Side_1_360

It is important to emphasize that all observations
indicate that it is the processor capacity that lim-
its the packet rate (pps) generated from a single
instance of the GenSyn process. Increasing the
packet size, constrained by the socket buffer
size, or the interface card, can increase the bit
rate generated. In the case of VoIP in (c), the pps
is plotted for different numbers of users for two
models of an 8 kbit/s voice channel. In the first
case, 10 byte packets sent every 10 ms, it is
observed that the GenSyn process reaches its
limit at approx. 8500 pps (2.5 Mbit/s incl. 28
bytes overhead) with 3000 users on one
machine. The similar observations for the sec-
ond case where 100 byte packets are sent 100 ms
apart, the limit is 2400 pps (2.4 Mbit/s incl. 28
bytes overhead) with 8000 users. The processor
capacity is the critical constraint. The exact
number of users specifying the knee point is
dependent on the hardware the GenSyn process
is running on.

It is observed that the activity rate in the finite
state machine (the number of state transitions

Figure 14 The constraints of a GenSyn process generating UDP packets from a single machine

0

Users

12000

10000

8000

6000

4000

2000

0

pps

500 1000 1500 2000 2500 3000

100

80

60

40

20

0

Mbit/s

observed

unconstrained

0

Users

12000

10000

8000

6000

4000

2000

0

pps

500 1000 1500 2000 2500 3000

100

80

60

40

20

0

observed Mbit/s

unconstrained

0

Users

24000

20000

16000

12000

8000

4000

0

pps

2000 4000 6000 8000

7 6 5 4 3 2 1 0

observed Mbit/s

unconstrained

• interpacket time = 10 ms


• UDP packet size = 10 bytes

0

Users

7000

6000

5000

4000

3000

2000

1000

0

pps

3000 6000 9000 15000

7 6 5 4 3 2 1 0

Mbit/s

observed

unconstrained

• interpacket time = 100 ms


• UDP packet size = 100 bytes

12000

(a) Constant bit rate source

• UDP packet size = 1024 bytes
  
  
  • Interpacket time = 125 ms
  
  
  
  


• Interface rate = 100 Mbit/s

(b) Variable video source (MPEG)

• UDP packet size = 1024 bytes


• Average frame size = 2.7 UDP packets


• Interframe time = 40 ms


• Interface rate = 100 Mbit/s

(c) Voice over IP source

• Interface rate = 100 Mbit/s

per time) influences the packet generation effi-

ciency. For example by decreasing the activity

rate in a two state CBR model by a factor of ten,

the packet rate constraint for a large number of

users was increased from 3000 to 4500 packets

per second.

Summing up, the major constraints while run-

ning a UDP model are

• The handling of simultaneous threads;


• Processing time for managing the dynamics
  of the finite state machine.

3 A Distributed Test Platform

GenSyn is currently being used for QoS perfor-

mance testing in an experimental, IP based com-

munication platform that will provide differenti-

ated services. To test its QoS mechanisms, a

controllable, and reproducible, mixture of traffic

streams with different characteristics is essential.

This traffic mixture is generated by GenSyn

using the source models currently available and