UE

SS

1

🡪

INVITE

UE sends INVITE including an SDP offer.

2

🡨

100 Trying

SS sends a 100 Trying provisional response.

3

🡨

183 Session Progress

SS sends 183 Session Progress including an SDP answer.

4

🡪

PRACK

UE acknowledges reception of 183 Session Progress.

5

🡨

200 OK

SS sends 200 OK for PRACK.

Supported

option-tag

precondition
Note1: the precondition option-tag is only required when the UE is configured to use preconditions.
Note 2: the precondition option-tag being required does not affect any other option tags in the Supported header as for instance prescribed in TS 34.229-1 [2] Annex A.2.1

Message-body

SDP body present but contents not checked

Require

present if UE is configured to use preconditions

option-tag

precondition

Message-body

The following SDP types and values.

Session description:

– v=0

– o=- 1111111111 1111111111 IN (addrtype) (unicast-address for SS)

– s=-

– c=IN (addrtype) (connection-address for SS)

– b=AS:37

Time description:

– t=0 0

Media description:

– m=audio (transport port) RTP/AVP (fmt) [Note 1, 4]

– b=AS:37

– b=RS:0

– b=RR:2000

Attributes for media:

– a=rtpmap: (payload type) AMR-WB/16000/1 [Note 1]

– a=fmtp: (format) mode-change-capability=2; max-red=220 [Note 1]

– a=ecn-capable-rtp: leap ect=0 [Note 2]

– a=rtcp-fb:* nack ecn [Note 2]

– a=rtcp-xr:ecn-sum [Note 2]

– a=ptime:20

– a=maxptime:240

Attributes for media security mechanism:

– a=3ge2ae: requested [Note 3]

– a=crypto:1 AES_CM_128_HMAC_SHA1_80inline:PS1uQCVeeCFCanVmcjkpPywjNWhcYD0mXXtxaVBR|2^20|1:4 [Note 3]

Attributes for preconditions: [Note 5]

a=curr:qos local none

a=curr:qos remote none

a=des:qos mandatory local sendrecv

a=des:qos mandatory remote sendrecv

a=conf:qos remote sendrecv

Note 1: The value for fmt, payload type (AMR) and format is copied from Step 1.

Note 2: Attributes for ECN Capability are present if the UE supports Explicit Congestion Notification.

Note 3: Attributes for media plane security are present if the use of end-to-access-edge security is supported by UE.

Note 4: transport port is the port number of the SS (see RFC 3264 clause 6).

Note 5: present if UE is configured to use preconditions

UE

SS

1

SS starts a timer (5 seconds) to wait for an optional REGISTER request from UE.
NOTE: if the UE does not send REGISTER and is configured to use preconditions, it may send UPDATE right away. In that case, the timer is stopped upon arrival of UPDATE.

–

EXCEPTION: Steps 2a1-2a3 describes behaviour that depends on UE implementation.

The “lower case letter” identifies a step sequence that takes place if such implementation was applied.

2a1

–>

REGISTER

Optional step: the UE may register for IMS on EPS.

2a2

<–

200 OK

Conditional step: if the UE sent REGISTER, the SS responds with 200 OK.

2a3

Timer from step 1 is stopped.

–

–

EXCEPTION: Steps 3a1 to 3a2 describe behaviour that depends on UE configuration; the “lower case letter” identifies a step sequence that takes place if such configuration was conducted.

–

3a1

–>

IF the UE is configured to use preconditions THEN the UE sends UPDATE

UPDATE contains a second SDP offer.

3a2

<–

200 OK for UPDATE

Conditional step: if the UE sent UPDATE, the SS sends 200 OK for UPDATE containing a second SDP answer.

4

<–

180 Ringing

180 Ringing is sent unreliably.

5

<–

SS sends 200 OK for INVITE

–

6

–>

ACK

–

Require

option-tag

precondition
Note1: the precondition option-tag is only required when the UE is configured to use preconditions.
Note 2: the precondition option-tag being required does not affect any other option tags in the Require header as for instance prescribed in TS 34.229-1 [2] Annex A.2.6

Message-body

The following SDP types and values shall be present.

Session description:

– v=0

– o=(username) (sess-id) (sess-version) IN (addrtype) (unicast-address for UE) [Note 2]

– s=(session name)

– c=IN (addrtype) (connection-address for UE) [Note 1]

– b=AS: (bandwidth-value)

Time description:

– t=0 0

Media description:

– m=audio (transport port) RTP/AVP (fmt) [Note 2]

– c=IN (addrtype) (connection-address for UE) [Note 1]

– b=AS: (bandwidth-value)

– b=RS: (bandwidth-value)

– b=RR: (bandwidth-value)

Attributes for media:

– a=rtpmap: (payload type) AMR-WB/16000 [Note 2] [Note 4]

– a=fmtp: (format) [Note 2, 3]

Attributes for preconditions:

a=curr:qos local sendrecv

a=curr:qos remote none

a=des:qos mandatory local sendrecv

a=des:qos optional remote sendrecv or a=des:qos mandatory remote sendrecv

Note 1: At least one "c=" field shall be present.

Note 2: The value for fmt, payload type and format is not checked

Note 3: Parameters for the AMR codec are not checked

Note 4: The AMR channel number shall be “/1” or omitted.

Require

present if UE is configured to use preconditions

option-tag

precondition

Content-Type

media-type

application/sdp

Content-Length

Value

length of message-body

Message-body

SDP body of the 200 OK response copied from the received UPDATE and modified as follows:

– IP address on "c=" lines and transport port on "m=" lines changed to indicate to which IP address and port the UE should start sending the media;

– "o=" line identical to previous SDP sent by SS except that sess-version is incremented.

– Attributes for preconditions: a=curr:qos remote sendrecv