Maintaining LAPD Links

This describes how to query the status of the OML, RSL, EML, and ESL, and the status of the PBSL when the PCU is in external mode. This also describes how to perform loopback test on LAPD links and how to reset LAPD links.

Prerequisites

Context

Figure 1 shows the internal transmission on the interface boards.

Figure 1 Internal transmission on interface boards

When the service incurs errors, you can query the status of LAPD links. If the status of links is faulty, perform Loop Test to loop back the signals sent by the CPU to determine whether the CPU transmission on the corresponding board is normal.

The LAPD link is categorized into OML, RSL, EML, ESL, and PBSL. Note that the PBSL is available in the case of external PCU only. Table 1 describes the links.

Table 1 Description of the LAPD links

Parameter	Meaning
OML	The OML is the operation and maintenance link between the BSC and the BTS. One OML corresponds to one site. If an OML incurs an error, its corresponding site and the RSLs on the site become faulty.
RSL	The RSL is the radio signaling link between the BSC and the BTS. One RSL corresponds to one TRX. If an RSL incurs an error, its corresponding TRX is faulty.
EML	The EML is the extended operation and maintenance link between the BSC and the BTS. Each HUB BTS or IP BTS requires one EML to report its software loading and logs.
ESL	The ESL is the signaling link between the BTSs. It is used to set up the signaling cross link between the HUB BTSs or IP BTSs.
PBSL	The PBSL is the signaling link between the BSC and the PCU. If the PBSL is faulty, the Pb interface board or the external PCU may be faulty.

There are two loopback types of LAPD links:

• Line loopback: The TDM BTS, HDLC BTS, and HUB BTS links support line loopback.
• IWF loopback: The HDLC, HDLC HUB, and IP links support IWF loopback.

Procedure

• Through GUI
  1. On the LMT, choose BSC Maintenance > Maintain Transmission and Signaling > Maintain LAPD Link. A window is displayed, as shown in Figure 2.
     Figure 2 Maintain LAPD Link window
     
     

  2. Set parameters in the LAPD Link area. Select NEs in the Candidate NE pane and add the NEs to the Selected NE pane.
  3. Click Query. A window is displayed, as shown in Figure 3.
     Figure 3 Query result of the LAPD link
     
     

  4. Select one or several links from the Query Result area, set the parameters in the Loopback Type area, and click Loop Test or Reset.
     NOTE:

     • When the Loopback Type is set to Line, a loopback timeout message is displayed if you click Loop Test. In this case, you need to manually break the E1 connection to connect the RX port and the TX port. This disrupts the link communication.
     • If you select all links, you can loop back and reset all links.
     • If you select one link or several links in the Query Result area, you loop back or reset only the link or the several links.
     • When the PCU is in external mode, you cannot select PBSL and OML, RSL, EML, and ESL at the same time.

• Through MML
  1. You can run the following commands on the LMT to maintain the LAPD links.
     • Run the DSP LAPDLNK command to query the status of LAPD links.
     • Run the LOP LAPDLNK command to loop LAPD links.
     • Run the RST LAPDLNK command to reset LAPD links.