Media Converters – Convert Copper Interfaces to Fiber and back

If you want to extend your LAN to include a department that is a few hundred meters from your main switch and cannot lay copper cables (due to the distance limitations), you can use Fiber (to copper) Media Converters. There is more to media converters than just the conversion – read this article to find out.

Fiber to Copper Media Converter - Architecture Diagram
Media Converter - Architecture / Connectivity Diagram

What is a Media Converter?

Fiber media converters have one copper (RJ-45) port and one fiber port. The copper port connects to the network switch and fiber port connects to the fiber cable.They are used for extending a LAN network for more than 100 meters to a few kilo meters through fiber cables and the fiber connection is converted in to copper connection at either end so that they can terminate on the copper UTP port of the network switch.

In the above architecture/ connectivity diagram for a media converter which is an example to illustrate how the media converter can be used and its connectivity details, there are two departments – Dept 1 and Dept 2. Both are having network switches with copper UTP ports. Since the distance between them is more than 100 meters (it could be anything between 100 meters and 70 KM – still you can use single mode fiber to connect both), its not feasible to take a copper UTP cable across to connect the two departments directly (Indirect methods like having network switches every 90 meters to boost the signals is still possible, but may not be feasible for longer distances as the network switches require racks, power supply, additional space etc. And each electronic component added in between becomes a potential point of failure too).

There are two cases: Either the network switches do not have any fiber ports (or) they have fiber ports. If there are no fiber ports, then we could use media converters at either end and use a fiber cable between the two departments to carry the data (Fiber cable termination is not as simple as copper termination which can be done using a UTP patch cord and plugging them in to the RJ-45 ports at either end. First the fiber cores need to be individually spliced, tested and terminated on a fiber patch panel/ pigtail/ coupler assembly. From the coupler, we can use a fiber patch cord to connect to the media converter). If the network switches have fiber ports (they may come with 2,4 or all 24 fiber ports), then we could insert a fiber module inside the SFP ports at either end and terminate the fiber patch cords from the fiber patch panel directly to the fiber ports of the switches at both the departments to establish a fiber link.

Why use Fiber Cables at all?

The Optical Fiber Cables use light as the transmission medium and hence it is not prone to EMI and other interferences that copper cables are prone to (especially in manufacturing environments, the interferences can be considerable). The Fiber cables are not electrical conductors and hence are not adversely affected by lightning and other power disturbances. Fiber cables support signals to be transmitted over longer distances – up to 70 km (approximate distance, can be more based on the product) using single mode fiber cables for example, without having the need to repeat the signals anywhere in between. Contrast this with copper UTP cables which needs to be repeated every 90 meters!

Fiber Cables are stable and offer investment protection – You don’t need to change the cables to support higher bandwidths, you just need to upgrade the fiber modules/ media converters at either end. Contrast this with copper UTP cables which have further distance restrictions (to support higher bandwidth) and some times don’t even support carrying of higher bandwidth which makes it imperative to change the copper UTP cabling as well when you upgrade to newer network infrastructure.

Why Media Converters?

Why not just buy network switches with direct fiber termination and fiber modules and connect the fiber cables directly to them? Why use media converters at all? This question does not have a technical answer but the answer is more commercial – media converters do not require fiber enabled switches (they can be used even with unmanaged entry level switches) and hence the connectivity solution is cost effective. For a single fiber link, changing the whole switches and buying fiber modules at either end might be a more expensive proposition. But direct termination of fiber links on network switches is also highly recommended.

Not just that, media converters give more options – you can buy a single pair of media converter (stand alone devices) at either end or get a chassis based system where you can insert multiple media converters from 1 to 18/19 in single increments – they are also hot swappable, come with redundant power supplies and offer power source consolidation. But network switches come with more rigid configurations – 2, 4, 24 or 48 ports only. If you want 5 fiber connections, for example, you may need to buy two network switches with 4 fiber ports each and 24/48 copper ports each irrespective of whether you are going to use the remaining fiber and copper ports! And yeah, some of the network switches do not have fiber interfaces at all!

Some interesting points about Media Converters:

  • There are multiple types of media converters – managed (SNMP) / unmanaged, 100 Mbps/ 1000 Mbps, Single Mode/ Multi Mode, having different fiber interfaces – SC/LC/ST etc, Stand-Alone Devices/ Chassis based systems (that can accommodate multiple individual media converter cards), Desktop/ Stand-Alone/Wall mountable types etc.
  • There are certain media converters that can do a rate conversion on the copper end – 10/100 Mbps and 10/100/1000 Mbps – Both ends determine the highest possible speeds supported on the copper network, and adjust to that speed on the fiber network.
  • Some media converters are intelligent enough to sense when they are no longer receiving the optical signals (due to fiber cable cuts, copper cable disconnections etc) and send an information immediately to the NMS/ management interface (supporting SNMP) so that appropriate action could be taken.
  • Fiber Media Converters require electrical power to function – but this power could be supplied over the Ethernet cable itself (along with data) through the IEEE802.3af POE standard. This works on only certain models that support POE.
  • Fiber Media Converters usually have activity, speed and link-on status indicators (LED’s).
  • Some Media Converters come with SFP slots – The advantage is, both single mode as well as multi mode modules could be populated in them to make them work as single mode (or) multi mode media converters (But either end in the same connection should be of the same type – either single mode or multi mode).
  • Slightly Off-topic, but there are certain fiber converters that convert single mode signals to multi mode and vice versa – If you are running a multi mode signal to a department and the department is required to be shifted to a far away place, you could just use this converter and convert the multi mode signal to a single mode one, to be propagated over longer distances using single mode fiber – instead of changing the entire end to end connectivity to single mode, that is.
  • Some fiber media converters can provide link redundancy by allowing to connect two fiber cables (one in active mode – transmitting, another in passive mode – not transmitting) so that when the active fiber gets cut or fails, the link will be immediately switched over to the passive fiber link (which now becomes active). This uses the spanning tree protocol like how network switches do.

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