dyer@spdcc.COM (Steve Dyer) (04/17/88)
I'm using a Telebit Trailblazer+ on one of my dialin ports, fixed at 19.2kb
using hardware flow control (gettydefs has EXTA and CTSFLOW defined). I'm
finding that effective UUCP throughput ranges between 80-100 bytes per second
when a UUCP neighbor without a Trailblazer dials in at 2400 baud, completely
negating any benefit of the neighbor's >1200 baud speed. The CTS light seems
to blink on every SD (send data) blink. People who dial in to this line at
2400 baud also report jerkiness (although this seems to be hidden and not
observable at 1200 baud.)
Note we don't appear to be losing data; the low transfer rate isn't due to
retransmissions, but due to (excessive?) throttling of the output stream.
Any ideas of what to try?
/Steve
--
Steve Dyer
dyer@harvard.harvard.edu
dyer@spdcc.COM aka {ihnp4,harvard,husc6,linus,ima,bbn,m2c}!spdcc!dyersl@van-bc.UUCP (pri=-10 Stuart Lynne) (04/18/88)
In article <871@spdcc.COM> dyer@spdcc.COM (Steve Dyer) writes: >I'm using a Telebit Trailblazer+ on one of my dialin ports, fixed at 19.2kb >using hardware flow control (gettydefs has EXTA and CTSFLOW defined). I'm >finding that effective UUCP throughput ranges between 80-100 bytes per second >when a UUCP neighbor without a Trailblazer dials in at 2400 baud, completely >negating any benefit of the neighbor's >1200 baud speed. The CTS light seems >to blink on every SD (send data) blink. People who dial in to this line at >2400 baud also report jerkiness (although this seems to be hidden and not >observable at 1200 baud.) > >Note we don't appear to be losing data; the low transfer rate isn't due to >retransmissions, but due to (excessive?) throttling of the output stream. > >Any ideas of what to try? I'm assuming that you are running on an IBM AT with SCO Xenix (as evidenced from cross posting and use of CTSFLOW). Do you have SCO's fix's for Telebit Support? Phone and ask for it if you don't. Why are you running with a fixed speed? SCO's software all seems to work very well using the auto baud feature. What I would think is happening is that you have turned hardware flow control on in the Telebit. When you do this and connect at slower speeds the Telebit seems to use CTS to regulate your dataflow down to the connect speed instead of bufferring it (which it will do if you just ignore CTS). SCO has implemented CTS flow control in their serial driver. But remember that CTS is not supported by the 8250/16450 Serial chip. It must be implemented higher up in the interrupt service routine. Meaning for every CTS state change you must service an interrupt, and do some work to get things stopped or started. This is very inefficent, you will see *two* state changes for every character you send. This increases your interrupt loading from 1 to 3 for each character sent. As an aside, here at home I *do* run with a fixed speed to solve other problems with my serial drivers and getty. I don't run into the same problem as seen here because the serial chip (8274) supports CTS directly. So even though I see the CTS light blinking madly away in tandem with the SD light it doesn't affect performance at all. I would suggest that you don't use hardware flow control unless you are connected in FAST mode. It does work well there. An alternate suggeston would be for Telebit to not worry about CTS for each character. Perhaps make it configurable, ATS??=n, where n is the number of characters to buffer before worrying about dropping CTS. -- {ihnp4!alberta!ubc-vision,uunet}!van-bc!Stuart.Lynne Vancouver,BC,604-937-7532
caf@omen.UUCP (Chuck Forsberg WA7KGX) (04/18/88)
In article <871@spdcc.COM> dyer@spdcc.COM (Steve Dyer) writes:
:I'm using a Telebit Trailblazer+ on one of my dialin ports, fixed at 19.2kb
:using hardware flow control (gettydefs has EXTA and CTSFLOW defined). I'm
:finding that effective UUCP throughput ranges between 80-100 bytes per second
:when a UUCP neighbor without a Trailblazer dials in at 2400 baud, completely
:negating any benefit of the neighbor's >1200 baud speed. The CTS light seems
:to blink on every SD (send data) blink. People who dial in to this line at
:2400 baud also report jerkiness (although this seems to be hidden and not
:observable at 1200 baud.)
:
:Note we don't appear to be losing data; the low transfer rate isn't due to
:retransmissions, but due to (excessive?) throttling of the output stream.
:
TeleGodzilla uses a TrailBlazer (not plus) with the current software ROMS.
For a brief period of time I had TeleGodzilla switch to 19200 bps and
enable flow control when an MNP connection was established at 1200 or
2400 bps. This had the same disappointing results as Steve has seen
with uucp.
Moral: With the current TB ROMS, It's OK to use flow control with PEP
but not MNP. A bit of a problem for UUCP, unless it's front ended
with Pro-YAM.
Chuck Forsberg WA7KGX ...!tektronix!reed!omen!caf
Author of YMODEM, ZMODEM, Professional-YAM, ZCOMM, and DSZ
Omen Technology Inc "The High Reliability Software"
17505-V NW Sauvie IS RD Portland OR 97231 503-621-3406
TeleGodzilla BBS: 621-3746 CIS: 70007,2304 Genie: CAF