This Technical Note focuses on troubleshooting techniques for a Leased Line Netopia Router and internal DSU, with an emphasis on North American T1 and Fractional T1 lines. Higher level datalink protocols like PPP, HDLC and Frame Relay are not referenced here but are the topic of another Technical Note.
Firmware Reference
- v5.3.7 (and later) - 4000 Series T1 Router
- v4.8.2 (and later) - R5300 T1 Router
Telnet into the Netopia router's Main Menu at 192.168.1.1 (if using the default IP setting). If your network has a different IP addressing scheme, modify this accordingly. Click Here! for instructions on using telnet and Hyperterminal (serial connection).
Login with the user name and password. The Superuser login is required to save changes.
If you are unsure of this, contact your network administrator.
Don't forget to press the Enter key to save any entries. Hitting the back space, delete or tab without first hitting enter will undo any changes.
The Esc key will take you back towards the main menu screen.
Once you have completed your configuration, you should reboot the Netopia to save and apply your changes.
The Netopia Main Menu Interface
The T1 Line card available in North America for the Netopia Router can connect to a T1 or Fractional T1 line and has both an S/A and RJ-45 interface with a switch to select between the two interfaces. The S/A interface can support synchronous (digital) connections from 56 Kbps to 1.544 Mbps (T1). Outside of North America the S/A interface can support synchronous connections up to 2.048 Mbps (E1).
Leased Lines in North American are based upon a 64,000 bits/s (64 Kbps) channel, referred as a DS0 (Digital Signal Level Zero). Twenty-four of these channels are grouped together to form a DS1, also referred to as a T1 (or T Carrier) line. Each channel can carry digitized voice or data.
Bits of data sent over a T1 line are sent in frames, and each T1 frame is twenty-four time slots of eight bits apiece. Therefore twenty-four timeslots multiplied by eight bits yields 192 bits in a T1 frame. Frames are sent at 8,000 times per second over a T1 line, for a payload data rate of 1,536,000 bits/s (1.536 Mbps).
There is an additional framing bit which is required to let end systems determine the start and stop of a frame. This produces a total of 193 bits per T1 frame, with a final T1 bit rate of 1,544,000 bits/s (1.533 Mbps). The user data rate will always be 1.536 Mbps, but only if clear channel is supported. If clear channel is not supported, each channel will be 56,000 bits/s for a total payload data rate of 1,344,000 bits/s (1.344 Mbps).
The Leased Line itself consists of four wires, or two pairs, terminated with a RJ-45 jack using pins 1,2,4,5. The RJ-45 cable itself connects to the built-in RJ-45 jack in the Netopia Router.
The Netopia Router has six WAN LED's which give a status of the WAN connection and are helpful in troubleshooting connection problems. These LED's are described as follows:
| LED | Status | Meaning |
|---|---|---|
| CH1 Traffic | Flashing Yellow | Packets in channel. |
| CH1 Link | Solid Green | Successful data connection. |
| Off | No data connection. | |
| WAN Ready | Flashing Red | Communication failed between Netopia and Telco. |
| Solid Green | Communication established between Netopia and Telco. | |
| Link Management | Off | Not used |
The Netopia Router's WAN Ready LED will blink red when there is no connection to the Telephone Company or remote network. Possible causes of this could be as follows:
- Bad or improperly pined out RJ-45 patch cable.
- Bad or improperly wired RJ-45 jack.
- Telephone company line problem.
A solid green WAN Ready LED indicates a physical connection between the local Netopia Router and remote equipment. Once this is done, the CH1 Link LED should come on indicating a connection to the remote network. If the CH1 Link LED does not come on, possible causes could be as follows:
- Incorrect line encoding;
- Incorrect framing;
- Incorrect number of DS0 channels;
- Incorrect first DS0;
- Incorrect buildout setting;
- Incorrect channel data rate;
- Incorrect clock source;
- Incorrect T1-S/A port setting.
All of these parameters are available and can be configured within the Netopia Router's console in the T1 Line Configuration screen. The Telephone Company or Leased Line provider provides this information. This screen looks like the following:
***************************************************************| T1 Line Configuration | |
| Line Encoding... | B8Zs |
| Framing Mode... | ESF |
| Transmit ANSI PRMs: | No |
| Number of DS0 Channels: | 2 |
| First DS0 Channel: | 1 |
| Contiguous Channels: | Yes |
| Buildout (-dB)... | Auto |
| Channel Data Rate... | Nx64k |
| Clock Source... | Network |
| Data Link Encapsulation... | PPP |
Return/Enter goes to new screen.
Enter Information supplied to you by your telephone company.
***************************************************************
B8ZS (Bipolar with Eight Zero Substitution) and AMI (Alternate Mark Inversion) are two types of line encoding schemes. Line encoding simply means taking frames of data (the zeros and ones) and representing them electrically on the line with a positive, negative, or zero voltage. If the line encoding is not correct for the Leased Line, then the CH1 Link LED will not be lit. B8ZS is the default setting and will work for most carriers.
ESF (Extended Superframe) and D4 are two types of framing modes. A frame is a grouping of zeros and ones grouped together ready to be transmitted over the Leased Line. If the framing mode is not correct for the attached line, then the CH1 Link LED will not be lit. ESF is the default setting and will work for most carriers.
The Number of DS0 Channels indicates how many 64 Kbps or 56 Kbps channels are allocated for the Leased Line. Below is a list of the most common DS0 channel allocations and the line speed they provide:
| Channels | Line speed | Type |
|---|---|---|
| 1 | 64,000 bits/s | Fractional T1 |
| 2 | 128,000 bits/s | Fractional T1 |
| 4 | 256,000 bits/s | Fractional T1 |
| 6 | 384,000 bits/s | Fractional T1 |
| 8 | 512,000 bits/s | Fractional T1 |
| 12 | 768,000 bits/s | Fractional T1 |
| 24 | 1,536,000 bits/s | Full T1 |
The number of DS0 channels programmed into the Netopia Router must match the number of DS0 channels available on the Leased Line. If these do not match, then the CH1 Link LED will not be lit. The default is two channels with the first DS0 being channel one.
The first DS0 channel is the first DS0 that is used for transmission on a Leased Line. Typically DS0 channels are allocated starting from timeslot number one. There may be cases however where DS0 channels are allocated starting from a number other than one. The first DS0 channel in the Netopia Router must reflect the correct first DS0 otherwise the CH1 Link LED will not be lit. The default setting is the first DS0 for transmission.
Buildout is the amount of signal attenuation (or resistance) applied to the Leased Line. The smaller the distance between equipment, the stronger the signal, the greater the need for signal attenuation. The farther the distance between equipment, the less attenuation needed, so a stronger signal is transmitted. The supported buildout values are Auto, 0db, -0.6db, -7.5db, -15.0db, -22.0db, where 0db offers no attenuation and -22.0db offers the most attenuation. The Auto setting looks at the incoming signal and selects the correct attenuation. If there are transmission problem across the Leased Line, be sure to set the attenuation to zero to ensure the signal is transmitted at full strength.
The Channel Data Rate defines the DS0 signal rate either being 64 Kbps or 56 Kbps. The default is 64 Kbps. The N simply means that N number of channels is multiplied by either 56 Kbps or 64 Kbps to derive the total line speed.
Clock Source determines where the Netopia Router will receive its transmit clock. The two options are Internal or Network, where Internal tells the Netopia Router that it will be providing the transmit clock on the Leased Line where as Network tells the Netopia Router that the network will be providing the transmit clock on the Leased Line.
Typically on a Fractional T1 line the clock is provided by the network but with a full T1 line (24 channels), clocking is typically not provided on the line so something on the line needs to provide a transmit clock. By setting Clock Source to Internal, the Netopia Router will provide the clock on the line. Only one device can provide the transmit clock on the Leased Line, if two devices are providing a transmit clock this could cause transmission problems and cause the CH1 Link LED to not be lit. The default setting is Network, which will work for most carriers.
The T1 card itself has a switch accessible on the rear of the Netopia Router to select between either the internal DSU or the S/A interface. Looking at the rear of the Netopia Router, if the switch is to the left, this indicates that the S/A interface is being used. If the switch is to the right, this indicates the internal DSU is being used. This switch must be set to the correct interface that is being used; otherwise the CH1 Link LED will not be lit.
By following the troubleshooting steps in this Technical Note, this should eliminate connection or communication problems between the Netopia Router and remote equipment over a Leased Line. If the Leased Line still does not work properly, please contact the Telephone Company or Leased Line provider. They will be able to check the Leased Line configuration and perform loopback and bit-error tests to determine the source of any Leased Line problem.