[c-nsp] Inverse multiplexing DS3s to larger interfaces?

[Hyunseog Ryu]

If you want to avoid to hit maximum-path 8 limitation,
you have to increase the pipe size, and reduce the number of circuit 
from the router viewpoint.
Ideal solution is to replace DS3s with higher bandwidth circuit such as 
OC3, OC12 or GE.
But as you said, there is limitation from one of your provider, who 
don't support more than DS3 pipe.

In that case, I can think of a couple of ways.

1) Try to find another carrier who support OCx level circuit, or 
pretending to do that.

If you are lucky, you can find another provider, who can fill up OCx 
requirement, and your headache may be gone.
Or you can use it to threaten current provider to support OCx circuit.
If they have multiple DS3s, I don't see the reason why they couldn't 
support OCx circuit.
If they don't want to spend the money on OC3c cards, it's their problem.
In order to support multiple DS3s, they should already have OCx support 
capability.

I think this is best case for you, because you don't have to worry about 
   TDM Mux/demux between different speed, and routing may become simpler.

2) Find the vendor who have DS3s-to-OCx converters.

Kentrox or Larscom, or others.
They may have some converters to map multiple DS3s to single OC3c or OC12c.
This may be cheaper solution, and you can buy OC3c or OC12c interface 
for GSR, and keep DS3s circuits as-is.
Routing may become simpler, but if there is some difference in mapping 
speed from either side, there may be some issue.
For an example, if you have 2 DS3s, and you map 2 DS3s to 1 OC3c,
there is difference in capacity from both side.
Actual circuit side is 2 DS3s, which is 88.420Mbps.
Router side is 1 OC3c, which is 155Mbps.
So if the router send the traffic more than 88Mbps or there is some problem
with TDM multiplexing, there may be packet loss or packet transmission 
delay.

3) If you want more sophiscated equipment, you can use Cisco ONS 15454
for 2) function.

For the quality of transmission, and long-term management,
if I were you, I will try solution 1) with some scalability planned.
Maintain 2 carrier providers, but if they couldn't meet your 
requirement, don't be afraid to ask for yourself to find another provider
to suit your needs.

If they can sell x number of DS3s, there is no reason not to support OCx
for equivalent bandwidth. It may take a couple of months to install 
fiber, but it's not a problem you can wait.


Hyun



Thomas D.Simes wrote:
> We've currently got a pair of GSRs tied together with 7 DS3s from two
> different carriers and are load balancing via OSPF.  This
> method has worked pretty well, but the technique tops out at
> maximum-paths 8 on the GSR.
> 
> I'm looking for a more scalable way to multiplex these DS3s into
> something larger and feed them into my GSRs to reduce the number of
> layer 3 paths between the two locations.
> 
> Going to larger interfaces is currently not an option with one of the
> carriers, and we want to maintain dual carriers for redundancy if
> possible.  We're currently using the 6 Port Packet over DS3 cards and
> the interfaces don't support multilink PPP or multilink frame-relay.
> 
> What have folks used that worked well for this application?
> 
> The Cisco ONS 15454 using enhanced DS3 cards looks like it
> might be a possibility, but I don't have any experience with the
> platform.
> 
> TIA!
>