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Hi

I am having some problems with a BT megastream 2 (E1) line which I
recently ordered, the 'B' end of which was supposed to terminate in a
rack in our datacenter. When BT installed the line, they only
terminated as far as the NTU and both the datacenter and BT refused to
cable the connection on to the rack where I have a 7204 router with a
serial port ready.

It's taken me 8 weeks to persuade the datacenter company to cable to
the rack and they have cabled two BNC/G703 cables to the appropriate
place. I attempted to use a spare Betterbox g703/x21 converter with
these cables but when I connect it there is no "link" light showing up
on the front panel. According to the manual this lights up "when the
E1/FE1 interface converter is receiving carrier from the E1 network".

At the "A" end of the circuit the NTU is right by the other 7204 and I
have simply plugged an X21 cable in to the correct trib and into the
serial port on the router.

Unfortunately I am not a network engineer by any stretch of the
imagination and I am getting a bit out of my depth. Could anyone
advise me whether this is a sane configuration?

(A) 7204--[x21]--NTU--megastr 2--NTU--[g703]--Betterbox
IC2001--[x21]--7204 (B)

Would I be better off paying my datacenter vendor to cable an X21
cable instead and forget about the converter? If I use NTU-x21-7204 at
both ends do I have to do any special configuration on the routers?

Any advice anyone could offer would be much appreciated. Apologies for
the newbie tech level of this post, but I guess we all have to start
somewhere!

Thanks,
Mark Wilson

Mark Wilson wrote:
> Hi
>
> I am having some problems with a BT megastream 2 (E1) line which I
> recently ordered, the 'B' end of which was supposed to terminate in a
> rack in our datacenter. When BT installed the line, they only
> terminated as far as the NTU and both the datacenter and BT refused to
> cable the connection on to the rack where I have a 7204 router with a
> serial port ready.
>
> It's taken me 8 weeks to persuade the datacenter company to cable to
> the rack and they have cabled two BNC/G703 cables to the appropriate
> place. I attempted to use a spare Betterbox g703/x21 converter with
> these cables but when I connect it there is no "link" light showing up
> on the front panel. According to the manual this lights up "when the
> E1/FE1 interface converter is receiving carrier from the E1 network".
>
> At the "A" end of the circuit the NTU is right by the other 7204 and I
> have simply plugged an X21 cable in to the correct trib and into the
> serial port on the router.
>
> Unfortunately I am not a network engineer by any stretch of the
> imagination and I am getting a bit out of my depth. Could anyone
> advise me whether this is a sane configuration?
>
> (A) 7204--[x21]--NTU--megastr 2--NTU--[g703]--Betterbox
> IC2001--[x21]--7204 (B)
>
> Would I be better off paying my datacenter vendor to cable an X21
> cable instead and forget about the converter? If I use NTU-x21-7204 at
> both ends do I have to do any special configuration on the routers?
>
> Any advice anyone could offer would be much appreciated. Apologies for
> the newbie tech level of this post, but I guess we all have to start
> somewhere!

What style of BT NTU have you got at the "problem" end?

Some BT NTUs support both G703 and X.21 but of course not
at the same time for a given circuit. This caught me out
once as I'd hooked things up to the right circuit on the
G.703 but the BT NTU was configured to use the X.21 port.

Get BT to check whether they have enabled the interface as
X.21 or G.703 on the NTU.

Alternatively, try swapping the TX and RX BNCs over on the
DSU [betterbox thing]!

-Pete L.

Hi

In the following I have used the term NTE and not NTU but I wouldn't worry
about the difference (I think it is just BT's term for DSU on a 2M)

I think BT will have configured the NTE to what was ordered and that is
probably X21, The fact that the NTE you have has both port types is
irrelevant. If you used a BT Project manager to assist in the order I
suggest you get back to him/her. If it becomes clear that he/she has not
checked out your requirements properly they will possibly convert the
service type at this end from X21 to G703 free of charge (but don't quote
me). But be very careful here as the X21 converter will be your
responibility so decide what you really want. (see below) Also not totally
sure about this part. I think BT will need to know if you are using an X21
converter as I feel they need to set the NTE up at that end slightly
differently than if you are using G703 on a router module, so be sure to
mention it.

I am not 100% sure here of all the configuration types on the BT network as
I don't work for them. but the technical reason for this is syncronisation
(could be refered to as clocking on the 2M cct). The X21 converter will
provide the syncronisation on the transit to the Service Providers network
and also the clocking to the router over the X21 interface. One point to
think about is that you may be better off using X21 in the NTE as it will be
BT's responsibility if you have an X21 clocking problem. (One less thing to
think about during any trouble shooting).. These problems usually show up
as CRC errors on the interface. If you have the network converted at the B
end to G703 delivered so your cabling is in use you will still need to make
sure the X21 converter is configured correctly. To this I mean there are 2
types of clocking on an X21 converter (I think theres 3 on an NTE but the
third is BT's responsibility here) Master and Slave. To understand this
think about your router settings. If you use a service providers line you
use a DTE at each router and clock the router off the SP's network, if you
connect a router to a router directly then you need a DTE on one end and a
DCE on the other with the DCE providing the clocking. In other words one
device provides the clocking. If neither end provides the clocking it
doesn't work and if both provide it the clocking it is going to clash, lots
of CRC's at best. This is the same for a service provider, although they
provide clocking on X21 interfaces to the user at both ends this is not a
different clock source, One of the X21's is a Master and provides clocking
to it's end user. It also syncronises the E1 line on it's transmit over the
SP's network and the othe end is the Slave end and generates the clock
presented to the end user from the 2Meg line, it also syncronises it's
transmit back over the 2Meg line based on it's recieve signal from the SP's
network. In this way the end sites recieve a syncronised clock at both ends
but there is only 1 clock source.

I think it is usually the A end that is set to master, but has been known to
be reversed.

Another consideration regarding configuring the X21 converter is that an E1
line can be provided in 2 forms, either a full 2048K which doesn't use
timeslots (correct ITU definition G703) or a channalised circuit giving 32
timeslots (0-31) where timeslot 0 is used for frameing (ensuring that
timeslots ane syncronised i.e. timeslot 5 onlt talks to timeslot 5) this
only gives 1984K (correct ITU definition G704 but has been termed
G703/G704), both are considered 2M circuits and both are E1 ccts also.

The above info was not intended to scare you into a decision but for you to
make an informed choice as you will have to fault this possibly in the
future, long after this info has been forgotton. BT will only test their own
kit and not your's (without extra payment at least). You may feel that a
small (relativley) outlay now in re-cabling may be cheaper in the long run
with potentially an extended outage whilst you diagnose a problem to an X21
converter, cable, interface. etc

I hope this has been informative.

Toby
..

"PJML" <> wrote in message
news:40c47c4f$...
> Mark Wilson wrote:
> > Hi
> >
> > I am having some problems with a BT megastream 2 (E1) line which I
> > recently ordered, the 'B' end of which was supposed to terminate in a
> > rack in our datacenter. When BT installed the line, they only
> > terminated as far as the NTU and both the datacenter and BT refused to
> > cable the connection on to the rack where I have a 7204 router with a
> > serial port ready.
> >
> > It's taken me 8 weeks to persuade the datacenter company to cable to
> > the rack and they have cabled two BNC/G703 cables to the appropriate
> > place. I attempted to use a spare Betterbox g703/x21 converter with
> > these cables but when I connect it there is no "link" light showing up
> > on the front panel. According to the manual this lights up "when the
> > E1/FE1 interface converter is receiving carrier from the E1 network".
> >
> > At the "A" end of the circuit the NTU is right by the other 7204 and I
> > have simply plugged an X21 cable in to the correct trib and into the
> > serial port on the router.
> >
> > Unfortunately I am not a network engineer by any stretch of the
> > imagination and I am getting a bit out of my depth. Could anyone
> > advise me whether this is a sane configuration?
> >
> > (A) 7204--[x21]--NTU--megastr 2--NTU--[g703]--Betterbox
> > IC2001--[x21]--7204 (B)
> >
> > Would I be better off paying my datacenter vendor to cable an X21
> > cable instead and forget about the converter? If I use NTU-x21-7204 at
> > both ends do I have to do any special configuration on the routers?
> >
> > Any advice anyone could offer would be much appreciated. Apologies for
> > the newbie tech level of this post, but I guess we all have to start
> > somewhere!
>
> What style of BT NTU have you got at the "problem" end?
>
> Some BT NTUs support both G703 and X.21 but of course not
> at the same time for a given circuit. This caught me out
> once as I'd hooked things up to the right circuit on the
> G.703 but the BT NTU was configured to use the X.21 port.
>
> Get BT to check whether they have enabled the interface as
> X.21 or G.703 on the NTU.
>
> Alternatively, try swapping the TX and RX BNCs over on the
> DSU [betterbox thing]!
>
> -Pete L.
>

Thanks to both of you for your suggestions. I'm going to try to
recable from the X21 port on the NTU. After I saw Pete's reply I was
straight on to BT who confirmed only the X21 is enabled.

Toby, your reply fills in a lot of gaps in my knowledge. It is exactly
the information I have been after so thanks very much for taking the
time to explain things.

Cheers,
Mark Wilson

(Mark Wilson) wrote in message news:<. com>...
> Thanks to both of you for your suggestions. I'm going to try to
> recable from the X21 port on the NTU. After I saw Pete's reply I was
> straight on to BT who confirmed only the X21 is enabled.
>
> Toby, your reply fills in a lot of gaps in my knowledge. It is exactly
> the information I have been after so thanks very much for taking the
> time to explain things.
>
> Cheers,
> Mark Wilson

I suspect that a key difference between X21 and G.703 on coax is that
the X21 is severly distance limited. I have some tables somewhere
if you want more info.