--- TIC-TECH message:
A bit of background that may answer some of John Keithly's questions -
IS receives frequent requests for guidance on purchase of hubs for locations
with more computers than wall jacks. Switch technology has benefits over
hubs: the device on each switch port gets the full bandwidth instead of
sharing with all devices on a hub; better isolation of problem devices; and
more useable hops before latency becomes an issue.
However, some switches don't interoperate well with each other. The district
switch technology standard at the MDF/IDF level is Cisco, so whatever is
used at the classroom distribution level needs to interoperate with the
Cisco switches. At the same time, many schools have told us they can't
afford to purchase Cisco switches. Based on these requests and parameters,
IS did some testing to determine which brand of inexpensive switch would
interoperate well.
The Allied Telesyn switches work well in this environment. They are
inexpensive enough that a school can afford to have a spare on hand and they
have a limited lifetime warranty. The "limited" part is that the fan and
power supply have a one-year warranty. The alternative was to require a
Cisco switch (about $300 for 8 ports vs. the $66 for an Allied Telesyn).
>Why are wall warts "bad"?
These are the type of integrated AC power plug and transformer that is
common on many electronics devices. When you plug one of these into an
outlet, you almost always lose the use of at least one other outlet because
of the size of the transformer. Having a standard power cord instead of a
combo plug/transformer is an advantage any time power outlets are in short
supply, and they usually are scarce in schools.
> how were these REQUIREMENTS arrived at?
The first requirement is that switches in MDFs/IDFs are Cisco managed
devices. This is part of the district's overall WAN design and is based on
the same considerations that lead us to select switches instead of hubs for
classroom use. The second requirement is that unmanaged switches not be
daisy-chained. This requirement is a reflection of the hop count limitations
that are inherent in Ethernet. Observing this limit makes it less likely
that any two devices within a building will attempt to send data over a link
whose hop count creates too much latency. When excess latency occurs, the
whole building network suffers because of retransmissions - it can actually
bring a building's network to its knees.
Thanks,
Judy
JMCNAMEE@seattleschools.org
-----Original Message-----
From: John Keithly [mailto:jkeithly@halcyon.com]
Sent: Sunday, December 17, 2000 9:02 PM
To: TIC-TECH@tic.ssd.k12.wa.us
Subject: Tic-Tech: Unmanaged Switches
--- TIC-TECH message:
I guess I'm a bit underwhelmed by these REQUIREMENTS.
Just out of curiosity, how were these REQUIREMENTS
arrived at?
Was this another "flash" district decision arrived at
without any input from the recipient schools?
I can accept the idea of limiting hops.
Why are wall warts "bad"? Are we now trying to
look nice?
I'd think reliability and performance would be more
important considerations. From my own experience of
3-5 years ago Allied Telesyn does not have a reputa-
tion of making quality hubs. I can't speak for their
switches. But it does make me a bit suspicious that
their switch prices appear so attractive.
Better choices could be HP, Cisco, Netgear, Linksys, SMC,
or Intel. I'd at least like to see some product perfor-
mance comparisons that demonstrate more than price and
wall wart issues went into making this REQUIREMENT.
I have the impression that using switches and hubs outside
of an IDF (such as in a classroom) is not an option. I
don't think this is pragmatic or sustainable for most
school usage plans. At Ballard we have many, many ports
in classrooms but still there are places where local switches
or hubs make sense for concentrating special configurations.
Just my own opinions here of course....
--John Keithly
jlkeithly@seattleschools.org
Tech Support
Ballard High School
-----Original Message-----
From: Dahlgaard, Andrew [mailto:ADAHLGAARD@seattleschools.org]
Sent: Thursday, December 14, 2000 3:29 PM
To: TIC-TECH@tic.ssd.k12.wa.us
Subject: Tic-Tech: Unmanaged Switches
--- TIC-TECH message:
All,
Operations has approved the use of these Allied Telesyn unmanaged switches
in the schools. The Networking guidelines REQUIRES all switches in MDF/IDF
are managed Cisco ports. The guidelines also REQUIRE that there be only one
hop from a managed port i.e., a chain that starts: Cisco port -->AT switch
--> HP Jet Direct Card is ok while: Cisco port -->AT switch --> AT switch
--> computer is bad.
Why are these switches are good?
First, it is a auto sensing 10/100 Mb full duplex switch instead of a 10 Mb
hub half-duplex, (faster, less collisions, and reset of hop count.) Second,
they have an internal power transformer and a "normal" computer power cable
to power the unit instead of a "wall wart" external transformer. Next, they
have a limited lifetime warranty. Last, they will be standard across the
entire district.
The quotes that we received from Graybar Electric Company, (425)468-5511,
are as follows:
AT-FS708 10/100 X 8 ports $065.96
AT-FS716 10/100 X 16 ports $177.69
AT-FS724i 10/100 X 24 ports $245.47
If you need to add ports at a school, your options are: 1) add ports to the
Cisco switches in the MDF or IDF; or 2) use on of the AT switch models
listed above, with the AT switch connected directly to a Cisco switch. These
options provide the best combination of quality, warranty, and price so they
have now become the district standard. Schools should no longer purchase
shared media hubs or generic switches.
Drew
Andrew J Dahlgaard
IS Project Lead & Acquisitions
Seattle School District #1
adahlgaard@seattleschools.org
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