Non-Anchor Asn Gateway - Cisco ASR 5000 series Product Overview

▀ ASN Call Procedure Flows
Upon initial network entry, when the DPF is in the anchor ASN Gateway, there is no R4 session. After a MS does a
handover to a target BS, it connects to the anchor GW over R4 via a different serving ASN Gateway. At this point, the
anchor GW session has an access R4 session and a MIP FA network session. The anchor GW can maintain the R6
session and a R4 session simultaneously.
Note that R6 and R4 tunnels are handled uniformly by the anchor GW as both are access-side tunnels. The anchor GW
can check the IP address of the non-anchor GW peer against the configured list of peer ASN Gateway's, so that it can
control which R4 connections are accepted.
The anchor GW handles all the Layer 3 processing for the subscriber without including any other rule and policy.
When an anchor GW receives a request message, it reads the source ID in this request and sends the response to this
source ID as destination ID. The anchor ASN Gateway remembers the source IP address of the peer from where the
message was received, if it is different from the source ID of the message. The response message is sent to this peer IP
address, which is the immediate peer.

Non-Anchor ASN Gateway

The non-anchor ASN Gateway hosts the following functions:
Serving DP Function: The subscriber data is not processed in the non-anchor GW. It relays the subscriber data
to anchor ASN Gateway over R4. When the inner IP packet emerges from R6 tunnel at the non-anchor ASN
Gateway, the packet is sent over R4 data path tunnel to the Anchor ASN Gateway.
Serving SFA Function: No packet classification is performed in this function. It provides only tunnel switching
between R4 to R6 or vice versa.
DHCP Proxy relay Function: DHCP messages are not processed in the non-anchor GW and relayed to the
DHCP proxy in the anchor ASN Gateway over R4. When the inner IP packet emerges from the R6 tunnel at
the non-anchor ASN Gateway, a check is made to see if DHCP proxy is co-located in the ASN Gateway. and
whether to process DHCP packet locally or not. If the session is not anchored locally, that is, the DHCP proxy
is not co-located, the non-anchor ASN Gateway sends the DHCP packet over an R4 data path tunnel to the
anchor ASN Gateway.
Relay Function: The non-anchor ASN Gateway provides relay functions to distribute received messages and
subscriber information. The message relay is supported for following functions:
Non-Anchor Session
A non-anchor session is created upon receiving an R6 Data Path Registration Request from the target base station. Note
that the non-anchor ASN Gateway session is identified by MSID only. This non-anchor ASN Gateway does NOT know
▄ Cisco ASR 5000 Series Product Overview
Context transfer
Paging
Accounting
Authentication
Handover (HO)
Radio Resource Controller (RRC)
ASN Gateway Overview
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