Sunday, 4 October 2015

Unable to connect to LTE network by using dongle due to missing APN information from dongle

Problem Description
Test user was unable to connect to LTE network by using dongle.


None
Handling Process
Customer configured "internet.test.com" as the APN in dongle and tried to attach to LTE network, however, the dongle cannot attach to LTE network successfully.
As per checking in PDN-GW, APN "internet.test.com" has been assigned for LTE service in DNS.
As per checking in MME, the error code for this subscriber is "unknown or missing APN". Meanwhile, MME was unable to decrypt the APN message of the subscriber in the log. Thus, we suspected the dongle was not sending any APN information to MME during the attach request.
According to 3GPP 23401 protocol, if UE does not provide any APN information, the EPS bearer will be establish by using the default APN of the subscriber:

As per checking in HSS, the default APN of this subscriber was "http.test.com", and this APN was not assigned for LTE service in DNS. Thus, using APN "http.test.com" to establish EPS bearer will not be success in the attach request.

Root Cause
N/A
Solution
1. Set up user trace in LMT FE. From the trace, MME was sending purge message to HSS after diameter authentication and diameter location update:


2. In HSS PGW, LST OPTGPRS. This subscriber has been subscribed to APN "internet.test.com" and "http.test.com". The default APN was "http.test.com".
3. Double checking on the APN configuration in dongle, it was "internet.test.com".
4. As per checking in PDN-GW, APN "internet.test.com" has been assigned for LTE service in DNS.
5. As per checking in MME, the error code was "unknown or missing APN". Meanwhile, MME was unable to decrypt the APN message in the log. Thus, we suspected the dongle was not sending any APN information to MME during the attach request.
6. Insert the SIM card to LTE handphone and use APN "internet.test.com" to attempt to attach to LTE network. Attach to LTE network successfully.
7. Double checking in PDN-GW, APN "http.test.com" was not allowed for LTE services.
8. According to 3GPP protocol, if UE does not provide any APN information, the EPS bearer will be establish by using the default APN of the subscriber. Thus, execute command MOD OPTGPRS in HSS PGW to configure APN "internet.test.com" as the default APN for this subscriber.
Example of the MOD OPTGPRS and CNTXID=1 is the context ID for APN "internet.test.com":
MOD OPTGPRS: IMSI="XXX", PROV=MODPDPCNTX, CNTXID=1, APN_TYPE=EPS_APN, DEFAULTCFGFLAG=TRUE;
9. Then, we tried to attach to LTE network by using the dongle. The UE attached to LTE network successfully.
Suggestions and Summary
In order to avoid similar attach issue, the default APN for the subscriber should be the APN that has been assigned for LTE service in DNS.

Budi Prasetyo

About Budi Prasetyo

All About LTE

Subscribe to this Blog via Email :