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Media Convertors vs. Inline SFP or GBIC

Level 3
Level 3

I have read over many posts on this forum, but I still have some questions......

Are there any gained advantages in using the Cisco SFP or GBIC to connect to the Fiber Cabling (besides Product Support) over external Media Convertors?

I am new to the Optical World. A design project was dropped in my hands. I have to connect 2 offices using Fiber. The actual underground cable run will be handled by an outside contractor. Short Distance (less than 1 km).

I have to come up with an equipment list and configure the network devices after they are purchased. I am looking at a 3750 Switch at each site and Transition Media Convertors hanging off of an Ethernet switchport (100 or 1000) that connect to the fiber. I am also looking to make those interfaces VLAN trunks.

Is it better to use the inline SFP modules instead?

(I figure using the External Media Convertors instead would be keeping it simple since I can attach it to an configurable ethernet port on the switch)


Are the fiber SFP modules configured like any other interface?

interface ethernet XX

swithport mode trunk


any thoughts appreciated

3 Replies 3

Level 7
Level 7

Advantages to Gigabit-speed SFP or GBIC:

* Takes up less space.

* It derives power from the switch it's plugged into. (Media converter requires a separate AC power outlet.)

* Covered under the warranty or Cisco SMARTnet maintenance contract you have on the switch it's plugged into. (Transition's media converters have a lifetime warranty, but the turn-around time on a replacement may not be as quick as what you get with a SMARTnet agreement.)


* Cost?

* Can only be used with Cisco devices. (Transition's media converter can be connected to any manufacturer's switch.)

What kind of fiber you are running between the two buildings?

Generally speaking, single mode fiber will require Cisco's LX/LH GBICs to run Gigabit Ethernet from 0 (zero) to 10km. These run $995 list price each (two are needed).

Multimode fiber can use the SX GBICs from 0 to 220-275m if 62.5-micron in diameter, and out to 500-550m if 50-micron. SX GBICs run $500 list price each (two are needed).

If 62.5-micron and longer than 220-275m but less than 550m, you can use LX/LH GBICs with specialized mode-conditioning patch cables. These cables are somewhat more expensive than regular patch cables: figure on 2X the price or a regular one.

If you can get by with a 100-megabit Fast Ethernet link over the fiber, then the media converters are the way to go. Over multimode, you can drive Fast Ethernet out to 2km in full duplex mode; over single mode, the least expensive ones can push to 20km with ease (also full duplex).

By default, the Transition 100-meg media converters autodetect duplex setting, so you can plug it into a 10/100 auto port on the switch and it will crank up to full duplex. Or, you can hard-code the port to 100 full and manually set the converter to be the same.

Configuration of the switchport as a VLAN access port or VLAN trunk port is the same, whether it's got a media converter or GBIC or SFP on it. On a fiber port in the switch (SFP or GBIC), speed is limited to 1000 megabit only: it cannot "down-shift" to 100 meg. And on Cisco's switches and routers, it's always full duplex. Copper ports can do 10/100 or 10/100/1000 autodetect speed and duplex, but these can also be hard-coded.

Hope this helps.

EDITED TO ADD: List pricing on Cisco's SFPs is the same as the GBICs.

Thanks alot,

You really know your stuff! That helped alot.


every one,

  we have encountered a problem..

one of out DCS systems network failed ,connecting two servers through OFC media and at both ends connected to D link GBIC201FL module. we have checked the cable with OTDR and found OK.

we are suspecting problem with GBIC and presently that model,spare is not can i put a

external media converter (MM to 100mbps ethernet converter instead of using the GBIC module..

please reply..