Core Switch and SDH Equipment Link

For connecting core switches over long distances (e.g., 150 km), SDH or optical transport equipment is recommended over direct switch-to-switch links due to distance limitations of standard Ethernet interfaces.Distance Limitations of Core SwitchesStandard core switches, such as Cisco 3750 or 6500 series, typically support 10G Ethernet over single-mode fiber up to 80 km without additional amplification or regeneration . For distances beyond this, like 150 km, direct switch-to-switch connections are not feasible due to signal attenuation and optical dispersion. Using only core switches would require intermediate devices or repeaters, which can complicate the network and reduce reliability.SDH and Optical Transport SolutionsSynchronous Digital Hierarchy (SDH) provides a reliable, long-distance transport backbone capable of supporting Ethernet services over distances exceeding 150 km. SDH equipment, such as Terminal Multiplexers (TM) and Digital Cross-Connects (DXC), can multiplex multiple client signals into high-speed STM-N frames, ensuring precise synchronization and high availability . SDH also supports Ethernet over SDH (EoS), allowing seamless integration of Ethernet traffic into the SDH network .Optical transport systems, like Cisco ONS or GE DXC-H, can carry 10G Ethernet over dark fiber for long distances. These systems often include features such as:Circuit emulation for legacy TDM services (TDMoE, TDMoIP, CESoPSN)High-capacity switching up to 400 Gbps with multiple Ethernet interfaces (1GE, 10GE, 40GE, 100GE)Protection mechanisms like 1:1 or 1+1 MPLS-TP and ERPS with sub-50ms switching Flexible grooming of SDH, PDH, and Ethernet traffic for efficient bandwidth utilization Recommended Architecture for 150 km LinkA typical solution for connecting two 3750 switches over 150 km would involve:Core switch → Aggregation router (e.g., Cisco ASR) → SDH or ONS transport → Aggregation router → Core switch .Using dark fiber with optical transport equipment (ONS or DXC-H) to extend Ethernet over long distances while maintaining signal integrity and protection.Implementing redundancy and protection using SDH's built-in MSP (Multiplex Section Protection) or DXC-H's ERPS/MPLS-TP features to ensure high availability .Key ConsiderationsEquipment selection: Choose SDH or optical transport devices certified for 10G Ethernet over the required distance. Cisco ONS, DXC-H, or similar platforms are suitable.Fiber type: Single-mode fiber is required for long-distance links. Ensure proper attenuation and dispersion management.Protection and monitoring: Use SDH or ONS features for traffic protection, monitoring, and fault management. TE links and member links can be configured for bandwidth allocation and redundancy .Integration: Ensure compatibility with existing Ethernet and MPLS networks, possibly using aggregation routers to interface between core switches and transport equipment.In summary, for a 150 km 10G Ethernet link, direct core switch connections are not practical. The recommended approach is to use SDH or optical transport equipment with aggregation routers to maintain high-speed, reliable, and protected connectivity between sites. This ensures long-term scalability, network stability, and service integrity.