Is It Easy as 1, 2, 3?
The impact of higher capacity 3G and LTE mobile services is evident globally: businesses are offered increased operational flexibility and efficiency; mobile subscribers have the freedom of Internet access anywhere they need it; and machine-to-machine applications are gaining momentum.
However, supporting high-capacity mobile services is not without its challenges. There is only so much wireless spectrum, there is only so much data we can modulate over this spectrum, and there is only so much capital to build out next-generation IP/Ethernet backhaul networks.
Traditionally, service providers offering both wireless (mobile) services and wireline (fixed) services have done so using completely separate networks, even when operating in the same areas. Driven by the incredible growth in 3G and LTE traffic, the wireless backhaul networks are rapidly transitioning to IP/Ethernet networks, whereas wireline networks made this transition sometime ago. To lower the total cost of network ownership a number of operators are now planning to deploy a single network to support both wireless and wireline services. What are the wireless network operator challenges that must be overcome for this network integration to occur? Integrated networks must address key requirements such as: backhaul SLA monitoring, cell site synchronization, network scaling, service QoS, and OAM.
Macrocells or Metrocells or…?
Alcatel-Lucent’s Bell Labs research division has forecast mobile traffic growth to almost double every year through 2015. In dense urban areas mobile operator macrocell deployments are reaching density and frequency re-use saturation. Heterogeneous networks are introducing metrocells to facilitate intelligent offload of macrocells, improving coverage, and enhancing capacity. However, offering seamless mobility between macrocells and metrocells requires consistent IP/Ethernet backhaul performance in terms of packet delay, delay variation, and packet loss. These metrics are closely monitored by mobile operators and strict SLA requirements bounding these parameters are placed on any wireline backhaul transport provider.
At a macrocell site, there is commonly space to add devices from both the mobile operator and backhaul transport provider to monitor these performance metrics; whereas space at metrocell locations will typically be at a premium, encouraging closer interaction between wireless and wireline backhaul organizations and potentially providing further momentum towards wireless and wireline network integration. However, even with wireless and wireline network integration, it will be mandatory that these metrics are monitored by mobile operations to ensure consistent mobile service performance in a heterogeneous network consisting of macrocells and metrocells.
When it comes down to the myriad of challenges of integrating wireline and wireless networks, we can sort those challenges into 3 interconnected groups: Synchronization Requirements, Network Scaling, and OAM Requirements.
Mobile operators globally have made the transition, or are quickly making the transition, to IP/Ethernet backhaul networks — by 2015 there is industry consensus that the majority of macrocell sites will have migrated to IP/Ethernet backhaul. A significant challenge that mobile operators face while transitioning to an IP/Ethernet infrastructure is addressing cell site synchronization requirements. An integrated, carrier-class, backhaul network must be able to meet the synchronization requirements of all the services it supports, regardless of the technologies it uses to transport and deliver them. Packet networks, however, were never required to support synchronization services. Fortunately several technologies are emerging to address the network synchronization challenge.
The requirements for synchronization distribution vary with respect to the different wireless technology generations. For example:
• Inter-cell site phase accuracy is required in CDMA, Universal Mobile Telecommunications System (UMTS), Time Division Duplex (TDD), LTE TDD, and LTE Multimedia Broadcast Multicast Services (MBMS).
• The Global System for Mobile Communications (GSM) or UMTS Frequency Division Duplex (FDD) networks does not have this phase requirement.
All these technologies have a requirement for the accuracy of the radio carrier frequency emitted by the cell site. This is necessary to provide efficient mobile handovers in the presence of Doppler Shift, a phenomenon which is induced by fast moving handsets. GPS receivers can be placed at cell sites to support phase synchronization requirements, but alternate wireline techniques can provide:
• Potential savings when many sites are involved.
• A backup synchronization source; a synchronization monitoring capability.
• A solution for cell sites where GPS receiver antenna placement is difficult.
Cell site frequency accuracy requirements can be met using Synchronous Ethernet, differential or adaptive clock recovery on Circuit Emulation Services, enhanced NTP, or IEEE 1588. Beyond GPS, IEEE 1588 is presently the only means to distribute highly accurate time for radio technologies that require phase synchronization.
IEEE 1588 utilizes a packet-based exchange of timestamps between two devices. This exchange can be used simply for the delivery of a frequency reference or it can be used for the delivery of frequency, phase, and time-of-day. This protocol was designed from the start to address microsecond or better accuracies. However, this level of accuracy, needed for phase alignment of the mobile technologies, does require the deployment of IEEE 1588 aware devices across an integrated wireless and wireless network.
Network scaling is another challenge to wireless and wireline network integration. Today mobile operators are using Wi-Fi solutions to offload the capacity demands on their mobile spectrum — this ultimately puts more pressure on the wireline network, as wireline networks are typically used to backhaul Wi-Fi hotspots.
Wireline-related traffic is also growing as the demand for video increases.
Placing increasing amounts of wireless and wireline traffic over the same infrastructure will ultimately demand an evolution to 100G optical and 100GE IP/MPLS networking at points in the network where higher levels of traffic aggregation occur.
Shared, and strategically placed, video content caching can also help address network capacity demands.
Network and equipment reliability will also be critical as networks are scaled to support thousands of cell sites backhauled to common geographic points in the network, as will be the support for packet-based QoS to ensure all services (including IEEE 1588v2 packet based synchronization services) operate correctly.
Perhaps one of the biggest challenges to wireless and wireline network integration will be the operational partitioning of the network to support organizational OAM requirements while also maintaining command and control. To cost effectively address this challenge operations can explore OAM solutions that support a common element, network, and services foundation while also maintaining operational command and control.
An OAM solution that promotes the use of similar operational approaches and tools reduces training costs and enables improved productivity through facilitating collaboration between wireless and wireline operational staff. Customized tool sets can also be developed to further productivity and collaboration between technology experts and staff with less experience.
A unified OAM solution can play a significant role in reducing the complexity involved in operating integrated wireless and wireline networks, improvements in the following areas are likely the initial ones that can be realized:
• Faster provisioning of end-to-end mobile backhaul services.
• Automating setup for backhaul SLA monitoring diagnostics.
• Improved MTTR by pin-pointing SLA violation to domain/root-cause.
• Accelerated troubleshooting and isolation of network faults.
• QoS policy consistency network wide across wireless and wireline.
• Simplified OSS integration into the existing operations environment.
Not As Easy As It Looks
Integrating wireless and wireline networks has been the goal for many operators globally. History has shown that this is difficult to do. Larger wireline operators still haven’t converged to a common wireline network. Adding wireless network demands complicates matters even further.
However, a significant technical barrier to integration has been eliminated with the emergence of IP/Ethernet as common networking paradigm in both wireless and wireline networks. Mobile operator demands on integrated wireless and wireline networks such as SLA monitoring, packet-based synchronization, network scaling, and operational network partitioning can be addressed with products and professional services that are available today.