Advanced IMS Scenarios & Service Engineering

Aims — what you can do after

• Read initial Filter Criteria and predict which Application Server a request hits — and what happens when it is down.
• Trace the full Cx command set, including the two the base course skipped.
• Distinguish re-INVITE from UPDATE, and explain the QoS-preconditions mechanism.
• Execute the MMTEL services: hold/resume, call waiting, diversion, barring and identity.
• Follow transfer (REFER) and conference call-flows.
• Route an emergency call: emergency registration, the service URN, and PSAP selection.
• Explain terminating access-domain selection, EPS fallback and single-radio continuity.
• Resolve a called number the way a network does, and understand interconnect topology hiding.
• Compute voice quality from captures, and correlate charging across nodes.

The idea that unlocks the course

                       Application Server (MMTEL, forwarding, ...)
                          ^                    |
                          |  ISC (SIP)         |  Sh (to the HSS)
                          |                    v
  INVITE --> S-CSCF --[ evaluate filter criteria in priority order ]--> onward
            #  matched a rule?  hand the request to that AS, then continue

The service layer: CSCFs route, Application Servers implement — filter criteria connect them.

Flow — services on both sides of a call

  UE-A     S-CSCF(orig)     AS(orig)     S-CSCF(term)     AS(term)     UE-B
   |          |               |             |               |          |
   |--INVITE-->|--filter------>|             |               |          |     originating services
   |          |<--(changed)---|             |               |          |
   |          |------------- INVITE -------->|--filter------>|          |     terminating services
   |          |               |             |<--(changed)---|          |
   |          |               |             |------------ INVITE ------>|     delivered
   #  a service that 'works from my phone but not for customers' tested only one side

One call crosses the service layer twice — originating and terminating.

Special path — emergency calls

  NORMAL:     UE -> P-CSCF -> S-CSCF -> (filters -> AS) -> callee
  EMERGENCY:  UE -> P-CSCF -> E-CSCF -> (location) -> PSAP
  #  forwarding, barring and identity-restriction must NOT apply to an emergency call

An emergency call takes a different path — it skips the whole service layer on purpose.

The MMTEL suite you exercise

Roughly half the course is offline reference call-flows — 20 annotated ladders that render with no lab, so it covers elements a single-VM lab cannot host.

Module breakdown