Transcript Slides - Terena

QoS Evaluation Model for a
Campus-Wide Network:
an alternative approach
Juan Antonio Martínez ([email protected])
Comunicacions - Servei d’Informàtica
Universitat Autònoma de Barcelona
Index
Objectives
 Classical approach to QoS
 Evaluating network availability: a generic model
 Extending the model to the services
 Practical results
 Comparison to other existing products and future
work
 Conclusions

Objectives
Determine if our network reaches the ‘5 9s’
objective (99.999% of availability)
 Obtain a generic model to evaluate the quality
of the network regarding
 Infrastructure
 Services
 The model must
 Be simple
 Adapt easily to network topology changes

Obtaining the model
The classical approach



Quality is evaluated as a combination of:
 Delay
 Jitter
 Packet loss
This approach is useful for WAN links and environments
 Easy to measure in both router endpoints
In our opinion, it is not suitable for LAN environments
 Parameters are difficult to determine (distributed
environment)
 Gathered data is not significant (burst traffic)
Problems of this model



Quality is not assigned a numeric value
In a LAN environment
 Network probes must be distributed through the
network
 In switched environments, each segment
provides a different value
 Expensive to implement
 Fluctuant values due to the traffic nature
In fact, there is not a model. It is just an evaluation
of the aforesaid parameters
Our model:the basis



Whichever the system is, it must:
 Be of low cost.
 Provide QoS as a numerical value.
 Be flexible enough to adapt itself to network
topology changes.
Our idea is to get data from :
 Simple tools like ‘ping’
 SNMP queries
We discard complex solutions (modified TCP stacks,
proprietary PING...)
Conceptual development of the
model



Assume that all network devices are known and
with SNMP management facilities.
Assume that the number of users affected by any
network device failure can be determined.
The idea beyond the process is
 Choose the critical network devices
 Weight them accordingly
 Determine the instant availability
 Compute the mean value
Choosing the devices and the
weights for the model
MODEM 2M
TÈRMICA
G5
G6
100
Taller
10
Bib
Hum.
6x100
10
3x100
100
CORE BUILDER
SI0SWFO1
SI0SWFO2
FTISW
BIBHUM1SW1
34M atm
100
FTI
CNM
SI
10
GW
IIIA
IFAEGW
10
CED
10
RECSWIT
B
Nord
1X100
1X100
C
Nord
10
THICK
SWITCH-LLET
2x 1 0 0
IFAE
C7P1SW1
A
10
ANCCSWIT
ANCCSWIT01
DRETSWIT
B
Centre
Doct
100
IIIAGW
AN E L L A CI E NTÍ FIC A
VETSWIT
1X100
2x100
1X10
CVC
C
Centre
CRM
10
10
Vet
3x10
2X100
1X10
10
Pl.
Cívica
2x10
B
Sud
C
Sud
1x 1 0
10
SAF
Piscina
SAF
Poliesportiu THICK
ICM
10
Hotel
Campus
10 TP
Fundació
UAB
10
Escola
Turisme
TP
10
M0SWIT
Estabulari
Xalet
1X10
1X100
M
10
MODEM 2M
Vila
iemb
HOTEL
Arqueologia
3x10
hottwp1
10
10
C.I
hottwp3
10
cibibfo
IBF
10
10
CAMPUS
UAB
Dispensari
15-05-2000
Mathematical analysis (I)

Let
 Kd be the relative availability coefficient
 di be a binary value that tells whether a
segment is accessible or not

For the mean value this implies
Mathematical analysis (and II)

If we sample at constant intervals

For efficient computing, this means

In this way, we can evaluate the availability with
the number of samples, the previous mean value
and the last sample.
Extending the model to the
services
Our first goal is to determine whether the
service is working or not (ok/not ok)
 The explained network model is suitable for the
services with few changes :
 Omission of the criticity values (Kc=1)
 A tool to determine instant availability is
needed (ping is no longer valid)

Details regarding practical
implementation
Network availability





Availability is computed based on ICMP tests (ping)
Second-level granularity
To compute the coefficients
 Kc1 : from the network topology.
 Kc2 : from our experience.
The global coefficient is computed as the arithmetic
mean value
A config file stores the network devices that will be
tested
config file example
[NETWORK]
#ip_name
gw
CB
si0swfo1+si0swfo2
c7p1sw1
anccswit
m0swit
cvcsw
cibibfo
hottwp1+hottwp3
dretswit
ecllefo
bhum1sw1
ftisw
recswit
vetswit
ip_address
158.109.0.3
158.109.0.26
158.109.2.233
158.109.8.236
158.109.8.235
158.109.20.214
158.109.4.200
158.109.29.208
158.109.31.200
158.109.25.201
158.109.25.220
158.109.184.203
158.109.21.202
158.109.27.222
158.109.30.201
availability coef.
0.203125
0.213541667
0.052340183
0.051626712
0.056078767
0.045519406
0.034218037
0.036843607
0.0355879
0.050313927
0.048658676
0.042323059
0.03678653
0.052368721
0.040667808
Service availability



The model is essentially the same, but now for each
machine we analyse its critical services
The system can
 Evaluate proper function of a service at a given
time
 Compute the availability over time
A proprietary MIB is used to determine the critical
parameters of each service (SNMP queries are
supported)
Monitoring requirements
A set of ‘C’ programs (one for each service)
 A global configuration file:

[SERVICES]
#host name
cc.uab.es
news.uab.es
ftp.uab.es
...

services to be tested
smtp pop imap
nntp
ftp
Optionally, for the services :
 A proprietary MIB with the data we want to
monitor (not mandatory)
 A modified version of the snmpd daemon
Practical Results in our
Campus Network
Environment




Development :
 PC Pentium II 300 + Linux RedHat 6.0
 gcc 2.91.66
Production:
 Ultra Enterprise 450 + Solaris 2.6 (gcc 2.95.2)
 PC Pentium II 400 + Linux RedHat 6.0 (gcc
2.91.66)
Our network availability has achieved monthly values
between 0.99843 and 1.0
For the services, we use it both for availability values
and to test that they are working properly.
Overview of the system




A set of routines that verify that the services are
working properly:
 bootp,dhcp,dns,ftp,http,smtp,pop,imap,radius,nntp
A C program that implements the mathematical model
Configuration file, which includes
 Coefficients for the model
 Servers and services to be monitored.
Optionally, a modified version of the snmpd daemon if
access to the proprietary MIB is desired.
Measured availability data
Network Availability Data
100,000%
99,500%
99,000%
98,500%
98,000%
Abr00 Mai00 Jun00
Jul00 Ago00 Set00
Oct00 Nov00 Dec00 Gen01 Feb01 Mar01
Avail.Data 99,916 99,916 99,916 99,932 99,929 99,940 99,844 99,912 98,636 99,993 99,970 99,985
‘on line’ service monitoring
Based on the programs that are used to check
service availability
 Useful to network operators to detect
network problems
 Operating modes :
 Interactive: provides a report with
configurable debug
 Cron-based : generates mail/sms messages
if any problems are detected

Interactive execution example
*** 14:35:06.308612 blues.uab.es:smtp ...
220 blues Sendmail 5.65v4.0 (1.1.19.2/17Dec99-1023AM) Tue, 7 Nov 2000 13:44:20 +
QUIT
221 blues closing connection
*** 14:35:06.351857 blues.uab.es:smtp 116b,0.0432s,2.6Kb/s OK!
*** 14:35:06.360239 blues.uab.es:pop3 ...
+OK POP3 blues v7.63 server ready
QUIT
+OK Sayonara
*** 14:35:06.512647 blues.uab.es:pop3 49b,0.152s,0.31Kb/s OK!
*** 14:35:06.521040 blues.uab.es:imap ...
* OK blues IMAP4rev1 v12.261 server ready
A01 LOGOUT
* BYE blues IMAP4rev1 server terminating connection
A01 OK LOGOUT completed
*** 14:35:06.622567 blues.uab.es:imap 121b,0.102s,1.2Kb/s OK!
*** 14:35:06.631185 news.uab.es:nntp ...
200 news.cesca.es InterNetNews NNRP server INN 2.3.0 ready (posting ok).
QUIT
205 .
*** 14:35:06.884128 news.uab.es:nntp 81b,0.253s,0.31Kb/s OK!
*** 14:35:06.892686 ftp.uab.es:ftp ...
220 koala FTP server (Version wu-2.5.0(1) Wed Oct 20 12:02:15 DST 1999) ready.
Comparison to other existing
products and future work
Comparison
As a monitoring tool, there are other existing
products, which are really powerful
 Big Brother
 NoCoL
 Regarding the graphic tools, they generate
no data, but simply display it.
 None of these gives a detailed model for the
network availability or monthly reports

Future work
Analysis and integration of multiple meters
 Improvement of the Web interface
 WAP interface to the monitoring system

Conclusions
Benefits of the system





Proper working of all servers and services is easy and
centrally verified
Easy adaptation to network changes
 Network devices
 New servers or services
Monthly reports of both internal and external
connectivity
Availability reports of the relevant services
Easy to integrate with graphic tools such as MRTG
For more information...
This presentation:
 ftp://ftp.uab.es/pub/terena/QoS.ppt
 The paper can be found at:
 ftp://ftp.uab.es/pub/terena/QoS.pdf

Doubts, comments, suggestions...