描述
Distance Is a Cable Problem Until It Becomes a Light Problem. Copper works beautifully for thirty metres and then stops being an engineering choice. Beyond that the signal needs repeaters, the cable gets thick and stiff, and every run becomes a lightning path between two buildings that happen to share an electrical ground. Single-mode fibre replaces all of that with a strand of glass and a laser, and the interface between the fibre and the switch is a small, hot-swappable module that costs less than the labour of pulling the cable. Choose the optic correctly and the run just works for a decade.
This is that module. The ONT-C311GD-L2S transmits at 1.25Gbps over single-mode duplex fibre through duplex LC/UPC connectors, reaching 20km on the 1310nm wavelength variant with a 40km option in the same family. DDM and DOM digital diagnostics are supported, so the switch can report optical transmit power, receive power and temperature, which turns a suspected cable fault into a number you can read from the management interface. The module is CE certified and compatibility is stated for Cisco and Mikrotik equipment, which covers the majority of small and mid-sized network cabinets. Options list the single module at 20km, a ten-pack at 20km, and a ten-pack at 40km, so a project can buy one spare or kit out an entire rack in a single order.
The uses are mundane and constant: linking two buildings on a campus without trusting the mains earth between them, running a warehouse office to a production floor switch across a long hall, connecting a gatehouse or a camera mast, joining a Mikrotik router to a Cisco distribution switch, or upgrading an ISP handoff where the carrier delivers single-mode glass. Wherever two pieces of equipment are further apart than copper wants to go, this is the part that closes the distance.
Copper degrades with length. Glass degrades with neglect, and you can measure both.
Key Features
- ✦ 1.25Gbps transmission over single-mode duplex fibre
- ✦ Duplex LC/UPC connectors, the standard interface in enterprise and carrier cabinets
- ✦ Reach options at 20km on 1310nm and 40km in the same module family
- ✦ DDM and DOM digital diagnostics support for live optical power and temperature readings
- ✦ Compatibility stated for Cisco and Mikrotik switches
- ✦ Hot-swappable SFP form factor, so a link can be changed without touching the switch
- ✦ Sold as a single module or as sealed ten-packs for rack-scale deployment
- ✦ CE certified for the intended network installation
Technical Specifications
- Model Number: ONT-C311GD-L2S
- Form Factor: SFP, hot-swappable
- Data Rate: 1.25Gbps
- Fiber Type: Single-mode duplex
- Wavelength: 1310nm on the 20km and 40km options listed
- Reach Options: 20km and 40km
- Connector: Duplex LC/UPC
- Diagnostics: DDM and DOM supported
- Stated Compatibility: Cisco and Mikrotik switches
- Order Options: Single 20km module, 10-pack 20km, 10-pack 40km
- Certification: CE
- Brand: ONTi
Where It Belongs
This module belongs wherever network runs outgrow copper. Campus links between buildings that have separate electrical supplies. Warehouse switches at opposite ends of a long production hall. Gatehouse, workshop and camera-mast connections back to a main cabinet. ISP handoffs and last-mile links where the carrier terminates in single-mode glass. Small data centres and comms rooms that need a spare optic on the shelf rather than a next-day order. Also useful for any network engineer standardising on a single module to reduce the number of part numbers in the spares kit.
Frequently Asked Questions
Q: Will it work in my Cisco or Mikrotik switch?
Compatibility is stated for Cisco and Mikrotik equipment. Confirm that your switch accepts third-party SFP modules, since some vendors restrict optics in firmware.
Q: What is the difference between DDM and DOM?
Both describe digital diagnostics on the module: the switch can read optical transmit power, receive power and temperature. That reporting is what turns a suspected fibre fault into a measurable value.
Q: Which variant do I need for a short building-to-building link?
The 20km 1310nm option covers far more than a typical campus run, and it is the lower-cost of the two reach options listed. Choose the 40km variant only for genuinely long spans.
Q: Can I buy a single module?
Yes. The listing offers one 20km module as well as ten-packs at 20km and 40km, so a single spare or a full rack can be ordered in one go.
Q: Is it plug and play?
It is a hot-swappable SFP module. Insert it into an SFP port, connect duplex LC single-mode fibre, and the link negotiates at 1.25Gbps.
Q: What connector does the fibre side use?
Duplex LC/UPC, which is the standard patch-lead connector in enterprise and carrier installations.
The EastSupplier Promise
Every unit is inspected before it leaves the warehouse. If a specification on this page does not match what arrives, we cover the return shipping and replace it. English-language support answers within one business day, and replacement parts for this category are stocked so that a working unit stays working.









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