Traffic Control

Sep 15, 2001 12:00 PM, By Chuck Stormon

Real-time traffic management for SS7 networks allows carriers better use of network data.

Carriers are experiencing tremendous subscriber growth and anticipating broad acceptance of enhanced digital services, which places a burden on virtually all infrastructure components, especially the SS7 network. This has created demand for real-time traffic management. Traditional OSS do not address this need well for two reasons: First, except for network-element alarm management, OSS typically do not operate in real time. Second, OSS typically look at one part of the network or one aspect of the network traffic. What is needed is a source of comprehensive, real-time traffic information and a set of tools to allow a carrier to manage traffic - based on policies - across all network domains.

For years, carriers have deployed non-intrusive probes to collect SS7 information for network troubleshooting, but until recently, interpreting the signaling data for business purposes has been the exception.

Real-time traffic management today offers carriers a way to manage and maintain the QoS their subscribers demand while acquiring data that can be used in higher-level operations and business applications. Traffic management is the process of monitoring and adjusting dynamic traffic flows in accordance with a set of policies that determines the relative priorities of optimizing QoS, network use, network security and revenues. This requires the support of a traffic-management system that can provide four vital capabilities to a carrier, all in real-time: traffic visibility, analysis, visualization and alarms.

Visibility
Monitoring systems used for network troubleshooting typically capture snapshots of signaling packets and store these in a database for interpretation by network engineers. Traffic management not only is concerned with the packets that are flowing across the SS7 network but also the way in which the entire network is being used to support the services that are offered to subscribers. Basic transactions such as mobile registrations, location updates and call setups make up the basis of the traffic information we’re interested in. Although it is possible to reconstruct (post-process) these transactions from a database of raw SS7 traffic, that doesn’t meet the real-time requirement. Therefore, the new generation of monitoring system designed for traffic management includes a level of sophistication that was not required of the previous generation of systems (that were developed primarily for network troubleshooting).

SS7 networks include redundant elements for reliability. This means that the multiple packets that make up a transaction may take different routes between source and destination. Constructing the transaction record on the fly requires careful configuration of the monitoring system and enough processing power to keep up with the flow of signaling information. Once the basic transactions are captured, the traffic-management system can format these into convenient and easily read transaction-detail records (TDRs) and call-detail records (CDRs).

A spreadsheet-like report is a convenient way to view CDRs. The software should allow the user to select which fields to display in which columns and to format the report as desired. The option to export the report to a spreadsheet program or to a standard format for other OSS tools also should be provided. Because SS7 transactions are used to construct each CDR, it is possible to retain these protocol messages and their relationship to the CDR. The CDR report can act like an index into the protocol messages and can be used by troubleshooters as well, eliminating any need for multiple monitoring systems.

The system should provide user-friendly, point-and-click interfaces for selecting transactions with specific properties (filtering), deciding which fields to display and in which order, and for setting up automatic reporting on a pre-determined schedule. (See Figure 1.) This allows reports to be generated for specific calling or called parties, failed calls, specific causes of call failure, calls handled by specific circuits, value added services - any slice of the data that is desired.

Figure 1. Filtering possibilities

Analysis
A modern traffic-management system can run many analyses. One of the simplest and most useful is the answer/seizure ratio (ASR) and network effectiveness ratio (NER). To set up this analysis, decide which calls are to be counted as successful and which are to be counted as failures. The ASR is the percentage of the call attempts that were answered. After factoring in the unanswered calls where the line was busy, those that rang but weren’t answered and those where the mobile station wasn’t available, you can determine the total NER.

Visualization
An effective traffic-management system can generate a variety of useful traffic visualizations automatically. The most basic are time-based graphs showing traffic intensity with the busiest hour highlighted in a different color or circuit use over a particular period of time with color highlighting of over- or under-used circuits. These and some of the more sophisticated charts can help carriers diagnose problems and improve service levels in meaningful ways.

Subscribers relate that one of the most vexing QoS issues affecting their satisfaction is the perceived frequency with which their calls are dropped. Many traffic visualizations allow mobile operators to look at the drop rates for connected calls.

Figure 2. The left axis shows the percentage of dropped calls while the right axis indicates the number of calls established by the BSC during the same period.

Using Figure 2, you can determine whether a particular BSC is dropping more than its share of calls on a percentage basis. If the goal is to determine how to decrease the percentage of dropped calls, you also can run a number of detailed sub-analyses. For example, to determine whether dropped calls are correlated with traffic intensity, one might plot both statistics against the same time axis for each BSC. If you find a strong correlation for a particular BSC, further analysis might indicate that additional capacity would resolve the problem.

Another possibility that may affect dropped-call rates is handoff efficiency. If a high percentage of dropped calls occurs during handoff, the chart in Figure 3 may help pinpoint that fact.

Figure 3. Handoff results are shown by percentage (left axis) in a multi-colored stacked bar chart. The white dots indicate the total number of hand-offs (right axis). All results are broken down by BSC.

Using visualizations such as these, a carrier can pinpoint the cause of network and QoS problems and devise means to resolve them quickly. One operator eliminated a significant percentage of dropped calls once the BSC’s operating parameters were tuned according to the actual traffic patterns experienced in each area. Without visualizations such as the ones shown here, such tuning is either accomplished by guesswork or manual analysis.

Alarms
Network elements today can monitor their own performance and generate alarms when their performance crosses a given threshold. Depending on the approach used for network management, the element either can be polled for its status or it can generate alarms or traps using the simple network-management protocol. With a modern traffic-management system, those same capabilities now can be set up for circuits and signaling links, not just network elements. Separate thresholds can be set, for any of the statistics (or ratios of statistics) monitored, to generate minor alarms (those requiring some level of response) or major alarms (those requiring an urgent response).

For example, it is fairly common to engineer signaling links to operate at 40% or less of their peak bandwidth capacity, but with the introduction of new digital services, traffic patterns can change unpredictably. The traffic-management system can be set up to generate a minor alarm if traffic exceeds 50% of a link’s capacity and a major alarm when it exceeds 80%. When alerted, it may be possible for the operator to reroute traffic, or in extreme cases, to curtail the digital service temporarily to preserve network integrity.

Revenue Implications
Carriers can leverage real-time traffic information to generate additional revenues. Analyzing uptake and usage rates for new services is interesting for marketing departments. Many carriers market services directly by sending a targeted subscriber a specifically chosen SMS message based on his real-time presence on the network and other elements in a subscriber profile. This is widely used to market services to roamers in places such as Europe where multiple carriers may compete for a roamer’s business.

Some carriers combine this targeted messaging capability with real-time information from a traffic-management system. The traffic-management data can identify market segments as small as one subscriber and offer specific value-added services (for example, a real-time “friends and family” service based on frequently called numbers) to that subscriber automatically based on his actual calling behavior.

Other applications go beyond marketing. A carrier can increase subscriber satisfaction when the network notices a subscriber’s dropped call, and then sends the customer an SMS letting him know that the airtime for the dropped call has been credited to his account.

However, most carriers are focused on directly increasing their revenues for existing service offerings. SMS is a lucrative service and by far the fastest growing digital service worldwide.

A traffic-management system is essential for managing SMS traffic and even can be a source of revenues. Some carriers experience (or suspect) a disparity between the number of SMS messages that they can bill their subscribers for and the number that their network handles. The key to collecting for these “foreign” SMS messages is being able to differentiate and measure them. Figure 4 shows traffic vs. time originating at a specific foreign SMS center including the number of messages submitted and number that were delivered successfully each hour over a 1-day period.

Figure 4. SMS messages sent for foreign SMS center

To bill the originating carrier successfully, it will be necessary to have this kind of detail available. It also may be necessary to provide a report of the TDRs, showing each of the individual SMS messages either directly from the traffic-management system or via a rating and billing application that interfaces to the system. Considering the alternatives of disallowing foreign SMS messages altogether or allowing them but not billing for them, this application alone could easily justify the entire cost of the traffic-management system.

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Stormon is Coherent Networks (www.coherentnetworks.com) CTO, North American Telecom.