Architecture Design

4.1 Typical System Topology

The reference topology for a critical data transmission security system organizes network zones in a layered defense model, where each boundary crossing requires explicit authorization and cryptographic verification. The design starts from the Internet edge and works inward through progressively more trusted zones, with the PKI/KMS and SIEM infrastructure positioned as shared services that support all zones without being directly reachable from untrusted networks.

The topology is designed for a medium-to-large enterprise with Internet-facing APIs, internal microservices, site-to-site replication, and privileged admin access requirements. Smaller deployments may consolidate the DMZ and App Zone onto fewer physical devices, while larger environments may replicate each zone across multiple availability zones or data centers for resilience.

Figure 4.1: Typical System Topology — layered zone architecture from Internet edge through DMZ (API Gateway, WAF, Reverse Proxy), Internal zones (App, Data, Admin), to IPsec VPN gateway for branch and cloud connectivity. PKI/KMS and SIEM shown as shared infrastructure services.

Zone Definitions and Trust Levels

4.2 Device Interconnection and Wiring

Physical and logical device interconnection follows a structured cabling plan that separates production traffic, management traffic, and replication traffic onto distinct VLANs and physical paths where feasible. Color-coded cabling conventions — orange for WAN/production, blue for management, green for replication — reduce miscabling risk during installation and maintenance. All rack-mounted appliances are connected to a dedicated out-of-band (OOB) management switch that provides console access and IPMI/iDRAC connectivity independent of the production network.

Figure 4.2: Data Center Equipment Rack Wiring — three-rack layout showing Edge Firewall, Core Switch, API Gateways (Rack 1), Application Servers and PKI/HSM (Rack 2), Database Servers, SIEM, and Backup Storage (Rack 3). Color-coded cabling: orange (production), blue (management), green (replication).

Physical Connectivity Matrix

4.3 High Availability and Redundancy Design

High availability is achieved through active-active or active-standby redundancy at every critical component, combined with health-check-based failover and automated certificate renewal to prevent availability gaps from cryptographic expiry. The design targets a Recovery Time Objective (RTO) of 30 seconds for Tier-0 flows and 5 minutes for standard flows, with a Recovery Point Objective (RPO) of zero for stateful gateway configurations synchronized via HA protocols.

4.4 Phased Deployment Plan

A phased deployment approach reduces risk by establishing foundational controls first and layering additional capabilities as operational confidence grows. Each phase has defined entry criteria, deliverables, and acceptance tests before the next phase begins. The typical delivery timeline for a medium enterprise is 8–16 weeks, depending on existing infrastructure maturity and organizational change management capacity.