PSTN Integration¶
2.3 PSTN Design¶
2.3.1 Global PSTN Strategy Overview¶
+-----------------------------------------------------------------------------+
| ABHAVTECH GLOBAL PSTN STRATEGY |
+-----------------------------------------------------------------------------+
| |
| PSTN CONNECTIVITY OPTIONS |
| |
| +-----------------+ +-----------------+ +-----------------+ |
| | LOCAL GATEWAY | | CCPP | | ITN (India) | |
| | (Premises PSTN) | | (Cloud PSTN) | | (Non-Geographic)| |
| +-----------------+ +-----------------+ +-----------------+ |
| | * Customer SBC | | * Provider SBC | | * Cloud-native | |
| | * Existing PSTN | | * Port numbers | | * 9XXXXXXXXX | |
| | * Zone/Edge | | * No hardware | | * No Zone/Edge | |
| | (India only) | | * Zone/Edge | | * India WFH | |
| | | | (India only) | | | |
| +--------+--------+ +--------+--------+ +--------+--------+ |
| | | | |
| v v v |
| +-----------------+ +-----------------+ +-----------------+ |
| | INDIA OFFICES | | EMEA & AMERICAS | | INDIA WFH | |
| | * Mumbai | | * London (CCPP) | | * 150 users | |
| | * Chennai | | * Frankfurt | | * Toll bypass | |
| | * Bangalore | | * New Jersey | | exempt | |
| | * Delhi/Noida | | * Dallas | | | |
| | * Pune/Hyd | | | | | |
| +-----------------+ +-----------------+ +-----------------+ |
| |
| STRATEGIC RATIONALE: |
| ==================== |
| India (LGW): * Leverage existing Tata/Airtel contracts |
| * Maintain CUBE investment |
| * DoT toll bypass compliance via Zone/Edge |
| |
| EMEA/Americas (CCPP): * No local compliance restrictions |
| * Simplified management |
| * Provider handles regulatory |
| |
| India WFH (ITN): * Exempt from toll bypass |
| * Works from any India location |
| * Tata Communications provider |
| |
+-----------------------------------------------------------------------------+
2.3.2 India: Local Gateway Architecture¶
2.3.2.1 Per-Circle LGW Requirements¶
+-----------------------------------------------------------------------------+
| INDIA LOCAL GATEWAY ARCHITECTURE |
+-----------------------------------------------------------------------------+
| |
| +-------------------------+ |
| | WEBEX CALLING | |
| | (Mumbai + Chennai DC) | |
| +-----------+-------------+ |
| | |
| +----------------+----------------+ |
| | | | |
| v v v |
| +--------------+ +--------------+ +--------------+ |
| | Zone: | | Zone: | | Zone: | |
| | Mumbai | | Karnataka | | Tamil Nadu | |
| | Circle | | Circle | | Circle | |
| +--------------+ +--------------+ +--------------+ |
| |Trusted Edge: | |Trusted Edge: | |Trusted Edge: | |
| |103.15.XX.XXX/24| |103.20.XX.XXX/24| |103.25.XX.XXX/24| |
| |10.1.x.x/16 | |10.3.x.x/20 | |10.2.x.x/16 | |
| +------+-------+ +------+-------+ +------+-------+ |
| | | | |
| v v v |
| +--------------+ +--------------+ +--------------+ |
| | LGW: CUBE | | LGW: CUBE | | LGW: CUBE | |
| | Mumbai (HA) | | Bangalore | | Chennai (HA) | |
| | ISR 4451-X | | ISR 4331 | | ISR 4351 | |
| | IOS-XE 17.12 | | IOS-XE 17.12 | | IOS-XE 17.12 | |
| +------+-------+ +------+-------+ +------+-------+ |
| | | | |
| v v v |
| +--------------+ +--------------+ +--------------+ |
| | PSTN: Tata | | PSTN: Tata | | PSTN: Tata | |
| | Mumbai SIP | | Bangalore | | Chennai SIP | |
| | +91-22-XXXX | | +91-80-XXXX | | +91-44-XXXX | |
| +--------------+ +--------------+ +--------------+ |
| |
| +--------------+ +--------------+ +--------------+ |
| | Zone: | | Zone: | | Zone: | |
| | Delhi | | UP West | | AP/Telangana | |
| | Circle | | Circle | | Circle | |
| +--------------+ +--------------+ +--------------+ |
| |Trusted Edge: | |Trusted Edge: | |Trusted Edge: | |
| |103.30.XX.XXX/24| |103.35.XX.XXX/24| |103.40.XX.XXX | |
| +------+-------+ +------+-------+ +------+-------+ |
| | | | |
| v v v |
| +--------------+ +--------------+ +--------------+ |
| | LGW: CUBE | | LGW: CUBE | | LGW: CUBE | |
| | Delhi | | Noida | | Hyderabad | |
| | ISR 4331 | | ISR 4331 | | ISR 4331 | |
| +------+-------+ +------+-------+ +------+-------+ |
| | | | |
| v v v |
| +--------------+ +--------------+ +--------------+ |
| | PSTN: Tata | | PSTN: Tata | | PSTN: Tata | |
| | Delhi SIP | | Noida SIP | | Hyderabad | |
| | +91-11-XXXX | | +91-120-XXX | | +91-40-XXXX | |
| +--------------+ +--------------+ +--------------+ |
| |
| TOLL BYPASS ENFORCEMENT: |
| ======================== |
| Webex checks user IP against Trusted Network Edge definitions |
| Routes PSTN calls ONLY through user's assigned Zone LGW |
| Roaming users (different zone) -> PSTN call BLOCKED |
| |
+-----------------------------------------------------------------------------+
LGW Specifications by Circle:
| LGW | Platform | IOS-XE | Capacity | HA | PSTN Circuits | Locations Served |
|---|---|---|---|---|---|---|
| lgw-mumbai-01/02 | ISR 4451-X | 17.12.2 | 1000 calls | Yes | 30 SIP channels | Mumbai, Pune |
| lgw-chennai-01/02 | ISR 4351 | 17.12.2 | 500 calls | Yes | 15 SIP channels | Chennai |
| lgw-bangalore-01 | ISR 4331 | 17.12.2 | 350 calls | No | 10 SIP channels | Bangalore |
| lgw-delhi-01 | ISR 4331 | 17.12.2 | 250 calls | No | 8 SIP channels | Delhi |
| lgw-noida-01 | ISR 4331 | 17.12.2 | 200 calls | No | 6 SIP channels | Noida |
| lgw-hyderabad-01 | ISR 4331 | 17.12.2 | 80 calls | No | 3 SIP channels | Hyderabad |
2.3.2.2 Zone & Trusted Network Edge Configuration¶
Step-by-Step: Creating Zones in Control Hub
- Navigate to Control Hub > Calling > Service Settings > Zones
- Click Create Zone
- Configure zone settings per circle
Abhavtech Zone Configuration:
| Zone Name | Telecom Circle | Locations | LGW | Trusted Edge IPs (Public) | Internal Subnets |
|---|---|---|---|---|---|
| Zone-Mumbai-Circle | Mumbai | Mumbai HQ, Pune | lgw-mumbai-01/02 | 103.15.XX.XXX/24 | 10.1.0.0/16, 10.6.0.0/20 |
| Zone-TamilNadu-Circle | Tamil Nadu | Chennai | lgw-chennai-01/02 | 103.25.XX.XXX/24 | 10.2.0.0/16 |
| Zone-Karnataka-Circle | Karnataka | Bangalore | lgw-bangalore-01 | 103.20.XX.XXX/24 | 10.3.0.0/20 |
| Zone-Delhi-Circle | Delhi | Delhi | lgw-delhi-01 | 103.30.XX.XXX/24 | 10.4.0.0/20 |
| Zone-UPWest-Circle | UP West | Noida | lgw-noida-01 | 103.35.XX.XXX/24 | 10.5.0.0/20 |
| Zone-APTelangana-Circle | AP/Telangana | Hyderabad | lgw-hyderabad-01 | 103.40.XX.XXX/24 | 10.7.0.0/20 |
Step-by-Step: Adding Trusted Network Edge
- Navigate to Control Hub > Calling > Service Settings > Trusted Network Edge
- Click Add Trusted Edge
- Configure IP ranges
# Control Hub - Trusted Network Edge Configuration
trusted_network_edges:
- name: "Mumbai-Edge"
description: "Mumbai office public IP range"
ip_addresses:
- "103.15.XX.XXX/24"
internal_subnets:
- "10.1.0.0/16"
- "10.6.0.0/20" # Pune backhauls through Mumbai
- name: "Chennai-Edge"
description: "Chennai office public IP range"
ip_addresses:
- "103.25.XX.XXX/24"
internal_subnets:
- "10.2.0.0/16"
- name: "Bangalore-Edge"
description: "Bangalore office public IP range"
ip_addresses:
- "103.20.XX.XXX/24"
internal_subnets:
- "10.3.0.0/20"
- name: "Delhi-Edge"
description: "Delhi office public IP range"
ip_addresses:
- "103.30.XX.XXX/24"
internal_subnets:
- "10.4.0.0/20"
- name: "Noida-Edge"
description: "Noida office public IP range"
ip_addresses:
- "103.35.XX.XXX/24"
internal_subnets:
- "10.5.0.0/20"
- name: "Hyderabad-Edge"
description: "Hyderabad office public IP range"
ip_addresses:
- "103.40.XX.XXX/24"
internal_subnets:
- "10.7.0.0/20"
2.3.2.3 Toll Bypass Enforcement Scenarios¶
+-----------------------------------------------------------------------------+
| TOLL BYPASS ENFORCEMENT - CALL FLOW SCENARIOS |
+-----------------------------------------------------------------------------+
| |
| SCENARIO 1: COMPLIANT - Mumbai User calling from Mumbai Office |
| =============================================================== |
| |
| 1. User at Mumbai HQ dials +91-80-12345678 (Bangalore external number) |
| 2. Webex detects user source IP: 10.1.50.25 |
| 3. IP matches Trusted Edge: Mumbai-Edge (10.1.0.0/16) |
| 4. Zone lookup: Zone-Mumbai-Circle |
| 5. Route Group: RG-Mumbai-LGW |
| 6. Call routes to lgw-mumbai-01 |
| 7. LGW sends call to Tata SIP trunk (Mumbai) |
| 8. [OK] CALL COMPLETES - Toll charged at Mumbai egress point |
| |
| +---------+ +---------+ +---------+ +---------+ +---------+ |
| | User |--->| Webex |--->| Zone |--->| Mumbai |--->| Tata | |
| | Mumbai | | Cloud | | Lookup | | LGW | | Mumbai | |
| |10.1.x.x | | | | [OK] Match | | | | PSTN | |
| +---------+ +---------+ +---------+ +---------+ +---------+ |
| |
+-----------------------------------------------------------------------------+
| |
| SCENARIO 2: BLOCKED - Mumbai User Roaming to Bangalore Office |
| =============================================================== |
| |
| 1. Mumbai user visits Bangalore office, uses office WiFi |
| 2. User dials +91-11-12345678 (Delhi external number) |
| 3. Webex detects user source IP: 10.3.50.100 |
| 4. IP matches Trusted Edge: Bangalore-Edge (10.3.0.0/20) |
| 5. User's assigned Zone: Zone-Mumbai-Circle |
| 6. MISMATCH: User in Bangalore but assigned to Mumbai zone |
| 7. [X] PSTN CALL BLOCKED - Toll bypass prevention |
| 8. User receives "PSTN calling not available" message |
| |
| +---------+ +---------+ +---------+ +---------+ |
| | Mumbai |--->| Webex |--->| Zone |--->| [X] CALL | |
| | User | | Cloud | | Lookup | | BLOCKED | |
| | @B'lore | | | | Mismatch| | | |
| |10.3.x.x | | | | | | | |
| +---------+ +---------+ +---------+ +---------+ |
| |
| WORKAROUND OPTIONS: |
| * Use Webex-to-Webex calling (always works) |
| * VPN back to Mumbai network |
| * Mobile cellular (outside Webex) |
| |
+-----------------------------------------------------------------------------+
| |
| SCENARIO 3: WFH USER WITH ITN - Working from Home in Tier-2 City |
| =============================================================== |
| |
| 1. WFH user assigned ITN number: +91-9XX-1000-XX |
| 2. User dials +91-22-12345678 (Mumbai external number) |
| 3. ITN numbers are EXEMPT from toll bypass rules |
| 4. No Zone/Edge check required |
| 5. Call routes directly to Tata cloud |
| 6. [OK] CALL COMPLETES |
| |
| +---------+ +---------+ +---------+ +---------+ |
| | WFH |--->| Webex |--->| ITN |--->| Tata | |
| | User | | Cloud | | Exempt | | Cloud | |
| | Home | | | | [OK] Pass | | PSTN | |
| +---------+ +---------+ +---------+ +---------+ |
| |
+-----------------------------------------------------------------------------+
2.3.2.4 LGW CUBE Configuration Template¶
! ============================================================
! CUBE Local Gateway Configuration Template - Mumbai
! Abhavtech.com - ABV-COLLAB-MIG-2026
! IOS-XE Version: 17.12.2 or later (REQUIRED)
! Platform: ISR 4451-X
! ============================================================
! --- Global SIP Settings ---
voice service voip
ip address trusted list
ipv4 52.114.148.0 255.255.252.0 ! Webex Calling signaling
ipv4 52.114.152.0 255.255.252.0
ipv4 52.114.156.0 255.255.252.0
mode border-element
media disable-detailed-stats
allow-connections sip to sip
no supplementary-service sip refer
stun
stun flowdata agent-id 1 boot-count 4
stun flowdata shared-secret 0 <secret>
sip
session refresh
early-offer forced
asymmetric payload full
! --- Codec Class ---
voice class codec 1
codec preference 1 opus
codec preference 2 g711ulaw
codec preference 3 g711alaw
codec preference 4 g729r8
! --- SIP Profile for Webex ---
voice class sip-profiles 100
rule 10 request ANY sip-header SIP-Req-URI modify "sips:" "sip:"
rule 20 request ANY sip-header To modify "<sips:" "<sip:"
rule 30 request ANY sip-header From modify "<sips:" "<sip:"
rule 40 request ANY sip-header Contact modify "<sips:" "<sip:"
rule 50 response ANY sip-header To modify "<sips:" "<sip:"
rule 60 response ANY sip-header From modify "<sips:" "<sip:"
rule 70 response ANY sip-header Contact modify "<sips:" "<sip:"
! --- Tenant for Webex Calling ---
voice class tenant 100
registrar dns:webexapis.com scheme sips expires 3600
credentials number +91226XXX0000 username <LGW-USERNAME> password 0 <PASSWORD> realm webex.com
authentication username <LGW-USERNAME> password 0 <PASSWORD> realm webex.com
sip-server dns:webexapis.com
srtp-crypto 1 AES_CM_128_HMAC_SHA1_80
session transport tcp tls
url sips
error-passthru
bind control source-interface GigabitEthernet0/0/0
bind media source-interface GigabitEthernet0/0/0
! --- Dial Peer to Webex Calling ---
dial-peer voice 100 voip
description Webex-Calling-Outbound
preference 1
destination-pattern .T
session protocol sipv2
session target dns:webexapis.com
session transport tcp tls
voice-class sip tenant 100
voice-class sip profiles 100
voice-class codec 1
dtmf-relay rtp-nte
srtp
no vad
! --- Dial Peer to PSTN (Tata Mumbai) ---
dial-peer voice 200 voip
description PSTN-Tata-Mumbai-Outbound
preference 1
destination-pattern 9[0-9].T
session protocol sipv2
session target ipv4:203.130.X.X ! Tata SIP SBC IP
voice-class codec 1
dtmf-relay rtp-nte
! --- Inbound from PSTN ---
dial-peer voice 201 voip
description PSTN-Tata-Mumbai-Inbound
incoming called-number .
session protocol sipv2
voice-class codec 1
dtmf-relay rtp-nte
! --- Inbound from Webex ---
dial-peer voice 101 voip
description Webex-Calling-Inbound
incoming uri via Webex
session protocol sipv2
voice-class sip tenant 100
voice-class codec 1
dtmf-relay rtp-nte
srtp
! --- URI Class ---
voice class uri Webex sip
host webexapis.com
! --- Certificate Configuration ---
crypto pki trustpoint WEBEX-TRUSTPOINT
enrollment terminal
revocation-check none
! --- TLS Profile ---
voice class tls-profile 1
trustpoint WEBEX-TRUSTPOINT
cipher suites tls13-aes128-gcm-sha256
cn-san-validate server
sni send webexapis.com
2.3.3 EMEA: Cloud Connected PSTN¶
2.3.3.1 UK CCPP Configuration¶
| Configuration Item | Value |
|---|---|
| CCPP Provider | IntelePeer UK |
| Service Type | Cloud Connected PSTN |
| Route Group | RG-UK-CCPP |
| Numbers to Port | +44-20-4960-0001 to +44-20-4960-0799 |
| Main Number | +44-20-4960-0000 |
| Toll-Free | +44-800-096-1000 |
| Emergency | 999 / 112 (auto-configured by CCPP) |
| Zone/Edge Required | NO (UK has no toll bypass regulations) |
| Data Residency | UK Data Centers (London/Manchester) |
Number Porting Process (UK): 1. Submit Letter of Authorization (LOA) to IntelePeer 2. IntelePeer coordinates with existing provider (BT) 3. Typical porting window: 10 business days 4. Port validation test conducted 24 hours before cutover 5. Numbers active on Webex Calling after port complete
2.3.3.2 EU CCPP Configuration (Frankfurt)¶
| Configuration Item | Value |
|---|---|
| CCPP Provider | IntelePeer EU |
| Service Type | Cloud Connected PSTN |
| Route Group | RG-EU-CCPP |
| Numbers to Port | +49-69-4960-0001 to +49-69-4960-0499 |
| Main Number | +49-69-4960-0000 |
| Toll-Free | +49-800-096-1000 (German) |
| Emergency | 112 (EU standard, auto-configured) |
| Zone/Edge Required | NO |
| Data Residency | EU Data Centers (Frankfurt/Amsterdam) |
| BSI C5 Compliance | Webex certified |
| EU Cloud CoC | Level 3 |
2.3.4 Americas: Cloud Connected PSTN¶
| Configuration Item | New Jersey | Dallas |
|---|---|---|
| CCPP Provider | IntelePeer US | IntelePeer US |
| Route Group | RG-US-CCPP | RG-US-CCPP |
| Numbers to Port | +1-201-496-0001 to 0799 (800) | +1-214-496-0001 to 0499 (500) |
| Main Number | +1-201-496-0000 | +1-214-496-0000 |
| Toll-Free | +1-800-096-1000 (shared) | Shared with NJ |
| Emergency | 911 (E911 enabled) | 911 (E911 enabled) |
| E911 Address | Validated per user | Validated per user |
2.3.5 DID Number Mapping¶
Working Document -- Not Yet Finalised
The DID number mapping table (per-site DID ranges, provider assignments, port/retain decisions, and migration timeline) is maintained as a separate working document and will be reintroduced here once the number ranges are confirmed and approved.
Pending confirmation: - Actual DID ranges per city from Tata/Airtel (India LGW sites) - Port vs retain decisions for EMEA and Americas numbers - Final toll-free number assignments - Number porting timeline aligned with site migration waves
Contact the Abhavtech project lead to obtain the current DID mapping workbook.