This document discusses various types of call forwarding in 3 sentences: It describes unconditional and conditional call forwarding scenarios as well as no reply, busy, and not reachable scenarios. The state transition models show the signaling flows between network elements like the GMSC, HLR, MSC, and VLR when a call is forwarded due to various conditions like absent subscriber, no reply, radio congestion, or detachment. Registration, erasure, activation, and deactivation functions are also covered with regard to managing call forwarding numbers and services.

1. Call Forwarding Akash Agrawal

2. Types CFU CFB NDUB UDUB CFNRC CFNRY Unconditional Conditional Early Call forwarding (GMSC) Late Call forwarding (VMSC)

4. Functional Description Registration (register a FTN, FTN to basic service group..) Erasure (erase a FTN, basic service group ) Activation (activate CF services) Deactivation (withdraw CF/SS ) Interrogate (get CF data)

5. State Transition Model

6. CFU MS B has CFU Activated. SRI PRN SRI ACK IAM PRN ACK Notify GMSC must increment fwd counter by 1 GMSC HLRb MSC/VLRb HLRc PSTNc MSa MSC/VLRc Setup SRI ACK (FTN, CFU) IAM 1. To fixed terminal 2. To MS SRI (NOF = 1, IT = forwarding)

7. CFNRC (MS not reachable detected on GMSC) PRN (IMSI b) PRN SRI ACK IAM PRN ACK Notify GMSC must increment fwd counter by 1 SRI VLR reported Subscriber B is not reachable due to derregister or Purge or detach. GMSC HLRb MSC/VLRb HLRc PSTNc MSa MSC/VLRc Setup IAM 1. To fixed terminal 2. To MS SRI (NOF = 1, IT = forwarding) SRI ACK (FTN, Absent MSb) PRN ACK (Absent MSb)

8. CFB (NDUB) PRN (IMSI b) 2. To MS SRI (MS C) PRN SRI ACK IAM PRN ACK Notify SRI MSC detect NDUB when paging MS, MSC gets forwarding info from VLR IAM Notify GMSC HLRb MSC/VLRb HLRc PSTNc MSa MSC/VLRc Setup IAM 1. To fixed terminal SRI ACK PRN

9. CFB (UDUB) PRN (IMSI b) 2. To MS IAM Notify SRI MSC detects UDUB during call setup. MSC gets FTN and forwarding info from VLR IAM Notify SRI (MS C) PRN SRI ACK PRN ACK MSc SETUP UDUB GMSC HLRb MSC/VLRb HLRc PSTNc MSa MSC/VLRc Setup IAM 1. To fixed terminal SRI ACK PRN

10. CFNRY PRN (IMSI b) 2. To MS IAM Notify SRI MSC starts no reply timer and the timer expired. VLR returns FTN, MSC forwards call. IAM Notify SRI (MS C) PRN SRI ACK PRN ACK MSc SETUP Call Confirm TIME OUT GMSC HLRb MSC/VLRb HLRc PSTNc MSa MSC/VLRc Setup IAM 1. To fixed terminal SRI ACK PRN

11. CFNRC (Radio Congestion) PRN (IMSI b) 2. To MS IAM Notify SRI MSC detects radio Congestion. VLR returns FTN, MSC increments redirection count by 1 IAM Notify SRI (MS C) PRN SRI ACK PRN ACK MSc SETUP Call Confirm Radio Congestion GMSC HLRb MSC/VLRb HLRc PSTNc MSa MSC/VLRc Setup IAM 1. To fixed terminal SRI ACK PRN

12. CFNRC (No Paging Response) PRN (IMSI b) 2. To MS IAM Notify SRI MSC waits for paging response and the timer expired. VLR returns FTN IAM Notify SRI (MS C) PRN SRI ACK PRN ACK MSc Paging No Response GMSC HLRb MSC/VLRb HLRc PSTNc MSa MSC/VLRc Setup IAM 1. To fixed terminal SRI ACK PRN

13. CFNRC (MS Detached) PRN (IMSI b) 2. To MS SRI (MS C) PRN SRI ACK IAM PRN ACK Notify SRI VLR detects MS detached. VLR returns FTN. IAM Notify GMSC HLRb MSC/VLRb HLRc PSTNc MSa MSC/VLRc Setup IAM 1. To fixed terminal SRI ACK PRN

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