VoLTE Call Flow with XCAP messages pptx.pptx

Vo-LTE Call Flow with Messages
Technical Support Team, Deployment Part
© Samsung Electronics. All Rights Reserved. Confidential and Proprietary.
Document Version 2.0
May 2016
Document Number: INJR-PR0516031

RF Technical Support © Samsung Electronics. All Rights Reserved. Confidential and Proprietary. 2
Establishing IMS Default Bearers
Vo-LTE UE attaches itself to the LTE network and establish a default Bearer for Internet Connect.

Vo-LTE UE establishes a default bearer for IMS Signaling.
Vo-LTE UE register Itself with IMS and subscriber for Registration Event.
Vo-LTE UE makes MO Call, a Vo-LTE Call.

• In Attach Request, EPSAttachType:2 which means, It means UE wants to attach both PS and CS to MME.
•In Attach Request, PDN connectivity Request is “Piggybacked Message”
(Piggybacking (data transmission) In two-way communication, wherever a frame is received, the receiver waits and does
not send the control frame (acknowledgement or ACK) back to the sender immediately. The receiver waits until its network
layer passes in the next data packet.)

• In Attach Request, this message denotes, whether UE is VoLTE Supported or not.
• “IMS PS voice preferred” denotes UE first priority is PS Call, whereas CS Voice Call is secondary priority.
• If UE supports Vo-LTE other messages are also important, exist in UE Capability Information, such as Semi persistent
scheduling, TTI bundling, SRVCC.
• UE denotes its other Vo-LTE features in “ueCapabilityInformation” under ‘featuregroupindicators’.

• It is necessary to know Default Parameters used for Internet, so that we can easily understand default bearers for IMS.
• It helps us to attend comparative analysis.
• Here, “eps-BearerIdenity 5”, “drb-Identity 1” and “priority 12”.

• Basically, this message is a reply from eNodeB to UE for Attach Request message sent by UE.
• Here “ACTIVATE_DEFAULT_EPS_BEARER_CONTEXT_REQUEST” message is piggybacked message.
• Here, QCI is 9, and APN, provide by the eNodeB to the UE.
• QCI 9 is typically used as a default bearer.
Note: UE does not send any APN while sending “PDN Connectivity Request” message for establishment of default bearers for internet
access. A list of APNs, an UE is allowed to use is stored in HSS. Network choose one of the APNs from the list and shares it with UE in
“ACTIVATE_DEFAULTS_EPS_BEARER_CONTEXT_REQUEST” message.
• Here, this is the address provided by the PDN gateway to the UE.
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• In Attach Accept, “IMS voice over PS session in S1 mode supported” is “1”, it tells, UE is allowed to make Vo-LTE Calls.
• For checking this message as “1”, MME first checks UE capabilities, Network Capabilities and UE subscription data from HSS.
• Later, UE sends request for IMS Connection Setup, with PDN connectivity request.

• For IMS connection setup, UE sends “PDN connectivity request”, here the PDN type IPv4 and IPv6, it means UE supports for
both IPv4 and IPv6 address types.
Note: It is mandatory for a UE to support IPv6 for Vo-LTE.
• Here APN name is IMS.
Note:
1.) This is the common APN for all UE, even in Roaming, the APN will be same, so it is a common APN.
2.) While setting up the IMS default bearers, but to setup IMS default bearer UE has to send the APN to the network.

• In PDN Connectivity Request, UE uses “Protocol Configuration Options” to address additional parameter of the network, to which UE is going to
connect. In this case Destination address is IMS.
• Each value has it specified Container ID, they are as follows:
Container ID 1: P-CSCF IPv6 Address Request. (Value to request P-CSCF Address Request to the network)
Container ID 2: IM CN Subsystem Signaling Flag . (Value to intimate network about the default bearer will use for IMS signaling)
Container ID 3: DNS Server IPv6 Address Request.
Container ID 12: P-CSCF IPv4 Address Request.
Container ID 13: DNS Server IPv4 Address Request.
Note: Each message has length “0” because UE is requesting these parameters from network.

• In “Activate Default EPS Bearer Context Request” UE receive requested parameter with values in Container ID.
• Here For Container ID: 3 , Length Value is 16, with contents, same with container ID 13, and Length value is 4.
Note: 1. It is highly recommended that the default bearers is used for SIP. This reduces the number of EPS bearer used. Where as
In multimedia operations, another configuration can be used.
2. Logical Channel priority for Internet Default Bearers is very low comapred to IMS Default Bearer for Voice, because IMS default bearers
is used for SIP signaling.

Vo-LTE Registration Overview
• Vo-LTE UE triggers the registration process by sending
Registration(unprotected) message to CSCF.
• CSCF Shares UE identity with HSS and gets authentication.
• CSCF picks authentication vectors from HSS and send back to UE
in 401 unauthorized message.
• UE checks the authentication message, checks network
authentication and send response in Register message.
• Then CSCF saved UE data into the database and sends 200K
message to the UE to intimate UE successful registration.
• Vo-LTE UE send unprotected message to CSCF to trigger
registration process , it is unprotected because it is send on default
TPC/UDP port 6909, that is used for unprotected SIP messages.

Register
The very first line of the register message is register header and main name of the SIP proxy of UE.
• UE has added via header, in this UE added IP address and TCP/UDP SIP Port.
• Here, the value of Max Forward is 70. It means UE sends this data in maximum hop 70. Every time UE sends this data to the next HOP
count reduce to 1.
“t: <sip:405854060113158@ims.mnc854.mcc405.3gppnetwork.org>”
• Here sip:405854060113158 this is the private Identity that UE shares, ims.mnc854.mcc405.3gppnetwork.org this is the domain name
of CSCF.
• Register message is special case, in this both “to” and “from” headers have same message.
• Caller ID is made up of 2 parts, where, 1st part is the random number generated by the UE, 2nd part is IP address added by the UE.
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Register Continue
• “CSeq”, this header has sequences number and method name, the Cseq number is incremented for each new request with in the
dialogue, simply said it acts as SIP with in the dialogue.
• “Authorization” It has all the parameter for authorization.
Digest: It is authentication scheme used for authentication, It is same as use to authenticate Web Browsers.
Username: Its has UE private Identity, which is checked by the CSCF and HSS.
realm: It is the proxy of the UE.
Nonce: This parameter is empty when UE sends Register message for tye first time. It has some value when UE
sends second time.
Response: This parameter is also empty and contains some values when UE sends Register message second time.

Register Continue
• Expiries: It tells how long the IMS registration will be valid. Here it is 600000, it means 166 Hrs (approx)
• Require and Proxy-Require: It indicates that this appliance supports security mechanism
• Security Clients: This headers has the list of Security mechanism that a SIP clients supports.
• P-Access-Network: This header tells about the access network of the UE. It here tells that UE is connected with E-UTRAN
Network in FDD mode. Also UE has mentioned its cell ID here.
• User-Agent: This header tells about the UE from which the request has been Initiated.

401 Unauthorized
• After getting registration message from UE, CSCF will consults by HSS by sharing UE private identity. If HSS intimate CSCF that UE is
entitled to use IMS services, then CSCF request HSS for authentication vectors .
• Here also “Digest” is the authentication mechanism . “Realm” parameter always have domain name of the network. “Nonce” is the
authentication channel sent by CSCF to UE.
• “Nonce” here made up of RNTI and AUTN.
• “Security Severs” In this header, server has told that which combination of parameters servers supports.

Register/200OK
• In “Register Request” here UE will register with secured port i.e. via Port-S, instead of Default Port.
• Port-S is used for Incoming data into the server and Port-C is used for outgoing data to the server.
• 200K: CSCF will compare response from both UE and Network, with XRES (Expected Response), if it matches than CSCF will assume
that UE is authentic and will make all the necessary entries for this UE in its data base.
• Finally CSCF sends 200K message to UE to mark successful registration.
• P-Associate: This header includes the UE public identities, for which entries were created during registration.
• In P-Associated “Mobile number is Public Identity”

Subscribe
• UE sends “Subscribe” message to CSCF for completion of the registration event.
• Most Important header in this message is “Event header” or “o” . This header denotes, that the events for which UE is subscribing here.
• Here the value of this header is Registration and length is 0 (as it is a request message).
• CSCF sends 200 OK message to UE to tells subscription is successful.

NOTIFY
• CSCF Sends “Notify” message to UE, Notify message is used to tell current state of the registration event.
• The current state is present in the bottom of the message in the form of XMLNS document .
• “200OK” UE sends 200OK message as a respond of Notify message.
• This message complete the subscription process.

MO Vo-LTE Call
• UE initiate the Vo-LTE call by triggering “Invite” message to CSCF. This Invite message
includes all the parameter require of media session origination UE wants to have.
• Once it reached to CSCF, it checks the availability of MT receiver availability.
• If its available, CSCF sends back message “100 Trying” to UE, and forward Invite
message to Terminating UE.
• Terminating UE responds with “183 Session Progress” message to UE to tell it is
working on resource reservation.
• After Receiving “183 Session Progress”, UE responds with “PRACK” message, for
which MT responds with 200 OK.
• Then it sends “Update” message to Terminating UE after added resource reservation,
• Terminating UE responds with “200OK” for the Update message. Indicating that all the
precondition for the session is matching.
• At this point Terminating UE starts alerting.
• Terminating UE sends “180 Ringing” message to MO UE.
• MO UE sends PRACK for this ringing message to MT UE.
• MT UE sends 200OK as acknowledgement to MO UE.
• When MT UE picks up the call, MT UE sends 200OK (for Invite) as ack.
• MO UE sends the ACK message, which leads to the completion of call.
• After this voice call data can be transmitted successfully.

MO Vo-LTE Call
• P-CSCF creates dedicated EPS bearer by sending AA request to PCRF.
• PCRF sends IP can modification request to PDN-GW.
• PDN-GW sends Create bearer request to S-GW.
• S-GW send Create bearer request to MME.
• MME sends Bearer Setup request to eNodeB.
• Then eNodeB sets up DRB by sending RRC reconfiguration setup to UE.
• This DRB have QCI 1 for voice call data and QCI 2 if it is video Call.

VoLTE Call Flow with XCAP messages pptx.pptx

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