Application of FTTR-B All-Optical Solution in Campus Networks

In a campus network, the FTTR to business (fiber to the room for business) all-optical solution is mainly used to provide wired and wireless access for user terminals. The FTTR-B main ONT integrates the functions of a mini OLT, AC, NAT gateway, DHCP server, and portal server, greatly simplifying the architecture of the campus network and cutting networking costs. As campus networks evolve, users seek better network experiences, leading to increased requirements for the FTTR-B all-optical solution, including redundancy protection and wireless roaming.

Redundancy Protection for FTTR-B Main ONT

The FTTR-B main ONT can connect to a maximum of 128 room ONTs, supporting access to over 1,000 users, which increases the need for better redundancy protection. FTTR-B redundancy protection focuses not only on the uplink PON interface but also on the downlink PON interface and the FTTR-B main ONT. Mature Type B and C solutions are available for the redundancy protection between the OLT and the FTTR-B main ONT. Given the redundancy protection requirements of FTTR-B, the dual FTTR-B main ONT redundancy protection solution is more suitable for the FTTR-B networking scenario.

As shown in Fig. 1, for redundancy protection between the OLT and the FTTR-B main ONT, a dual-active FTTR-B main ONT solution can be used to replace the common Type B and C protection solutions. This solution supports both single-OLT single-homing and dual-OLT dual-homing protection. Services are switched by the FTTR-B main ONT, and the switching process is quick, with low requirements for OLT and minimal impact.

For redundancy protection between the FTTR-B main ONT and room ONTs, a proper mode is usually selected based on the service scenario. For example, room ONTs used for wireless coverage, which provide service protection through multi-point overlapping coverage, generally adopt Type B dual-homing protection. Multi-port room ONTs used for camera access typically employ Type C dual-homing protection. When the dual FTTR-B main ONT services use L3 routing, direct network connectivity between the main ONTs is required to ensure that the WAN-side addresses remain unchanged and services are not interrupted during the switching of the devices connected to the left and right main ONTs. When the services use L2 bridging, direct network connectivity between the main ONTs is not necessary. In this case, when devices connected to the left and right main ONTs are switched, the MAC addresses can be actively refreshed to quickly restore the L2 paths.

l Type B dual-homing protection of FTTR-B: In the network architecture, a 2:N ODN is required. The left and right main ONTs are connected to the 2:N ODN, and the room ONTs are connected to the ODN properly. Communication should be established between the left and right main ONTs to negotiate the active/standby roles of the downlink PON interface, and synchronize the configuration information of the room ONT to ensure that the room ONT is not disconnected during the active/standby switching of the downlink PON interface. The room ONTs are unaware of the protection switching process.

l Type C dual-homing protection of FTTR-B: In the network architecture, two 1:N ODNs are required, and the left and right main ONTs are connected to their respective ODN. The room ONT needs to connect to the left and right ODNs via dual uplink PON interfaces. Communication should be established between the left and right main ONTs to negotiate the active/standby roles of the downlink PON interface and synchronize the configuration information of the room ONT. This ensures that during active/standby switching of the downlink PON interface, the left and right uplink PON interfaces of the room ONT are notified to perform the same switching. The room ONT needs to allow services to be switched accordingly based on the active/standby status.

STA Roaming Across FTTR-B Main ONTs

For a large campus, multiple FTTR-B main ONTs usually have built-in mesh controllers to manage wireless roaming for their associated stations (STAs). A user STA may roam from FTTR-B main ONT 1 to ONT 2.

Mesh Controller Interworking Enables STA Roaming Across Main ONTs

The FTTR-B main ONT has a built-in mesh controller. The 802.11k standard allows a STA to scan for APs with a specific SSID over the air interface and continuously learn and update the neighbor AP list, which enables the STA to quickly measure signal strength and select a roaming target.

When the STA starts roaming to the AP of FTTR-B main ONT 2 based on the roaming policy, main ONT 1 queries the mesh controller of main ONT 2 according to the local neighbor AP list and notifies it that the STA will roam to the corresponding target AP. After the target mesh controller agrees, the roaming can proceed.

A STA Roams to an FTTR-B Main ONT Across L3 Routes

The FTTR-B main ONT operating in L3 mode performs NAT translation on service packets, causing the WAN-side addresses to vary from one main ONT to another. When a STA roams to a different FTTR-B main ONT across L3 routes, the network application link is disrupted due to the change in the WAN-side address. To solve this problem, the egress gateway for the STA should be fixed to the original FTTR-B main ONT.

An L2 “LAN connection” is added to the uplink PON interfaces of all FTTR-B main ONT to facilitate L2 interconnection between them. Each FTTR-B main ONT is enabled with a DHCP server, which assigns different network segments and gateway addresses (local main ONT addresses). When a STA roams to the AP of a new FTTR-B main ONT and attempts to renew its IP address via a DHCP request, the new main ONT enables the original FTTR-B main ONT to renew the STA’s original IP address and the original gateway IP address. As a result, the addresses on both the WAN and LAN sides remain unchanged, preventing any interruption to network application links.

The ZTE FTTR-B all-optical solution for campuses not only simplifies network deployment but also improves network reliability and user service experience. It allows operators to upgrade the campus network from "bandwidth connection" to "service experience", facilitating a strategic transformation in a new era.