lkw@csun.edu (Larry Wake) (12/08/88)
We have pretty much settled on using a high-speed serial connection to
bridge Ethernet segments located in two buildings on campus. Our
proposed method is to use a cisco gateway server on each end, with what
they call their "T1" interface (for reasons that may become clearer, I
would like to avoid the term T1, though). The cable between the two
buildings is T1-quality twisted pair (22 gauge dual D-screen), owned by
the university, not the phone company; the run is about 2800'. Each
cisco board has a V.35 connector, and they will talk HDLC.
After talking with many, many vendors, we are still confused as to what
we need to drive the serial line. Some (including cisco) say we need a
CSU/DSU, others say only the DSU portion is necessary, and still others
say only the CSU. Prices range from $1500 to $5000 a side.
So, we still need to know what the technological difference between
the different types of equipment is to justify the wide price range. In
a nutshell, our main concern is: what is the most cost effective way to
get a high speed (T1 or T1-C rate) connect between the two cisco boxes?
If anyone has any direct experience and/or product recommendations, we
would love to hear from them. More general questions include: what is a
CSU? What is a DSU? Which of these is required only for telco
connects, and which can be eliminated in a private setup such as ours?
Thanks in advance,
--
Larry Wake lkw@csun.edu
CSUN Computer Center uucp: {hplabs,rdlvax}!csun!lkw
Mail Drop CCAD BITnet: LKW@CALSTATE
Northridge, CA 91330ron@ron.rutgers.edu (Ron Natalie) (12/09/88)
I'd go with one of the slick CSU/DSU pairs on the market today. The Verilink one seems to be pretty good for the price. The CSU (customer service unit) is a device that sits between the customer equipment and the phone companies circuit and provides some diagnostic services like remote loopback. For T1 speeds, they also provide enforcement to complience with the various 1's density requirements and such. The input and output to a CSU look the same. Usually a DB-15 connector which have two pairs of pins actually in use, one for the transmit side and one for receieve. Presumably you can get away without this box on your own wire, but it's nice to have anyhow. The DSU (data service unit) is what you think of a MODEM in the digital service. It talks V.35, RS-232, or RS-449 to the CISCO box and converts that into the transmit and recieve signals to the CSU. The DSU is infact a modem that will get your data as far as the next step in the digital facility. The DSU has the appropriate connector for the data equipment side (DB-25 for RS-232 DB-37 for 449, whatever the V.35 connector is called) and a DB-15 with the two pairs going to the CSU. You can get both in the same box usually called a CSU/DSU or sometimes an ISU (Integrated Service Unit). It used to be that the phone company provided both, then just the CSU, and now you pretty much can do what you please. To work with the CISCO box, you are going to at least need the DSU. You may be able to do without the CSU, but having one is convenient for debug purposes. The confusuion stems from the fact that while DSU's are common for slower speeds like 56K and slower, it is only recently that boxes like the cisco T1 units want to talk T1 data rates directly into a single channel. In the past T1 was always made up of multiplexed slower circuits, and the multiplexor had a part to it that played the roll of DSU, requiring only a CSU for the T1 line. My recommendation is for the new VeriLink CSU/DSU pair that they call the Connect 1. We can get them (University Price) for about $2500 each end. We know the comparable product from Digital Link works because Cisco used one of our Digital Link modems to test out their boards with originally and we ran with them for quite some time. -Ron