[Sis-SCPS-INTEREST] SCPS data rate anomalies: please explain??

[Feighery, Patrick D.]

>From your description, obtaining 85+ percent of the bandwidth, assuming
all of the bandwidth is dedicated to you, should be quite possible.

First let's talk about bandwidth.

If you are using pure rate control over the WAN environment (which you
are) then the rate control parameter BIF_RATE contains the rate which
SCPS will try and push out date over the interface. This assumes it has
data to be send and buffer sizes do not further constrains data flow.
Therefore in each of your examples you are overdriving the link.  Also
be aware that SCPS in TAP mode makes the assumption (good or bad) that
ethernet frames will be the data link layer.  I've also make the
assumption that the pre-amble is not going over the RF.  Therefore we
can probably set the rate control to 3 Mbps

Now for buffer sizes.

In general you need to set the buffer sized to 1 to 2 times the
bandwidth delay product.  Lets assume bandwidth is 3 Mbps and RTT delay
is 550 msec, therefore buffer sizes on the WAN side should be at least
206250 bytes and probably no more that 412500 bytes.  For a first try
use 412500 bytes.

Now I am looking at you rfile and, well that is exactly what you
have.... However you have commented out AIF_TAP_NAME AND BIF_TAP_NAME.
They are required and used for internal scps processing. Uncomment-out
those and you should get what you are expecting.   Let me know....

	Pat

>>-----Original Message-----
>>From: sis-scps-interest-bounces at mailman.ccsds.org 
>>[mailto:sis-scps-interest-bounces at mailman.ccsds.org] On 
>>Behalf Of Dan Miller
>>Sent: Friday, May 05, 2006 1:53 PM
>>To: SCPS mailing list
>>Subject: [Sis-SCPS-INTEREST] SCPS data rate anomalies: please 
>>explain??
>>
>>Okay, now that I've gotten rid of the collisions, I can finally start

>>evaluating this system.  I'm seeing several odd things that 
>>I'm hoping 
>>someone can clarify for me.  I started out with the rfile that I'll 
>>include at the end of this message.
>>
>>My satellite connection is 3072000 bits/second in each direction. 
>>I have 550 msec RT delay (via an external hardware satellite 
>>simulator).
>>Theoretical max thruput thus is 384KB/sec (assuming no data
overhead).
>>My target thruput is roughly 85% (~330KB/sec) based on past 
>>experience 
>>with other systems.
>>
>>So originally I configured both gateways as shown below.  However, I 
>>wasn't seeing what I expected to see:
>>
>>    * My data throughput with these settings was very low
>>    * Consistency is terrible!!  Data rates not only are low, 
>>they vary
>>      all over the place
>>
>>I base my expectations on two measures: 
>>1. What do I see with the same hardware, no tcp acceleration, 
>>and no RT 
>>delay.  This gives me a measure of the capabilities of the linux 
>>drivers, our drivers, and our hardware.
>>2. We previously used a proprietary tcp acceleration package which we

>>are trying to get away from. 
>>
>>In both of these cases we see very high consistency; basically, 
>>variations in data rate are in the third significant digit 
>>across many 
>>runs.  Case 1 gives over 88% Max, case 2 gives 82% to 88% 
>>depending on 
>>configuration, but any given configuration is very consistent.
>>
>>Anyway, to try to improve my throughput, I've been playing 
>>with BIF_RATE 
>>and BIF_BUF;
>>(all thruputs in KBytes/second)
>>
>>BIF_RATE      BIF_BUF      min thruput      max thruput
>>========      ========      ========      =========
>>4096000         422400            170                  230
>>8000000         600000            270                  320
>>8000000         800000            290                  340
>>
>>I had tried some intermediate rates and buffer sizes that I don't 
>>remember numbers for, but they were in between the results I 
>>show here.  
>>You can see that with my current settings I'm getting up to the rates

>>that I'm expecting, but the variation suggests to me that I 
>>still have 
>>something wrong.  Also, the rate/buffers that I'm specifying 
>>have *no* 
>>correlation to real data, which is a problem if I need to 
>>configure for 
>>different settings...
>>
>>Can anyone shed light on any of this??
>>
>>Dan Miller
>>
>>
>># GW Resource File - comments are allowed, starting with '#'.
>>#    Comments can be anywhere EXCEPT between parameter values.
>>
>># interface A info
>>AIF_NAME    eth0
>>AIF_RATE    100000000
>>AIF_BUF        32768
>>AIF_CC        1
>>AIF_TCPONLY    1
>>AIF_MTU     1500
>>#AIF_TAP_NAME    tap0
>>
>># interface B info
>>BIF_NAME     eth1
>>BIF_RATE     3072000
>>BIF_BUF     422400
>>BIF_CC         0
>>BIF_MINRTO     600000
>>#BIF_TAP_NAME    tap1
>>
>>
>># IPFW info
>>C_DIVPORT    52000     
>>C_TAP_REMOTE_ACCESS 1
>>
>>
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