Telco Local Loop

Unanswered Question
Apr 15th, 2008


I need an opinion from the experts.

I am working with my ISP on getting a 6M pipe at my disaster recovery location. The will provide me with 4T1s but I asked them that I wanted them on different local loops so they all don't go down at the same time.

I know that I could bundle them on the router creating a multilink interface but, will the ISP be able to bundle them as well if the are coming from different CO? I am trying not to configure any load balancing on the router.

Can anyone help? Thanks in advanced.

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Overall Rating: 5 (1 ratings)
Paolo Bevilacqua Tue, 04/15/2008 - 05:48

As long the ISP have the data interfaces is the same router, the can regroup them.

Using "different local loops" doesn't really mean much and is a matter for telco and not the ISP at layer3.

rgarcia1801 Tue, 04/15/2008 - 05:51

But if that router goes down all the T1s will be down (which is what I am trying to avoid), correct?

nygenxny123 Tue, 04/15/2008 - 06:10

If all t1's are entering the same router in your DR site...and the router goes down..yes..the t1's will be useless.

Split the t1's and use HSRP so you will have redundancy.

rgarcia1801 Tue, 04/15/2008 - 06:14

Please read the stament above my post, I was referring to the ISP router.

nygenxny123 Tue, 04/15/2008 - 06:29


the fact that you are requesting different local loops is of no concern to the ISP. Once

the t1's are dropped off, they can multilink them, or connect them however they want

sundar.palaniappan Tue, 04/15/2008 - 06:38


You are on the right track. You don't want any single point of failure that would cause the multilink connection to become useless. If you can get the Telco to use different loops and different physical layer components on their network that would provide some resiliency to your backup design.

As Paolo pointed out earlier it shouldn't matter to the ISP how the T1 mapped through the Telco network. The only requirement being all the T1s on both ends have to come into the same router.



rgarcia1801 Tue, 04/15/2008 - 06:46


Thank you for your reply. So my assumption is true, the Telco needs to have both T1s coming out from the same router in order for them to be able to bundle them. But they will have no choice but provide me with T1s in the same loop.

Now, if I choose to use different loops. Do I have to create any load balancing in my router? Will I be able to create a multilink?

Paolo Bevilacqua Tue, 04/15/2008 - 06:58

Hi, as mentioned before, a long you have a single router, all circuits will terminate in there and that is one single point of failure. On the other hand routr don;t fail much and cisco laso a replacemente shipping service in supposedly 2 hours (depedns on the city).

If you want to MLPPP then you need to concert that with your ISP.

sundar.palaniappan Tue, 04/15/2008 - 07:04

Multilink would do the load balancing for you at layer 2. All the layer 3 configuration for the link would reside on the multilink interface. You won't be able to use the multilink configuration if the T1s are terminated in different router(s) as you aren't doing multichassis-multilink. T1s coming out of the same router doesn't mean Telco wouldn't be able to map them through different paths on their network.



alukes Tue, 04/15/2008 - 14:21

Keep in mind that it is very likely that the telco is carrying all local loops in one cable to your building. A back hoe will disrupt all the local loops at once.

If you want physical layer redundancy, you will have to have two cable paths to two separate telco central offices. The cables should enter the building at different locations. Expensive.

PAUL TRIVINO Wed, 04/16/2008 - 12:29

Just my 2 cents worth, but if this is already a DR site, you'll have this 6mb sitting doing nothing (except perhaps replication?) most of the time. Most hosted DR sites do a pretty good job watching for Bubba with the Backhoe, so different physical paths is not *quite* as much worry, IMHO.

OTOH if the DR site is so critical it MUST be up when it's in use, the business shouldn't have too much heartburn paying for 2 x (4xT1) for redundancy.


kdm61 Wed, 04/16/2008 - 12:55


I work for a large telco and here is the scoop on your T1's.

1)You cannot get more than one T1 on a local loop i.e. access link. You can however drop T1's out of a higher level ckt such as DS3 or SONET but these are not coming across a Local Loop i.e Copper Facility.

2)If you want to bundle T1's you must have a higher level ckt multiplexing/demultiplexing them i.e. DS3, OC3,OC12 etc. or if you aren't concerned with T1's and only want the bandwidth you can purchase a ckt that isn't TDM based (All T1's are TDM based). An option in our network would be an MPLS over ethernet in increments of 10/100/1000 Mbps which would give you the bandwidth but of course are not TDM ckt's.


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