Cisco Cisco ASR 5700 Guide De Dépannage
Contents
Introduction
Problem: MME Attach Failure because of Silent Drops
Solution
Related Information
Introduction
This document is about the counters used to check the number of attach failures, which happens
due to the silent drops of attach procedures in Mobility Management Entity (MME).
due to the silent drops of attach procedures in Mobility Management Entity (MME).
Problem: MME Attach Failure because of Silent Drops
Basic call flow for the Attach Procedure in Evolved Packet System (EPS).
Main steps during the attach procedure.
User Equipment (UE) sends Attach Request towards MME. This Attach Request also
contains PDN Connectivity Request.
contains PDN Connectivity Request.
1.
MME perform all Authentication and ciphering related procedure with UE.
2.
MME sends the Create Session Request to Serving Gateway (SGW) and SGW creates a
session with Packet Data Network (PDN) Gateway (PGW) and SGW respond with Create
Session Response to MME.
session with Packet Data Network (PDN) Gateway (PGW) and SGW respond with Create
Session Response to MME.
3.
MME sends Attach Accept to UE and Initial Context Setup Request to eNodeB.
4.
eNodeB performs the E-RAB (Evolved – Radio Access Bearer) setup procedure with UE.
5.
eNodeB sends Initial Context Setup Response to MME after E-RAB with UE was set up.
6.
UE sends Attach Complete to MME and here attach procedure is considered as successful.
7.
MME sends Modify Bearer Request to SGW to send eNodeB S1-U (S1-User Plane)
information to SGW.
information to SGW.
8.
Attach procedure gets failed due to various reasons but here are the 2 ways to handle
those failures:
those failures:
MME sends an Attach Reject message to UE.
1.
MME does not send an Attach Reject message to UE and silently discard the Attach
Procdeure.
Procdeure.
2.
When MME sends an Attach Reject then you either have EPS Mobility Management (EMM) or
EPS Session Management (ESM) cause associated with that Attach Reject and MME have
various counters to track these values.
EPS Session Management (ESM) cause associated with that Attach Reject and MME have
various counters to track these values.
MME can discard Attach Procedure silently without sending any Attach Reject to UE. Here are a
few possible reasons:
few possible reasons:
Autentication Failed : If an Attach Request fails because of Authentication Failure and no
Attach Reject is sent or when there is a maximum re-transmissions of Authentication
Attach Reject is sent or when there is a maximum re-transmissions of Authentication
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