Cell Relay Archive

["Mark S. Lewis" <msl@NetEFX.com>]

Netwizards:

I've been researching the various encapsulations used on xDSL lines and
looking their various benefits.  From what I have determined so far, these
are the main variations:

1. Ethernet encapsulation used mostly with transparent bridging.  This seems
like the easiest to implement especially for an Ethernet based CPE.
However, it is not a very smart way to use the link.  Many employ filtering
to avoid sending unnecessary LAN traffic over the WAN.

2. Frame relay (RFC1490) multiprotocol encapsulation can be used with
routing.  This seems like a reasonable approach for data traffic.  Routing
provides better use of the link.  Plus you get the benefits of frame relay,
namely link management and multiplexing of logical connections.

3. ATM using FUNI (RFC 1483) provides an interface between frame relay and
ATM.  Since it is a variable length packet encapsulated like frame relay but
with ATM addressing, it would seem to perform and be managed like frame
relay.  Aside from providing an interface to ATM, is there any other
particular benefit to this encapsulation over frame relay?

4.  ATM using cell-based encapsulation (AAL5?) can be used to provide the
additional ATM services for time-sensitive applications.  Not knowing much
about ATM at this point, what other benefits are provided using this
encapsulation?

5.  PPP is being used over 2, 3, & 4 above.  This provides the benefit of
dynamic link negotiation, including IP addresses, DNS and other values.  Of
course it supports multiple protocols, and can also provide authentication.
What other benefits are there of PPP?  Which link layer encapsulation would
be preferable?

Are there any other significant variations?  If so, what are the benefits?
All comments and clarifications are appreciated.

... Mark

msl@NetEFX.com