Architecting BYOC Premise Disaster Recovery with Active-Active SBCs

How-To-Articles
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Architecting BYOC Premise Disaster Recovery with Active-Active SBCs

What This Guide Covers

You will configure a stateless, active-active Session Border Controller cluster that routes inbound and outbound SIP traffic across multiple data centers into Genesys Cloud CX. The end result is a carrier-grade failover mechanism that maintains call continuity, preserves SIP dialog state during site outages, and eliminates manual trunk reconfiguration during a disaster event.

Prerequisites, Roles & Licensing

  • Licensing Tier: Genesys Cloud CX 3 (or CX 2 with the BYOC Telephony Add-on). Workforce Engagement Management is not required for this telephony path, though WEM capacity planning should account for DR traffic redistribution.
  • Granular Permissions: Telephony > Trunk > Edit, Telephony > SBC > Edit, Telephony > Route > Edit, Organization > Site > Edit, Telephony > Provider Edge > Edit
  • OAuth Scopes: telephony:trunk:read, telephony:trunk:write, telephony:sbc:read, telephony:sbc:write, telephony:provider-edge:read
  • External Dependencies: Dual-homed carrier circuits (SIP Trunk or PRI over SIP), DNS provider supporting weighted round-robin or geographic routing, SBC platform supporting stateless signaling and media proxy (Cisco CUBE, AudioCodes Mediant, Ribbon CX, or Genesys Cloud SBC Edge).
  • Network Requirements: RFC 5626 compliant NAT traversal, RFC 3261 SIP stack, BGP/ECMP or DNS-based load balancing, SRTP/TLS 1.2+ support, sub-150ms RTT between SBC sites and Genesys Cloud edge.

The Implementation Deep-Dive

1. Stateless SBC Architecture and DNS Load Balancing

Active-active disaster recovery for BYOC telephony requires a fundamental shift from stateful to stateless signaling design. Genesys Cloud CX manages all dialog state server-side. When an SBC operates in stateful mode, it pins INVITE transactions, media streams, and SIP options to a single physical node. If that node loses connectivity to the primary site, the surviving SBC lacks the transaction context, resulting in immediate call teardown. We design the SBC cluster to proxy only Layer 4/Layer 7 signaling and media, without maintaining call leg state.

Configure each SBC site with independent SIP outbound profiles pointing to the Genesys Cloud SIP URI. The SBCs do not register to each other. They register independently to Genesys Cloud using the same authentication credentials. DNS load balancing distributes inbound carrier traffic across the SBC VIPs. You will use SRV records for SIP routing and A records for DNS health monitoring.

DNS Configuration Example:

_sip._udp.dr-primary.example.com. 30 IN SRV 10 60 5060 sbc-vip-primary.example.com.
_sip._udp.dr-secondary.example.com. 30 IN SRV 10 60 5060 sbc-vip-secondary.example.com.

Set the DNS TTL to 30 seconds. This value balances failover speed against DNS query volume. Lower TTL values increase resolver load but reduce traffic black-holing during a site failure. Higher TTL values cache unhealthy nodes longer, causing call setup delays.

The Trap: Configuring SBCs in stateful dialog mode for active-active routing. Stateful SBCs maintain INVITE transaction state, media negotiation context, and SIP OPTIONS keep-alive timers locally. When the primary site fails, the secondary SBC receives mid-call SIP messages (BYE, CANCEL, Re-INVITE) for dialogs it never initiated. The SBC responds with 481 Call/Transaction Does Not Exist. Genesys Cloud interprets this as a network partition and drops the call. The architectural failure is assuming SBCs need to track call state. Genesys Cloud handles state. The SBC must function as a transparent proxy.

Architectural Reasoning: Stateless signaling eliminates single-node transaction dependencies. Each INVITE routes to whichever SBC VIP resolves first. Genesys Cloud assigns a unique Call-Id and From/To tag pair. Subsequent SIP messages for that dialog route to the same SBC only if the carrier uses the same source IP/port, which we control via DNS sticky sessions or SBC-side source-NAT. This design ensures that if Site A loses uplink, Site B continues processing new INVITEs without state reconciliation overhead. You will configure the SBC to strip Via headers referencing the primary site and rewrite Contact headers to point to the active SBC VIP. This prevents SIP routing loops during failover.

2. Genesys Cloud BYOC Trunk and SBC Registration Configuration

Genesys Cloud does not natively load-balance across multiple SBC IPs within a single BYOC trunk definition. The platform resolves the sipUri field at call initiation and maintains a persistent TCP/TLS connection to that resolved address. To achieve active-active distribution, you will configure the BYOC trunk to point to a DNS pool name that resolves to multiple SBC VIPs. Genesys Cloud performs DNS resolution per call attempt, not per trunk lifecycle.

You will create the BYOC trunk via the Telephony API to ensure configuration consistency across environments. The payload must include explicit codec preferences, dial plan mappings, and SRTP enforcement.

API Endpoint: POST /api/v2/telephony/providers/edges/trunks
HTTP Method: POST
OAuth Scopes Required: telephony:trunk:write, telephony:sbc:read

JSON Payload:

{
  "name": "DR-Active-Active-BYOC-Trunk",
  "type": "BYOC",
  "sipUri": "sip:dr-pool.example.com:5061",
  "authUsername": "genesys_byoc_user",
  "authPassword": "encrypted_secret_ref",
  "dialPlanId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "siteId": "primary-site-id",
  "outboundCallerId": "18005550199",
  "codecPreferences": [
    {
      "name": "G711U",
      "use": true,
      "prefer": true
    },
    {
      "name": "G711A",
      "use": true,
      "prefer": false
    },
    {
      "name": "G729",
      "use": true,
      "prefer": false
    }
  ],
  "useSipOptions": true,
  "sipOptionsInterval": 30,
  "transportProtocol": "TLS",
  "mediaEncryption": "SRTP",
  "maxConcurrentCalls": 5000,
  "routingStrategy": "ROUND_ROBIN"
}

The sipUri field must resolve to the DNS pool name, not a static IP. Genesys Cloud caches DNS records for 60 seconds by default. The sipOptionsInterval of 30 seconds forces the platform to probe the resolved address frequently enough to detect SBC unavailability without overwhelming the DNS resolver.

The Trap: Binding a single SBC IP to the BYOC trunk sipUri field and relying on Genesys Cloud-side trunk failover. Genesys Cloud marks a BYOC trunk as unhealthy only after three consecutive SIP OPTIONS failures or INVITE timeouts. This validation window typically spans 45 to 90 seconds. During a premise outage, inbound carrier traffic continues routing to the down SBC IP. Calls fail with 503 Service Unavailable or timeout. The platform does not automatically shift traffic to a secondary SBC IP unless you provision multiple BYOC trunks and configure routing rules, which introduces manual failover steps and complex dial plan logic.

Architectural Reasoning: DNS-driven load balancing shifts failover responsibility to the network layer, not the application layer. Genesys Cloud treats the DNS pool as a single logical destination. When Site A fails, the DNS provider removes the unhealthy VIP from the rotation. New call attempts resolve to Site B. Existing calls on Site B continue unaffected because Genesys Cloud maintains dialog state server-side. You must configure the SBCs to accept SIP OPTIONS probes and respond with 200 OK within 500 milliseconds. This ensures Genesys Cloud health checks pass consistently across both sites. The maxConcurrentCalls parameter defines the platform-side limit, not the SBC limit. You will synchronize this value with the SBC call processing capacity to prevent admission control mismatches.

3. Active-Active Media Routing and Codec Negotiation

Media routing in an active-active BYOC architecture requires strict SDP consistency across all SBC sites. Genesys Cloud negotiates media endpoints during the INVITE/200 OK exchange. The platform advertises a media IP address and port range in the SDP c= and m= lines. The SBC must accept these parameters and establish RTP/RTCP streams directly to the Genesys Cloud media edge.

Configure each SBC site with identical codec negotiation policies. You will enforce G711U as the preferred codec, with G711A and G729 as fallbacks. Genesys Cloud does not transcode mid-call. If the carrier sends G729 and the SBC negotiates G711U, the call fails during media setup.

SBC SDP Handling Configuration:

  • Enable SDP Pass-Through for Genesys Cloud leg.
  • Disable Media Proxy for inbound carrier leg unless transcoding is required.
  • Set Early Media Handling to Reject or Proxy based on carrier requirements.
  • Enable RTCP Multiplexing to reduce UDP port consumption.

The Trap: Mismatched media encryption settings across SBC sites. Genesys Cloud enforces SRTP for all BYOC trunks. If Site A SBC advertises SRTP in the SDP crypto attribute and Site B SBC advertises RTP only, calls routed to Site B fail with 488 Not Acceptable Here. The platform rejects the INVITE because the media encryption negotiation does not match the trunk configuration. This trap manifests as intermittent one-way audio or immediate call drops, with logs showing SDP negotiation failed: mismatched crypto attributes.

Architectural Reasoning: Genesys Cloud validates SDP parameters against the BYOC trunk configuration before establishing media streams. All SBCs in the active-active pool must advertise identical a=crypto, a=rtpmap, and a=fmtp attributes. You will configure the SBCs to strip carrier-specific SDP attributes (such as a=sendrecv variations or proprietary vendor tags) before forwarding to Genesys Cloud. This prevents SDP parsing errors on the platform side. Media flows directly between the carrier and Genesys Cloud through the SBC as a transparent proxy. The SBC does not anchor media unless you require call recording or lawful intercept, which introduces stateful dependencies. For pure DR routing, stateless media proxying ensures that if Site A fails, Site B continues routing RTP streams without renegotiation. You will configure the SBC to respond to SIP UPDATE messages instead of Re-INVITE for mid-call media changes. This reduces signaling load and prevents call drops during codec renegotiation.

4. Health Checks and Automated Failover Logic

Genesys Cloud performs health checks on BYOC trunks using SIP OPTIONS probes. The platform sends probes to the resolved sipUri address at the interval defined in sipOptionsInterval. You must configure the SBCs to respond to these probes while simultaneously monitoring upstream carrier connectivity.

Implement dual-layer health checking:

  1. Genesys Cloud Side: SIP OPTIONS to sip:dr-pool.example.com:5061. The SBC responds with 200 OK.
  2. SBC Side: DNS health monitoring using ICMP/TCP probes to the Genesys Cloud SIP URI and carrier gateways.

Configure the DNS provider with active health probes. The provider marks a VIP as unhealthy after two consecutive probe failures. The DNS rotation immediately removes the unhealthy VIP. Traffic shifts to the remaining site within the TTL window.

The Trap: Relying solely on Genesys Cloud-side trunk health checks for failover. Genesys Cloud marks a BYOC trunk unhealthy only after repeated probe failures. During a premise network partition, the SBC VIP remains reachable via DNS, but carrier uplinks are down. Genesys Cloud continues routing outbound calls to the unhealthy SBC. Calls fail at the carrier layer. The platform does not detect the failure until the SIP transaction times out (typically 30 seconds). This creates a 30 to 60 second black hole for outbound traffic. Inbound traffic fails immediately because the carrier cannot reach the SBC.

Architectural Reasoning: Health checks must validate the entire call path, not just the SBC VIP. You will configure the SBCs to monitor carrier gateway reachability using SIP REGISTER or OPTIONS probes to the carrier SIP URI. If the carrier link fails, the SBC signals the DNS provider via API or SNMP to remove its VIP from the rotation. This proactive removal prevents traffic from reaching a dead end. Genesys Cloud health checks validate platform-to-SBC connectivity. SBC-side health checks validate SBC-to-carrier connectivity. Both layers must align. You will configure the SBC to log health probe results to a centralized SIEM. Correlate Genesys Cloud trunk status with SBC health metrics to detect asymmetric failures. This design ensures that failover occurs before call attempts fail, not after.

Validation, Edge Cases & Troubleshooting

Edge Case 1: SIP Re-INVITE Storms During Partial Failover

The Failure Condition: Mid-call media renegotiation triggers when one SBC site loses network connectivity. Genesys Cloud sends Re-INVITE messages to renegotiate media endpoints. The surviving SBC receives Re-INVITEs for calls it never anchored. The SBC responds with 481 Call/Transaction Does Not Exist. Genesys Cloud interprets this as a media failure and drops the call.
The Root Cause: Stateful media proxy configuration on the failing SBC. When the SBC anchors media, it maintains RTP stream state. If the SBC loses connectivity, the RTP stream drops. Genesys Cloud detects media loss and initiates renegotiation. The surviving SBC lacks the media context and cannot respond.
The Solution: Configure SBCs for stateless media pass-through with Genesys Cloud as the media anchor. Disable media proxying unless transcoding or recording is required. Enable SIP UPDATE method support on the SBC for mid-call media changes. Genesys Cloud prefers UPDATE over Re-INVITE for media renegotiation. This reduces signaling overhead and prevents dialog state mismatches. Verify SBC configuration matches Genesys Cloud media handling requirements. Reference the Genesys Cloud SBC Integration Guide for exact SDP handling parameters.

Edge Case 2: Early Media and Call Progress Tone Leakage

The Failure Condition: DTMF tones or modem handshakes route incorrectly during DR failover. Genesys Cloud receives early media before call completion. The platform routes the call to an agent prematurely. The agent hears carrier progress tones instead of the customer. Call quality degrades, and false completions increase.
The Root Cause: SBC site B lacks proper early media handling configuration. The SBC forwards 183 Session Progress or 180 Ringing with SDP media attributes. Genesys Cloud accepts the media stream and routes it to the skills-based routing path.
The Solution: Enforce early-media: reject on SBC SIP profiles for the Genesys Cloud leg. Configure the SBC to strip SDP attributes from 183 responses. Ensure Genesys Cloud Architect flows strip early media before routing to queues. Validate that carrier circuits do not send in-band progress tones during DR failover. If early media is required for call progress, configure Genesys Cloud to use platform-generated tones instead of carrier-provided media. This prevents tone leakage during failover transitions.

Edge Case 3: DNS TTL Propagation Delay During Rapid Flapping

The Failure Condition: Carrier circuit flaps cause DNS resolution to alternate between healthy and unhealthy SBC VIPs. Calls experience intermittent timeouts. Genesys Cloud logs repeated 503 Service Unavailable responses. Agent productivity drops due to call setup delays.
The Root Cause: Aggressive DNS TTL values combined with carrier-side DNS caching. The DNS provider removes the unhealthy VIP, but carrier resolvers cache the old record for the TTL duration. Traffic continues routing to the failing site.
The Solution: Implement SBC-side health-based DNS publishing using RFC 6742 dynamic DNS updates. Configure the SBC to update DNS records based on real-time health probe results. Set DNS TTL to 60 seconds minimum to reduce resolver load. Use a global server load balancer with active health probes instead of relying solely on DNS TTL. Configure Genesys Cloud to use TCP transport for BYOC trunks to reduce UDP packet loss during flapping. Monitor DNS resolution latency using synthetic monitoring tools. Correlate DNS cache expiration with call setup metrics to identify propagation delays.

Official References