PDN Gateway Overview
▀ Features and Functionality - Base Software
▄ Cisco ASR 5x00 Packet Data Network Gateway Administration Guide
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IMS Emergency Bearer Handling
With this support, a UE is able to connect to an emergency PDN and make Enhanced 911 (E911) calls while providing
the required location information to the Public Safety Access Point (PSAP).
E911 is a telecommunications-based system that is designed to link people who are experiencing an emergency with the
public resources that can help. This feature supports E911-based calls across the LTE and IMS networks. In a voice over
LTE scenario, the subscriber attaches to a dedicated packet data network (PDN) called EPDN (Emergency PDN) in
order to establish a voice over IP connection to the PSAP. Signaling either happens on the default emergency bearer, or
signaling and RTP media flow over separate dedicated emergency bearers. Additionally, different than normal PDN
attachment that relies on AAA and PCRF components for call establishment, the EPDN attributes are configured locally
on the P-GW, which eliminates the potential for emergency call failure if either of these systems is not available.
Emergency bearer services are provided to support IMS emergency sessions. Emergency bearer services are
functionalities provided by the serving network when the network is configured to support emergency services.
Emergency bearer services are provided to normally attached UEs and to UEs that are in a limited service state
(depending on local service regulations, policies, and restrictions). Receiving emergency services in limited service state
does not require a subscription.
The standard (refer to 3GPP TS 23.401) has identified four behaviors that are supported:
Valid UEs only
Authenticated UEs only
MSI required, authentication optional
All UEs
To request emergency services, the UE has the following two options:
UEs that are in a limited service state (due to attach reject from the network, or since no SIM is present), initiate
an ATTACH indicating that the ATTACH is for receiving emergency bearer services. After a successful
attach, the services that the network provides the UE is solely in the context of Emergency Bearer Services.
UEs that camp normally on a cell initiates a normal ATTACH if it requires emergency services. Normal attached
UEs initiated a UE Requested PDN Connectivity procedure to request Emergency Bearer Services.
IP Access Control Lists
IP access control lists allow you to set up rules that control the flow of packets into and out of the system based on a
variety of IP packet parameters.
IP access lists, or access control lists (ACLs) as they are commonly referred to, are used to control the flow of packets
into and out of the system. They are configured on a per-context basis and consist of “rules” (ACL rules) or filters that
control the action taken on packets that match the filter criteria. Once configured, an ACL can be applied to any of the
following:
An individual interface
All traffic facilitated by a context (known as a policy ACL)
An individual subscriber
All subscriber sessions facilitated by a specific context
Important:
For more information on IP access control lists, refer to the
IP Access Control Lists
chapter in the
System Administration Guide
.
