Transitioning from 3G to LTE is complex -- and, for most carriers, unavoidable. Customers will demand faster speeds and better Quality of Service (QoS), and traffic volume will only increase. To retain customer loyalty and strengthen their brands while minimizing capital expenditures and operating costs, carriers need to understand both LTE and Ethernet test and operations solutions that will enable fast deployments, effective trials, and sustainable QoS.

LTE Gets Ready; Trials Are Key
Without question, LTE is on the brink of widespread implementation. In the U.S. and Europe, 17 commercial LTE networks are online and 73 more will be operating by the start of 2013¹. Additionally, 140 carriers are committed to LTE deployment and 56 have pilots underway. The competitive pressures driving the upgrade are much greater than when 3G technology was deployed and the increasing demand for bandwidth is continuing unabated.

Because of major changes to the existing radio-access and core networks relative to previous-generation CDMA and 3GPP deployments, LTE offers significant performance gains. These changes include the replacement of base station by the new eNodeB, and the replacement of the core network by a new evolved packet core. The downlink uses orthogonal frequency division multiplexing radio access, while the uplink uses signal-carrier frequency-division multiple access. Both the uplink and the downlink use multiple-input multiple-output (MIMO) antenna technology.

Important LTE capabilities also include:
• time-division duplex and frequency-division duplex operation modes
• peak downlink data rates up to 326 Mbps with 20 MHz bandwidth
• peak uplink data rates up to 86.4 Mbps with 20 MHz bandwidth
• scalable bandwidth covering 1.4, 3, 5, 10, 15 and 20 MHz
• increased spectral efficiency of between two and four to one relative to HSPA
• no more than 10 milliseconds round-trip latency between user equipment and the base station

Several factors make time-compressed LTE deployments complex. First adopters tend to have exacting QoS demands, which require more troubleshooting and issue management. There are more test points requiring monitoring, and huge volumes of data need to be correlated across the network. More interfaces must be tapped, and the signaling that goes with service delivery is much more complex.

Trials are key to successful first deployments, and successfully managing these trials will let service providers move out of initial deployments in time to beat competitors to market. A successful trial requires setting a clear framework, communications with all network equipment manufacturers (NEMs), monitoring the NEMs, uniformly run test cases, capturing and evaluating huge volumes of data, and quickly adapting when things go wrong.

Fully integrated test platforms that provide on-the-fly measurements from the radio access network to the network core are needed to provide measurements during LTE trials. These platforms let trial teams replicate services in as many different scenarios and environments as are practical for all relevant standards and on different frequency bands.

Testing can verify all functions critical to future LTE services, including data capacity and throughput, network coverage, end-to-end network latency, seamless handover with legacy networks, interoperability of multi-vendor devices, and QoS.

The latest testing tools support the rapid execution and analysis of LTE field trial tests with flexible key performance indicators (KPIs), correlation of user plane and control plane data, interactive measurements with preferred UE devices, and the latest permutations of LTE standards. The tools work for all vendors’ equipment and enable “apple to apple” comparisons. The result is that operators can make LTE equipment purchasing decisions based on objective criteria.

Managing Ethernet on the LTE Highway
To use Ethernet as a cost-effective, carrier-grade technology for LTE, operators must thoroughly understand the key aspects and best practices of operations, administration, and management (OAM) for various layers and functions of the network. These layers include the access link, connectivity, and service layers. (See Figure 1.)

Figure 1. Overview of Ethernet OAM

Access Link Layer
Link-layer OAM functionality in the First/Last Mile is defined by the Ethernet first-mile standard. It is media independent, and operates at a slow rate of 10 frames per second. Ethernet OAM packet data units work only in point-to-point, full-duplex networks, and are not forwarded by peer devices. They require minimal configuration and deliver the following functions: device discovery, remote failure indication, remote loopback, and link monitoring.

Adjacent devices exchange identification information and OAM capabilities during network initialization. With remote failure indication, network devices can notify peer devices in the event of failures. The remote loopback is a link-layer mechanism that operates at the frame level. Link monitoring delivers event notifications, such as status and diagnostics information, that are stored in peer-accessible local management information bases.

Connectivity Layer
The connectivity fault management (CFM) IEEE 802.1ag standard specifies protocols and protocol entities within the architecture of virtual LAN (VLAN)-aware bridges. These protocols and protocol entities enable the detection, verification and isolation of connectivity failures in virtual bridged LANs. Networks operated by multiple, independent organizations can use these capabilities when each organization has restricted management access to the other’s equipment.

This standard specifies protocols, procedures and managed objects in support of connectivity fault management. These allow discovery and verification of the path through bridges and LANs taken from frames addressed to and from specified network users. The standard also enables detecting and isolating a connectivity fault to a specific bridge or LAN.

Continuity Check Message (CCM) Verification
CCM verification is among the most important CFM tests because it checks the CCM interval rate, compares the received CCM interval rate against the expected CCM interval rate, and checks for missing messages. (See Figure 2.)

Figure 2. OAM continuity check messages

When emulating an Ethernet device, the tester collects CCMs and calculates their interval rate. If the tester misses 3 CCMs, it declares loss of continuity (LoC). LoC is cleared when the tester detects 2 consecutive CCMs. LoC can be used to issue traps to the management system, to update the alarm log, or initiate a switchover to a protection link.

Loopback and Link Trace Tests Are Necessary Pit Stops
Loopback tests are necessary when conducting connectivity and diagnostic tests that include verifying bandwidth throughput or detecting bit errors. (See Figure 3.) For example, the user can send a loopback message (LBM) as a single event or repetitively.

Figure 3. OAM loopback test

A tester can use loopback tests both in-service and out-of-service. During in-service tests, the loopback test occurs in the presence of user traffic. The in-service loopback only applies to a configured Ethernet virtual circuit (EVC). For instance, the LBM causes only the configured EVC to loopback at the demarcation device; the other EVC/VLAN continues to pass through the demarcation device.

One application for the LBM is to provide connectivity to a remote demarcation device. A tester can send an LBM to the demarcation device. The demarcation device then provides a loopback response within a specified period of time. If the tester receives no response within that period of time, it declares a LoC.

The link trace traces the path to a target media access control address once a link trace message initiates the action.

Services Layer Puts Providers In The Drivers' Seat
This International Telecommunication Union-Telecom Y.1731 recommendation, developed in conjunction with the IEEE 802.1ag standard, specifies mechanisms required to operate and maintain the network and service aspects of the Ethernet layer. The recommendation also specifies Ethernet OAM frame formats as well as the syntax and semantics of OAM frame fields.

Y.1731 defines two sets of functions for fault management and performance monitoring. The fault management functions include many components described in the previous CFM section, such as continuity check, loopback (ETH-LB), and link trace.

The performance management functions include:

Frame loss: collects counter values applicable for ingress and egress service frames, where the counters tally the number of transmitted and received data frames between a pair of maintenance endpoints.

Frame delay: measures one- and two-way frame delay as well as frame delay variations for on-demand OAM.

Ensuring Optimal QoS Wins the LTE Race
Compared to 3G, LTE presents more QoS issues because of the complexity of LTE technology and the inherent challenges of introducing new services. Service providers must ensure that they can identify and troubleshoot any user, service, or network problem in a very short period of time in order to deliver the highest possible standard of customer care.

Potential QoS issues for LTE networks include massive increases in data usage, new radio access network infrastructure, and the complexity of the network core.

KPIs that provide real-time information on LTE performance and an end-to-end view that enables fast root-cause diagnosis are important factors that help resolve problems before they affect customers. To this end, network monitoring is a vital tool.

For example, a leading provider of telecommunications solutions in Europe is using JDSU services to provide end-to-end, real-time monitoring and troubleshooting of its LTE network, ensuring QoS while managing growing volumes of high-bandwidth traffic and increased network complexity.

Mobile operators can track an extensive set of key performance indicators (KPIs) that include network performance and data service quality using a new generation of service-assurance solutions. These tools also help operators manage network infrastructure and deliver an outstanding customer experience with easily configured KPIs and thresholds that pinpoint critical service and network problems -- complex network-wide service information is automatically interpreted and correlated. Clear, simple presentations of this information along with guided analyses then help installation and maintenance teams resolve problems efficiently.

Operators need to focus on the right KPIs and the essential data to maximize the efficiency of network assurance and minimize operating expenses. Carriers should look to monitor just the service-focused KPIs that are important to their business rather than hundreds of available KPIs that will overwhelm operations teams. They should be attentive to KPIs such as network functionality and data service quality to evaluate how to resolve service-affecting issues. Composite KPIs can reduce the number of KPIs without losing detail. Operators will most likely need to capture all of the control plane data but can be more flexible about the user plane. An intuitive interface makes it easy to understand signaling messages and clearly highlights failures.

In addition, next-generation assurance tools can analyze subscribers' networks and service interactions, correlating these transactions into a single context and tracing them from real time to several weeks in the past. As an example, many different individual transactions must be completed across the entire network to successfully set up a call. Effective troubleshooting demands that this series of inter-related transactions be presented in a single end-to-end view of the complete LTE network. With this comprehensive view, an operations team can diagnose complex issues quickly and reliably. And, this approach moves a large volume of troubleshooting from a niche area occupied by handful of specialists into one in which less-experienced technicians are able to effectively diagnose problems.

Transitioning from 3G to LTE adds significant complexity to monitoring and troubleshooting mobile data services. Carriers will need to plan and execute LTE trials and solve a number of problems that will inevitably occur during deployment. New equipment requires evaluation; new services need verification; and problem-resolution times need to be shortened. Fortunately, operators can substantially speed and improve LTE deployments by using advanced test solutions to help minimize these challenges.

Endnote
1. Global Mobile Suppliers Association (GSA). www.gsacom.com

 Rafael Andrade is Network Solutions Architect, JDSU, Communications Test and Measurement business unit. He has more than 14 years of experience in design, deployment, and testing of some of the largest voice and data networks in the world. For more information, visit www.jdsu.com.

What’s your take on this subject? Leave a comment and get the conversation going.