Oracle Communications EAGLE (Software)
 

PLA-Support>Sun Systems>CommsGBU>Global Signaling Solutions>SN-SND: Tekelec Eagle 5
 

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Created from <SR 3-12817408961>

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Goal

Question 1 : Do you know how to determine the RTT of a association in STP ?
I found in the result of cmd="sctp -a" show:   "RTT between RMIN and RMAX inclusive = 22"
Does it mean that the RTT of this association is 22 ms. (i attached the log).

Question 2 : In Sigtran user guide document, it said:
"As a general rule, setting CWMIN to a value equal to half of the traffic rate in an RTT interval should allow adequate retransmit-recovery time while preventing excessive load to the peer.
CWMIN = (Bytes/Sec * RTT) / 2 bytes"
What is the traffic rate ? Does it mean the real traffic rate ?

Question 3 : Sigtran User Guide Page 94 said: Use the Weighted Average RTT for defining RMIN. So should i change RMIN of this assoc from 120 to 34 ?

Question 4 : Sigtran User Guide Page 93 said: RMAX can be set to the worst recorded RTT. So should i change RMAX of this assoc from 800 to 115.

Question 5 : For CWMIN, from the log we have the peak traffic of this association is 699 TPS = 699*150 = 104850 byte/s. (104850 * 0.034)/2 =1782 so we will not change CWMIN (default 3000).

Question 6 : What about bufsize, what is different between CWMIN and Bufsize? What value should I set for Bufsize ?

Solution

Q1. Do you know how to determine the RTT of a association in STP ? I found in the result of cmd="sctp -a" show:  RTT between RMIN and RMAX inclusive = 22
  Does it mean that the RTT of this association is 22 ms. (i attached the log).

Answer 1 : RTT is the Round Trip Time, this is to say the time measured from a transmitted packet until it receives its acknowledgement.

• The counter named "RTT between RMIN and RMAX inclusive" indicates the number of times the measured value for RTT exceeded the RMIN value (default value is120 ms) but did not exceed the RMAX value (default value is 800 ms).
• In your case the RTT exceeded the RMIN value 22 times. It means retransmissions occurred. Normally the RTT should not exceed the RMIN value. And indeed you can see retransmissions in your sctp -a output.
• You can also use the command pass:loc=xxxx:cmd="assocrtt " to get values on the measured RTT.
• Here is an output example, the maximum values exceeded the RMIN of 200, which is not good :

• You can also check the measurements to see the MAX values for RTT. The counter is named ASMAXRTO. The measurements are computed over the last 30 min.
  See below an example, the ASMAXRTO equals 120 ms which is the expected value so that the E5-ENET card can guarantee the TPS values.

Q2: In Sigtran user guide document, it said: "As a general rule, setting CWMIN to a value equal to half of the traffic rate in an RTT interval should allow adequate retransmit-recovery time while preventing excessive load to the peer.
CWMIN = (Bytes/Sec * RTT) / 2 bytes"
What is the traffic rate ? Does it mean the real traffic rate ?

Answer2 :

Yes the traffic rate is the real traffic in byte per sec. You need an analyzer to get this information.
The measurements can give you an average only as the values are computed over the last 30 min. You have counters about the number of received and transmitted octets : MOCTTRAN and MOCTRCVD.
here is an example :

• The CWMIN value is the minimum value in bytes to which the association will come back in case of congestion. This is the minimum value of bytes that Eagle can receive without any acknowledgment.
• When a packet is marked for retransmission the Congestion window (Cwind) is closed down to the CWMIN value.
• CWMIN can’t be set less than 3K and should not exceed the remote peer reception window (Advertised Reception window).
• Retransmissions will cause a temporary reduction in traffic throughput (CWMIN).
  
  

Q3 : Sigtran User Guide Page 94 said: Use the Weighted Average RTT for defining RMIN. So should i change RMIN of this assoc from 120 to 34 ?
Answer3 : You cannot consider having a good view of your network behavior with only one output for "assocrtt"; Normally an analysis of the quality of your network has to be done over a long period of time.
In your case the "Weighted Average RTT" is lower than 120 ms, so this is perfect you are sure not to have retranmissions. Don't change the value of RMIN, leave it at 120 ms.

Q4 : Sigtran User Guide Page 93 said: RMAX can be set to the worst recorded RTT. So should i change RMAX of this assoc from 800 to 115.
Answer4 : same as above. No, keep the value of 800 ms, you never know what can happen in the future on the network under particular conditions, it is good having some margin.
Your "assocrtt" output shows that you have a good quality as the RTT values are short. So you have plenty of margin, that would be sad to reduce them. There is no reason.

Q5 :For CWMIN, from the log we have the peak traffic of this association is 699 TPS = 699*150 = 104850 byte/s. (104850 * 0.034)/2 =1782 so we will not change CWMIN (default 3000).
Answer5 : No, don't change the CWMIN. Your rept-stat-iptps is made for a period of 30 sec.

Q6 : What about bufsize, what is different between CWMIN and Bufsize? What value should I set for Bufsize ?
Answer6 : The recommended value is 200k, so it is better not to change it except if you have particular conditions on your network showing that it is not a good value.

• The bufsize represents the maximum number of bytes that Eagle can store in case of need of retransmissions.
• The Cwmin window indicates the maximum number of bytes Eagle is accepting to receive without any acknowledgements, when we are in congestion conditions. This is a way to ask the far end to strongly reduce the packets it sends to the Eagle.
• When the congestion window CWIN is coming back to the CWMIN value, we say the window is closed.
• Under normal conditions (no congestion, no delay), the CWIN = BUFSIZE

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