ePDG supports PDN connection,
session establishment and release, along with support for dedicated
bearer creation, deletion and modification that is initiated by
During the initial attachment,
the ePDG "default EPS QOS", and "APN-AMBR" values
are populated in the create session request based on the values
received from the SWm interface. If these values are missing in
the messages received on the SWm interface, ePDG encodes the mandatory
or conditional IE with the values set to zero.
When a new PDN connection
is established, ePDG allocates and sends a default EPS bearer ID
to the PDN gateway. After the initial attach, a default bearer is
created for the session, and the IP address is allocated and communicated
to the UE.
A GTP-C and GTP-U tunnel
is successfully established between the ePDG and P-GW, and an IPSec
tunnel is established between the UE and ePDG. Traffic is allowed
to flow between these established tunnels.
ePDG sends a "delete
session request" message to P-GW, and handles the corresponding "delete
session response" message from the P-GW during the following
- UE/ePDG initiated
detach with GTP on S2b
- UE requested PDN disconnection
with GTP on S2b
- AAA initiated detach
with GTP on S2b
ePDG handles the received "create
bearer request" message and sends a "create bearer response" message
for the dedicated bearer creation triggered from the P-GW.
After the dedicated
bearer is created, a new GTP-U tunnel is established between ePDG
and P-GW, and traffic mapping to the TFT of this bearer occurs.
ePDG supports up to 16 packet filters per bearer.
ePDG also stores mapping
information between the uplink packet filters received from the P-GW
(For example; in the Create Bearer Request message), and the corresponding
S2b bearer. ePDG matches these filters and decides if the uplink
packets should be allowed or dropped.
ePDG receives the "delete
bearer request" message and sends a "delete bearer
response" message for the dedicated bearer deletion triggered
by the P-GW.
ePDG clears the bearer
path (GTP-U tunnel) corresponding to the EBI received. In the case of
a linked EBI, the PDN connection and its associated bearers are
deleted. The TFT mapping for the deleted bearer is also deleted.
ePDG handles the received "update
bearer request" message and sends a "update bearer response" message
for dedicated bearer modification triggered from the P-GW. ePDG
updates the UL TFT mapping for the associated bearer using the "bearer
ePDG supports path failure
detection for control plane by using Echo Request and Echo Response
messages. A peer's IP address-specific counter is reset every time
an Echo Response message is received from the peer's IP address.
The counter is incremented when the T3-RESPONSE timer expires for
an Echo Request message sent to the peer's IP address. The path
is considered as down if the counter exceeds the value of N3-REQUESTS.
ePDG initiates the Echo
requests once retransmission timeout occurs for the request sent
to the P-GW. The retransmission for GTP messages is handled by running
the retransmission timer (T3-RESPONSE) and for N3-REQUESTS timer,
the message is retransmitted after the retransmission timer expires.
After all the retransmissions are over, echo handling is initiated.
The GTPC configuration
has the configuration command, no gtpc path-failure detection-policy
<CR> using which on path failure detection, SNMP traps/alarms
are generated notifying that P-GW has gone down, but the sessions
are not deleted. The SNMP trap is sent only once per peer, and not
for every session. When this command is not configured, path failure
detection and the subsequent cleanup action is enabled by default.
Detection of path failure
for user plane is supported using the Echo Request/ Echo
Response messages. A path counter is reset every time an Echo Response
is received and incremented when the T3-RESPONSE timer expires for
any Echo Request message sent. The path is considered as down if
the counter exceeds the value of N3-REQUESTS.
By default, path failure
detection is not configured for ePDG.