Designing a Global SIP Routing Architecture with Least-Cost Routing (LCR) and Time-of-Day Logic

How-To-Articles
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Designing a Global SIP Routing Architecture with Least-Cost Routing (LCR) and Time-of-Day Logic

What This Guide Covers

  • Architecting an advanced Outbound Route configuration in Genesys Cloud to optimize carrier costs across a global BYOC (Bring Your Own Carrier) deployment.
  • Implementing Least-Cost Routing (LCR) combined with Time-of-Day (ToD) logic to automatically shift outbound SIP traffic between regional SIP trunks based on dynamic pricing and bandwidth constraints.
  • The end result is a highly resilient, cost-optimized telecommunications footprint that automatically handles failover and selects the most economical path for every outbound call without manual intervention.

Prerequisites, Roles & Licensing

  • Licensing: Genesys Cloud CX 1, 2, or 3 with BYOC Cloud or BYOC Premise.
  • Permissions: Telephony > Route > Edit, Telephony > Trunk > Edit, Telephony > Site > Edit.
  • Infrastructure: Multiple SIP Trunks configured across different AWS regions or physical data centers.

The Implementation Deep-Dive

1. Understanding the Site and Trunk Hierarchy

In Genesys Cloud, outbound routing is determined by the Site associated with the User or the Edge Group making the call.

Architectural Reasoning:
A common mistake is assigning all users to a single “Global” Site and attempting to route all international calls out of a single carrier trunk in US-East. This results in massive latency (tromboning audio across the Atlantic) and exorbitant international dialing rates.

Instead, implement Regional Sites (e.g., Site_US_East, Site_EU_West) and bind them to regional SIP trunks.

2. Configuring Least-Cost Routing (LCR)

LCR requires multiple trunks configured for the same destination number plan, prioritized by cost.

Implementation Steps:

  1. Navigate to Admin > Telephony > Sites and select your Site.
  2. Go to the Outbound Routes tab.
  3. Create a Route for a specific Number Plan (e.g., UK_National).
  4. The Trunk Cascade: Add your primary (lowest cost) UK carrier trunk as Priority 1.
  5. Add your secondary (higher cost, but reliable) global carrier trunk as Priority 2.
  6. Genesys Cloud will automatically attempt the call out of Priority 1. If the carrier returns a 503 Service Unavailable or 480 Temporarily Unavailable, the Edge automatically hunts to Priority 2.

The Trap:
Improper SIP response code handling. If your primary carrier rejects the call with a 404 Not Found or 486 Busy Here, Genesys Cloud will not hunt to the next trunk. It assumes the number itself is invalid or busy, not that the trunk is down. Ensure your SIP carriers are configured to return 503 during capacity outages so the failover logic triggers correctly.

3. Implementing Time-of-Day (ToD) Routing

LCR handles cost and failover, but ToD handles off-hours bandwidth and specific regional tariffs (e.g., calls are cheaper on Carrier B after 8 PM).

Architectural Reasoning:
Genesys Cloud does not have a native “Schedule” dropdown on Outbound Routes. To achieve ToD routing, you must use Call Routing Classifications and Architect Inbound Flows for system-generated outbound calls (like Callbacks), or rely on SBC (Session Border Controller) logic.

SBC-Driven ToD Implementation:
If you are using BYOC Premise or a managed SBC (like AudioCodes or Ribbon) in front of your BYOC Cloud trunks:

  1. Route all traffic for the target destination out of Genesys Cloud to your SBC.
  2. On the SBC, configure a Routing Policy based on the SIP INVITE timestamp.
  3. If Time < 08:00 or Time > 20:00, route the INVITE to Carrier B. Otherwise, route to Carrier A.
  4. The SBC abstracts this complexity from Genesys Cloud, keeping your internal Sites and Routes clean.

Architect-Driven ToD Implementation (For Callbacks/Campaigns):
If you don’t have an SBC, you must control the routing before it hits the telecommunications layer.

  1. In your Architect flow, before dialing out, use an Evaluate Schedule action.
  2. Based on the schedule, set a custom Participant Data attribute or alter the dialing prefix (e.g., prepending 999 to the number).
  3. Create an Outbound Route in Genesys Cloud that specifically matches the 999 prefix, strips it, and routes the call out of the designated off-hours trunk.

Validation, Edge Cases & Troubleshooting

Edge Case 1: The “Emergency Mode” LCR Bypass

  • The Failure Condition: A major fiber cut takes down your primary carrier. LCR correctly hunts to the secondary carrier, but the secondary carrier cannot handle the massive sudden influx of 10,000 concurrent calls, causing SIP timeouts and dropped calls.
  • The Root Cause: LCR hunting happens sequentially per call. 10,000 calls hitting Trunk A, failing after 2 seconds, and then hitting Trunk B creates a massive bottleneck on the Edge.
  • The Solution: Implement a manual “Trunk State Toggle” via the API. If your monitoring detects a primary carrier outage, use a script to immediately set the primary trunk’s state to Out of Service via the Telephony API. This removes it from the LCR cascade entirely, routing calls instantly to Trunk B without the 2-second timeout penalty per call.

Edge Case 2: Early Media and Post-Dial Delay (PDD)

  • The Failure Condition: Customers complain that when they make an outbound call, there is 8 seconds of dead air before they hear a ringback tone.
  • The Root Cause: LCR hunting takes time. If Trunk A takes 4 seconds to return a 503, and Trunk B takes 4 seconds to setup the call, the user experiences 8 seconds of PDD.
  • The Solution: Ensure your carriers are providing proper 180 Ringing or 183 Session Progress with SDP (early media). If a carrier is notorious for high PDD, demote them in your LCR priority list, even if their cost is slightly lower. The savings aren’t worth the degraded user experience.

Official References