoded, the significance of each byte is easily determined. FTS protocol decodes help to find errors or problems in a link in a fraction of the time it would ordinarily take.
DSR (Data Set Ready)
A Control Signal that is sent by a DCE device indicating to the DTE device that the DCE is ready to transmit or receive data. (See also TD, RD, RTS, CTS, CD, DTR, RI)
DTE (Data Terminal Equipment)
Data Terminal Equipment. An example would be a PC serial port. In a typical RS-232 link a DTE device, such as a PC, talks to a DCE device, such as a modem. DTE and DCE are complimentary interfaces. A DCE device always transmits on pin 3 and receives on pin 2 of a DB25 connector, a DCE device does the opposite.
DTR (Data Terminal Ready)
A Control Signal sent by the DTE device to the DCE, letting it know that the DTE is ready. (See also TD, RD, RTS, CTS, DSR, CD, RI)
The actual rate at which data is going across a link. SerialBERT reports the actual speed of the data being received, so that it can be compared with the baud setting. If the link is working properly, the two should be nearly the same.
When a receiving device determines that the data it received does not match the data that was transmitted by the sending device, an error is generated. This will usually result in the data being re-sent (see CRC).
In BERT Testing, the percentage of cases in which the received bit pattern differs from that which was transmitted. SerialBERT calculates the rate and displays it in the Statistics Window. For example, if SerialBERT had received 40,448 bits and one of them was an error, the Error Rate would be .001992%. SerialBERT also calculates the number of errored blocks and seconds. In the example above, we had 50 blocks received, with 1 error for a rate of 2% and in the 13 seconds it took to receive those bits, 1 second had an error for a rate of 7.692308%. The error rates are used by SerialBERT to determine the Line Grade.
The most widely used local area network standard, Ethernet was originally developed at Xerox's Palo Alto Research Center (PARC) in 1973. It was the first practical method for linking PCs together to share files, printers and other devices. Frontline's Ethertest program is used to analyze Ethernet networks.
In a protocol analyzer, a filter is a way of limiting the amount of data captured or displayed to help the user to focus in on the data of interest. Frontline's Ethertest uses two different types of filters. Capture Filters specify the data to be captured by Ethertest, so that only the data the user is concerned with is captured. Display Filters don't affect what data gets captured, but limit the data the user sees on the screen. For example, a capture filter could be set up so that only the data passing between two IP addresses was captured, or a display filter could be imposed on data already captured to limit the data displayed to that which passed between two IP addresses.
As it's name implies, flow control is a method for controlling when a device sends (or doesn't send) data. Flow control can be done with hardware or software. In software flow control schemes, a particular character (the Xoff, or Transmit off character) is sent to the transmitting device to tell it that it the the receiver is unable to accept any more data. The sender will then wait until it receives the Xon character before sending any more data.
Data is placed in a frame for transmission over the wire by the Data Link protocol. The frame includes not only the data, but any other information needed to get that data to it's proper destination, and to be sure that it arrives intact. Depending on the protocol used, this may include error correction, source address, destination address, etc.
Another name for a CRC.
Frame relay is a digital service based on the older X.25 packet-switching technology. Frame relay is often used to connect local area networks with major backbones or to interconnect LANs. For more information on Frame Relay see the Basic Guide to Frame Relay Networking.
Frontline Test System
The Frontline Test System (FTS) is a family of products for troubleshooting and analyzing data communication equipment and networks. Serial products include Serialtest Async (for testing async circuits, up to 115.2K bps) and Serialtest ComProbe (for testing sync circuits up to 64K bps and async circuits up to 38.4K bps). Ethertest, our Ethernet analyzer; and our new line of industry-specific analyzers including FTS4BT, our Bluetooth analyzer, FTS4Control for troubleshooting Industrial Automation and Supervisory Control And Data Acquisition systems (SCADA) and FTS4ZB, our 802.15.4 & ZigBee analyzer
High Level Data Link Control. One of the most common data link layer (layer 2) protocols.The HDLC protocol is defined by International Standards Organization (ISO) for use on both point-to-point and multipoint (multidrop) data links. It supports full duplex transparent-mode operation and is now extensively used in both multipoint and computer networks.
Any system for determining how two things work together. RS-232 and RS-485 are electrical interfaces that spell out how two serial devices can communicate with one another.
Short for Internet Protocol. Part of the TCP/IP protocol suite, originally developed for wide area networks (notably, the internet) now also used in LAN, frame relay and other data traffic. (see IP Address, below).
Every node on the internet must have a unique identifier. This is accomplished by way of an IP Address. An IP Address is a 32 bit number, usually written as 4 decimal numbers (or octets), each representing 8 bits of the address, separated by periods. A typical IP Address would be written as 192.128.42.6.
A term used in BERT testing, it is a measure of the quality of a communications link which can range from Excellent to Poor. SerialBERT defaults to the CCITT Recommendation G.821 standards, but the quality parameters can be set by the user.
Acronym for Media Access Control. A unique number that identifies a particular Network Interface Card and hence a specific device on the network.
MOdulator/DEModulator. A modem is a device that converts digital signals from a PC into analog signals that can be sent over a telephone line; another modem performs the analog to digital conversion at the receiving end.
A form of synchronous communication that uses sync characters to frame the data. Monosync uses a single sync character at the start and end of each frame, bisync uses two.
On a network, any piece of equipment connected to a communication network. Most nodes on a network are computers, but nodes could also be printers, scanners, etc.
In Serialtest, Operating Mode selects between monitor and source modes. In monitor mode Serialtest is passively monitoring data on the circuit, either in both directions (monitor both), just the DTE data (Monitor DTE) or just the DCE data (monitor DCE). In source mode, Serialtest can actively test the circuit by transmitting a string or file.
In SerialBERT, Operating Mode lets you choose to send data, receive data, or send and receive data.
Data is grouped in packets for transmission over the circuit by the Data Link protocol. The packet includes data, and any other information needed to get the data to it's proper destination. Depending on the protocol used, this may include error correction, source address, destination address, etc.
Serialtest, in monitor mode, is a passive monitor, meaning that it has no effect on the data being transmitted, it simply watches it as it goes by. The circuit operates exactly as it did before in the absence of Serialtest.
A form of error checking, parity checking adds an extra bit to each byte of transmitted data. If even parity is used, the bit added to the end of the byte would make an even number of ones, if odd parity is used, it would make an odd number. For example, let's suppose we are using even parity and we send the byte 0101101. This byte contains an even number of ones (four) so the bit we would add at the end would be 0. If we were using odd parity, we would add a 1 to make the total of ones equal to 5 (an odd number).
In BERT (Bit Error Rate Testing), a known sequence of bits is sent over a link, and then compared at the other end to see that the bit pattern received is the same as the pattern that was sent. SerialBERT provides eight different pre-defined bit patterns, plus a user definable pattern.
Number of bits per second divided by the maximum speed of the network, expressed as a percentage.
PPP (Point to Point Protocol) is a standard protocol for transmitting IP packets over serial lines. PPP allows you connect to the Internet over a telephone line, and become a node on the internet. If you are reading this on the Internet, chances are you are connected to the internet via PPP.
A protocol is a set of rules governing the transmission of data between two points for a specific layer (or layers) that determine how data is transferred over a network. IP and TCP are examples of common network protocols.
A tool used to examine data transmissions that decodes the data and shows it in it's native protocol for easier analysis. Serialtest Async, Serialtest ComProbe and Ethertest are all protocol analyzers.
RD (Receive Data)
The RS-232 line that actually carries the incoming data. (See also TD, CD, RTS, CTS, DSR, DTR, RI)
As it happens. All FTS products show you data, statistics and frame information as it is actually occurring on the circuit. You can also capture data to memory or to disc and review it later.
RI (Ring Indicator)
A control signal used by a modem to indicate the occurrence of a telephone ring signal. Used by auto-answer modems so that they know when to "answer" the incoming call. (See also TD, RD, RTS, CTS, DSR, DTR, CD)
A standard, established by the Electronic Industries Association (EIA) in 1969 to define the electrical characteristics for connecting Data Terminal Equipment (DTE) and Data Circuit Terminating Equipment (DCE). The standard dictates the voltage ranges, control signals and pin assignments. A typical example would be a connection between a PC (a DTE device) and a modem (a DCE device). The RS-232 standard is the most common serial interface today. FTS products Serialtest Async, Serialtest Spy, Serialtest ComProbe, SerialBERT Async and SerialBERT ComProbe all troubleshoot RS-232 links.
Similar to RS-485, the RS-422 standard enables signals to travel greater distances than RS-232 (4000 ft versus 20 ft) with greater immunity to noise. RS-422 employs a pair of wires for transmission, a pair for reception plus a ground wire and an additional pair for each control signal used.
An enhanced version of RS-422, RS-485 allows up to 32 devices to communicate at half-duplex on a single pair of wires, plus a ground wire, at distances up to 1200 meters (4000 feet). Data is transmitted differentially on two wires twisted together, referred to as a "twisted pair." The properties of differential signals provide high noise immunity and long distance capabilities. An RS-485 network can be configured two ways, two-wire or four-wire. In a two-wire network the transmitter and receiver of each device are connected to opposite ends of a twisted pair. Four-wire networks have one master port with the transmitter connected to each of the "slave" receivers on one twisted pair. The "slave" transmitters are all connected to the "master" receiver on a second twisted pair.
Uses a DB25 connector, designed to supercede RS-449. The RS-530 is a balanced interface that was designed to replace the more expensive V.35 connector. RS- 530 can operate to speeds of 2 Mpbs.
A control signal sent by a DTE device to a DCE device to inform the DCE that the DTE has data ready to send. (See also TD, RD, CD, CTS, DSR, DTR, RI)
Synchronous Data Link Control. Full duplex (receive and send at the same time), synchronous protocol transparent to the receiving hardware. Calculates the positions of fields within the frame from the start and end flags.
Serial.sys is the standard driver supplied with Windows NT (and Windows 2000) that controls the serial ports on a PC. When FTS is started, it temporarily replaces serial.sys (or, on Windows 9x and Me systems, serial.vxd) with it's own driver which performs the data capture functions, as well as those that serial.sys usually performs. For this reason, FTS works only with serial ports that work with Microsoft's standard driver.
Serial.vxd is the standard driver supplied with Windows 9x (and Windows Me) that controls the serial ports on a PC. When FTS is started, it temporarily replaces serial.vxd (or, on Windows NT and 2000 systems, serial.sys) with it's own driver which performs the data capture functions, as well as those that serial.vxd usually does. For this reason, FTS works only with serial ports that work with Microsoft's standard driver.
Data that is transmitted sequentially, one bit at a time. For example, if a byte consists or eight bits, a parallel link would send one byte (all eight bits) simultaneously over eight data lines. A serial transmission would send that same byte one bit at a time, over a single data line.
Serial Port
A port that sends and receives serial data. Most PC's are equipped with one or two serial ports. FTS asynchronous products capture data to the serial ports of the monitoring PC.
Serial Line Internet Protocol. SLIP is a TCP/IP protocol, often used to connect to the internet.
System Network Architecture. A proprietary network architecture designed by IBM. It uses seven layers, like the OSI model, but unlike the OSI model it uses a standard protocol for each layer.
Because asynchronous communications use no clock to regulate data transmission, start bits and stop bits are used to signal the beginning and end of a byte.
Because asynchronous communications use no clock to regulate a transmission, start bits and stop bits are used to signal the beginning and end of a byte.
A continuous sequence of characters.
Serial data is transmitted in one of two ways, synchronous (sync) or asynchronous (async). Async communications involve the use of a start bit to signal the beginning of a character and a stop bit to signal the end of the character. Sync communication uses a clock to synchronize the sending and receiving devices, along with a sync character(s).
In a synchronous transmission, sync characters are used to mark the start and end of a frame.
The number of seconds that two devices on a circuit have been unable to communicate because they have been out of sync. SerialBERT Async and SerialBERT ComProbe track the number of sync lost seconds.
Transport Control Protocol/Internet Protocol. Developed by the Department of Defense for the Arpanet (the precursor to the Internet). One of the most flexible and widely used protocols, it includes FTP (File Transfer Protocol), SMTP (Simple Mail Transfer Protocol).
The RS-232 line that actually carries the outgoing data from one device to another. (See also CD, RD, RTS, CTS, DSR, DTR, RI)
As each byte is captured by FTS, the time of capture is recorded and displayed. This is essential for troubleshooting timing problems on a circuit.
Universal Asynchronous Receiver/Transmitter. The chip that takes parallel data from the PC and converts it to serial so that it can be sent out the serial port.
USART
Universal Synchronous/Asynchronous Receiver/Transmitter.
The number of data bits in a byte, usually seven or eight. FTS serial products allow you to select the word length to match that of the circuit under test.
X.25 is a standard network access protocol for attaching different types of computer equipment to a packet-switched data network (PSDN). A PSDN is an interconnecting set of switching nodes that enables subscribers to exchange data using a standard protocol and packet-switching technology. This protocol is particularly useful for communication between different types of computer systems and for accessing public databases.
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