Cell Relay Archive

[Walt Weber <waltweber@sprintmail.com>]

Anouch Gharagozlou wrote:

> Hi everybody,
>
> It seems that many telecom providers are willing to offer IP services
> directly over Sonet or SDH by-passing ATM levels.
>
> They say Quality Of Services guaranty may not be a problem with the huge
> amount of bandwidth provided.
>
> This may be a frequently asked question by now. What do you think about
> this technology?
> Is that mean the death of ATM after so many promises it gave ?
> What are the pros/cons ?
>
> Can anyone direct me to more litterature on this subject ?
>
> Thanks
> Anouch Gharagozlou

This is more of a question for the group than a response.  I come from a
transmission background - microwave radio, optical systems, then into ATM.
So I am not overly familiar with IP and routers.

In my opinion, there are 2 things to be considered when deciding whether to
use one protocol to transport another.  One is the extra overhead to put the
payload data into frames, packets, cells or whaterver.  The other is the
utilization of the available bandwidth - some means to stat mux the data so
that a high per cent of the bits in the stream are carrying user data..  For
example, a DS1 carries 24 DS0s with very little overhead, but if, on
average, only 8 DS0s are actually in use, there is a waste of bandwidth.

It seems like there is a factor for throughput and one for cost per bit of
throughput.  If you own your own physical link, the second factor may not be
as iimportant.  So if I am running a fiber between some buildings to
interconnect my LAN, the overhead is more important that utilization.  But,
if I am leasing facilities to interconnect my locations, a high utilization
might let me lease 3 T1s instead of 5.

How does a network using routers and IP over Sonet compare with a network
using IP over ATM on a throughput as well as cost per bit basis?

Let's say a customer has 3 voice T1s and another T1 for data.  Today, I
could put all off this traffic on a single NxT1 ATM pipe and do away with at
least 1 T1 and lilkely the customer would not notice any difference in voice
performance while gaining data performance..  Could I do the same with an IP
solution?