Session Setup Using Accounting-Interim - Cisco ASR 5000 Administration Manual

RADIUS-based Enhanced Wireless Access Gateway Overview
Step Description
21 The GGSN processes the Create PDP Context Request and allocates the MPC IP address in the Create PDP Context
Response message. It also negotiates the QoS to be used for this subscriber session and sends the same in Create PDP
Context Response message.
22 The R-eWAG processes the Create PDP Context Response message, and creates the binding between the Wi-Fi IP address
and the MPC IP address in the R-eWAG session.
23 The R-eWAG sends an Accounting-Response message to the Wi-Fi AAA server to acknowledge the Accounting-Start
message.
24 The UE initiates data transfer to the destination in APN network with Source IP set to its Wi-Fi IP address. This packet gets
routed to the R-eWAG from the WLAN network.
25 The R-eWAG performs NAT on this data packet (Layer 3 to Layer 7), from Wi-Fi IP address to MPC IP address.
26 The R-eWAG sends the NATd IP packet encapsulated over the GTP-U tunnel created with the GGSN.
27 The GGSN decapsulates the IP packet received over the GTP-U tunnel and sends it to the destination APN network. Note
that this IP packet contains the source IP address set to the MPC IP address.
28 The data packet received in the downlink direction from the APN network is processed by the GGSN. This downlink
packet contains the destination IP address set to the MPC IP address.
29 The GGSN encapsulates the IP packet over the GTP-U tunnel and sends it downlink to the R-eWAG.
30 The R-eWAG performs reverse-NAT on the downlink IP packet (received over the GTP-U tunnel from the GGSN) and
converts all MPC IP addresses to Wi-Fi IP addresses from Layer 3 to Layer 7.
31 The R-eWAG sends the plain IP packet downlink to the UE.

Session Setup using Accounting-Interim

The R-eWAG supports session creation based on the first Accounting-Interim message for scenarios where RADIUS
Accounting-Start message cannot be generated with IPv4 address assigned to the UE, but can send an Accounting-
Interim message when IPv4 address actually gets assigned.
The iPhone is one such example where by default it starts in IPv6 mode. As the R-eWAG does not support IPv6, session
creation based on IPv6 address-based Accounting-Start is not possible. Therefore, if the
CLI configuration is enabled, R-eWAG creates the session based on the first accounting-interim. If this configuration is
not enabled and the Accounting-Interim is received at R-eWAG, it will be acknowledged when existing session is found
for this message, else it gets dropped.
Note that once the session is created at R-eWAG, the consecutive Accounting-Interim messages received by R-eWAG
will be treated in the same way as in the case of session-creation based on Accounting-Start. This means that any
accounting-interim message that consists of AVPs (apn, acct-session-id, and others) that do not match existing session
parameters will get dropped (and call not replaced). So, in the iPhone scenario, the new call with the accounting-interim
will be created only after the existing session gets cleared using administrative reasons, idle-timeout, and so on. Until
then, R-eWAG will drop Accounting-Interim with different AVP values.
This section presents call flow for session setup using accounting-interim scenario.
Cisco ASR 5000 Enhanced Wireless Access Gateway Administration Guide ▄
How it Works ▀
interim create-new-call
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