| You can do it, I'm not sure you'll be happy. There are a few
issues unrelated to the VNswitch.
- there might be a significant amount of multicast traffic required
by 16 Elans. The multicast traffic could easily exceed the bandwidth
of a T1 link... only 1.5 Mb/s of raw BW. In terms of user BW,
protocol efficency may be low (eg, for small packets) so the actual
application saturates at about 1Mb/s.
The traffic level is strongly related to the end station
population and application. 16 is a pretty large number, I assume
there's a significant number of end stations. You'll need to
characterize multicast traffic levels and see if a T1 is enough for
for any actual user data. This is a "LAN problem"... that's why
routers are so popular in the WAN (terminate multicast domain).
- delay might be enormous and this could heavily impact LAN operation.
The applications run on a LAN are sometimes not tolarant of delay...
the notorious example is LAT. Email is ok... everything else is in
between.
The distance between sites affects this ( add > 5uS/KM each way).
If the sites are close, no problem. Unless, of course, the phone
company routes the T1 through a satelite... most satelites today are
FEO, about 40K miles I believe.
- T1 is a major bottleneck between two high performance LAN pieces.
The EA's support a large number of 10Mb/s segments, the aggregate
switched BW for each VNswitch is > 100 x the T1 link. It's difficult
to imagine an application/configuration where high capacity VLANS'
span two sites but only 1.5Mb/s is needed to suppport the users...
even given the traffic filtering of the switches. Consider a large
file transfer, say 10 Mbytes. For a local operation this would take
about 10 seconds even it the switch had a lot of other traffic
concurrently. Across the T1, this will be 100 seconds in absence
of other traffic. If congestion occurs, might never happen.
On the bright side - The T1 modPHY should work fine with the VN-ea.
It's only the T1 bottleneck I question...
Related to fractional T1 - modPHY modules generally operate ATM, not
fractional anything. Fractional generally relates to a "structured
channel", meaning TDM which is the opposite of ATM. ATM typically
uses "clear channel" service. Clear channel means you lease the
whole line. Some phone companies are offering usage-based charges
on ATM but this is not common yet.
|
| Hi,
Tx for replying to my Question.
> - there might be a significant amount of multicast traffic required
> by 16 Elans. The multicast traffic could easily exceed the bandwidth
I will not have a lot of stations on these VLANS (Maybe 5-20max on each VLANS).
So I do not expect to have a lot of multicast/broadcast traffic.
> Related to fractional T1 - modPHY modules generally operate ATM, not
> fractional anything. Fractional generally relates to a "structured
> channel", meaning TDM which is the opposite of ATM. ATM typically
> uses "clear channel" service. Clear channel means you lease the
> whole line. Some phone companies are offering usage-based charges
> on ATM but this is not common yet.
So , if I understand properly we have to use the full T1 as a clear channel and
the VNSwitch will run ATM only over a full T1.
See I thought it would be possible to use only a few channels from the T1, then
these channels would terminate on the CSU/DSU and the CSU/DSU would connect to the
VN/EA ATM port at T1 speed (I know that the ATM port will not do TDM and use a few
channels).
Would I require a special cable to adapt the T1 Modphy interface to the CSU/DSU ??
How would you configure this for redundancy ?
Tx
Michel
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