Preparing For The Promise Of 4G

Author: Atul Bhatnagar
Driven by the increased consumer demand for wireless data bandwidth, cellular data speeds have increased over the last decade by a factor of 10 every 3-5 years. Reporterlink has estimated that wireless data traffic will increase ten-fold between 2009 and 2017 – a 59 percent CAGR. Fueled by a rapid increase in interactive data and multiplay applications, data traffic is expected to hit 1.8 exabytes/month . Video is the largest bandwidth consumer today, a trend that will continue in the foreseeable future.
(Fig. 1)

Mobile carriers are hard at work developing next generation of networks to handle the huge increase in mobile traffic. Long Term Evolution (LTE), also referred to as 4G, is widely acknowledged as the next generation technology for both voice and data wireless transmission. With the exception of the air interface, LTE is an all-IP network – taking advantage of and converging with IP network technology. LTE has some impressive capabilities:

• Support for multiple-input, multiple-output (MIMO) antenna technology, including 2x2 and 4x4 configurations.
• 300 Mbps downlink and 150 Mbps uplink bandwidth when using 4x4 MIMO.
• Latencies of less than 5 ms.
• Hundreds of users per cell.

Most major telecom equipment manufacturers (TEMs) and carriers have announced their intention to develop and provide LTE products and services. As of early 2010, 51 providers in 24 countries have made commitments . Early deployments are expected in Asia and North America in 2010, with significant expansions in all major markets in 2012. 2013 will see some 85 million LTE subscribers and nearly half a billion people will use LTE by 2015.

In order for enterprises and carriers to be fully ready for the 4G transition, they must fully test their devices and networks:
• From end-to-end, from the radio tower through the IP core.
• At scale, using well modeled scenarios based on actual subscriber usage patterns.
• At load, especially over the mobile backhaul network as it necessarily moves from TDM to Ethernet-based infrastructure.

End-to-End Wireless Testing

Wireless network testing must encompass not only the latest technologies, but incorporate the interactions between existing systems and emerging solutions.

Wireless service, end-to-end

End-to-end testing of a wireless service must separately test the components in each of the radio access network, wireless core network, and Internet core networks, test each of the three subsystems independently and test the entire system end-to-end. As wireline and wireless networks converge, multiple types of interface speeds must be tested in conjunction, including 10 GE, 40 GE, and 100 GE.

Proper testing occurs at multiple levels, usually in a sequential manner:
Compliance testing is an essential first step in ensuring correct operation and interoperability. Compliance tests are built from RFC and other standards.
Functional testing further exercises device capabilities with combinations of options, multiple connections, differing types of traffic, and many sequences of operations.
Performance testing measures raw capacity, such as the maximum number of connections, maximum rate of connection establishment, and maximum uplink and downlink throughput.
Scalability testing measures real world ability to handle a complete user community, and requires realistic traffic loads that meet and exceed network capacity.

LTE Service Validation
Multimedia and peer-to-peer applications account for the lion’s share of the 3G and 4G bandwidth usage. The perception of service quality is everything to the customer, and the lynchpin in preventing customer churn. Networks must forward and shape traffic so as to ensure balanced quality of experience (QoE) for all network users.

As smart wireless devices become more and more prevalent, service providers must be able to test their networks with exponential amounts of application traffic in diverse mixes. They must anticipate the deluge of voice, video, P2P, gaming, and other data traffic on their wireless networks.

In addition to traditional network based packet metrics such as latency, jitter, and packet loss, service providers need to use QoE testing to understand the user experience prior to network deployment. This requires the ability to correlate QoE statistics on an aggregated and per-user basis, determine if the service level agreements (SLA) are being met, and understand the impact of one service on another as they compete for network resources.

Traffic shaping and QoS policies are critical to the integrity of these SLAs, and a growing and important trend in service provider network traffic shaping is the use of data packet inspection (DPI). DPI goes beyond the typical processing of header information and looks at the data within the packet to determine the type of traffic being processed. DPI allows for better network control, prevents unauthorized users and service types, limits denial of service attacks, malicious traffic, and allows providers to manage bandwidth-intensive data such as P2P.

Subscriber modeling, including multi-UE emulation, allows telecom equipment manufacturers (TEMs) and service providers to assess the performance of their service delivery. Test engineers must:
• Define how users connect to their service provider network.
• Designate upstream and downstream bandwidth for each subscriber.
• Specify which applications are used and how they behave when traversing the network and interacting with each other.
• Configure multi-service traffic distribution for each subscriber.
• Model usage for each application with advanced timelines for traffic load profiling over an hour, a day, or a number of days.
• Measure QoE per-application, including response latency, packet loss, jitter, MOS scores for VoIP, and MDI and MOS_V for video.

Validating Mobile Backhaul
Mobile backhaul is the network for transporting mobile traffic between cell sites (BTS/NodeB’s) and radio controllers (BSC/RNCs). Backhaul is one of the major contributors to the high costs of building out and running a mobile network at approximately 25-30 percent of total operating expenses. Rapid growth in mobile broadband traffic, however, has overloaded TDM circuits.

Adding additional TDM circuits to address this challenge is not a viable option. Operators are instead looking to move to packet-based backhaul techniques using IP and Ethernet to gain a lower cost per bit. Using Carrier Ethernet for wireless backhaul potentially allows operators to support large bandwidth increases from cell sites, while only incurring small increases in operational costs.

PDH vs. Ethernet: Annual Mobile Backhaul Service Charges per Connection

The move from TDM to Ethernet-based transport does not come for free. TDM circuits are well established at providing ultra-high reliability, voice quality of service, and accurate timing. Ethernet technology requires careful attention to match these capabilities.
Testing for Ethernet-based mobile backhaul systems can be split neatly into performance testing and conformance testing. Performance testing determines how a deployment will handle real world traffic interactions at full scale, while conformance testing determines if the appropriate standards have been implemented on networking devices correctly.

It is essential that wired and wireless components now be tested with the same types and scale of traffic seen in actual network deployments. The iPhone is the perfect example of a high performance, multimedia-capable device, and is the tip of the iceberg of what is to come. Networks, both wireless and wired, must forward and shape handheld-driven traffic so as to ensure balanced quality of experience (QoE) for all network users.

Such increases will require providers to understand the network’s ability, including mobile backhaul, to deliver services to millions of customers in a timely and consistent fashion. In order to accomplish this goal, providers must employ subscriber modeling in order to understand what their networks can handle in real world situations.

The transition from 3G to 4G wireless networks and the required interoperability with legacy technologies will unleash a level of unprecedented complexity. Legacy technologies need to seamlessly interact with newer technologies in order to attract subscribers and limit maintenance and upkeep costs.

Service providers will continue to support multiple wireless technologies. It is essential that the wireless core network be tested using multi-UEs, subscriber modeling, and end-to-end network testing.
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