[c-nsp] channelized OC-12 for aggregation

[Geoffrey Pendery]

We're an enterprise (not service provider) and our hub sites each
aggregate about 10 DS-3's, a handful of OC-3's and a handful of DS1's.
We're getting actual raw circuits from carriers (not Frame, ATM, MPLS,
Ethernet, etc) and today we're aggregating them via MGX ATM switches -
non-IP traffic like TDM voice trunks was a past requirement that is
gradually fading away.

We're starting to brainstorm our non-ATM future, and the current
thinking is that we'll mux the various circuits up into channelized
OC-12 router interfaces.
>From cruising all the Cisco documentation, the hardware options seem
to be pretty much confined to one particular SPA - SPA-1xCHOC12/DS0
and just a question of what to put it into:
ASR 1000's (which we've used a little and are optimistic about)
7600 Routers (which we're as comfortable with as is possible, given
all the caveats and BU-split issues, including the fact that we're
actually running SXH5 on ours right now)
12000 Routers (which we assume are out-of-our-league-expensive overkill)

We're not talking about BGP, IPv6, or MPLS (at least, not yet, though
they're likely to be required in the future...) just pretty
conventional IPv4 routing stuff here.  We need fairly flexible/robust
QoS, but Enterprise not Provider (10 buckets is more than enough, we
don't need 100,000).  Only odd requirement I can think of is WCCP to
connect possible WAN Accelerators.

So my real questions :
1.  Anybody have experience with this particular SPA?  Good/bad?
2.  If we went with 7600, we'd have to switch to SRD from SXH - what
sort of nasty surprises should I expect there?
3.  We're on regular 7600 chassis right now, not 7600-S, is there a
compelling reason (like end-of-support - 2015? - or critical feature
support lacking) that warrants getting off the "classic" 7600 chassis?
4.  Anybody got the warm and fuzzies using ASRs for this sort of
thing?  1004 vs 1006?
5.  Am I missing an obvious option?


Thanks,
Geoff