G.703 NTU Connections

Curiosityx · 29 Sep 2008 at 17:27

Greetings one of our customers have recently had a leased line installed, we asked them to present the connection on X.21 but have presented it on G703 instead as per the image below.

I now require a Balun to connect our router via Ethernet to the BT NTU, ive never had to spec the above before and am slightly unsure of which cables/connectors are required, currently im looking at the products below.

http://www.blackbox.co.uk/solutions...doc=mt242a-m&tx=WAN&sx=G.703/G.704 Converters

G.703 Balun 2.048-Mbps, Female

Could someone help me the coax cable needed between the NTU and the "Black Box"? I believe that the connection then from the "Black Box" to the router is Rj45?

Regards

atomiser · 29 Sep 2008 at 18:07

ummm i doubt very much that box will convert the coax feed into ethernet? more likely a g.703 presented as a twisted pair connection instead of a coax? what you probably need is some sort of transceiver, instead of just a balun? if they even exist? i'm a bit confused as since you knew you had a router with an ethernet port, why did you ask for an x.21 presentation? typically an x.21 connection would be provided as a serial interface for you to connect your router to using a serial wic? looks like they've given you the sort of interface you would normally plug a pbx into...?!

bigredshark · 29 Sep 2008 at 19:40

The balun you have is the one we use for the same job by the look of it, I couldn't tell you the cable type but I seem to recall it's not the big thick coax you'd expect but much thinner stuff...a lot like

http://www.blackbox.co.uk/solutions...3-0002-bnc&tx=Cable Products&sx=Serial Cables

but the cable specifically for g.703 is

http://www.blackbox.co.uk/solutions...etnu703-2m&tx=Cable Products&sx=Serial Cables

I suspect either will work just fine, there's not a lot of complexity to coax really...

atomiser · 29 Sep 2008 at 22:16

so those boxes do actually convert between whatever protocol is used on the coax side and ethernet on the twisted pair side? that's kinda cool! i thought they literally just changed the presentation from coax to twisted pair in terms of form factor, not including signalling!

when it comes to coax i've worked with both 50 ohm and 75 ohm... it's been a while, but from what i remember we used 50 ohm stuff for old ibm mainframe stuff and 75 ohm for telephony... so you might want to make sure the coax is 75 ohm? i can check with one of our telephony guys in the office tomorrow if you want confirmation?

bigredshark · 29 Sep 2008 at 22:25

atomiser said:
so those boxes do actually convert between whatever protocol is used on the coax side and ethernet on the twisted pair side? that's kinda cool! i thought they literally just changed the presentation from coax to twisted pair in terms of form factor, not including signalling!

when it comes to coax i've worked with both 50 ohm and 75 ohm... it's been a while, but from what i remember we used 50 ohm stuff for old ibm mainframe stuff and 75 ohm for telephony... so you might want to make sure the coax is 75 ohm? i can check with one of our telephony guys in the office tomorrow if you want confirmation?

I can't really remember exactly the conversion they do, we don't deploy them any more so it's only legacy solutions...

Curiosityx · 29 Sep 2008 at 23:42

atomiser said:
so those boxes do actually convert between whatever protocol is used on the coax side and ethernet on the twisted pair side? that's kinda cool! i thought they literally just changed the presentation from coax to twisted pair in terms of form factor, not including signalling!

when it comes to coax i've worked with both 50 ohm and 75 ohm... it's been a while, but from what i remember we used 50 ohm stuff for old ibm mainframe stuff and 75 ohm for telephony... so you might want to make sure the coax is 75 ohm? i can check with one of our telephony guys in the office tomorrow if you want confirmation?

From what i can make out it takes a 75ohm balanced or unbalanced coax connection and converts it to a 120ohm Rj45 connection for termination on an NTE

atomiser · 30 Sep 2008 at 08:00

So on your router you simply have an rj45 twisted pair WAN interface, as opposed to an actual Ethernet interface?

Curiosityx · 30 Sep 2008 at 11:35

atomiser said:
So on your router you simply have an rj45 twisted pair WAN interface, as opposed to an actual Ethernet interface?

Well all has been resolved to an extent, were going to have the presentation changed back to X.21. Otherwise i imagine we would have had to install an E1 interface to accommodate the connection.

mdjmcnally · 30 Sep 2008 at 13:17

The only way I know of BT presenting Lease Lines as Ethernet is if it is a LES circuit or BT provide a router as well and the Ethernet Presentation is the Ethernet port off the router.

Surely if the lease line is being presented as X.21 you will need an X.21 interface on the router still.