[c-nsp] DS3 breakdown for T1 resale

[Bill Wichers]

> Hi, we have a 3845 with a NM1T3-E3 card connected to the
> Internet. We are thinking about offering T1 access to the
> Internet to a dozen customers, maybe more over time. Cost is a
> determining factor, as usual. T1 service would be resold with
> block of static IPs from a /21, and we need to handle the
> routing.

The routing part is really easy, unless you are giving BGP feeds to your
customers which would require a bit more CPU on the router.

> We were looking at using VWIC-2MFT-T1 on NM-2FE-2W network
> modules to get up to 20 T1 lines (max. on a 3845 with DS3
> installed), starting with just 3 or 4 T1 ports.
>
> Any suggestion on that setup to minimize upfront and long term
> costs, offer additional services, maybe get a 7500 with a T3 to
> the Internet on one side, and a channelized CT3 card to the CO ?

Best is probably a 7200 or 7500 chassis for the router since I don't think
there are any large-scale channelized interfaces available for the
28xx/38xx routers. In a 7200 I'd use a PA-MC-T3 to feed your T1 customers
and a PA-FE-TX to link the aggregation router into your network (or an
appropriate WAN-type interface if that's what you need). You could use a
low-end NPE, as long as it has enough memory for your needs since you
shouldn't be CPU limited.

In a 7500, the cheapest CT3 blade you can get used is the CT3IP which
takes a channelized T3 and can also break out 4 channels to v.35 ports.
These occasionally show up on Ebay, but are also available from some of
the used equipment vendors. They're usually really cheap since they're EOL
and offer poor port density too. Much better (but also much costlier)
would be a PA-MC-T3, in which case you'll also need a VIP if you are going
to use a 7500 chassis. A VIP2-40 will work fine, but if you need BGP and
don't want to run out of memory soon a VIP2-50 or better would be a better
choice. You can use an FEIP blade (old CxBus FE blade) to get a fast
Ethernet port, or you can use a PA-FE-TX in either a second VIP or the
other slot of the same VIP as the PA-MC-T3 is in (if you use a VIP2-40
check this though, I'm not sure if you will run into SRAM limitations with
that config. A VIP2-50 will work though). Cost for a PA-FE-TX or FEIP is
similar on the used market. If you don't need BGP you could get by with an
RSP2, but an RSP4 will give you more flexibility should you need BGP in
the future.

I personally would consider the CT3 route *far* superior since I've done
it both ways (lots of CSUs and v.35 cables in the early days, and now all
CT3 interfaces). The CT3 offers much, much better reliability, far fewer
pieces of equipment to deal with, and a lot less headaches when problems
come up. Basically with a CT3 any circuitry problems probably won't be on
*your* end (and if they are you'll know quick since it would affect all
your customers). For us the breakover is around 8 T1 circuits at which
point the CT3 is cheaper per circuit. You'll pay some fixed amount for the
CT3 circuit regardless of how many timeslots you use, and then you'll have
a cost for each T1 that you break out to a customer too.

The cheapest way to get started would be to use a PA-MC-4T1 or a
PA-MC-8T1, and then switching over to a CT3 when you fill that up. If you
have 12 customers up front, just go the CT3 route from the beginning. As
soon as the CT3 is economical you'll want to switch since it will make
things much easier to manage and a lot more reliable too.

     -Bill

*****************************
Waveform Technology
UNIX Systems Administrator