PLNOG12: Solving the LTE Backhaul Challenges (Ezra Mizrahi)

### Overview In this presentation at PLNOG12, Ezra Mizrahi from MRV addresses the network challenges associated with LTE mobile backhaul deployment. With mobile operators facing explosive bandwidth demand driven by video acceleration, gaming, and location-based services, the transition to LTE focuses on maximizing user quality of experience (QoE) while preserving the average revenue per user (ARPU). Mizrahi reviews the shift from legacy 2G/3G infrastructures to flat, all-IP Carrier Ethernet architectures, evaluating the requirements for transport, synchronization, security, and quality of service.

### Key Topics - **Evolution of Mobile Backhaul Architecture**: The move from 2G (TDM) and 3G (ATM/Ethernet with central radio network controllers) to LTE's flat all-IP architecture. LTE introduces direct base station-to-base station communication across the X2 interface alongside the S1 interface to the Evolved Packet Core (EPC). - **Front-Haul and Small Cells**: Alternative infrastructure approaches including Wi-Fi offload, Cloud RAN (using the Common Public Radio Interface / CPRI for front-hauling), and small cell deployments (femtocells, picocells, microcells) to expand capacity and coverage. - **Standardization and MEF Specifications**: The role of MEF 22.1 and MEF 22.2 standards in defining Ethernet mobile backhaul requirements, link and service OAM, quality of service performance objectives (QPO), and multi-class of service models supporting wholesale access. - **Timing and Synchronization**: Transitioning from legacy TDM or GPS timing to packet-based network synchronization using IEEE 1588v2 and Synchronous Ethernet (SyncE) for frequency, phase, and time-of-day alignment.

### Technical Details - **Core Interfaces & Control Protocols**: LTE relies on the S1-C interface between the base station (eNodeB) and Mobility Management Entity (MME) for control and signaling, S1-U to the Serving Gateway (SGW) for user traffic, and X2-C/X2-U between base stations for rapid handovers and low-latency coordination. - **Quality of Service (QoS)**: Implemented through Quality of Service Class Identifiers (QCI), managing parameters like Guaranteed Bit Rate (GBR) for time-sensitive services, Non-GBR for best-effort traffic (e.g., FTP), and Maximum Bit Rate (MBR). - **Scale and Security**: Scaling requires E-LAN multipoint-to-multipoint topologies and IPv6 as an eNodeB can communicate with up to 32 neighbor base stations. Unlike 3G's encrypted cellular channels, the all-IP LTE nature exposes vulnerability to untrusted networks, requiring IPsec tunnels that introduce packet overhead and potential latency. - **Protection and Testing**: Multi-layer protection spans Layer 1 (loss of signal), Layer 2/MPLS, and Layer 3 (using BFD and VCCV alongside Ethernet OAM). Network SLA verification utilizes built-in test features moving from RFC 2544 to ITU-T Y.1564.

### Takeaways Operators deploying LTE must modernize their transport to high-capacity, multi-class Carrier Ethernet networks with rigorous end-to-end OAM and multi-layer protection. MRV highlights solutions such as their OptiSwitch product family and Pro-Vision management software, illustrating real-world implementations including an early Nordic LTE E-LAN deployment using packet synchronization and a North American 3G/small cell wholesale network.