||The UE initiates the Attach procedure by the transmission of an
Attach Request (IMSI or old GUTI, last visited TAI (if available), UE Network
Capability, PDN Address Allocation, Protocol Configuration Options, Attach
Type) message together with an indication of the Selected Network to the
eNodeB. IMSI is included if the UE does not have a valid GUTI available. If the
UE has a valid GUTI, it is included.
||The eNodeB derives the MME from the GUTI and from the indicated
Selected Network. If that MME is not associated with the eNodeB, the eNodeB
selects an MME using an "MME selection function". The eNodeB forwards the
Attach Request message to the new MME contained in a S1-MME control message
(Initial UE message) together with the Selected Network and an indication of
the E-UTRAN Area identity, a globally unique E-UTRAN ID of the cell from where
it received the message to the new MME.
||If the UE is unknown in the MME, the MME sends an Identity
Request to the UE to request the IMSI.
||The UE responds with Identity Response (IMSI).
||If no UE context for the UE exists anywhere in the network,
authentication is mandatory. Otherwise this step is optional. However, at least
integrity checking is started and the ME Identity is retrieved from the UE at
Initial Attach. The authentication functions, if performed this step, involves
AKA authentication and establishment of a NAS level security association with
the UE in order to protect further NAS protocol messages.
||The MME sends an Update Location (MME Identity, IMSI, ME
Identity) to the HSS.
||The HSS acknowledges the Update Location message by sending an
Update Location Ack to the MME. This message also contains the Insert
Subscriber Data (IMSI, Subscription Data) Request. The Subscription Data
contains the list of all APNs that the UE is permitted to access, an indication
about which of those APNs is the Default APN, and the 'EPS subscribed QoS
profile' for each permitted APN. If the Update Location is rejected by the HSS,
the MME rejects the Attach Request from the UE with an appropriate cause.
||The MME selects an S-GW using "Serving GW selection function"
and allocates an EPS Bearer Identity for the Default Bearer associated with the
UE. If the PDN subscription context contains no P-GW address the MME selects a
P-GW as described in clause "PDN GW selection function". Then it sends a Create
Default Bearer Request (IMSI, MME Context ID, APN, RAT type, Default Bearer
QoS, PDN Address Allocation, AMBR, EPS Bearer Identity, Protocol Configuration
Options, ME Identity, User Location Information) message to the selected S-GW.
||The S-GW creates a new entry in its EPS Bearer table and sends a
Create Default Bearer Request (IMSI, APN, S-GW Address for the user plane, S-GW
TEID of the user plane, S-GW TEID of the control plane, RAT type, Default
Bearer QoS, PDN Address Allocation, AMBR, EPS Bearer Identity, Protocol
Configuration Options, ME Identity, User Location Information) message to the
||If dynamic PCC is deployed, the P-GW interacts with the PCRF to
get the default PCC rules for the UE. The IMSI, UE IP address, User Location
Information, RAT type, AMBR are provided to the PCRF by the P-GW if received by
the previous message.
||The P-GW returns a Create Default Bearer Response (P-GW Address
for the user plane, P-GW TEID of the user plane, P-GW TEID of the control
plane, PDN Address Information, EPS Bearer Identity, Protocol Configuration
Options) message to the S-GW. PDN Address Information is included if the P-GW
allocated a PDN address Based on PDN Address Allocation received in the Create
Default Bearer Request. PDN Address Information contains an IPv4 address for
IPv4 and/or an IPv6 prefix and an Interface Identifier for IPv6. The P-GW takes
into account the UE IP version capability indicated in the PDN Address
Allocation and the policies of operator when the P-GW allocates the PDN Address
Information. Whether the IP address is negotiated by the UE after completion of
the Attach procedure, this is indicated in the Create Default Bearer Response.
||The Downlink (DL) Data can start flowing towards S-GW. The S-GW
buffers the data.
||The S-GW returns a Create Default Bearer Response (PDN Address
Information, S-GW address for User Plane, S-GW TEID for User Plane, S-GW
Context ID, EPS Bearer Identity, Protocol Configuration Options) message to the
new MME. PDN Address Information is included if it was provided by the P-GW.
||The new MME sends an Attach Accept (APN, GUTI, PDN Address
Information, TAI List, EPS Bearer Identity, Session Management Configuration
IE, Protocol Configuration Options) message to the eNodeB.
||The eNodeB sends Radio Bearer Establishment Request including
the EPS Radio Bearer Identity to the UE. The Attach Accept message is also sent
along to the UE.
||The UE sends the Radio Bearer Establishment Response to the
eNodeB. In this message, the Attach Complete message (EPS Bearer Identity) is
||The eNodeB forwards the Attach Complete (EPS Bearer Identity)
message to the MME.
||The Attach is complete and UE sends data over the default
bearer. At this time the UE can send uplink packets towards the eNodeB which
are then tunneled to the S-GW and P-GW.
||The MME sends an Update Bearer Request (eNodeB address, eNodeB
TEID) message to the S-GW.
||The S-GW acknowledges by sending Update Bearer Response (EPS
Bearer Identity) message to the MME.
||The S-GW sends its buffered downlink packets.
||After the MME receives Update Bearer Response (EPS Bearer
Identity) message, if an EPS bearer was established and the subscription data
indicates that the user is allowed to perform handover to non-3GPP accesses,
and if the MME selected a P-GW that is different from the P-GW address which
was indicated by the HSS in the PDN subscription context, the MME sends an
Update Location Request including the APN and P-GW address to the HSS for
mobility with non-3GPP accesses.
||The HSS stores the APN and P-GW address pair and sends an Update
Location Response to the MME.
||Bidirectional data is passed between the UE and PDN.