Cell Structure and Troubleshooting

Cell Site Structure and troubleshooting from OSS This procedure covers basic structure and troubleshooting of a site from an OSS perspective in situations where a site does not restore whether partially or completely, for example after a rehome or software upgrade.

BTS Hierarchy: In order to troubleshoot a site from the BSC it is necessary to have a knowledge of the logical hierarchy of the BTS (In the BSC) as compared with its physical elements. Physically the BTS is made up of RUs (Replaceable Units) such as the DXU, TRU, etc. Logically these RUs are known as MOs (Managed Objects). The Main MO of any site, the TG (Transceiver Group) is not associated with any hardware at the BTS but resides in the BSC. It can be thought of as an “Address” of the site within the BSC. Connecting the TG to the Site in the Field is the DIP (Digital Path). It represents the T1 (Abis Interface) link to the BTS. In the BTS itself there are RUs, which are represented by MOs in the BSC. BSC

BTS DXU

TG

RXOCF RXOTF RXOIS

DIP (RBLT) TRU

TRU RXOTRX RXOTX RXORX RXOTS (-0&&-7)

TRU RXOTRX RXOTX RXORX RXOTS (-0&&-7)

RXOTRX RXOTX RXORX RXOTS (-0&&-7)

BTS Hierarchy Managed Objects RXOTG-XX RXOCF-XX RXOTF-XX RXOIS-XX RXOTRX-XX-Y RXOTX-XX-Y RXORX-XX-Y RXOTS-XX-Y-0&&-7

Definition Transceiver Group Control Function Timing Function Interconnect Switch Transceiver Controller Transmitter Receiver Time Slots

Physical representation Entire RBS/DIP (usually) DXU Oscillator within the DXU Switch in the DXU TRU Transmitter within the TRU Receiver within the TRU Time Slots within the TRU

Numbering convention: All MOs in a site share the number of the TG. For example, if a site has TG 46, all of the sub-MOs will have number 46. The MOs related to the TRUs will have additional numbers added to them which refer to the TRU’s assignment within the TG. For example, TRU #0 in RXOTG-46 will have RXOTRX-46-0, RXOTX-46-0, RXORX-46-0, and RXOTS-46-0-0&&-7. The additional designations on the time slots refer to the time slot position within that TRU (i.e. TG 46, TRU 0, TS 0 thru 7). Any object in this list has a superior and a subordinate MO. What this means is that in order to perform certain operations it is necessary to remember the status of subordinate and superior MOs. When loading and deblocking always follow the hierarchy from top to bottom, and when taking out of service always follow the hierarchy from bottom to top.

Troubleshooting example #1 – Sector down When experiencing trouble at a site always get the “Big Picture” of how the site is behaving. Is the whole site down, or only certain sectors? Run the following commands to see at what level the site is experiencing problems: AL (print alarm list) RLC2 RP 3L 2P = LLEC: (print cell resources)

ALLIP This will give an overview of all the alarms that exist on the BSC at the time which may point you in the right direction for your specific site, then with the RLCRP command you will see which sectors have resources and which don’t. In our example, if sector B was down you would probably see alarms in the alarm list related to the TRUs at the site as well as the CF. You would see alarms for Logical Channels Availability, and probably alarms on the CF and the individual TRUs. They would look like this in the alarm printout: What you’re looking at Alarm header: gives the alarm class (A1=critical, take immediate action, A2=less critical, take action during wkg hours, A3=take action within a week, O1 &O2=observation only), switch name (i.e. PLT12C0), alarm number, date and time the alarm occurred. The alarm information is printed underneath. When investigating an alarm look at the date and time stamp to see when it came in. A1/APT "PLT12C0 C000G00" 560 010302 0606 CELL LOGICAL CHANNEL AVAILABILITY SUPERVISION CELL SCTYPE CHTYPE CHRATE SPV PL223B BCCH SDCCH TCH FR 1 A3/APT "PLT12C0 C000G00" 550 010302 RADIO X-CEIVER ADMINISTRATION MANAGED OBJECT FAULT MO RXOCF-46

0603

RSITE PL223

A2/APT "PLT12C0 C000G00" 551 010302 RADIO X-CEIVER ADMINISTRATION MANAGED OBJECT FAULT

ALARM SLOGAN BTS INTERNAL

MO RXOTRX-46-2

0603

RSITE PL223

ALARM SLOGAN OML FAULT

The alarm on the CF, “BTS Internal”, means a fault on the CF which is caused by an RU inside the BTS (TRU, PSU, ECU, etc.) The “OML FAULT” alarm on the TRX means that the TRU has lost communication with the BSC. If the whole site were down due to a T1 failure, you would see the Cell Logical Channels Availability Supervision alarms for all 3 sectors, plus the following alarms on the CF, and the DIP: A2/APT "PLT12C0 C000G00" 551 010302 RADIO X-CEIVER ADMINISTRATION MANAGED OBJECT FAULT MO RXOCF-46

0603

RSITE PL223

A1/APT "PLT12C0 C000G00" 548 010302 DIGITAL PATH FAULT SUPERVISION

0603

DIP 46RBLT

HG

ALARM SLOGAN OML FAULT

DIPEND

FAULT ALL1

SECTION

A2/APT "PLT12C0 C000G00" 549 010302 DIGITAL PATH UNAVAILABLE STATE FAULT DIP UAS 46RBLT -

UASR

UASB

SECTION

DATE 010314

TIME 152955

0603 BLOCKING

DATE 010302

TIME 060301

In this case we have an OML Fault on the CF and the whole site has lost communication with the BSC. Also there are faults on the DIP which indicate the fault code (ALL1) and the state (Unavailable).

RLCRP The RLCRP command gives the resources for a cell, i.e. number of BCCH, SDCCH, CBCH (always 0) and TCH. If the cell is up and carrying traffic the printout will look like this: