Quality of Service Blog

Asterisk provides tool for reporting QoS.

It can be actived by adding fallowing rule to given context:

exten => h,1,Set(CDR(userfield)=${RTPAUDIOQOS})

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In that case all metrics would be added at the end of CDR file. Default it is Master.csv located at /var/log/asterisk/cdr-csv/

Added fields look like this:
ssrc=408070608;
themssrc=12192;
lp=0;
rxjitter=0.000581;
rxcount=376;
txjitter=0.000031;
txcount=399;
rlp=0;
rtt=0.000000

–

Explanation of fields could be found at http://wiki.kolmisoft.com :

• Our Receiver
  • ssrc – our synchronization source
  • rxcount – no. received packets/Received packets
  • lp – lost packets/Lost packets
  • rxjitter – our calculated jitter(rx)/Jitter

• Our Sender
  • themssrc – their synchronization source
  • txcount – transmitted packets/Sent packet
  • rlp – remote lost packets/Lost packets
  • txjitter – reported jitter of the other end/Jitter
  • rtt – round trip time/RTT

TRPR (TRace Plot Real-time) is a program which analyzes output from various sources and creates output suitable for plotting.

It can analyze output files from:

• tcpdump
• Network Simulator 2
• mgen

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TRPR is able to prepare IP QoS metrics such as:

• mean rate of packets stream
• differential interarrival packet delays
• transmission delay
• packet loss
• end other

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TRPR can distinguish each flow according to: source and destination IP, source and destination port, flow id and type of transmission (TCP or UDP).

Example:

./trpr latency drec input input.drc auto X,X,192.168.10.116/4000 output output.txt

• input.drc: output file from mgen
• 192.168.10.116/4000: destination IP and port which identifies flow
• output.txt: file ready for plotting
• information about other parameters can be found here.

–

What if I wanted to have mean values of metrics in given flow?

Linux awk tool can be used for providing metrics from output.txt.

First of all we have to remove from our file few lines from the beginning, which are used for plotting.

Awk script for getting mean value can look like (2nd column in our file is one with latencies):

BEGIN { FS = " "} {
allV = $2 + allV;
all = all+1;
} END {
mean = allV/all
print "Mean Latency: " mean
}

After executing:

awk -f script.awk output.txt

we should get mean delay of our flow.

What is important: source and destination MUST BE synchronized if metrics such as latency and interarrival time are important for us. It would be fine even if one of them would be source of time for another.

Multi Generator is one of  free traffic generators.  Current release is mgen 4.2b4. Source could be downloaded here. I installed it on fresh and default Centos 5.3 (2.6.18-128.el5) linux. In order  to work mgen properly, libstdc++.so.5 must be installed:

yum install libstdc++.so.5

and after according to manual:

tar -xvf src-mgen-4.2b6.tgz
cd mgen-4.2b6/unix/
make –f Makefile.linux mgen

and add directory to PATH:

export PATH=$PATH:/path/to/mgen-4.2b6/mgen

Mgen can sent and receive traffic. That’s why one host acts as sender and other as receiver

Now we can make a test:

Create script on sender side: test_input.mgn with:

0.0 ON 1 UDP DST 192.168.10.116/4000 PERIODIC [10.0 1024] TOS 0x10
10.0 OFF 1

It says that we send to 192.168.10.116 on port 4000 PERIODIC traffic. Each packet is 1024 bytes long and in one second 10 packets are sent. What is more, we set on each packet ToS = 0×10. Notice, that 1024B includes IP header. Mgen stops sending packets after 10s.

On receiver side mgen must listen on given port. In order to do this we create script test_listen.mgn:

LISTEN UDP 4000

Please remember to allow traffic to go through your firewall! Or simply type:

service iptables stop

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First we must start listening on receiver side:

mgen input test_listen.mgn output test_output.drc

In test_output.drc would be stored captured data for using with TRPR in order to provide QoS metrics.

Now we can start sending packets. We do it on sender side by:

mgen input test_input.mgn

After 10s mgen terminates itself and we can prepare other things with test_output.drc, which would be shown in next posts.

It is worth to read about other avaliable options in mgen. According to particular needs they might be very useful.

Recently I’ve installed the newest  Asterisk 1.6.2.6.  I dealt  with Asterisk few times in past but never focused on QoS capability. What I found interesting is that in sip.conf there are fields for setting ToS field (with default values provided):

• tos_sip=cs3   (SIP signalling messages)
• tos_audio=ef    (RTP audio)
• tos_video=af41    (RTP video)
• tos_text=af41    (RTP text)

Settings are also avaliable for other protocols:

Even those parameters are named ToS they actually set DSCP. It might be misleading, because ToS it is full byte, whilst DSCP is a 6-bits part of ToS field.

It is possible to set ToS using iptables. The pity is that only 5 values are valid: iptables -m tos -h

• Minimize-Delay 16 (0×10)
• Maximize-Throughput 8 (0×08)
• Maximize-Reliability 4 (0×04)
• Minimize-Cost 2 (0×02)
• Normal-Service 0 (0×00)

As you noticed, only one of 4 bits (11, 12, 13, 14) from ToS octet can be set Sample firewall rules:

iptables -t mangle -N mark-tos
iptables -t mangle -A OUTPUT -j mark-tos
iptables -t mangle -A mark-tos -p icmp -j TOS --set-tos 16

In example only icmp packets are marked. Setting ToS using iptables isn’t so useful as setting DSCP.

Below is example of setting two classes for:

• signaling
• media

It was created for SIP and H.323. There is many differences between them and it seems that SIP is becoming much more popular nowadays thanks to its simplicity.

Both have got signaling and media layer. Usually network ports that are used for these purposes are:

1.For SIP:

• signaling: TCP/UDP 5060, TCP 5061 (secure TCP)
• media: UDP, depends on configuration

2. For H.323

As example was based on Avaya solution in which there are Communication Manager and Gateway/Gatekeeper.

• signaling: TCP/UDP 1719, TCP/UDP 1720
• media: UDP, depends on configuration

For signaling we ascribed DSCP class CS4 , whilst for media EF.

Iptables should look more or less like this

—

MEDIA:

#out
iptables -t mangle -A mark-media -p udp -s $IP_1 -d $IP_2 --dport $RTP_RANGE -j DSCP --set-dscp-class ef
#in
iptables -t mangle -A mark-media -p udp -s $IP_2 -d $IP_1 --sport $RTP_RANGE -j DSCP --set-dscp-class ef
where:

IP_1 and IP_2 – IP’s ranges of endpoints

RTP_RANGE – UDP ports ranges for RTP

—

SIGNALING:

#out
iptables -t mangle -A mark-signaling-sip -p tcp -s $SIP_ENDPOINT_IP -d $SIP_GW_IP --dport 5060:5061 -j DSCP --set-dscp-class cs4
#in
iptables -t mangle -A mark-signaling-sip -p tcp -s $SIP_GW_IP --sport 5060:5061 -d $SIP_ENDPOINT_IP -j DSCP --set-dscp-class cs4

where:

SIP_ENDPOINT_IP – SIP endpoint

SIP_GW_IP – SIP Proxy/Registrar
#out
iptables -t mangle -A mark-signaling-h323 -p tcp -s $AVAYA_ENDPOINT_IP -d $AVAYA_CM_IP --dport 1719:1720 -j DSCP --set-dscp-class cs4
iptables -t mangle -A mark-signaling-h323 -p udp -s $AVAYA_ENDPOINT_IP -d $AVAYA_GW_IP --dport 1719:1720 -j DSCP --set-dscp-class cs4
#in
iptables -t mangle -A mark-signaling-h323 -p tcp -s $AVAYA_CM_IP --sport 1719:1720 -d $AVAYA_ENDPOINT_IP -j DSCP --set-dscp-class cs4
iptables -t mangle -A mark-signaling-h323 -p udp -s $AVAYA_GW_IP --sport 1719:1720 -d $AVAYA_ENDPOINT_IP -j DSCP --set-dscp-class cs4

where:

AVAYA_ENDPOINT_IP – H.323 endpoint

AVAYA_CM_IP – Avaya Comunication Manager

AVAYA_GW_IP – Avaya Gateway/H.323 Gatekeeper

In example we assumed that there is proper FILTER chain in iptables configured allowing transmission over above TCP/UDP ports

Chains: mark-media, mark-signaling-sip, mark-signaling-h323 should be added to PREROUTING chain in mangle table:

ptables -t mangle -A PREROUTING -j mark-signaling-sip
iptables -t mangle -A PREROUTING -j mark-signaling-h323
iptables -t mangle -A PREROUTING -j mark-media