Trend Toward Access Network Convergence
After ten years of high speed development, optical broadband access has expanded from traditional home broadband into other fields. Driven by big video, 5G services, and SDN/NFV evolution, optical broadband access has reached a new development stage with the ultimate goal of fixed-mobile convergence (FMC).
With the development of 4K/8K HD video services, home broadband is moving from the traditional 100M era to the 1G era. Hence, the deployment of 10G PON has become a focus of attention. High bandwidth requires large-capacity central office equipment. New-generation OLTs basically match convergence equipment in switching capacity and slot bandwidth, and it is inevitable that the OLTs will integrate with the convergence equipment.
5G that could achieve much higher speeds than 4G is nearing commercialization. 5G will provide the internet of everything (IoE) connectivity that is ubiquitous, convenient, fast, smart and reliable, which will trigger a revolution in production modes, business models and people lifestyles. Network service provision will be based on services instead of access modes because whether access is wired or wireless will be irrelevant to users. Service convergence is bound to drive network convergence, which in turn will lead to equipment integration.
Furthermore, network architecture is becoming increasingly flat and simple, which requires the access equipment to be integrated for centralized management. Meanwhile, the maturity of SDN/NFV also drives a profound transformation of the network architecture. A wireline network including optical access needs to conform to this trend, which necessitates adjustments to equipment form factors. For access offices where space, power consumption and performance restrict each other, integration of access and other equipment is inevitable.
TITAN-Based Integrated Access Solutions
ZTE's TITAN is designed to accommodate access network development trends and help operators implement service convergence. Based on a high-end router platform, it converge with products like PTN, high-end router, and OTN in terms of architecture, allows mixed insertion of cards, and supports built-in X86 blade servers. Different integrated products can be rapidly launched to meet operators’ network re-architecture needs.
In addition to the traditional fixed access services, TITAN also offers multiple convergence solutions for the 5G era including 5G fronthaul and backhaul, built-in CDN, built-in BNG and built-in OTN, to fulfill the requirements of high bandwidth, low latency and differentiated QoS.
TITAN-Based 5G Fronthaul
A WDM-PON architecture uses a point-to-multipoint tree topology to save massive amounts of fiber or uses the idle fiber resources of the existing PON to reduce network construction and maintenance costs. Fig. 1 shows a TITAN-based unified 5G optical access platform. The 5G DU pool and AAU are connected through the WDM-PON to fronthaul mobile services. This solution supports management of transparent service transmission.
The TITAN OLT unified optical access platform can be deployed according to the specific field conditions. If conditions permit, the wired and wireless access offices can be co-located. A dedicated OLT-based fronthaul network can be built when large fronthaul capacity is required.
The TITAN-based WDM-PON 5G fronthaul network architecture has several features. It supports both CPRI and eCPRI standards as well as 4G/5G hybrid networking, and provides large bandwidth with 25 Gbps per channel (smooth upgrade to 50 Gbps per wavelength in the future). It also features high density, with an OLT card providing 16 wavelength channels and a single backbone fiber offering 16×25G access capability. Multiple wavelengths are first converged by an AWG and then distributed to branch fibers, thus saving substantial backbone fiber resources.
TITAN-Based 5G Backhaul
Compared with 5G fronthaul, 5G backhaul has lower bandwidth and latency requirements. Especially, 5G low-frequency integrated small cells with high density deployments require less than 5 Gbps bandwidth. TITAN uses the TDM-PON to carry the small cell backhaul traffic, which can reuse an operator’s existing ODN (Fig. 2). As the TDM-PON develops and bandwidth demand increases, 10G PON technology has matured and higher-rate 50G PON technology will be introduced. In actual deployments, small split ratios such as 1:8 can be selected and, in light of the user traffic concurrency rate, a single PON port can be used to serve multiple 5G small cells, to substantially reduce operator Capex.
5G backhaul equipment needs complete L3 functions and IP FRR-based service protection functionality. The new-generation TITAN OLT adopts a fully distributed router-style hardware architecture and basically matches IPRAN equipment in capabilities. In the future, TITAN will support such technologies as segment routing and smooth migration to SDN, allowing forwarding and control separation, cloud-based control plane, and open APIs for rapid service deployment and automated O&M. Moreover, the TITAN with a support for network slicing can realize service isolation and domain-based management.
TITAN's Built-in BNG
In the cloud-based BNG solution, the BNG control plane runs in a cloud, while the BNG forwarding plane is moved to the TITAN. This mechanism integrates the OLT with the traditional BNG forwarding plane and avoids the deployment of dedicated BRAS equipment for a forwarding plane, thus flattening the network and reducing the network cost (Fig. 3). These two planes can be implemented using interfaces such as OpenFlow (OF) and Netconf. When control is decoupled from forwarding, the control plane can be based on a universal hardware platform, helping operators reduce investment and O&M complexity. The forwarding plane is controlled centrally by an SDN architecture. An SDN controller, which integrates management and control functionalities, and a service orchestrator are deployed to enable end-to-end automatic network configuration and opening up of network capabilities.
TITAN's Built-in A-CDN
As shown in Fig. 4, a CDN edge node, called an access CDN (A-CDN), is deployed through building blade servers into an OLT. A-CDN mainly stores time-shifted TV (TSTV), TV on demand (TVOD), and hotly sought-after VOD programs. TITAN offloads local traffic through its GW proxy functionality so that users can access programs stored in the nearest A-CDN. By intercepting 70% of the VOD traffic, the following objectives can be achieved:
● Improving user experience: High-bit-rate 4K/8K/VR services can be deployed close to end users to take advantage of the high bandwidth of PON. This ensures high throughput, low latency, no congestion and great service experience. It can also effectively cope with the traffic bursts caused by heavy demand for hot videos within a short period of time.
● Saving network bandwidth: By deploying services close to end users and intercepting 70% of the VOD traffic, A-CDN significantly reduces the bandwidth required by the convergence network, metro network and related network equipment and the load on the CDN central node, effectively cutting the bearing cost of the big video network.
● Simplifying engineering implementation: The TITAN with built-in blade servers supports low power consumption, high performance, on-demand deployment and strong scalability. It does not require reconstruction of the equipment room and frequent network upgrades, greatly reducing the workload of service deployment and capacity expansion.
● Efficient and smart CDN: A-CDN can use real-time information of the access network to schedule content and services in a smart, efficient way to further improve user experience and network transmission efficiency.
● Shared infrastructure: The TITAN OLT with its built-in blade servers constitutes an edge cloud computing platform and an NFVI platform, which can be shared by VNF, CDN and other edge computing services. This advances the construction of edge and service clouds at a low cost.
TITAN's Built-in OTN for Integrated Transmission and Access
TITAN can include built-in 100G OTN cards to integrate transmission and access. Managed by a unified network management system, it realizes end-to-end mapping of user traffic into OTN timeslots, simplifies service deployment and O&M, and enables end-to-end deployment of large-granularity, low-latency services while ensuring that service transmission is transparent with fixed latency and no jitters. Furthermore, in contrast to the traditional OTN equipment, the TITAN with integrated transmission and access reduces equipment room space and decreases power consumption, hence considerably cutting Capex and Opex for the operators.
With a deep understanding of the network trends and the aim of delivering FMC services, ZTE has launched an innovative integrated OLT architecture, and a series of solutions, including 5G fronthaul and backhaul, built-in BNG, built-in A-CDN, and transmission/access integration, to help operators prepare for the 5G era.
[Keywords] Access network convergence, TITAN, 5G fronthaul, FMC, built-in A-CDN, integrated transmission and access