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SLAC QBSS Testbed
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Differentiated Services (DiffServ) are cited in terms of increasing
performance by labelling packets with "expedited forwarding
(forward me first)" and "assured forwarding (drop me last)".
However, IEPM is leading the way in making use of the QBone Scavenger
Service (qbss), where DiffServ is used to provide less than best effort.
Huge data transfer will be trickled across the network and will
back down whenever other applications need the bandwidth.
Data trasfer tools
There are two tools we can now use to transport data over the Wide
Area Network with packets marked for QBone Scavanger Services:
bbftp
bbftp is a software designed to quickly transfer files accross
a wide area network. It has been written for the babar experiment in
order to transfer big files (more than 2 GigaBytes). To perform our
test we have introduced one extra-option, that allows for packets to
be marked for QBSS.
bbcp
bbcp is a tool developed at SLAC by Andy Hanushevsky to
"securily and quickly" copy data from source to destination. The
application has been officially patched to allow packets' marking for QBSS;
this means setting the TOS (type of service) of the packets to be 0x20.
The user can mark packets for QBSS using one of the application
options:
bbcp -q tos-value .....
Cisco 7200
The following is the layout of the first QBSS test bed we created at SLAC.
We have two Cisco 7200 back to back, connected via a 10/full ethernet
connection, this allows us to easily congest this link and to measure
the perfomances of the variuos traffic types.
Router configuration
The configuration of the router consists of:
- defining the type of traffic(i.e: QBSS, priority);
- defining the policy that will be applied to
each class of traffic (i.e= guaranteed bandwidth) ;
- applying the policy to the interfaces through which the traffic is going to flow.
This is accomplished in the router with the following commands:
class-map match-all qbss
match ip dscp 8
class-map match-all hi-priority
match ip dscp 10
policy-map qos-policy
class qbss
bandwidth percent 1
random-detect
class hi-priority
bandwidth percent 30
random-detect
class class-default
bandwidth percent 69
random-detect
interface ...
service-policy output qos-policy
Cisco 6509 SUP2/MSFC2
The following is the layout of the second QBSS test bed that we built
using Cisco 6509 with SUP2/MSFC2 configuration:
The two switches are connected together using a 100 mbps line and they
connect to the rest of SLAC and to the test network with a Gigabit
line.
The MSFC2s have only virtual interfaces, the routing is
performed by the PFC2 (Policy Feature Cards) on the switch, and
traffic policing can be achieved configuring QoS (Quality of Service)
on the switch ports.
Our bottleneck is a 100mbps line, of type 2q2t: this means
we can define two queues, with two threshold each. The thresholds
indicate the level of congestion that triggers drop of
traffic. Traffic with different DSCP (Differentiated Services Code
Point) can be assigned to the any of the two queues and to one of the
two threshold.
Given there are only two queues available, we have assigned the QBSS
to a queue by itself, and the Priority and the Best Effort traffic to
the second queue.
The QBSS queue gets assigned a 5% of the total bandwidth available and
the rest is assigned to the second queue.
At this point we can use
policing to limit the Priority traffic to get 30% of the bandwidth.
The configuration we have implemented is the following:
set qos
enable(enable Qos)
set qos dcsp-cos-map
8:1(map QBSS to COS 1)
set qos dcsp-cos-map
10:7(map priority traffic to Cos 7)
set qos wrr 2q2t 255
5(define the bandwidth for each queue)
set qos map 2q2t tx 1 2 cos
0(map cos 0 [Best Effort] to queue 1 threshold 2)
set qos map 2q2t tx 2 2 cos
1(map cos 1 [QBSS] to queue 2 threshold 2)
set qos map 2q2t tx 1 2 cos
7(map cos 7 [Priority] to queue 2 threshold 2)
set qos policer aggregate
policer1 rate 30000 policed-dscp erate 30000 drop burst
3200(define a policer for limiting priority traffic)
set qos acl ip acl1 trust-dscp
aggregate policer1 ip any any dscp-field 10(define ACL
to select priority traffic and police it with the previusly defined policer)
Revised September 21, 2001.
URL:
http://www-iepm.slac.stanford.edu/monitoring/qbss/qbss.html
Comments to
iepm-l@slac.stanford.edu