SMS: Can Networks Handle The Explosive Growth?

WAP and the Wireless Internet may make the headlines, but right now SMS is driving the wireless data revolution. GSM Association predicts a doubling of SMS traffic before the end of this year to a total of 10 billion messages.

SMS traffic is a high-margin revenue source for network operators. Tariffs vary, but if one takes a very conservative average, then 10 billion messages will generate over two billion dollars of income.

D2 Mannesmann now caters for more than 400 million short messages a month, compared with 323 million for the whole of 1998! However, the best is still to come as 3G networks will experience even higher SMS throughputs, possibly over 20,000 messages a second.

SMS is a near-perfect bearer for wireless information services. If you want a stock price, real-time football scores, or airline departure times, then a 160-character message does the job. Moreover, this information can be accessed using regular mobile phones.

Be ready for anything

In the past market research consistently underestimated the demand for GSM services. Today's growth projections may again turn out to be very conservative.

This add up to three rather obvious conclusions: One, operators need to develop a comprehensive strategy. Increasing capacity incrementally seems the easy option, but when traffic levels go on rising and growth becomes exponential it quickly becomes impractical and expensive. Loads cannot be balanced when a dozen or more SMSCs are employed and software upgrades can take several weeks to implement. This means that the total cost of ownership increases, especially when more and more systems are added to accommodate increased traffic.

Two, the SMSC should never be a bottleneck. Operators who compromise on capacity run the risk of having their network choke due to increasing traffic levels and if the quality of service falls subscribers will churn.

And finally the solution should be mature and proven to be stable, scalable and future proof. The SMSC must be ready for high-speed SS7 and other developments such as GPRS, and 3G.

Two kinds of bottleneck

SMSC's that can only deliver a few hundred short messages/second are obviously bottlenecks. Operators who started out with low-performance systems can either make a major upgrade to a high-performance system (1500 Msg/sec or more) or they can increase throughput by the addition of more stand-alone systems.

When such a system also has a single point a failure then a number of subscribers will have no service during failure. These problems are compounded when additional low performing stand-alone systems are added. CMG's solutions are fault tolerant redundant systems that exceed the high demands of network operators.

The second 'bottleneck' is self-imposed. Operators are limited by their current infrastructure capacity for SMS messages and may need to increase their SS7 capacity so that a High performance SMSC will run at an optimal level. In general this bottleneck has been found to be 1000 msg/sec. Interestingly this has led to the erroneous perception that an SMSC does not need to exceed this figure.

If this were the case, then one would question the reasons why seven of the world's largest GSM operators have elected to use the Highest performing SMSC available (CMG HP SMSC supports 2500 msg/sec). It also ignores the important fact that the industry is working hard on standards that will enable higher speeds to be reached over SS7 links. See sidebar "High-speed pipes remove constraints and expand the market".

High-speed pipes remove constraints and expand the market - Currently, a maximum of 16 logical links (see first circle in the figure below) can be made between two network nodes, e.g. between an SMSC and an STP or MSC. Throughput is also constrained by the throughput of the SMSC and the guaranteed performance of the MSC. The latter will typically run at 20 to 40% of maximum capacity. The inevitable result is a somewhat complex topology and a practical limit on the messaging capacity of the network. High-speed SS7: one big pipe - The upcoming high-speed SS7 protocol effectively turns a 16-slot E1 link into a single 2 Mbps pipe (see second circle in the figure above). This releases the throughput of a high-performance SMSC. Instead of having 16 x 64 Kbps links the network moves up to 16 x 2 Mbps. In addition, the topology is simpler since fewer links are needed. If low-performance SMSCs are used there is no win; the throughput of the link goes up but the SMSC cannot do anything with it. Messaging throughput can only be increased by adding even more stand-alone systems. This also increases the complexity of the infrastructure.

How do you measure performance?

Now data throughput has become a business critical issue operators need to take a very careful look at the way performance is measured; what assumptions does the tendering vendor make about the way the SMSC will perform on Operator's live network?

CMG believes that in the absence of industry benchmarks, operators need to ask any SMSC vendor a number of questions, the most obvious being their actual definition of a Short Message.

One would assume that this refers to a message sent from one party to another, but a performance figure may be based on 'map' messages. These are the internal messages sent between the SMSC and MSC, e.g. they are used to establish the location of the called party. A 'real' message can have four 'map' messages that the SMSC has to handle, but this is a dubious way of defining performance.

Another question that needs to be asked is the way messages are stored. The store and forward mechanism is an integral part of the SMSC architecture, but the storage medium differs between vendors. Thus, either hard disk or solid-state memory can be employed. The latter is indeed fast but it is also volatile, so there is a serious danger that messages will be lost in the event of a crash.

At CMG all SMSC stability and performance tests are performed under full store and forward capabilities, using actual customer traffic profiles that are replicated in a laboratory environment.

SMS going forward

CMG will deploy SMS over high-speed SS7 and is also actively involved in the development of solutions involving Gigabit Ethernet, SS7 over IP and 3G.

At the end of this year a scalable SMS Prepaid solution that easily keeps up with CMG's 2500 msg/sec SMSC and allows for differentiated charging will be released.

Synergistic links with WAP

SMS offers a global footprint and global roaming. It is robust, scaleable and incorporates a store-and-forward mechanism, which makes it perfect for push.

GPRS will not be operational until 2001 and the market will have to invest in new devices before this market sector can take off. This means that WAP information services will (in the near future) be delivered over SMS or a circuit-switched link. SMS is close to the delivery model of GPRS, but there is some confusion about the ability of this service to deliver a steady stream of content.

There is a network delay of about seven seconds between the SMSC and the subscriber's mobile and this would be an issue if a concatenated series of messages were delivered in the regular way. CMG's delivery mechanism, however, is based on a synergistic link between the WAP Service BrokerTM and the SMSC. This allows for the delivery of a fast, smooth, uninterrupted flow of short messages to the subscriber's mobile.

Conclusions

The wireless data revolution that is about to take off is based on standards such as WAP, the entry of the computing industry, smart phones and wireless PDAs, and packet-switched services. The latter will enable mobile IP and end-to-end solutions. However, the perception that the market has to wait for a new bearer service is not correct. SMS is ideal for many applications this robust, proven service is already in place; and SMS has unique features such as the store-and-forward mechanism.

SMS is therefore kick-starting the revolution and in future it will complement GPRS and 3G services. Thus, it is almost impossible to overstate the importance of SMS as a bearer for data and therefore the need for operators to deliver a robust, mature, stable and scaleable SMS service, the faster the better.