[cisco-bba] Re: [c-nsp] IP DSLAM ( Fully Distributed BRAS)
swmike at swm.pp.se
Tue Aug 9 04:57:23 EDT 2005
On Fri, 5 Aug 2005, Vusi Ndebele wrote:
> I wanted to get some views and experiences of the much touted 'IP DSLAM'. As
> far as I can tell, many of the DSLAMs on the market right now are more
> Ethernet DSLAMS effectively bridging with a bit of fancy snooping etc for
> multicast. I call an IP DSLAM a box that has encapsulates subscriber traffic
We use the DSLAM as a media converter. It does the same job as a Cisco
2950 or 3550 would do in a ETTH environment. Private vlan (or one vlan per
customer) for security, IGMP snooping, L2+ access lists for spoofing
protection, DHCP snooping to populate the access lists, etc. Routing is
done upstream from it.
The DSLAM does conversion from ethernet uplink (tagged vlans) to untagged
ethernet over ATM. The customer can then terminate it as bridged IP over
ethernet to one or more ports in their CPE, or as route/bridged in their
CPE and do NAT in the CPE.
Personally I would like to completely do away with all the ATM stuff, it
does nothing for me. I want Ethernet over DSL directly without the ATM.
Prioritization can be done using .1p or some other queueing mechanism.
Too bad this only happened on VDSL, I wish there were more ADSL2+ CPEs
that would do it.
IP over Ethernet over ATM means high probability that even the smallest
packet will use three ATM cells instead of two (as in IP over ATM). Bad
for low-bandwidth high density VOIP (many phones in one place). Not so
much a problem for residential as they usually only have 1-2 calls at any
given time and uplink seldom is less than 800kilobit/s on physical line.
Mikael Abrahamsson email: swmike at swm.pp.se
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