Ip Address Allocation; Network Layer Service Access Point Identifier Allocation; Routing Area Identification Encoding; Differentiated Services Code Point Marking - Cisco ASR 5000 Administration Manual

RADIUS-based Enhanced Wireless Access Gateway Overview

IP Address Allocation

When a UE attaches to the WLAN network it obtains an IP address from the WLAN network (Wi-Fi IP address). Also,
when the R-eWAG creates PDP context with the GGSN, the GGSN assigns a remote MPC IP address to the UE. In the
Create PDP Context Request message the end-subscriber-address IE will be empty (indicating dynamic address
assignment by the GGSN), which makes the GGSN assign and return an IP address in the response message.
eWAG performs NAT between the Wi-Fi IP address and the MPC IP address during data transmission.

Network Layer Service Access Point Identifier Allocation

The R-eWAG allocates Network Layer Service Access Point Identifier (NSAPI) values before sending the Create PDP
Context Request message to the GGSN. Although the R-eWAG acts like an SGSN in terms of GTP tunnel
establishment, it also manages NSAPI allocation as WLAN UE's proxy for the purpose of leaving the Gn'-based R-
eWAG transparent to the WLAN UE.
Important:
WLAN connection with the same GGSN, if the UE uses NSAPI 15 for GPRS PDP context then context replacement
will occur at the GGSN.

Routing Area Identification Encoding

The Routing Area Identification (RAI) is encoded using PLMN-ID in "3GPP-SGSN-MCC-MNC", if received in
Accounting-Start/Interim. Otherwise, the RAI is encoded using the MCC MNC or PLMN ID configured at the R-
eWAG.

Differentiated Services Code Point Marking

Differentiated Services Code Point (DSCP) levels can be assigned to specific traffic patterns in order to ensure that data
packets are delivered according to the precedence with which they are tagged. The DiffServ markings are applied to the
IP header for every subscriber data packet transmitted in the downlink and/or uplink direction. The four traffic patterns
have the following order of precedence:
1. Background (lowest)
2. Interactive
3. Streaming
4. Conversational (highest)
In addition, for class type Interactive, further categorization is done in combination with traffic handling priority and
allocation-retention priority. Data packets falling under the category of each of the traffic patterns are tagged with a
DSCP marking. Each traffic class is mapped to QCI value according to mapping mentioned in TS 23.203. Therefore,
DSCP values must be configured for different QCI values. The following table lists mapping for traffic class to QCI.
Table 1. Traffic Class to QCI Mapping
GPRS QoS Class Identifier Value
In this release, the R-eWAG always assigns the NSAPI value 15. For simultaneous GPRS and
UMTS QoS Parameters
Traffic Class THP Signalling Indication
Cisco ASR 5000 Enhanced Wireless Access Gateway Administration Guide ▄
Feature Description ▀
Source Statistics Descriptor
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