UE

SS

1

UE attempt an IMS speech call a result of an initiation of the rSRVCC procedure

2

🡪

INVITE

UE sends INVITE with the first SDP offer.

3

🡨

100 Trying

SS sends a 100 Trying provisional response.

4

🡨

200 OK

SS responds INVITE with 200 OK.

5

🡪

ACK

UE acknowledges.

Request-Line

Request-URI

sip:sti-sr@atcf.visited2.net

NOTE: This value was received by the UE in the preceeding registration procedure

To

addr-spec

sip:sti-sr@atcf.visited2.net

NOTE: This value was received by the UE in the preceeding registration procedure

Message-body

The following SDP types and values.

Session description:

– v=0

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

– s=(session name)

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

– b=AS: (bandwidth-value)

Time description:

– t= (start-time) (stop-time)

Media description:

– m=audio (transport port) RTP/AVP (fmt)

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

– b=AS: (bandwidth-value)

– b=RS: (bandwidth-value) [Note 7]

– b=RR: (bandwidth-value) [Note 7]

Attributes for media:

– a=rtpmap: (payload type) AMR-WB/16000 [Note 8]

– a=fmtp: (format) mode-change-capability=2; max-red= (att-field) [Note 9]

– a=rtpmap: (payload type) telephone-event/16000

– a=fmtp: (format)

– a=ecn-capable-rtp: leap ect=0 [Note 3]

– a=rtcp-fb:* nack ecn [Note 3]

– a=rtcp-xr:ecn-sum [Note 3]

– a=rtcp-rsize [Note 3]

– a=ptime:20

– a=maxptime:240

Attributes for media security mechanism:

– a=3ge2ae: requested [Note 4]

– a=a=crypto:1 AES_CM_128_HMAC_SHA1_80inline:WVNfX19zZW1jdGwgKCkgewkyMjA7fQp9CnVubGVz|2^20|

1:4FEC_ORDER=FEC_SRTP" [Note 4]

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

Note 2: Void.

Note 3: Attributes for ECN Capability may be present if the UE supports Explicit Congestion Notification.

Note 4: Attributes for media plane security are present if the use of end-to-access-edge security is supported by UE.

Note 5: Void

Note 6: Void

Note 7: The RR value must be greater than 0. The RS value can be any value.

Note 8: The AMR channel number shall be “/1” or omitted.

Note 9: values from 0 to 220 are allowed

Content-Type

media-type

application/sdp

Feature-Caps

feature-param

+g.3gpp.ti= (value)

Note: The value of this parameter shall be the same as the Transaction Identifier sent by the SS in the preceding CS call setup.

Content-Length

Value

length of message-body

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: (bandwidth-value) [Note 5]

– b=RR: (bandwidth-value) [Note 5]

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 1]

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

Note 1: The value for fmt, payload type (AMR) and format is copied from step 2.

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: The bandwidth-value is copied from step 2.