 | Issue: | AME 2012 |
| Article no.: | 10 | |
| Topic: | Mobile backhaul transition in Africa requires new testing | |
| Author: | Adar Eyal | |
| Title: | General Manager, Israel, Eastern Europe and Africa | |
| Organisation: | Ixia | |
| PDF size: | 312KB |
About author
Adar Eyal is General Manager, Israel, Eastern Europe and Africa at Ixia. He has over 25 years of experience in the telecom and data communications markets, with an emphasis on managing teams in leading companies. In addition, he has international sales experience across EMEA and Latin America. Mr Eyalalso held several senior sales positions at Comverse and was the European sales director at SpearHead Technologies, which specialized in security solutions. Adar founded and managed the Telecom group of HP Israel and the 3Com Israel sales office. Most recently Mr Eyal worked for RadCom as VP of sales Europe and worldwide strategic alliances.
Article abstract
Africa’s short-term focus on immediatemobile service needs has left backbone networks underdeveloped. Before deploying IP/Ethernet mobile backhaul, levels of performance, quality,reliability, failover and synchronisationmust at least match those of legacytechnologies. The MEF (Metro Ethernet Forum)addresses these issues bydefining procedures and protocols, including accurate clock synchronization protocol, and by providinga certification process.The MEF also outlines a phased implementation approach, starting with offloading traffic and finally reaching All-IP network.
Full Article
In the last five years, Africa has been one of the fastest-growing mobile markets in the world. With over 82 million mobile users in Africa, mobile networks produce a positive and significant impact on economic growth. The impact can be twice as large in developing countries as in developed countries – Nigeria’s mobile market is growing at over 100 per cent per year.
There are many opportunities in Sub-Saharan Africa for information and communication technology (ICT) to build a foundation for long-term economic development. There have been very successful increases of access to basic voice communications, but without comparable improvement in broadband connectivity. Broadband access in Sub-Saharan Africa has not kept pace with the rest of the world. The one critical point that needs development is the domestic backbones.
Backbone networks are high capacity, fibre-optic networks that link disparate geographic areas. They transport high volumes of communications traffic to customers. Africa’s short-term focus on mobile networks to address immediate service needs has left backbone networks underdeveloped – creating major bottlenecks in the rollout of high-bandwidth services and the upgrading of cellular networks.
Africa presents great telecom and datacom opportunities – the extension of services, the stabilisation of governments and resources, and the active competition currently in place are all contributing to a rapidly growing advancement in the continent’s mobile infrastructure. With a focused drive towards privatisation and enterprise growth embraced by developing countries such as Uganda, Tanzania, Nigeria, the Sudan, South Africa and Kenya, mobile infrastructures have drastically scaled up and improved.
Moving from a TDM (Time Division Multiplexing) based infrastructure to Carrier Ethernet creates a new set of technical demands and requirements on both the carriers and network equipment manufacturers that establish these next-generation networks. Delivering the promise of bandwidth, applications and QoE(Quality of Experience) will require both of these entities to perform pre-deployment testing in order to provide their customers a seamless transition to the always-connected, constantly mobile world of the future. Before carriers widely deploy IP/Ethernet in mobile backhaul networks, they must ensure that the critical performance characteristics of reliability, voice quality, and synchronization inherent to TDM technologies are matched.
Explosion of mobile broadband data
Infonetics Research shows that the subscriber count of cellular mobile broadband access exceeded wireline broadband access in 2010 – 540 million mobile broadband subscribers compared to 480 million wireline broadband subscribers. Worldwide wireless broadband subscribers are expected to have an astounding CAGR (Compound Annual Growth Rate) of 37 per cent from 2009 to 2014 as user numbers zoom from 354 million to 1.7 billion. Data traffic grew globally at a rate of 280 per cent during each of the last two years, and is forecast to double annually over the next five years.
Right on the heels of smart phones is a new wave of intelligent tablets. Apple’s new iPad and iPad2 has sold over 3 million units to date, surpassing the early growth rates of the original iPhone, including over 800,000 iPads equipped with 3G wireless access. Tablet devices will consume huge amounts of data on the network – acting more like a netbook computer than a smart phone.
Technologies such as HSPA (High Speed Packet Access) and evolved HSPA (HSPA+) are improvements that lead to better utilisation of the existing radio spectrum. HSPA improves the end-user experience by increasing peak data rates to 14 Mbit/s in the downlink and 5.8 Mbit/s in the uplink. HSPA+ offers even better bandwidth capabilities, with peak data rates of 42Mbps downlink and 11Mbps uplink. With 240 commercial deployments in over 110 countries worldwide, HSPA implementations are well under way. LTE (Long-Term Evolution), as defined by 3GPP (Third Generation Partnership Project), is widely acknowledged as the next-generation technology for both voice and data wireless transmission. LTE is an All-IP network that takes advantage of, and converges with, the wealth of IP network technologies and supports rates of 300 Mbps downlink and 150Mbs uplink as well as latencies of less than 5ms, when using 4×4 MIMO.
Growth in mobile broadband data strains backhaul networks
Mobile backhaul is the network for transporting mobile traffic between cell sites (BTS/NodeBs) and radio controllers (BSC/RNCs). Backhaul is one of the major contributors to the high costs of building out and running a mobile network – estimated to be approximately 25-30 per cent of total operating expenses. Mobile operators must optimise their networks with the most cost efficient backhaul techniques as demand increases. TDM circuits have historically inter-connected base stations to regional network controllers – which worked fine for voice only systems and low-bandwidth data traffic. However, the rapid growth in mobile broadband traffic has overloaded legacy networks and they are unable to keep up with the uptake in wireless traffic growth.
Adding additional legacy capacity to address this challenge is not a viable option. The monthly cost for legacy backhaul technologies (e.g. PDH – Plesiochronous Digital Hierarchy) increases linearly with traffic growth. Flat Rate charges for data services prevent carriers from passing increased expenses on to consumers. 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 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
Making the leap from TDM to IP/Ethernet backhauls
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. 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. Networks, both wireless and wired, must forward and shape handheld-driven traffic so as to ensure balanced QoE for all network users.
Such increases require providers to understand their network’s ability to deliver services to millions of customers in a timely and consistent fashion. Providers must employ subscriber modelling. Subscriber modelling emulates real-world traffic patterns and data levels. It’s not enough to just simulate users and applications – service providers must be able to test network reliability down to the behaviour and experience of each individual subscriber.
The MEF (Metro Ethernet Forum) is the leading organization developing technical specifications and implementation agreements to promote interoperability and deployment of Carrier Ethernet and its use in mobile backhaul. The MEF 22 Mobile Backhaul Implementation Agreement defines:
• Use cases and migration strategy
• Services (classes of service, service types, service performance)
• Generic interworking function
• Synchronization and clock recovery
The MEF 22 outlines a phased implementation approach (see figure below). The first phase is supplying packet offload of data services from TDM links to IP/Ethernet using Carrier Ethernet services. In this phase Voice traffic remains on a separate TDM network. This hybrid approach solves some issues but is not an ideal solution as it forces carriers to maintain and pay for two separate networks.
Hybrid network: separate legacy Voice and new packet Data networks
A minority of operators worldwide have started to take the plunge to a single IP/Ethernet network carrying integrated data, voice, and video traffic. Carriers must have confidence, however, that the proposed backhaul approach will match TDM characteristics in terms of reliability, voice quality, and timing/synchronization.
Single IP/Ethernet network for both Voice and Data
Preferred packet timing/synchronization technologies
The MEF addresses reliability and failover by defining a new set of OAM (Operation, Administration, and Maintenance) protocols and procedures. MEF 10.2 defines service attributes such as bandwidth profile and service performance. It is important to test that a device or system can support EVCs (Ethernet Virtual Circuits) with defined service performance in terms of frame delay, frame delay variation, and frame loss ratio.
The MEF published MEF 9, 14, and 21 certification standards to formalise Carrier Ethernet standards and interoperability. To date the MEF does not have a certification standard that is specific to mobile backhaul.
Maintaining sync
Conquering timing issues is one of the fundamental challenges of using Carrier Ethernet for mobile backhaul. Cell sites must be synchronized in order for inter-base station handovers to function properly and reliably. This is one of the major considerations holding back the move to a converged IP/Ethernet backhaul. To address the issue, MEF 22 recommends the use of IEEE specification 1588v2 and ITU-T Sync-E.
IEEE 1588v2 defines a protocol for achieving highly accurate timing and synchronization in a packet network. Clock information is distributed using dedicated timing packets between a master and slave node. Synchronization packets are always exchanged between a master and slave regardless of the amount of data traffic. 1588v2 delivers both frequency and phase, and it can be used for FDD (Frequency Division Duplex)and TDD (Time Division Duplex) system timing solutions. The IEEE 1588v2 packets are fully Ethernet and IP standards compliant and backward compatible with all existing Ethernet and IP routing and switching equipment.
Scalability and stress tests go beyond functional testing and measure how well a synchronization scheme scales in a real network. For example, it is important to test the capability and capacity of a boundary clock or PTP (Precise Time Protocol), enabled network (i.e. IEEE 1588 compatible) in achieving synchronization across thousands of network nodes. Equally important is testing devices or networks under high data rates and a high number of ordinary clocks achieving synchronization while measuring both data rate and synchronization performance. Data measurements should include packet delay variation (minimum delay, maximum delay, jitter, and distribution). A critical aspect of synchronisation performance is PTP message prioritization under the maximum traffic load data rate.
The use of IP/Ethernet in mobile backhaul has much promise, but must be proven and tested before it is widely deployed.
The mobile market in African countries is a promising and growing area, where saturation points are far in the future in terms of devices and users. As mobile broadband data demands continue to explode, the cost of TDM scales up exponentially in relation to traffic growth. Operators are making the investment to move to the eventual IP/Ethernet backhaul networks. Mobile backhaul services must be tested before deployment for data plane traffic capacity and QoS handling along with maintenance and fault handling/recovery.
