TSU 100 FAQs

• Can T1 Service Units be used on fractional T1 circuits?
  All ADTRAN T1 Service Units can be used for full or fractional T1 access with one to 24 DS0s or channels mapped to provide the desired T1 bandwidth.
  (ID 60)
  
  
• Can a TSU xx0 be used on a DDS/56k line?
  No. T1 and DDS have different electrical characteristics, including format and signal levels. TSUs (T1 Service Units) are used with T1 circuits and DSUs (Data Service Units) are used with DDS circuits.
  (ID 61)
  
  
• Can I use my TSU on a frame relay circuit?
  Yes, ADTRAN’s TSU xx0 units can be used on frame relay circuits to provide WAN access from an external FRAD (Frame Relay Access Device). These units are not, however, frame relay aware. They simply provide the layer 1 connection between your circuit provider and your DTE equipment. (ie: router, FRAD, etc.)
  (ID 62)
  
  
• Will the TSU xx0 encapsulate frame relay?
  TSU xx0 units can be made frame relay aware when an NxIQ Module (1200255L1) is installed. The NxIQ Module can provide detailed performance monitoring of a frame relay network. Additionally, ADTRAN offers a wide variety of products that provide frame relay encapsulation. The ADTRAN FSU (Frame Relay Service Unit) and ATLAS (ADTRAN's Total Access System) product lines provide full support for frame relay access.
  (ID 63)
  
  
• How many T1s can be terminated in a TSU xx0 unit?
  Two T1s can be terminated in a TSU xx0 unit. One T1 can be terminated with the built-in network interface. Additionally, a second T1 can be terminated using the Full Drop-and-Insert Module (1200065L1), a DS-1 interface.
  (ID 64)
  
  
• Is it possible to pre-configure and test ADTRAN’s TSU xx0 units prior to installation?
  Yes, all TSU xx0 units can be pre-configured using front panel access. For testing purposes, a T1 can be simulated by connecting the NETWORK interfaces of the TSU xx0 units using a T1 crossover cable. The T1 crossover connects pins 1 to 4 and 2 to 5 (ie: the Rx pair 1,2 to the Tx pair 4,5).
  (ID 65)
  
  
• Which voice module can be used for leased line modem applications with the TSU xx0 products?
  The E&M Module can be used in the TSU xx0 units for leased line modem applications. The module must be configured for TO (Transmit Only) mode.
  (ID 66)
  
  
• How can I determine what alarm I am getting when the alarm indicator is on on my TSU xx0?
  To view the active alarms from the front panel of the TSU xx0 units:
  
  1. Select:1) Status from the main menu.
  2. Then select Active Alarms.
  3. Press ENTER to view the list of currently active alarms.
  
  (ID 68)
  
  
• What is LOS (Loss of Signal)?
  An LOS is an alarm indication that occurs when the CSU does not receive a valid T1 signal (i.e., approximately 1.544 Mbps, nominally 3V peak). A common cause of LOS is an improperly wired cable from the demarcation point to the TSU. Additionally, if excessive zeros are received on an AMI line, LOS can be declared.
  (ID 70)
  
  
• What is Blue/AIS (Alarm Indication Signal) Alarm?
  Blue Alarm, commonly referred to as AIS or Keep Alive, is declared when the CSU is receiving unframed all ones on the network interface indicating an upstream circuit problem, incomplete, or mis-configuration within the telco.
  (ID 71)
  
  
• What is Red Alarm?
  Red Alarm is declared when the CSU cannot synchronize on the framing pattern on the network interface. This may be due to excessive errors on the T1 or an incorrect framing pattern. Red Alarm will be declared if an Out of Frame (OOF) condition exists for 2.5 seconds or more. A common cause of Red Alarm is a mismatch on framing configuration (D4 versus ESF) between the telco and the costomer's CSU.
  (ID 72)
  
  
• Are ADTRAN's T1 products flash upgradable?
  Many of ADTRAN's TSUs (T1 Service Units), TDUs (T1 Data/Service Units), and HSUs (HDSL Service Units) are flash upgradable using ADTRAN's T-Flash software. The T-Flash software package and detailed instructions on firmware upgrades can be found on ADTRAN's web site.

  The following products are upgradable using ADTRAN's T-Flash software: TSU 100, TSU 100e, TSU 120, TSU 120e, TSU 600, TSU 600e, TDU 110, TDU 120, HSU 100, and HSU 600.
  (ID 73)
  
  

• Can I remotely monitor/access the TSU xx0 units?
  There are several ways to remotely monitor/access the TSU xx0 units. They can be accessed using T-Watch PRO or a VT 100 terminal session through the Chain In port located on the rear of the unit. Additionally, Telnet support is provided via a 10BaseT port in "e" products or with the SNMP Agent Module in non "e" products.
  (ID 75)
  
  
• Which units does T-Watch PRO^® support?
  T-Watch Pro, ADTRAN’s PC-based management software, provides a full GUI interface for management of the following units: ESF CSU ACE, CSU RM, TSU, TSU LT, TSU RM, TSU ESP, TSU 100, TSU 100e, TSU 120, TSU 120e, TSU 600, TSU 600e, HSU 100, HSU 600, TDU 110, TDU 120, TDU 120e.
  (ID 76)
  
  
• Which ADTRAN TSU units support SNMP Management?
  ADTRAN’s TSU "e" series products have a built-in SNMP Agent providing SNMP Management from the Ethernet interface. The TSU "e" products include the following: TSU 100e, TSU 120e, TSU 600e. The TSU ESP also supports SNMP when the 10BaseT Module is installed. Additionally, the Agent Module provides SNMP Management when it is installed in the non "e" series of TSU xx0 products.
  (ID 77)
  
  
• How do I extend a plain old analog telephone line to a remote location (Off Premise Extension) using voice FXO and FXS cards?
  Take a 2-wire loopstart telephone line from the telco and connect it to the FXO card. The FXO converts the analog voice signal into a binary representation that the T1 can transfer to the remote site. It also takes the ~25mA loop current that indicates the off hook /on hook condition, and the ~100 VAC ring voltage and converts them into a 2-bit binary representation called signal bits. The remote site uses an FXS card and connects it to a plain old telephone. The FXS card converts the digital voice back to analog and the signal bits back to DC loop current and AC ring voltage for the phone. For more info, see the POT Line to Remote Phone section of our on-line VOICE TUTORIAL.
  (ID 270)
  
  
• How do I extend a plain old telephone (POT) line from the PBX, across a T1 to a remote phone using voice FXO and FXS cards?
  The customer takes a 2-wire loopstart telephone line from the station side of the PBX and connects it to the FXO card. The FXO converts the analog voice signal into a binary representation that the T1 can transfer to the remote site. It also takes the ~25mA loop current that indicates the off hook/on hook condition, and the ~100 VAC ring voltage and converts them into a 2 bit binary representation called signal bits. The remote site uses the FXS card to connect to a plain old telephone. The FXS card converts the digital voice back into analog and the signal bits back to DC loop current and AC ring voltage for the phone. For more info, see the POT Station to Remote Phone section of our on-line VOICE TUTORIAL.
  (ID 271)
  
  
• How do I tie two PBX Trunks together using voice FXS cards?
  Connect the FXS card to an analog trunk line on PBX A. A T1 connects sites A and B. The opposite site, PBX B, also has an FXS card connected to an analog trunk line. If 1234 dials 1235, the PBX connects the two stations without the use of external trunks. When 1234 dials 5678, PBX A recognizes it as a remote extension and seizes the 2w analog loop provided by the FXS. The remote FXS immediately rings and the remote trunk (on PBX B) connects. The two PBXs are now connected and PBX A passes the DTMF digits over to PBX B. PBX B then routes the call to 5678. For more info, see the PBX Trunk to PBX Trunk (with FXS) section of our on-line VOICE TUTORIAL.
  (ID 272)
  
  
• How do I tie two PBX Trunks together using voice E&M cards?
  You must connect the E&M card to an E&M interface on the PBX. Unlike a POTs line, E&M does not have a DC offset on the talk path. The talk path is on a set of wires that are separate from the -48 VDC signaling lead wires. The voice signal is modulated onto the tip and ring when operating in a 2-wire full duplex configuration. In the 4-wire configuration, the voice is transmitted onto the T/R pair and received on the T1/R1 pair. The signaling (on hook, off hook) is still done with 48 VDC but it rides on the E&M leads. The PBX is an "M lead originate" device and the ADTRAN E&M card is an "E lead originate" device. When PBX A wants to place a call, it raises the M lead. The PBX does this by applying -48 VDC to the M lead. Our E&M card sees -48 VDC and converts that -48 VDC into signal bits. The remote E&M card sees the bits coming from the other side and converts the signal back to analog by grounding the E lead. This causes current to flow from the PBX to the ADTRAN E&M card on the E lead. When PBX B sees that the E lead has gone high, it knows a call is coming in and rings the appropriate phone. When the ringing phone goes off hook, PBX B then signals PBX A by applying -48 VDC to the M lead. Our E&M card sees that the M lead now has voltage and transmits signal bits back to PBX A. The ADTRAN E&M card at site A converts the bits back into an analog state by grounding the E lead. Now current is flowing from PBX A into the ADTRAN E&M card A. The originating PBX A has now seen the E lead return high and the connection is complete. For more info, see the PBX Trunk to PBX Trunk (with E&M) section of our on-line VOICE TUTORIAL.
  (ID 273)
  
  
• How do I extend voice circuits from a T1 port on the PBX to a POTs at a remote location using DSX and FXS cards.
  The PBX connects to an ADTRAN DSX card. Across the T1 at the remote site, the customer will use FXS cards to connect to POTs. Each phone line leaves the PBX on a single DS0. The remote site uses a FXS card to convert the DS0 to analog and connect to a plain old telephone. The FXS card converts the digital voice back to analog and the signal bits back to DC loop current and AC ring voltage for the phone. For more info, see the PBX with a T1 to Remote POTs section of our on-line VOICE TUTORIAL.
  (ID 274)
  
  
• How do I extend voice circuits from the E&M port on the PBX to a POTs at a remote location using E&M and FXS cards.
  At the PBX site, the customer connects an analog E&M port on the PBX to an ADTRAN E&M card. At the remote site, POTs are connected to FXS cards. The E&M card must be connected to an E&M interface on the PBX. Unlike a POTs line, E&M does not have a DC offset on the talk path. The talk path is on a set of wires that are separate from the ­48 VDC signaling lead wires. The voice signal is modulated onto the tip and ring when operating in a 2-wire full duplex configuration. In the 4-wire configuration, the voice is transmitted onto the T R pair and received on the T1, R1 pair. The signaling (on hook, off hook) is still done with 48 VDC but it rides on the E & M leads. The PBX is a "M lead originate" device and the ADTRAN E&M card is an "E lead originate" device. When the PBX wants to place a call, it raises the M lead. The PBX does this by applying ­48 VDC to the M lead. Our E&M card sees ­48 VDC and converts that ­48 VDC into signal bits. The remote FXS card sees the bits coming from the other side and converts the signal back to analog loop start and rings the phone. When the phone goes off hook, the FXS card sends signal bits back to the E&M card. The ADTRAN E&M card at site A converts the bits back into an analog state by grounding the E lead. Now current is flowing from PBX A into the ADTRAN E&M card A. The originating PBX A has now seen the E lead return high and the connection is complete. For more info, see the PBX with Analog E&M to Remote POTs section of our on-line VOICE TUTORIAL.
  (ID 275)
  
  
• How do I tie an analog station, on PBX A, to an analog trunk, on PBX B using voice FXO and FXS cards?
  PBX A uses a station (2-wire analog loop) to connect to the FXO card. The FXO converts the analog voice signal from PBX A into a binary representation that the T1 can transfer to the remote site. It also takes the ~25mA loop current that indicates the off hook/on hook condition, and the ~100 VAC ring voltage and converts them into a 2 bit binary representation called signal bits. The remote site uses an FXS card to connect to a Trunk (2-wire analog loop) on PBX B. The FXS card converts the digital voice back to analog and the signal bits back to DC loop current and AC ring voltage for PBX B. For more info, see the PBX Station to PBX Trunk section of our on-line VOICE TUTORIAL.
  (ID 276)
  
  
• How do I create a dedicated point-to-point hotline (Private Line Automatic Ringdown) using voice FXS cards? When one caller goes off hook on either end, I want the opposite side to automatically ring without dialing.
  You can connect a plain telephone to the FXS card. The remote side also uses an FXS card to connect to a plain telephone. Side A goes off hook and loop current flows from the FXS card through the phone. The signal bits tell the remote phone to ring. When the remote phone goes off hook, loop current flows from the remote FXS through the remote phone, and the talk path is established. For more info, see the Phone to Phone Hotline section of our on-line VOICE TUTORIAL.
  (ID 277)
  
  
• How do I extend a DID (Direct Inward Dial) line from the telephone company using voice FXO and FXS cards?
  This connection seems backwards when compared to the OPX line. Remember with a DID line, the telco acts like the switch (FXO) and the customer supplies the battery (FXS). The customer connects the telco DID line to our FXS card and the DID trunk of the PBX to the FXO card. These voice lines originate from telco and terminate into the PBX. They will never originate from the PBX. When a call comes into the telco's switch with your telephone number, the telco closes a switch connected to your cable pair. This causes loop current to flow from the FXS card. The FXS card sends signal bits across the T1 to the FXO card who then closes his switch causing loop current to flow from the DID interface card on the PBX. The PBX then signals the telco (with a wink) that it is ready for the call. The PBX does this by reversing the battery's polarity. When the Telco sees this wink, the Telco then passes the DNIS digits through the talk path into the PBX. The PBX uses the DNIS digits to route the call to the appropriate phone. The call can terminate from either end. If the person at the PBX hangs up the loop current (from the PBX to the telco) will stop flowing and Telco will return to an idle condition by opening their switch. The call can also be terminated from the telco side if the incoming caller hangs up. When this happens, the telco opens their switch and loop current stops flowing. The PBX then returns to an idle condition. For more info, see the Direct Inward Dial section of our on-line VOICE TUTORIAL.
  (ID 278)
  
  
• How can I use the DNIS delay option of the voice FXS cards to signal an "off hook" condition back to the telco after a simulated delay needed to allow my called device time to answer. For example, my called device will be a Fax Server.
  The TSU's network port is connect to the telco's T1 line. The FXS card uses its analog 2-wire ports to connect to (in this example) the fax server. When a call comes in from telco, the FXS card then sends ring voltage to the fax server. The fax server responds by answering the call. The FXS card winks back to telco that the server is ready for DNIS. At the same time the FXS card winks, it starts counting down the time configured under the DNIS delay option. The fax server receives the DNIS tones and uses them to route the call to the appropriate fax machine. This procedure takes a few seconds to route and for the fax machine to answer. When the DNIS delay time has expired, the FXS card sends an off hook condition to the telco for the remainder of the call. For more info, see the Telco to TSU 600 to Fax Server section of our on-line VOICE TUTORIAL.
  (ID 279)
  
  
• What is the pin-out for RJ-45 of the E&M module for the TSU 100, TSU 120, TSU 600 products?
  The following table describes the pin-outs:

  RJ-45 Pin	Name	Description
  1	Ring	Customer TX Tip; also 2W Tip
  2	Tip	Customer TX Ring; also 2W Ring
  3	E-Lead	Customer originate E-Lead
  4	SG	E-Lead ground return
  5	SB	M-Lead battery source
  6	M-Lead	Network originate M-Lead
  7	Tip 1	Customer RX Tip 1 (4W only)
  8	Ring 1	Customer RX Ring 1 (4W only)

  
  (ID 281)
  
  
• What is Red Alarm?
  Red Alarm is declared when the CSU cannot synchronize to the framing pattern on the network interface. This may be due to excessive errors on the T1 or an incorrect framing pattern. Red Alarm will be declared if an Out of Frame (OOF) condition exists for 2.5 seconds or more. A common cause of Red Alarm is a mismatch on framing (D4 versus ESF) between the T1 service provider and the TSU. For more information, please see ADTRAN Technical Support Note Troubleshooting an Alarm Condition on ADTRAN TSU Products with Loopback Test.
  (ID 282)
  
  
• What is Blue/AIS (Alarm Indication Signal) Alarm?
  Blue Alarm, commonly referred to as AIS or Keep Alive, is declared when the CSU is receiving unframed all ones on the network interface indicating an upstream circuit problem or an incomplete or misconfiguration within the T1 Circuit. It can originate at the Smart Jack if it does not recognize a valid T1 signal from the CSU (possibly caused by a broken wire pair on pins 4 and 5 or excessive Line Build Out on the CSU), or it may be a result of equipment failure in the Telco network. Typically this alarm points to a problem elsewhere in the T1 circuit, and not at the unit displaying the Blue alarm. For more information, please see ADTRAN Technical Support Note Troubleshooting an Alarm Condition on ADTRAN TSU Products with Loopback Test.
  (ID 283)
  
  
• What is LOS (Loss of Signal)?
  An LOS is an alarm indication that occurs when the CSU does not receive a valid T1 signal (i.e., approximately 1.544 Mbps, nominally 3V peak). The wire pair on pins 1 and 2 may be discontinuous or the T1 may not be connected or activated. LOS can also be invoked because of excessive zeros on an AMI circuit. For more information, please see ADTRAN Technical Support Note Troubleshooting an Alarm Condition on ADTRAN TSU Products with Loopback Test.
  (ID 284)
  
  
• What is a Yellow alarm?
  Remote Alarm Indication (RAI) is being received at the Network Interface to indicate that the far end is in Red Alarm. It may be inferred that the path from the far end to the near end is good since the RAI is being received successfully. (Note: "far end" refers only to the far end of the local loop, which may extend to the customers' "other" site, or may only go to an intermediate Central Office.) In ESF, the Yellow Alarm is transmitted over the Facility Data Link (FDL). In SF (or D4), it is transmitted inband, by setting the second bit in every DS0 to zero; consequently, it is possible for payload data to mimic the code and cause a "false yellow alarm". Typically this alarm points to a problem elsewhere in the T1 circuit, and not at the unit displaying the yellow alarm. For more information, please see ADTRAN Technical Support Note Troubleshooting an Alarm Condition on ADTRAN TSU Products with Loopback Test.
  (ID 285)
  
  
• What is a CRC (Cyclic Redundancy Check) error?
  The "checksum" (actually CRC-6) calculated on the received data does not match the "checksum" calculated by the transmitting equipment. A CRC error indicates that one or more bit errors have occurred on the T1. For more information, please see ADTRAN Technical Support Note Troubleshooting an Alarm Condition on ADTRAN TSU Products with Loopback Test.
  (ID 286)
  
  
• What is a BPV (Bipolar Violation) error?
  The CSU detected two consecutive marks of the same polarity in the received AMI signal. (Remember that the T1 signal is always AMI; the line code may be AMI, or AMI with B8ZS.) For more information, please see ADTRAN Technical Support Note Troubleshooting an Alarm Condition on ADTRAN TSU Products with Loopback Test.
  (ID 287)
  
  
• What is a FER (Framing Error)?
  The CSU detected bit errors in the framing bits, but not enough to cause a Red Alarm. For more information, please see ADTRAN Technical Support Note Troubleshooting an Alarm Condition on ADTRAN TSU Products with Loopback Test.
  (ID 288)
  
  
• What is a PLL (Phase-Locked Loop) alarm?
  The clock circuit in the CSU is unable to synchronize to the selected clock source. For more information, please see ADTRAN Technical Support Note Troubleshooting an Alarm Condition on ADTRAN TSU Products with Loopback Test.
  (ID 289)
  
  
• What is a Code Violation?
  The CSU has detected "CRCs" (if framing is ESF) or "BPVs" (if framing is D4). For more information, please see ADTRAN Technical Support Note Troubleshooting an Alarm Condition on ADTRAN TSU Products with Loopback Test.
  (ID 290)
  
  
• What is a XS0 (Excess Zeros)?
  Excessive zeros have been transmitted from the V.35 interface toward the T1. Actually only a warning, indicating that if the T1 is susceptible to ones density problems (i.e., line code is AMI) then the possibility exists that some circuit element may lose synchronization. For more information, please see ADTRAN Technical Support Note Troubleshooting an Alarm Condition on ADTRAN TSU Products with Loopback Test.
  (ID 291)
  
  
• What is a clock slip?
  The FIFO buffers on the DTE interface have probably over-run (causing the previously processed data to be repeated) because the clock on the Network Interface is of a different frequency from the clock on the DTE interface. This usually indicates multiple clock sources, so verify the timing source for the circuit (i.e. T1, CSU) and that you have the correct Timing Mode selected. For more information, please see ADTRAN Technical Support Note Troubleshooting an Alarm Condition on ADTRAN TSU Products with Loopback Test .
  (ID 292)
  
  
• What is a PLL (Phase-Locked Loop) alarm?
  The clock circuit in the module is unable to synchronize to the clock on the Network Interface. For more information, please see ADTRAN Technical Support Note Troubleshooting an Alarm Condition on ADTRAN TSU Products with Loopback Test.
  
  (ID 293)
  
  
• What is a No EXT Clock alarm?
  The module does not recognize an external transmit clock at the DTE interface, pertinent only when the DTE Transmit Clock is set to External. Confirm that the device connected to the Nx56/64 is indeed providing timing. If so, then confirm that the V.35 cable is supplying clock on pins U and W. The ADTRAN unit must be set for DTE timing under NETWORK configuration.
  (ID 294)
  
  
• What is an Open Loop?
  The module is unable to detect the flow of sealing current, most likely because the CSU/DSU is not connected or the cabling is not correct. For more information, please see ADTRAN Technical Support Note Loopback Adapters and Crossover Cables for T1 and DDS Circuits.
  (ID 295)
  
  
• Default passwords (passcodes) for ADTRAN products.
  Note: Where the product has no default password, Default Password will be N/A.
  
  

  Product	Key sequence (wake up unit)	Default Password
  TSU/TDU XX0	<CTRL>PTT	N/A
  TSU/TDU XX0"e" TSU XX0 "2nd Gen"	<CTRL>PTT	ADTRAN
  TSU/TDU ESP	<CTRL>PTT	adtran (for Telnet only!)
  TSU LT	<CTRL>PTT	N/A
  HSU XX0	<CTRL>PTT	N/A
  T3SU 300	Hit enter a few times	adtran
  Agent card	<CTRL>PTT	ADTRAN
  TSU Router Module/L128/L768/1.5	Hit enter a few times (CTRL-R to refresh screen)	N/A (Hit enter at login prompt)
  Atlas 800/800Plus/810Plus/550	<CTRL> L	Password
  NxIQ	Hit enter a few times	adtran
  TSU IQ/DSU IQ	Hit enter a few times	adtran
  FSU/FSU 5622 Express 5110/5200/5210	Hit enter a few times	adtran
  Smart 16/16e	Hit enter a few times	PASSWORD (if enabled)
  MX2800	Hit enter a few times	adtran

  
  (ID 304)
  
  
• Where can I find the power consumption requirements (for UPS and battery back-up applications) for ADTRAN products?
  The power consumption (in WATTS) can be found under the Product Specifications section of the data sheet for the specific ADTRAN device.
  (ID 326)
  
  
• What is QRSS?
  QRSS stands for Quasi-Random Sequence Signals and is a test pattern run on the T1.
  (ID 335)
  
  
• What does UAS mean?
  UAS is UnAvailable Seconds. This is a count of the number of seconds that a circuit is not available.
  (ID 336)
  
  
• What is the difference between 1^st Generation and 2^nd Generation TSUs?
  1^st Generation TSUs were the initial hardware release by ADTRAN. This is reflected by the first 4 digits of the part number. Part numbers beginning with 1200 are 1^st Generation units. Part numbers beginning with 1202 are 2^nd Generation units. The functionality and features of these units are the same; 2^nd Generation is just a later hardware release of the unit. Also, the 2^nd Generation units include embedded SNMP ('e'version).
  

  TSU 100e	1202.052L1		TSU 100 (without built in 'SNMP')	1202.052L2
  TSU 120e	1202.052L1		TSU 120 (without built in 'SNMP')	1202.129L2
  TSU 600e	1202.076L1		TSU 600 (without built in 'SNMP')	1202.076L2

  
  (ID 376)
  
  
• Can I use the same software/firmware to upgrade my TSU xx0 that I use to upgrade my TSU xx0e?
  Yes. If your regular TSU xx0 (not the 'e' version) is a 2^nd Generation unit, it will accept the same software upgrade. These units can be upgraded via Xmodem. Verify that the part number on the bottom of the unit indicates a 2^nd Generation unit (1202.xxxLx). If you have a 1^st Generation unit, it will not support Xmodem flash and must be flashed using ADTRAN's T-Flash software.
  (ID 377)
  
  
• What is Network Loopback?
  A loopback connects the opposite end's transmit(TX) to receive(RX) so that the T1 data stream is returned to its originating device for verification. This allows the originating device to check for errors in the pattern.
  (ID 378)
  
  
• What is the difference between a Line and Payload Loopback?
  Line loopback
loops all of the received data back toward the network. The transmitted data is the identical data that is received and is not reframed or regenerated. This tests right up to the T1 interface of the ADTRAN unit.
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• Payload loopback
performs the same functionality as the line loopback, except the payload loopback sends the received data through the payload so that it is reframed and regenerated out the network. This test also verifies the internal hardware of the local ADTRAN device.
(ID 379)


• Should I use an FXS or FXO module for my DID lines in my Total Access 750/850 or TSU XX0/XX0e?
  If your phone system has a DID interface, you will need an FXO card set for Dial Pulse Terminate (DPT) mode.
  (ID 406)
  
  
• What option modules do I need in my ATLAS 550, TA750, TA850 or TSU XX0 to interface to DID lines on my PBX?
  If your PBX has a true DID interface, this means that it is supplying 'battery' for the 2-wire analog voice circuit. This application requires an FXO module in the ATLAS 550, TA750, TA850 or TSU XX0 which provides loop closure and the passing of DTMF or MF tones to the PBX. The Telco circuit must be RBS signaling (E&M Wink) for this application.
  (ID 455)
  
  
• What option modules do I need in my ATLAS 550, TA750, TA850 or TSU XX0 to extend analog Telco DID lines to a remote site?
  If you have analog DID lines from Telco, you cannot use an ATLAS 550 FXS card to extend this line to a remote site. The ATLAS 550 FXS card is not Part 68 compliant. However, if you have the TA750, TA850 or TSU XX0 channel bank with Part 68 compliant FXS cards, these cards can convert the analog signal to digital T1 at the main site. At the remote site, an FXO card operating in DPT mode would be required.
  (ID 456)
  
  
• Can non-sequential channels be mapped to a single Nx56/64 V.35 port in the TSU Multiplexor series?
  Yes, if the channels are not being DACed through different paths in the network but are on a point to point network, they can be non-sequential and still function as one logical data stream.
  (ID 476)