IV DAS Pilot Project

6. Difficult Things in Progressing

6-1 Frequent change of communication process(CSD –> SMS –> GPRS)

Substantially, communication is much important to secure TDAS construction and stable operation. Therefore GSM(using CSD) was originally selected as the most stable and reliable process, but owing to a low success ratio and limit for increasing of capacity it changed into SMS, and again changed into GPRS finally due to the additional cost of SMS. In the process much time has been spent, and we have suffered much trial and error. We can judge that this problem was happened by reasons as follows.

6-1-1 The low assignment of TELKOMSEL for CSD capacity and their afraid of affecting the voice capacity to be used for general customer with increasing CSD capacity act on low success ratio in Indonesia and as limit of increasing.

6-1-2 TELKOMSEL and PLN engineer’s experience and understanding shortage for TDAS and modem, using in special purpose not only internet using.

6-1-3 Understanding and supporting of TELKOMSEL engineer in Semarang is insufficient than that of head office, the appointed service supporting didn’t keep in several times. So time delay and a few modem revise happened.

6-2 Differency of installation method

In case of KEPCO earthing ground independently but in Indonesia earthing is connected commonly with crossarm, switch case and control box. Also connection for lighting arrestor shall be connected in front of the switch connection but it is not followed. This differency already was revised by PLN with checking of KEPCO. Following [Figure 4-7] is the example of wrong installation.

[Figure 4-7] Example for wrong installation

6-3 Frequent earthing pilferage

Owing to the increased copper price earthing pilferage happened in some places. Especially some places happened repletely. If earthing is not, facility protection and normal operation of TDAS can not be expected.

In addition, as some of the antennas installed on site were found to be damaged, site patrol must be conducted continuously and periodically to prevent facilities from being stolen or damaged. [Figure 4-8] below shows lost ground wire and damaged antenna.

[Figure 4-8] Earthing pilferage

6-4 Unstable Wireless Communication Network

6-4-1 Communication Environment in Semarang

Followings are the sources of unstability in the wireless communication network now in place for the distribution automation system in Indonesia. We have developed several resolutions to address such issues which required significant amount of time and effort.

1. As APN network traffic increases, the wireless communication carrier (TELKOMSEL) disconnects modems which do not exchange data with main server for a certain period of time from APN network
2. If the main server fails to send command when the GPRS network covering the wireless communication section is in unstable state, corresponding modem IP is lost in the main server about 8 minutes later and the modem tries reconnection, however, some of such modems fail to reconnect to APN network
3. When GPRS network connectivity is cut, modems try to reconnect to the upper application layer rather than make PPP connection necessary for initial connection with GPRS network, resulting in reconnection failure
4. GPRS connectivity loss and reconnection failure happens when the fixed line communication network (TELKOM network between Semarang-Jakarta) is maintained without prior notice

6-4-2 Results of Communication Environment Analysis

Because of the issues from (1) through (4) in 6-4-1 above, modem that does not recognize communication network status for a certain period of time fails to maintain connection with main server and we have found the following results after a series of tests.

1. Even if communication network is in poor state (low signal quality), normal connection is maintained if signal quality is restored in about a minute
2. GPRS network connection is cut 1 minute after signal quality deteriorates, however, modem recognizes disconnection with main server and tries to reconnect about 8 minutes after main server sends a command
3. Depending on communication signal quality per site, some modems connect to APN network while others fail and try reconnection repeatedly
4. Even in case of modems which failed to reconnect as described in (3), normal connection is made if modem is turned off and on to restart
5. As event occurs on site, it is possible for modem to transmit data as intended and communication network connection is restored then
6. Continuous observation of ping status between DAS main server and modem IP revealed that ping failed for several seconds or minutes at the longest at some locations (ping failure lasting for several minutes indicate disconnection between main server and FRTU), which implies changes in wireless data communication signal quality at modem installation site
7. Judging from the results of several iterative tests conducted in DCC on connection between modem and main server, the primary source of low communication success rate between DAS main server and FRTU is believed to be frequent changes in wireless data communication signal quality at modem installation site

6-4-3 Resolutions

According to the analysis result in 6-4-2 above, KEPCO made the following attempts to improve the stability and reliability of communication.

Firstly, to prevent forced disconnection by the wireless communication carrier, FRTU was configured to generate an event at certain interval (every 15 minutes) to notify APN of communication between modem and main server and maintain communication network connection thereby.

Secondly, modem firmware was modified as below so as to restart modem and establish connection with APN again. Such modification was intended to resolve the previous issue that modem would try to reconnect with the upper application layer rather than PPP of GPRS communication network, failing to make connection with APN.

1. Modem checks its IP connection state every 2 minutes after initial connection with APN
   
2. Modem monitors GPRS network all the time and restarts right away regardless of time interval if connection with GPRS network is cut< br/>
   

However, the two above resolutions work only if the wireless communication network is restored to its normal state and communication issue may be resolved before the 1st resolution is tried if the 2nd resolution is proven to be successful.

Lastly, fundamental solution to the deterioration of on-site data communication quality is improvement of communication quality and, to that end, continuous discussion and commitment to improvement between PLN and the wireless communication carrier (TELKOMSEL) will be required. Stabilization of communication network will require further observation in the future and it may be necessary to consider other communication platform if it is difficult to maintain communication stability on the as-is platform.