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GPRS service impossible in one PCU of SGSN Issue Report

1. The happened issue:

The GPRS service under V BSC is abnormal, some subscribers can activate PDP

context successfully, but they can not perform data transmission, so they cannot access

to any internet web page.

2. Analysis of the root cause

1. We tested under M BSC which also connected to Huawei SGSN with abnormal mobile

phone and sim card, the GPRS service is normal, so it shows that this issue is just exist

under V BSC;

2. We tested under V BSC with abnormal MS for both FTP and HTTP services, all of

them were abnormal. We tested under V BSC with normal MS for both FTP and HTTP

services, all of them were normal, we saved all necessary trace messages;

From the abnormal MS user trace of SGSN, we found that the reason why some terminal

can not use GPRS service under the V BSC is that the many data packet was lost in the

BSS side. Compare with the trace in the BSC side, the BSC did not receive the

retransmission packets. So it means all the retransmission packets were lost in the

transfer network between the BSC and SGSN.

Also we found that all the lost data packets are the big packet. So we think the transfer

network can not transfer the big packet. Then we did the PING test between SGSN and

the V BSC, we found that if the payload of PING packet is bigger than 1472 bytes, the

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