PACS is a wireless system using TDMA and designed for local loops and personal communications. It can operate in TDD or FDD mode using different frequencies for uplink and downlink. Handoffs are mobile-controlled and complete quickly. The PACS network uses an AIN architecture with an Access Manager, AIN switch, and SCP to provide services like basic call control, roaming, and handoff management without an MSC or HLR/VLR. Intersystem handoffs follow the IS-41 anchor switch approach.

1. Personal Access
Communications System (PACS)

2. Personal Access Communications
System (PACS)
 PACS is a low-power PCS system developed at Telcordia (formerly
Bellcore).
 PACS is designed for wireless local loop (see Chapter 23) and for
personal communications services.
 TDMA is used in PACS with eight voice channels per frequency
carrier.
 The speech coding rate is 32 Kbps.
 Both TDD and frequency division duplexing (FDD) are
accommodated by the PACS standard.
 In FDD mode, the PACS uplink and downlink utilize different RF
carriers, similar to cellular systems.

3.  The highly effective and reliable mobile-controlled handoff (MCHO)
completes in less than 20 msec.
 PACS roaming management is supported by an IS-41-like protocol.
 Like GSM, PACS supports both circuit-based and packet-based
access protocols.
Personal Access Communications
System (PACS)

4. PACS Network Signaling
Personal Access Communications Systems (PACS) supports:
• Basic call control
• Roaming
• 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 Service Control Point (SCP).

5. PACS Architecture
AM
AIN
switch
Radio port (RP)
Radio Port Control Unit (RPCU)
AM
ISDN
ISDN
trunk
AM
HLR
VLR
AIN
AIN
SCP
AIN PSTN
Interface P
InterfaceA
SCP = Service Control Point
STP = Signal Transfer Point
STP SS7
Portable
Fixed Access Unit

6. Access Manager (AM)
• The access manager in the radio port control unit (RPCU), it provides:
• The RPCU has to deal with INTER-RPCU handoff (similar to inter-BSC handoff)
and inter-radio port (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.
• Pg. 125 notes that the RPCUs could be connected via an IP network to the VLR, thus
by passing the AIN/ISDN Switch (SSP) for all non-call associated (NCA) signaling.
Radio control
Managing the rps, trunk provisioning, RP to RP link
transfers
Non-radio service control Call control (managing the B channels), switching, routing

7. AIN/ISDN Switch
Note: The textbook often refers to this as the AIN Service Switching Point (SSP).
Uses:
• SS7 ISUP to set up trunk and for inter-system handoff
• SS7 TCAP to support mobility management and transport AIN messages
between switch and SCP; the AIN messages are basically remote procedure
calls (RPC) calls to the SCP
• ISDN for:
• call control {standard ISDN},
• automatic link transfer (ALT) {FACILITY message for handoff}, and
• non-call associated (NCA) signaling {for example, communication between RPCU and VLR for
registration and authentication - REGISTER message - which is encapsulated in an AIN NCA-Data
message}
Also provides:
• Automatic Code Gaping (for traffic load control)
• Automatic Message Accounting (for access charging)

8. AIN Service Control Point (SCP)
Provides service logic, databases, and operations to support:
– Home Location Register (HLR)
– Visitor Location Register (VLR)
– Access Manager (AM)
– Authentication Center (AuC)
Communicates with:
– the switch via AIN TCAP
– external PCS databases via IS-41 protocol

9. PACS Intersystem Handoff
• PACS Intersystem Handoff/automatic link transfer (ALT)
follows IS-41 anchor switch approach.

10. 3 alternative inter-RPCU handoff
methods
Switch
RPCU RPCU
old new
Before ALT
Switch
RPCU RPCU
old new
After ALT (Switch Loopback)

11. Switch
RPCU RPCU
old new
c. After ALT (Direct Connect)
Switch
RPCU RPCU
old new
d.During ALT
(Three-Way Calling Connections)
Note: (d) illustrates that the switch is
doing bridging, but the traffic is not
using any radio capacity in the new cell -
until the mobile arrives
Switch
RPCU RPCU
old new
e. After ALT
(Three-Way Calling Connections)