Cisco ASR 5000 Series Product Overview Download

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Serving Gateway Overview

How the Serving Gateway Works ▀

Cisco ASR 5000 Series Product Overview ▄

OL-22938-02

Step

Description

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 included.

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 tunnelled 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.

Cisco ASR 5000 Series, Product Overview

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