VoLTE Emergency Call Session

Landslide LTE Emergency call flow functionality supports UE (MME Nodal) and IMS (IMS Node) simulation. The customer SUT may be an EPS subsystem or a combined EPS, IMS with subsystems behind IMS core (such as PSAP). The former case (EPS subsystem) is two-arm testing where the Landslide simulates UE and P-CSCF. The latter case (EPS, IMS and subsystems) is one-arm testing with UE simulation only.

The illustration below shows a logical flow of IMS VoIP Emergency Services

This above diagram illustrates the following emergency scenario:

UE dials an emergency number (eg. 911), which is detected by eNodeB and emergency attach is initiated.
The attach creates/allocates the default bearer to the SOS APN for the emergency SIP signaling.
UE accomplishes SIP emergency Registration toward the P-CSCF dedicated for emergency operations.
UE initiates emergency session establishment resulting in the SOS APN (emergency P-CSCF) using the Rx interface to request establishment of a dedicated bearer
The P-CSCF (in addition to other tasks) establishes an RTP path toward PSAP (Public Safety Answering Point -Emergency Call Center).
The emergency session is established.
UE or PSAP ends the emergency session and PSAP optionally originates callback session to UE over non-emergency P-CSCF.

The following illustrates Logical Emergency Call Flow with one APN.

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Emergency Call Testing

2-arm Testing

(Any combination of MME, SGW, PGW, PCRF.)

In the two-arm testing scenario, Landslide MME Nodal and IMS node are used to verify the ability of the EPC to allocate, use and release bearer resources for normal and emergency APNs. This scenario also supports emergency specific IMS service information notification to PCRF over Rx interface using the Service-URN AVP.

1-arm Testing

(Any combination of MME, SGW, PGW, PCRF, IMS Core, and some components behind the IMS Core, e.g.; PSAP)

In the one-arm testing scenario, MME nodal and possibly other Landslide test applications (e.g. PCRF Node) are used to test the EPC and supporting IMS core network supporting a PSAP. MME Nodal test case's emulated UEs support the IMS emergency call procedures.

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Functionality/Procedures

The Emergency translation procedure applies to an emergency phone number specified in Phonebook | SIP Endpoints | Public User Name. If a translation procedure finds mapping of Telephone URI to Service URN, the telephone number is substituted by the Service URN.

URN and UE Detectable Emergency Session Establishing procedure occurs

Else

Non UE Detectable Emergency procedure occurs

The IMS Node test case recognizes Non UE Detectable Emergency procedure as an Emergency case if the phone number in Request TEL URI is mapped to a service URN on IMS Node side.

UE Detectable Emergency Session Establishment

UE recognizes the calling phone number as an emergency by translating to an Emergency Service URN

• 911 to urn:service:sos (US)

• 110 to urn:service:sos.police (Japan)

• 118 to urn:service:sos.marine (Japan)

The emergency service URN is used as the Request URI in the emergency call setup request (SIP INVITE)

UE Detectable Emergency Session Establishment for the UEs with credentials

UE is considered as having credentials if its public user identity is known. In the MME Nodal test case a UE’s public user identity is known if Phonebook | SIP Subscribers | Public User Name is not empty and not equal to Anonymous.

The UE establishes:

Emergency Registration
Emergency Call Setup.

UE Detectable Emergency Session Establishment for the UEs with no credentials

UE is considered as not having credentials if its public user identity is unknown (also referred to as anonymous UE). In the MME Nodal test case, a UE has no credentials if Phonebook | SIP Subscribers | Public User Name is equal to Anonymous. In such a case, UE establishes:

Emergency Call Setup without a prior Emergency Registration.

Non UE Detectable Emergency Sessions with credentials

MME Nodal test case emulates Non UE Detectable Emergency in one of the following two ways:

If the APN to which the UE is attached is not Emergency capable

If the APN to which the UE is attached is Emergency capable and the called number is not recognized as an emergency number. That is, the number is not translated to an emergency type (urn:service:sos or urn:service:sos.xxx). That is, URN mapping does not exist.

In the case of Non UE Detectable Emergency, the UE establishes a Normal non-Emergency Registration.

The next UE actions depends on P-CSCF response (SIP response) to the SIP REGISTER command.

If response messages are in the range of 3xx to 6xx (See RFC 3261), the UE stops any further activity.

If the response messages are in the range of 1xx - 200 with P-Asserted-Identity as one of the following:

<tel:an_emergency_number>
<urn:service.sos>
<urn:service:sos.xxx>

UE attempts Emergency Call Session established with Request URI set to one of the above values converted to a URN emergency type.

NOTE: If the conversion is not possible the UE stops any further activity.

Non UE Detectable Emergency Sessions without Credentials

In the MME Nodal test case, the UE has no credentials if Phonebook | SIP Subscribers | Public User Name is Anonymous.

The UE establishes a normal Call Setup.

If response messages are in the range of 3xx to 6xx (See RFC 3261) from the P-CSCF, the UE stops any further activity.
If response messages are in the range of 1xx-200 (See RFC 3261), UE proceeds to establish a normal call.

Processing of SIP 380 Response (Alternative Service)

In case of Emergency, the 380 (Alternative Service) response assumes the XML document in PIDF format (RFC 3863) is attached to the message with Content Type: application/pidf+xml.

Emergency SIP REGISTER message

The sos parameter in the Contact header indicates that this is an Emergency Registration request.

Emergency SIP INVITE

The emergency SIP INVITE is recognized by Request URI (with URN emergency type). That is, INVITE urn:service:sos SIP/2.0.

An Emergency number that is not recognized by the UE is treated as a normal call (Non UE Detectable Emergency Session).

To provide PSAP callback, the Call setup includes the UE phone number (caller number), accomplished by two P-Preferred-Identity headers:

P-Preferred-Identity: <sip:public_user_name@domain>
P-Preferred-Identity: <tel:ue_phone_number>

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