Contents Telektronikk - Telenor

152
δ τ
Figure 8 Deterministic introduction of CDV
Connection 1
Connection 2
Connection N
δ τ
Resulting Cell Stream
• • • • • •
Figure 9 Test traffic with deterministic CDV introduced
more, prior to entrance in the analyser we
need the UPC algorithm to test that conforming
cells are not lost.
This is a very complicated task, and
instead we suggest the following much
simpler alternative outlined in the following
sections.
It should be noted that the following description
applies to the Ericsson policing
algorithm which in the strict sense is not
a peak cell rate (PCR) scheme, alhough
the algorithm implemented does in fact
satisfy all of the criteria set by the network
operators which are using the system.
If a strict PCR mechanism is to be
tested then the clusters of cells should be
reduced to two.
2.5.1 Testing of CDV for a single
connection
Let the test traffic be deterministic traffic
constructed in the following manner:
Consider initially a CBR cell stream with
interarrival time T between cells (upper
•
•
•
line in 8). Since the CDV tolerance is d,
take now the first cell and delay it by the
allowed amount d. Since cell sequence
integrity must be maintained also the
� �
δ
next cells must be delayed, and delay
T
� �
δ
them just so much that
T
+ 1 cells are
� �
δ
coming back to back. Let cell no.
T
+ 2
� �
δ
have no delay but at cell no. + 3
T
you start to repeat the whole procedure.
Thereby a periodic sequence (the lower
one at the figure) is generated which can
be programmed into the HP traffic generator.
In the UPC algorithm of the switching
system the leak rate should be set such
that it exactly decrements a single cell
arrival to zero in T time units. The
threshold value should be put to
� �
δ
2 + in accordance with the
T
argument given in [2].
2.5.2 Testing of CDV at the STM-1
rate
To generate a CDV of 300 µs (which was
the network operator requirement) it has
been explained that bursts of 3 and 3
cells for a single connection must be sent
from the traffic generator.
In order to reduce the time necessary to
perform these tests involving CDV limitations,
either a single connection of sufficiently
high bandwidth must be involved
in the measurement, or several connections
which together have the desired
bandwidth must be measured upon.
Obviously, there is an upper limit to the
bandwidth of a single connection which
may be measured with the appropriate
CDV introduced. Therefore the latter of
these two measurements is seen to be
simpler to achieve using the available
traffic generator and should reduce the
test period.
A graphical representation of this idea is
presented in Figure 9.
The above traffic can be generated using
a memory based traffic generator such as
the Hewlett Packard Broadband Test
Equipment.
3 Test results
Before the performance measurements
outlined in this report were made, requirements
for the various values were
given by some network operators. At
least one network operator presented the
following requirements:
- The CLR should be less than 10 –10
measured over a 12 hour period.
- The CER should be less than 5 x 10 –10
measured over a 12 hour period.
- The CMR should be less than 10 –13 .
(For practical reasons it was stated that
only one misinserted cell was allowed
to be recorded during a measurement
period of 12 hours.)
- The average CTD was to be less than
250 usec.
- The CDV was to be less than 300 usec
with a probability of 1 – 10 –10 .