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November 2007 | Volume 10/ Number 11
TMC Lab Review

IMS Testing Made Easy with Navtel Communications Inc

Navtel, a company around since 1976, offers a comprehensive IMS testing platform. Navtel is targeting their testing platform to advanced communications labs of the network operators and the development and QA labs of network equipment manufacturers. The Navtel platform is perfectly suited for testing IMS P/S/I-CSCF Session Border Controllers, IMS Border Gateway Functions (BGF), Application Servers such as IP Centrex and Presence Servers, and PacketCable Call Management Servers. Their flagship InterWatch product comes in two versions: a rack-mountable version and a portable version. Running on the Sun Solaris operating system, and leveraging hardware-based generation and analysis, the platform is the industry’s most scalable - it scales by simply adding modules to the chassis.

Navtel’s history is from the data world, coming from the days of ATM, Packet-over-Sonet and other high-speed interfaces. Navtel leveraged their strong in-house hardware developers and their experience in doing line-rate generation and analysis, and high-performance signaling testing when building their IMS test solution. Navtel built their solution from the ground up to ensure scalability and performance. Conversely, several competitors of Navtel use off-the-shelf Server blades, which limit the overall scalability and performance. Further, off-the-shelf Server blades are generic and aren’t designed specifically for testing while custom hardware can be designed with key test functions built-in. For example, when testing media you require line-rate media streams on a gigabyte pipe generating up to 28,000 to 30,000 simultaneous media streams on a single Ethernet port, performing quality analysis, delay/jitter analysis, and MOS score analysis. This is very difficult to do using off-the-shelf Server blades. Navtel on the other hand has custom FPGAs (Field Programmable Gate Arrays) and integrates the RTP generation capability and analysis inside the FPGAs.

Although Navtel’s platform offers numerous advantages for testing scalability and performance, its multi-user architecture has proven to be one its most popular features. Combined with Navtel’s software licensing model whereby the software is licensed by chassis, the InterWatch facilitates the cost-effective sharing of the chassis across multiple test beds, all conducting fully independent tests. This multi-user capability does not degrade performance because each user has independent hardware resources.

They only charge customers a single license fee for the entire chassis and you can execute tests as many times as you like as long as the hardware resources are available. Many competing solutions require a separate license fee each time you add a user and often it requires additional hardware, since the hardware is dedicated to an individual user. Navtel boldly claims, “In terms of capacity and scale, we have the lowest cost per end-point in the industry.”

Some of the comprehensive media test capabilities integrated with SIP, H.248 (BGF) and NCS include:

• QoS measurements for delay, loss, jitter & MOS with user defined thresholds.

• Call Records for each call that failed the path signalling and media tests.

• User-defined wave files and Packetization intervals.

• Negotiate and transmit several codecs simultaneously.

InterWatch currently supports TLS and IPsec and SRTP (Secure RTP) is under development. Navtel has recently released IMS AKA authentication, with and without IPsec, along with normal HTTP Digest authentication.

Protocols supported include SIP-over-TCP, UDP and with TLS/IPsec, H.248 with TISPAN extensions/packages over TCP and UDP, NCS, DQOS, and IPsec. The large capacity specifications are very impressive. It features up to 256,000 unique SIP or NCS (cable/MSO VoIP) subscribers, 374,000 unique endpoints for H.248 (IMS Border Gateway Function Testing - BGF), 128K Unique RTP streams for SIP and NCS, and 192,000 RTP streams for H.248 (BGF). Further, a single Navtel chassis can handle thousands of calls per second independent of protocol. The registration rate is very impressive, handling up to 1,000 registrations per second per port on a sustained basis. You can run up to 8 ports on a single chassis giving you up to 8,000 registrations per second per chassis, which Navtel claims is the fastest on the market.

Navtel can on-the-fly analyze and calculate the number of active calls, MOS/R-Factor scores, signaling statistics, and bandwidth utilization broken down by audio, video, DTMF, and signaling. You can also analyze the traffic by media type, such as G.729, AMR,H.263, H.264, G.711, G.721, G.726, G.723.1, and ILBC.

Ease of use is a big part of Navtel’s strategy. Unlike competing solutions which require writing complex testing scripts, Navtel has designed an easy-to-use user interface to configure your tests. TMC Labs was very impressed with the user interface and how a lot of the complexity was abstracted from the user (see Figure 1). Navtel commented, “When we look at the competitors, we can talk about scale, we can talk about performance, but at the end of the day our customers will not be able to leverage the scale and performance if they cannot use the tool.” They added, “During an evaluation, within an hour of being on site and hooking up the platform, we want to hand over our test solution to our customers to drive the evaluation.”

Navtel helps you to minimize the number of components needed to test IMS applications. InterWatch can simulate the subscribers plus the edge and core network elements. Unlike many solutions that require separate components, Navtel creates a single application that can simulate the entire IMS cloud, including subscribers, the edge, and more. This allows you to, for example, isolate specific components such as the P-CSCF (Proxy-Call Session Control Function) while simulating end user equipment from a single platform. Further, since the entire IMS architecture is contained within the Navtel platform, this grants you the ability to easily correlate statistics amongst the entire IMS cloud and drill-down and isolate issues. The promise that IMS holds is not just SIP calling, but also instant messaging, advanced applications, and more. Well, Navtel’s flexibility lets you simulate presence, instant messages, call forward, call hold, and more on a large scale.

You can also easily create conditional branching call flows from the tool for advanced functionality.

The testing tool lets you simulate real-world scenarios by specifying what percentage of the calls actually get through (connect), receive a busy, no answer (keeps ringing), are call drops, or some error. You can even send corrupted SIP messages to test what would happen. TMC Labs knows that one misbehaving SIP phone can crash your network, so the ability to send a corrupted SIP message is a nice feature.

Most importantly, using this tool you can measure response times for just about anything. While it comes by default with the ability to measure the network response time to various SIP requests such as registration (Registration to 200 OK), it also lets you define your own custom KPI (Key Performance Indicator) points. Using the graphical call flow tool you simply highlight the starting SIP message and the ending SIP message and it will automatically calculate the minimum, average and maximum response latency in real time. So, for example, you can create a KPI that measures the time from the SIP invite to the 180 ringing message (see Figure 2). It is important to note that Navtel uses hardware-based measurements. Software-based timestamp calculators are inaccurate, especially when under load. Navtel’s hardware-based FPGAs are accurate up to 40ns (nanoseconds) and are unaffected by heavy load.

Sample Test Scenario

From a single user interface you can for example configure it to run 100 registrations per second on all the endpoints, generate 10 simultaneous calls per second, with 50% of calls as basic calls and 50% of calls placed on-hold. At same time, you can generate floods, such as 50% of floods are invites, 25% are BYEs, and 25% registration and at the same time have users subscribing and publishing information.

You can also configure it such that 50% of the calls get responded to normally, 10% of calls get responded to with a busy message, 10% of the calls get responded to with PRACK, 10% of the calls will be declined, 10% of the calls will not be answered and 10% of the calls will be responded to with a user-defined error. Detailed statistics are provided for each scenario and flow so that you can track in real-time the exact behavior of the network.

Hacker and Theft of Service Testing

Another scenario that you can easily test with this tool is what happens when the SIP registration expires. This is a critical test for any IMS network which requires stringent authentication and security. Just after the registration expires you can test whether the end point can still make a call or access any service on the IMS network. Similarly, you can negotiate one codec but generate media with another type with higher bandwidth to test the Theft of Service Protection for the devices under test.

You can set when you want to start as well as stop media during any part of the call. The stop media feature is critical because if you look at the key functions for the border gateways and session border controllers in the IMS network, one of their roles is to open signaling pinholes and then close them when the calls are terminated. So what happens when they open them, but don’t close them? You then have signaling pinholes that could be exploited by hackers. The tool allows you to continue to generate media even after call termination and it can detect on the receiving side whether media was received and for how long after the call was terminated, so as to verify that media pinholes are closed after calls are terminated.


One of the key advantages of InterWatch is that, with just a few simple clicks, you can initiate very complex tests. Further, Navtel claims to have the industry’s highest number of emulated subscribers/endpoints, highest call and registration rates, and highest number of RTP streams per single chassis, making it the most scalable IMS testing platform on the market today. Perhaps just as important, or even more so, the user interface is easy to navigate, making it easy to configure tests without the learning curve of complex scripts. The InterWatch platform is feature-complete - we couldn’t think of any feature lacking in this system. IT

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