Wireless and Mobile Network Architectures. Chapter 7 PACS Network Signaling. PACS Network Signaling. We describes network signaling for the Personal Access Communications System (PACS) PACS supports basic call control, roaming, and handoff management
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Wireless and Mobile Network Architectures Chapter 7 PACS Network Signaling
PACS Network Signaling • We describes network signaling for the Personal Access Communications System (PACS) • PACS supports basic call control, roaming, and handoff management • Does not use MSCs or HLR/VLR, but uses Advanced Intelligent Network (AIN) protocol with an Access Manager (AM), AIN switch, and AIN SCP, SSP
Advanced Intelligent Network (AIN) • By taking full advantage of the network intelligence generated by SS7 advancements • the Advanced Intelligent Network (AIN) can deliver new and profitable services to subscribers. • In the AIN environment, new services are not tied to the call-processing logic of individual switching systems, but are defined through the interworking of these switches and other network elements. • A switch is alerted to the need for AIN processing through various types of triggers that can accompany a call.
PACS Network Interfaces • The RPCU provides management and control functions between the RP and the local exchange network. • The access manager (AM) in the RPCU, it provides: • radio control : managing the RPs, trunk provisioning, RP to RP link transfers • non-radio service control : call control (managing the B channels), switching, routing • The RPCU has to deal with inter-RPCU handoff (similar to inter-BSC handoff) and inter-RP handoff. • Note: an AM is also located in the AIN SCP; the two interact with the ISDN/AIN Switch providing tunneling/de-tunneling (i.e., encapsulation) of the ISDN REGISTER messages over AIN.
The major goal of PACS network signaling • Utilize the existing AIN network entities, such as AIN SCP and SSP • there is no need to create new entities, such as MSC, using in other PCS systems. • In PACS signaling, telephony switching functions are separated from the PCS-related signaling • To achieve this goal • Noncall-associated signaling is introduced to minimize the modifications to the AIN SSP; that is, the AIN SSP does not interpret the PCS-related or IS-41-like signaling message • Many functions of the MSC have been removed from the SSP and moved to the AM and RPCU • The creation of the RPCU introduces a new kind of handoff : inter RPCU handoff
PACS Network Elements • AIN/ISDN Switch • The AIN switch is equipped with SS7, ISDN, and AIN capabilities. • SS7 ISUP is used in the switch to set up the trunks in call control and intersystem handoff. • The SS7 TCAP is used to support mobility management, and to transport AIN message between the switch and the SCP. • Triggering and querying • Triggering is the process of identifying calls that need AIN handling • Querying is the process of assembling an AIN message to an AIN SCP at a trigger detection point • ISDN/AIN Interworking • Noncall-associated (NCA) signaling provides a generic method for the SCP to communicate with an ISDN connected device through the switch
PACS Network Elements • AIN SCP • The AIN SCP provides the service logic, database, and operation capabilities to support HLR, VLR, AM and Auc. • The SCP communicates with the switch using AIN TCAP and the external PCS database using the IS-41 protocol. • The HLR contains a PCS application process, end-user service profiles, and accounting management capabilities. • Intelligent peripheral • 지능망 서비스에서 제공되는 각종 안내 멘트를 제공하고, 사용자와의 음성 인터페이스를 통해서 필요한 정보를 제공하며, 서비스를 위해 필요한 각종 정보(사용자 번호, 비밀번호, 서비스 선택 등)를 수집하는 기능을 제공합니다.
PACS Network Interfaces • AIN interface • During the call-processing procedure, the switch may detect the need for AIN processing at trigger detection points (TDPs) • Then process between the AIN switch and the AIN SCP • ISDN interface • The RPCU communicates with the switch via ISDN basic rate interfaces (BRIs)
In ISDN signaling, every message contains a common mandatory information element, referred to as the call reference. • ALERT • B channel selection • CALL-PROC • call establishment from the called party to calling party • CONN , CON-ACK • call acceptance by the called party • REL , REL-COM • SETUP • Call initiation from calling party to called party • FACILITY • To request permission for a handoff operation (AIN switch RPCU) • REGISTER • To inform the VLR to carry out various operations
AIN/ISDN Interworking • With NCA signaling, the switch provides interworking functions between the SCP/VLR(AIN) and the RPCU (ISDN). • The ISDN messages exchanged between the switch and the RPCU are of type REGISTER • The AIN messages exchanged between the switch and the VLR are of type NCA_Data
MSG Type Invoke Component of Facility REGISTER Switch envelopNCAData RPCU VLR REGISTER (ISDN message) NCA_Data (AIN message) REL-COM MSG Type Package Type Component Type Component NCA_Data Unidirectional Invoke(Last) nCAData NCA Signaling Initiated by the RPCU • The RPCU initiates NCA signaling by sending an ISDN REGISTER message to the switch. • The switch forwards the information to the VLR using an AIN NCA_DATA message. <NCA signaling initiated by the RPCU> <NCA message format translation (ISDN to AIN)>
MSG Type Package Type Component Type Component NCA_Data Unidirectional Invoke(Last) VLR nCAData RPCU Switch NCA_Data REGISTER (AIN message) (ISDN message) REL-COM MSG Type Invoke Component of Facility REGISTER envelopNCAData5 NCA Signaling Initiated by the VLR • The VLR initiates NCA signaling by sending an AIN NCA_DATA message to switch. • The switch sends an ISDN REGISTER message to the RPCU. <NCA message format translation (AIN to ISDN)> <NCA signaling initiated by the VLR>
NCA Signaling Initiated by the VLR • The REL-COM message is to clear the invocation and the call reference of the REGISTER message. • The major goal of NCA signaling is to disassociate the AIN SSP from PCS-related signaling. • When the PCS signaling message is modified in the feature, there will be no need to change the switch. • NCA Signaling design feature • The AIN SSP only translates the NCA signaling from one format to another, the SSP does not interpret the message. • In the ISDN interface between the AIN SSP and the RPCU, the call reference is cancelled after every ISDN NCA message • In the AIN interface between the AIN SSP and the AIN SCP, the unidirectional TCAP message format is used instead of the general AIN transaction format- the query/response TCAP format
New Switch New Switch Old Switch Old Switch Old RPCU New RPCU Old RPCU New RPCU Intersystem Handoff Before the ALT After the ALT
Inter-RPCU hand-off approaches (b) After ALT (Switch Loopback) (c) After ALT (Direct Connect) (a) Before ALT (e) After ALT (Three-way Calling Connection) (d) During ALT (Three-way Calling Connection)
Inter-RPCU hand-off approaches • To minimize the impact of inter-RPCU handoff on the AIN SSP, tow anchor-RPCU handoff approaches have been proposed. • In the switch loopback, • The old RPCU dials the new RPCU to make the connection through the switch. • disadvantage : handoff consumes two more links between the switch and the RPCUs • In the Direct connection, • The RPCUs are connected with trunks • Disadvantage : extra trunks are required to connect the RPCUs and an inter-RPCUs handoff protocol is required • Three-way calling connection • Utilize the existing three-way calling facility of the AIN switch • Minor modifications to the RPCU , does not consume extra trunks