The attach procedure in LTE/EPS is quite similar as the GPRS attach in 2G/3G. It brings the UE from EMM_deregistered state to EMM_registered.
In addition to that the procedure also establishes the default SAE bearer for the UE and thus allocates the required IP addresses for the subscriber in the external packet data network.
There are seven steps in the attach procedure : random access, initial NAS message, NAS security, S1 initial setup, RRC security + UE capability, SRB2/DRB setup, and NAS reply.
In a live network, attach failure categories include (possible reject causes are
defined within 3GPP TS 24.301):
- EPS Services not allowed
- Non‐EPS Services not allowed
- EPS services not allowed in this PLMN
- Unknown or missing APN(MME‐5‐GW)
- Unknown PDN address or PDN type
- Service option not supported
- Request service option not supported
The interface of S1‐MME will associate with S6A (MME to HSS diameter signaling) and S11(MME to SGW) interface, to spot the failure reason.
S6A signaling analysis includes update location request and update location answer.
According to the 3GPP standard attach failure cause value, the problem can be demarcated. The main network reasons cause value impact the S1 attach success rate are #111, #3, and #0. For #33 cause value, the reason is that the user-initiated release message, it is suggested to investigate the wireless side combined with user data investigation.
For #111 cause value, the reason is that the eNB does not respond in time, it
is needed to investigate the wireless side.
Through LTE signaling analysis, it is able to output 4G terminals’ MSISDN and IMSI information, which frequent attempts to access the 4G network but failure, and selected the thematic analysis of the target user: the reasons value of the attach failure is #7 or #15.
To realize batch acquisition of the users automatically, to determine whether the user had replaced the USIM card and whether the 4G function was on and other information.
All of this information will be automatically pushed to the market for targeted marketing. (see attached figure for S1 and S6A cause values).
Source: LTE Optimization Engineering Handbook, Xincheng Zhang © 2018 John Wiley & Sons Singapore Pte. Ltd
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