Any network will have its share of degradation, whether it is delay,
jitter, packet loss, duplication of packets, or other impairments, so it is
imperative that real time applications running over IP be tested in a lab
setting with these impairments in place and modifiable. In this way,
evaluators can assess how certain products work under certain emulated
conditions in a controllable testing environment instead of relying on
guesswork or happenstance.
PacketStorm offers two IP network emulators: The 1800E and 2600E, which
have very similar functionality and in only differ in scope -- the 2600E
would be preferred for larger or more heavily trafficked networks. For our
purposes, we find no reason to differentiate the two, so we will refer to
the emulators as the PacketStorm 1800E/2600E.
The PacketStorm 1800E/2600E can emulate many applications over the
network, including VoIP, IP conferencing, cable telephony, VPN, QoS, Diff
Serv, and wireless IP, employing one user-friendly interface. In addition,
the emulators contain network capture and replay capabilities to analyze and
report on delays and packet loss percentages on an IP network, can be
accessed remotely through any browser, and can support multiple kinds of
network interfaces -- 10/100 base-T Ethernet, GigE, T1/E1, DS3, E3, OC-3,
Generally, documentation is important when using any communications product,
but for learning testing equipment, this is especially true. There is often
important functionality that users would have difficulty applying or even
finding without manuals and help files. PacketStormï¿½s IP Network Emulator
Operations Manual is very detailed and has an excellent table of contents.
Users looking for specific information about impairments, modifiers, and
other functionality can certainly find it here. However, help files are
limited on the GUI itself. Context sensitive help files would be
particularly effective when users are attempting to understand what each
attribute does specifically. For a more complete understanding of how to set
up entire applications, there should be many examples of frequently used
scenarios available to peruse on screen.
There are only a few testing products that address the need to emulate
specific network conditions. The PacketStorm 1800E/2600E does so, as does
the Cloud from Shunra Software and EMIP-1 from CC&T Technologies, which
were both reviewed in the August 1999 issue. The following is a list of the
more distinctive features of the PacketStorm 1800E/2600E:
- Multiple interfaces: 10/100, GigE, T1/E1, DS3, E3, OC-3, and OC-12.
- Unit can be invisible to the network (bridging mode) or be seen as a
network device (routing mode) with each port being assigned an IP
address and doing ARPs with its neighbor.
- Modifiers allow users to insert values into various IP header fields,
such as for the source address, destination address, or for network
- Dynamic emulation with a toggle feature includes packet counters and
timers, thus impairments can be time varying.
- ToS and Diff Serv emulation provides impairments for each ToS (5
levels) or DSCP value/level (64 levels).
- Nine network queues emulate traffic conditions at the edge of the
network, including Weighted Fair Queuing and Random Early Detection.
- The Accumulate & Burst impairment allows a number of packets to
accumulate before they burst out; an inter-burst gap time can also be
specified to create bursty traffic typically found on the Internet.
- GUI allows independent order of impairments; for example, doing a
fragment before or after a re-order will produce different results.
After familiarizing ourselves with the graphical interface, which has a ï¿½click
and drop,ï¿½ ï¿½connect the boxesï¿½ feel to it, we were ready to attempt
simple VoIP emulation tests. First, we needed to call from one VoIP product
to another through a PacketStorm 1800E/2600E (we had both emulators in our
lab at different times during our testing). We then chose between routing an
Ethernet bridge mode. We went with the bridge mode because we decided to use
the Siemens optiPoint 100 advance IP phones that were reviewed for the
January issue of Internet Telephonyï¿½. Routing mode is an attractive
alternative if users want to use other interfaces, such as T1, E1, or OC-12,
but it does involve extra network configuration.
We connected one of the Siemens IP phones to a hub on our network with a
regular Ethernet cable running to one of the ports in the back of the
PacketStorm 1800E/2600E. The other phone was connected directly to the box
using a crossover Ethernet cable and designated an unfamiliar static IP
address so that the phone would work on its own tiny network. In this way,
the PacketStorm 1800E/2600E acted as if it were the Internet or intranet,
allowing the packets from the VoIP calls to pass through. After connecting
the cables, we looked for the green lights that indicated that the emulator
saw the IP phones. At first, the only green signal showing was the power
source light, but that was rectified when we awakened the emulator by auto
running each port from the port configuration setting, in effect registering
the IP phones to the emulator.
From there, we created a new emulation script on the GUI. We placed two
bi-directional end points down on the screen. These end points allow packets
to run from the source to the destination in either direction. Then, we
double-clicked on one of the bi-directional end point icons, entered the IP
address of one of the Siemens IP phones in the Start Address field, and
selected the correct port of the PacketStorm 1800E/2600E that the phone was
connected to. We did the same when configuring the other end point, except
we used the information intrinsic to the second IP phone.
Afterwards, we set up one of the simplest tests possible. We added delay
as the only impairment affecting the VoIP calls but set it for a minor 10ms
delay. We called from one Siemens IP phone to the other, and started the
test. The Packet Flow indicator changed from red to green, signifying that
the application was running. As expected, we could hear very little delay in
the conversation. After setting the delay for a whopping 1,000ms, the
conversation slowed up considerably because it took approximately one second
for the recipient of the dialogue to hear what was being said. Without a
doubt, this showed that the PacketStorm 1800E/2600E was indeed emulating the
delay impairment. We then added other impairments into the script, such as
jitter and burst drops, and began hearing these impairments in our phone
conversation. As we increased the degradation of each impairment, we
noticeably heard it in our conversation. For example, if we set the jitter
impairment high, we would hear a shaky, uneven voice on the line. If we set
the burst drop impairment high, we would have trouble hearing the
conversation or some words would be lost even when listening intently. In
this way, the PacketStorm 1800E/2600E accurately emulates what would happen
under adverse conditions on a VoIP network.
Thus far, we had only tested our applications on the PacketStorm server,
so we decided to access the GUI remotely from a Windows 2000 client on our
network. We set up the Control Port parameters, which included specifying
the serverï¿½s IP address, and enabled the GUI to be browser accessible. We
then entered the serverï¿½s IP address, which immediately downloaded the
Java application we needed to run the GUI remotely. After putting in the
assigned password, the GUI came up and appeared as if we had directly
accessed it. Upon further examination of the Web version of the GUI, we
found it a little slower, and it did freeze up on occasion. However, it was
easily accessible and was usually very serviceable.
The bottom line for the PacketStorm 1800E/2600E is that a plethora of IP
network applications can be emulated so that labs and MIS departments can
receive an accurate assessment of what might happen under certain network
conditions, making the system a very valuable testing tool. The software
installation was so simple that it was not even worth detailing in this
review. While not perfect, the GUI was intuitive, could be accessed
remotely, and did not have a large learning curve associated with it,
although help files would have been nice for learning more advanced scripts.
Also, a simulation of the packet flow would have made the more complex
applications easier to understand and therefore create. Overall though, both
the PacketStorm 1800E and PacketStorm 2600E are highly recommended, mainly
because of their outstanding set of features.
To The February 2002 Table Of Contents ]