[j-nsp] XFP and XENPAK

[Richard A Steenbergen]

On Thu, Sep 13, 2007 at 02:59:34AM -0700, Benny Sumitro wrote:
> Hi List,
> 
> Is there any differences between 10GE interface using XFP and XENPAK in 
> Juniper?

Besides the obvious differences of size/form factor and fiber connectors, 
XENPAK and XFP are very different technologies on the backend.

The biggest difference for the end user is that on XENPAK the framer is 
located on the optic itself, which essentially makes that optic "hard 
coded" for a particular media and framing. XFP implements the framer on 
the host board, making the optic itself media agnostic (not to mention 
cheaper to produce). You can take the same XFP and use it for 10GE LAN 
PHY, 10GE WAN PHY, OC192, even 10G fibre channel. Generally speaking this 
means that any vendor producing anything less than an extremely low-end 
device can easily implement LAN/WAN PHY framing on the board, and control 
it via a simple software switch. I can only speak to the 10G XFP cards on 
the MX960 specifically, but they implement LAN/WAN PHY support about as 
well as you could possibly hope for (with full SONET alarms when in WAN 
PHY mode). With XENPAK, you have to change out the entire optic, and you 
usually end up paying a huge premium for "LW" optics (and good luck even 
trying to FIND EW).

The other major difference is the interconnection technology used. XENPAK 
uses XAUI, which is four (4) lanes of 3.125G serial interfaces, while XFP 
uses XFI which is a single 10.3125G channel. The use of XAUI makes XENPAK 
"naturally suited" to some exotic "4 lane" technologies such as LX4 and 
CX4, which split the 10G signal into 4 individual lower speed signals. In 
the case of LX4 for example, 4 slightly different colored wavelengths and 
an integrated mux/demux are used to provide WDM, allowing you to get much 
longer distances over old low-grade MMF plant than you could possibly get 
with a single native 10G interface. Since XFP uses a single 10G channel, 
you won't find LX4 optics and the like produced.

Generally speaking XFP is superior to XENPAK technically, and is cheaper 
to produce, but you'll find a lot of existing hardware that is still 
XENPAK based. The only other 10G optic technology still in production to 
have any market penetration is X2, which is essentially XENPAK technology 
in a smaller form factor (closer to original GBIC size).

-- 
Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)