1. Chap 5. IS-41 Network Signaling
Network Computing LAB.
홍 정 표 ( )

2. Signaling System No. 7 Signaling System NO. 7 PSTN signaling protocol
interconnection between a PCN and the PSTN
There are six types of SS7 signaling links.
Two Types, A-Link (access link) and D-Link (diagonal link)
STP
SCP
HLR
MSC
SSP
Trunk
PSTN
PCN (PCS Network)
(SCP)
A-Link
D-Link

3. Signaling System No. 7 SS7 protocol Layers OMAP MAP TCAP SCCP ISDN-UP
MTP Level 3
MTP Level 2
MTP Level 1
OSI Layers
Application
Presentation
Session
Transport
Network
Data Link
Physical
The SS7 Layers

4. Signaling System No. 7
MTP (Message Transfer Part) – Transfer Signaling information
MTP Level 2 provides reliable transfer of signaling message
MTP Level 3 provides message routing and network management
SCCP (Signaling Connection Control Part)
Provides additional functions such as GTT to the MTP
TCAP (Transaction Capabilities Application Part)
Provides the capability to exchange information between using noncircuit-related signaling
ISUP-UP (Integrated Services Digital Network User Part)
Establishes circuit-switched network connections
OMAP (Operations, Maintenance, and Administration part)
Application of TCAP
MAP (Mobile Application Part)
Both IS-41 & GSM MAP are implemented at this layer

5. Interconnection and Message Routing
STP
MSC
Tandem
PSTN
PCN
Type S (A-Links)
Type 2A with
SS7 interface
Type 2A with
SS7 interface
STP
MSC
Tandem
PSTN
PCN
Type S (D-Links)
STP
MSC
End
Office
PSTN
PCN
Type S (A-Links)
Type 2B with
SS7 interface
STP
STP
Type S (D-Links)
Type 2B with
SS7 interface
End
Office
MSC
PSTN
PCN

6. Interconnection and Message Routing
SS7 message routing is preformed at the MTP and the SCCP of a node (SSP,STP or SCP)
Signaling messages are delivered with the actual destination address at the MTP
MTP level receives messages from TCAP, SCCP, ISUP
DPC (destination point code) of the message uniquely identifies the destination node
Routing to the destination node is determined by the MTP using lookup tables

7. Mobility Management Using TCAP
TCAP operation
More than 50 TCAP operation are defined
For three purposes
Inter-MSC handoff, automatic roaming, operations, administration, and maintenance
TCAP message consists of two portions
Transaction portion – define package type
QueryWithPermission, Response
ConversationWithPermission, Unidirectional
Component portion – define number and types of components
INVOKE, RETURN RESULT
RETURN ERROR, REJECT

8. Mobility Management Using TCAP
PCN1
PSTN
PCN2
STP1
STP2
STP3
STP4
MSC1
VLR1
HLR
VLR2
MSC2
RegistrationNotification (INVOKE)
RegistrationNotification (INVOKE) T1 T2
RegistrationNotification (RETURN RESULT)
RegistrationCancellation (INVOKE)
RegistrationNotification (RETURN RESULT) T3
RegistrationCancellation (RETURN RESULT)
RegistrationCancellation (INVOKE) T4
RegistrationCancellation (RETURN RESULT)
QualificationRequest (INVOKE) T5
QualificationRequest (RETURN RESULT)
ServiceProfileRequest (INVOKE) T6
ServiceProfileRequest (RETURN RESULT)

9. Mobility Management Using TCAP
IS-41 TCAP message flow for MS registration
Transaction 1
When MS is in MSC2’s service area, MSC2 sends a RegistrationNotification(INVOKE) to its VLR(VLR2)
Transaction 2
If MSC1 is net served by VLR2, then VLR2 sends a RegistrationNotification(INVOKE) to the MS’s HLR
Transaction 3
HLR sends a RegistrationCancellation(INVOKE) to the MS’s previously visited VLR (VLR1)
Transaction 4
The cancellation propagates to MSC1
Transaction 5
After T2 is completed, VLR2 creates a registration record for MS
Sends a QualificationRequest(INVOKE) to HLR to check MS’s qualification for receiving services
Transaction 6
VLR2 sends a ServiceProfileRequest(INVOKE) to HLR to obtain the service profile for the roaming MS

10. PCN/PSTN Call Control Using ISUP
STP
STP 4 1 2 3 5
End
Office
Tandem
MSC 6 7
Step 1
IAM
IAM
COT
Step 2
COT
ACM
ACM
Step 3
ANM
Step 4
ANM
Conversation using trunks (6) and (7)
Signaling path from
PSTN to PCN
REL 1 2 3 4 5
Step 5
REL
RLC
Step 6
Signaling path from
PCN to PSTN
RLC 5 4 2 3 1

11. PCN/PSTN Call Control Using ISUP
Typical message flow for type 2A with SS7 land-to-mobile call setup and release involving a tandem switch
When MIN is dialed, end office (EO) notices that the number is for wireless service
Suppose that EO has HLR query capability
EO sends a query message to obtain MS’s TLDN (temporary local directory number)
Messages exchanged among switches, VLR and HLR are TCAP messages

12. PCN/PSTN Call Control Using ISUP
Step 1
After the MS’s TLDN is obtained, EO sends an Initial Address Message (IAM) to the PCN MSC to initiate signaling for trunk setup
When IAM is sent, IAM timer is set at the EO
EO expects to receive a response from MSC within timeout period
Step 2
If IAM sent from the EO to tandem specifies a continuity check, selected trunk from tandem to EO
After continuity check is successfully completed, Continuity Message (COT) is sent from EO to tandem, and trunk is set up
Same procedure could be performed when MSC receives IAM from tandem

13. PCN/PSTN Call Control Using ISUP
Step 3
When IAM arrives at MSC, MSC pages the MS
One of following three events occurs
MS is connected with another call
This situation is referred to as call collision
Call is processed with call forwarding or call waiting, or MSC returns REL message to EO with a cause indicating the busy line situation
MS is idle
MSC send Address Complete Message (ACM) to EO
Message informs EO of MS information, charge indications, and end-to-end protocol requirements
When the EO receives the ACM, the IAM timer is stopped
Ms does not answer the page
MSC returns REL message to EO

14. PCN/PSTN Call Control Using ISUP
Step 4
When MS answers call, an Answer Message (ANM) is sent from MSC to EO
Call is established through trunk path (6)(7)
Step 5
EO sends a Release Message (REL) to indicate that specified trunk is being released from the connection
Trunk is not set to idle is EO until a Release Complete Message (RLC) message is received
Step 6
When MSC receives REL from EO, relies with a RLC
After RLC is sent, EO and tandem waits for 0.5 to 1 sec. before it seizes the released trunk for the next call