[cisco-voip] T1 xover or straight through?

Wed Jun 3 17:44:10 EDT 2009

Except it is not owned by the customer. 

From: smithsonianwa at gmail.com [mailto:smithsonianwa at gmail.com] On Behalf Of
Tim Smith
Sent: Wednesday, June 03, 2009 4:40 PM
To: Voice Noob
Cc: Dane; cisco-voip at puck.nether.net
Subject: Re: [cisco-voip] T1 xover or straight through?

IAD would still be considered customer equipment as well I'd think.

Cheers,

Tim

On Wed, Jun 3, 2009 at 11:06 PM, Voice Noob <voicenoob at gmail.com> wrote:

I have had providers install an IAD device where they take the circuit from
the Telco into their IAD. Then they hand of a PRI to my equipment from the
IAD. In this case you need a Crossover T-1 cable.

From: cisco-voip-bounces at puck.nether.net
[mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Tim Smith
Sent: Wednesday, June 03, 2009 7:37 AM
To: Dane
Cc: cisco-voip at puck.nether.net
Subject: Re: [cisco-voip] T1 xover or straight through?

Hi Dane..

Simple rule for this.

1. Customer Equipment to Customer Equipment = T1/E1 cross over cable
2. Customer Equipment to Network = Straight through cable

Customer Equipment = PBX, Voice cards on routers, key systems 
Network = the PSTN, your carrier, etc

Bit more info to help explain hopefully :)

Your 3845 T1 voice interface has pin outs as follows

Pin
1 - Receive (RX) Ring
2 - RX Tip
4 - Transmit (TX) Ring
5 - TX Tip

Think of receive as your ear and transmit as your mouth
Straight through cables connect pin 1 to 1, 2 to 2, 4 to 4, 5 to 5.

So when connecting customer to customer equipment with a straight through
cable
You are essentially connecting ear to ear and mouth to mouth.
To get complete circuits you need ear to mouth and mouth to ear

An E1/T1 cross over cable "crosses" the RX and TX connections as follows:
Pin 1 to Pin 4
Pin 2 to Pin 5
Pin 4 to Pin 1
Pin 5 to Pin 2

Network / PSTN equipment has different pinouts.. i.e. it expects RX on pin's
1 and 2, and expects TX on Pins 4 and 5 from your equipment. Hence straight
through cable required.

Also dont forget if this is ISDN you also have a layer 2 network / user
element to consider. i.e. if you connect 2 x customer equipment together -
one side needs to be configured as Network side, and the other as user.

Hope this helps a bit..

Cheers,

Tim

On Wed, Jun 3, 2009 at 7:04 PM, Dane <dane at pktloss.net> wrote:

First I wanted to say thanks for the replies and information.

Second, well I got it sorted out finally.  I took down one of the
PRI's after hours from the IAD and connected it to the 3845 with a
straight through cable just to test.  It did not come up which is what
I think I and everyone who responded on this list would have expected.
 I connected the IAD to the 3845 with a T1 crossover just as I have
the IAD connected to my CMM-6T1s and it came up.

Now the kicker is that this same 3845 T1/PRI port connected to the
AT&T demarc requires a straight through cable.

I have to be honest and admit that this confuses me.  Of course its
4am and I have been busting my ass since 6am so I am not able to
mentally sort this out.  Have to give it some thought when I have my
wits how the 3845 port takes either a T1 crossover or a straight
through depending on the other side apparently.

Anyway, I thought it was interesting to note and share.

Thanks again for the help.

On Mon, Jun 1, 2009 at 12:31 PM, Go0se<me at go0se.com> wrote:
> As a general rule a T1 crossover cable is always required between PBXs no
> matter how you interconnect them. I'm not aware of a T1 controller that
will
> auto-mdix. You can build your own T1 crossover - cross pins 1&2 to pins
4&5.
> (1 to 4 and 2 to 5)
>
> -Go0se
> http://atc.go0se.com
>
> -----Original Message-----
> From: cisco-voip-bounces at puck.nether.net
> [mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Dane
> Sent: Monday, June 01, 2009 11:28 AM
> To: cisco-voip at puck.nether.net
> Subject: [cisco-voip] T1 xover or straight through?
>
> Anyone know if you need a straight through or t1 crossover to go from
> an IAD to a 3845 with a PRI port?  We have some IAD's that terminate
> with CMM's and those use t1 crossovers.  Not sure about the 3845
> ports.
>
> Connecting to AT&T circuits to the 3845's required straight through.
> Wish I had one to test.
>
> Just wondering if anyone might know, wondering if the 3845s can handle
> either / or, and if the requirement comes from the demarc side (either
> AT&T or IAD's).
> _______________________________________________
> cisco-voip mailing list
> cisco-voip at puck.nether.net
> https://puck.nether.net/mailman/listinfo/cisco-voip
>
>
>
>
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