MOBILE TEST AND MONITORING - Mastering the tools
Test and monitoring has transitioned from being a ‘necessary evil' to maintain the 
network, into a key business enabler, according to Michele Campriani, allowing operators to rapidly expand their service portfolios and at the same time reduce operating expenses
The race is on as mobile operators across the globe accelerate their migration path to mobile data services. This rush stems from explosive customer demand for web-based services, the opportunity to capture increased average revenue per user (ARPU) while reducing operating expenses, as well as the desire to stay one step ahead of the competition. Most industry insiders agree - in the not-so-distant future, it will be rich mobile services such as videoconferencing, mobile gaming and presence that will set mobile operators apart.
As the technical early adopters have experienced, however, the transition to converged networks supporting mobile data services presents complicated challenges. At the heart of the problem lies the fact that most of the time, IP and PSTN-based services are operating in parallel during the convergence phase. While the operator may well understand how to measure service quality and SLAs on legacy traffic, new IP-based services are much different, and require vastly different monitoring techniques and service quality measurements.
Hence this new world of mobile data services has greatly expanded the role of network troubleshooting and monitoring tools. In essence, they have transitioned from being a ‘necessary evil' to maintain the network, to a key business enabler, allowing operators to rapidly expand their service portfolios and at the same time reduce operating expenses. As the nature of networks and services has evolved, so have these tools. In the sections below, we take a closer look at how a mobile operator can most effectively utilize protocol analysis and network monitoring tools to successfully launch and manage mobile data services.
New access technologies such as 3G/UMTS and 3.5G/HSPA have finally provided the cost-effective ‘edge' bandwidth required to offer mobile data services. For the operator, once these services are offered, they will likely experience a burst in network usage driven by adoption of the new services, as well as porting legacy traffic over the new infrastructure.
At this point, the core of the mobile network is one of the most vulnerable areas. This is due to the fact that the core network is typically tailored to access network bandwidth... so as the operator migrates from GSM to UMTS to HSPA, for example, it will amplify core infrastructure weaknesses.
It is critical at this point that the operator be able to correlate and monitor all activity occurring over network elements interconnected through various protocols and interfaces. The operator must simultaneously correlate information exchanged by each device involved in transactions, including those on the internal signaling network as well as external connections for calls made to/from subscribers of other operators.
The complexity lies in the fact that there are many signaling exchanges and interfaces involved during data transactions, each giving a different level of visibility into network and service issues. For example, in a UMTS network, the Gn interface is the most crucial in providing overall visibility into the network (eg for ‘macro' problems and issues related to authentication with external networks), while the Gi interface provides information on the quality of IP traffic and services. So unless the Gn and Gi interfaces are correlated, there is no way to test the interconnection between the operator data network and the external data network (e.g. the Internet).
Thus managing each of these interfaces, as well as all of the traffic traversing them becomes of high importance for high-quality mobile data services. This type of monitoring is easily provided by a new breed of distributed monitoring system. Here are example interface correlations, and the key information they provide:
- Gn/Gi - to check the interconnection between the operator data network and the external data network for snapshot of state of services. After the Gn/Gi correlation, monitoring either the Gb or the IuPS helps triangulate on location of problem
- Iu/Gn/Gi - comprehensive view of both the core and access network signaling messages of a 3G / 3.5G data session (PDP context)
- Gb/Gr - to decrypt signaling messages of a data session over the Gb
- Iu/Gr - to analyze the data session activation and authentication phases
Compared with voice services, mobile data services require vastly different monitoring and troubleshooting techniques. For legacy voice, it is generally assumed that if the network has high QoS, service quality is good. For data services, this is no longer true. This is due to the fact that most mobile data services are UDP/IP and TCP/IP-based, with many of them being high-bandwidth and interactive, hence highly affected by packet loss, TCP resets/latency and application-layer issues such as DNS and HTTP anomalies.
Thus for data services, understanding the service actually experienced by the end user (or "quality of experience" -QoE-), now becomes the important metric. Unfortunately, QoE cannot be provided by usual network node element metrics and tests. Here are basic measurement guidelines for the major mobile data service types.
- Background services such as web, FTP and e-mail are not time-sensitive, so delay and jitter are not a big issue. More important for these services is throughput per call, traffic per call and packet loss.
- Streaming services such as webcasting and video viewing are much more real-time sensitive. For these services, delay-related measurements such as jitter and delay are most important.
- Conversational services such as video calls and mobile gaming must be based on all of the above... throughput, packet loss, jitter and delay.
- Thus the operator must now integrate more measurement types, and know how each affects the other.
As an example of these new measurements, the screenshot in Figure 2 shows a few key TCP user-plane statistics that can be used at either a summary level, or in a drill-down level to assess how TCP resets and TCP delay times are affecting services. TCP is a very important protocol-under-monitor for mobile data services as it most directly affects service responsiveness once a service link had been established.
Perhaps the most important element of service monitoring and troubleshooting lies in understanding what is happening at the application layer. After all, it is protocols such as DNS and HTTP that ultimately determine service availability. In Figure 3, we see a summary-level view of DNS response codes over selected set of records. In this example, we see clearly that we must drill down further and investigate the cause of the DNS name failures to achieve high service availability. Other DNS-related information we might want to investigate are average DNS response times, top DNS addresses and occurrences and DNS query types (host, mail, domain name, etc). This measurement and the one above are only a small sampling of new measurements that must be learned.
In summary, while the lure of competitive differentiation, OPEX reduction and increased ARPU are driving operators towards mobile data services, there are significant challenges that must be overcome for successful introduction. At the most basic level, the operator must integrate a multitude of new measurements and network monitoring techniques that provide insights into the IP-based services. The good news is that significant advancements have been made in capabilities of network monitoring and protocol analysis systems. Mastery of these new tools is critical for the operator hoping to introduce and manage multimedia mobile data services.
Michele Campriani is General Manager of Sunrise Telecom's Protocol Product Group. www.sunrisetelecom.com
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