From: Mark Detrick (mdetrick@xxxxxxxxx)
Date: Tue May 30 2000 - 20:28:41 GMT-3
See below,
You are confusing various technologies and layers. Some info on DSL...
Line codes:
CAP - in certain ways analogous to modem encoding - popular as an old
technology but fading fast. No longer being developed.
DMT - ANSI T1.413, ITU 992.1 G.DMT, ITU 922.2 G.LITE, ITU 994.1 G.HS
These are all current standards for ADSL line codes. G.HS is a handshaking
standard.
G.Lite is a spliterless protocol that only goes up to 1536/512
down/upstream.
G.DMT is full rate and runs at 8032/1024 down/upstream.
Layers...
Once the DSL line code trains, which is layer 1 then layer 2 becomes active.
Layer 2 is most often ATM PVCs. Once the ATM is active then layer 3 can
work. This would include protocols such as: DHCP, PPPoA or PPPoE.
If you are using PPPoE then the PPP session extends from the PC to what ever
is terminating the PPP session, often a 6400. The CPE converts the PPPoE to
PPPoA and if needed performs NAT as well. If you are using PPPoA then the
PPP session extends from the CPE (usually a 633, 678, 627, 827 or 1417) to
the terminating device. The last method of connection is when the CPE has
been configured for bridging and no PPP is used, RFC 1483 is used instead
either SNAP or MUX. The bridged frames terminate using irb or rbe on some
router, could be at the provider or final destination such as an enterprise.
The CPE may send request to a DHCP server to gain information on how to set
itself up for the user's side. For example, when a Cisco 678 receives a
DHCP response that has a gateway IP and subnet mask, lets say 192.168.1.0
and 255.255.255.0, it will configure the following:
1. Gateway 192.168.1.1
2. Subnet mask 255.255.255.0
3. The CPE will become the DHCP server for the user's subnet it is connected
to and pass out addresses 192.168.1.2 through 192.168.1.254.
If it doesn't receive the subnet mask from the DHCP server (purposely
configured by the admin) then the CPE will not be a DHCP server it will just
use that gateway address given, 192.168.1.1. All this automation allows
easier IP management of private addresses by the provider.
A 633 SDSL modem has a serial interface on it, which can connect to a 2511.
Do you know what type of DSL you have, ADSL, SDSL, IDSL? It is all
completely different.
Hope this helps.
Mark Detrick
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