Avamprogetto 2b

Area of responsibility of CSP LEMF site nonnon --coincidentcoincident LEMF MDMDMD LILI--HPHP Access LineAccess LineAccess Line GWGWGW LELE NTNTNT DNDN--HPHP MD Hosting Facility DN ProviderDN ProviderDN Provider DN ProviderDN ProviderDN Provider Area of responsibility FacilityFacilityFacility FacilityFacilityFacility of PTSS Area of responsibility of ISDN-- DN ProviderDN Provider

InitialInitialInitial AddressAddressAddress MessageMessageMessage (IAM)(IAM)(IAM) SETUPSETUPSETUP MessageMessageMessage AnswerAnswerAnswer MessageMessageMessage (ANM)(ANM)(ANM) CONNECTCONNECTCONNECT MessageMessageMessage TargetTargetTargetTarget ‘‘‘‘ssss

CommuniCommuniCommuniCommuni ----

CCCCCC ---linklinklink cationcationcationcation ReleaseReleaseRelease MessageMessageMessage (REL)(REL)(REL) DISC/REL/REL COMDISC/REL/REL COMDISC/REL/REL COM MessageMessageMessage LostLostLost subsequentsubsequentsubsequent MessagesMessagesMessages accordingaccordingaccording to ITUto ITUto ITU ---T Rec. Q.931T Rec. Q.931T Rec. Q.931 contentcontentcontent ReleaseReleaseRelease CompleteCompleteComplete MessageMessageMessage (RLC)(RLC)(RLC)

ttt

Figure 27 Signalling sequences for release of a CC link as a result of an error in the LEMF

Unless otherwise explicitly stated in Table 5, the REL messages at the handover point between the CSP and the ISDN-DN provider and at the handover point between the PTSS and the ISDN-DN provider contain the same cause value indicating the location of the error.

The LEMF is not required to support all the cause values of Table 5. Table 5 merely indicates how the cause values shall be interpreted by the receiving entity. In principle, all the CSP needs to know is whether the error lies in the LEMF. The detailed determination of the reason falls under the responsibility of the PTSS. As the PTSS itself knows the status (all cause values are given by the LEMF), it does not need a separate message from the CSP or the ISDN-DN provider.

Table 5 Cause values and location in case of release of a CC link as a result of an error in the LEMF ITU-T Q.850 (05/98) Cause Definition Location Failure caused by value

16 Normal Call Clearing user (0000) LEMF (normally, LEMF must not release a CC link)

27 Destination Out of Order user (0000) LEMF

31 may be different at PTSS Normal, Unspecified user (0000) LEMF

side since the ISDN delivery

network translates any cause

value not appearing in this

Table into 31

41 Temporary Failure user (0000) LEMF

47 Resource Unavailable, user (0000) LEMF

Unspecified