What is a passive optical network (PON)?

What is a passive optical network (PON)?

A passive optical network, or PON, uses fiber-optic technology to deliver data from a single source to multiple endpoints. “Passive” refers to the use of optical fiber cables connected to an unpowered splitter, which in turn transmits data from a service provider network to multiple customers. Technically, only the splitter is passive, because the network still needs electrical power at the source and receiving ends to function.

There are both passive and active optical networks (AONs). The primary differences are the number of fibers per user required and the splitter component used in PON architectures. AONs use a powered (or “active”) router or aggregated switch to distribute data from service provider to customers, and each user service requires a dedicated fiber and router/switch port. By contrast, PONs use one router/switch port and a single fiber between router/switch and the passive splitter to serve multiple subscribers, sharing the capacity of the wavelength.

A PON, then, uses fewer router ports and fiber connections to serve subscribers than an AON. The PON architecture minimizes possible points of failure, making it ideal for service providers needing to supply fast, reliable connectivity to homes, hospitals, hotels, resorts, campuses, and other subscriber locations.

What problems does a passive optical network solve?

Because a PON service can support multiple clients from a single router/switch port and uses unpowered splitters to direct and send data to users, service providers incur lower operational costs, avoid climate control for splitters, and require less equipment and fiber than they would delivering services over an AON architecture.

The use of fiber-optic cabling gives users access to some of the highest-speed connections available, and PON is energy-efficient: less electrical equipment translates into lower power consumption. Additionally, PON can transmit data both downstream and upstream at similar speeds without quality loss.

How does a PON work?

There are two main standards for PON architectures: Gigabit PON (GPON) and Ethernet PON (EPON). Both have specifications for data transfer speeds of 1 Gbps to 10 Gbps. Since communication flows from one source (service provider) to multiple subscribers, PON architectures use point-to-multipoint links. Using a splitter, a single fiber-optic strand from an optical line terminal (OLT) can be replicated across many branches to deliver service to 128 unique locations.

To set up a PON architecture, the service provider starts by building an optical fiber network. The access end of this fiber network connects directly to clients, while the other end connects to a router/switch using an OLT located in a service provider central office or point of presence (POP). The OLT converts Ethernet traffic into PON traffic.

Keep in mind that optical networks transfer data using light beams transmitted through fiber-optic cables. After data/light in the cable leaves the OLT, it travels to a beam splitter located closer to subscribers. Using passive technology, the splitter replicates the light wavelengths and directs them to an optical network unit (ONU) or an optical network terminal (ONT) closer to the user service area. To accomplish this without electrical power, the PON splitter uses mirrors and glass to refract the light to where it needs to go.

The ONU/ONT directs the fiber-optic wavelengths to one of several places near subscribers:

• Fiber to the home (FTTH)
• Fiber to the building (FTTB)
• Fiber to the curb (FTTC)
• Fiber to the neighborhood (FTTN)

Juniper implementation of PON technology

One issue with brownfield PON architectures is the form factor and scalability of OLT technology. Traditionally, to deploy fiber-based services, providers would deploy bulky, dedicated OLT shelves that consumed space and power and incurred operational costs. Juniper fixes that problem by adding our Unified PON technology to the mix.

When service providers integrate Juniper Unified PON with their PON architectures, they get a solution built on open standards, including 10G XGS-PON (ITU-T) and 10G EPON (IEEE). By following these industry specifications, Juniper delivers innovative PON technologies that are easy to use and compatible with other standards-based PON systems, including ONU/ONTs from third-party vendors.

Juniper Unified PON OLT is hot-pluggable with built-in Ethernet-to-10G PON media access control (MAC) bridging. It plugs directly into our ACX Series Universal Metro Routers, which support small form-factor pluggable plus (SFP+) transceiver ports. Operators can select, on a port-by-port basis, whether each 10G port will support PON or Ethernet services.

There are many applications of Juniper’s Unified PON: 

• High-density PON aggregation
• 10G XGS-PON and 10G EPON services
• Residential broadband services
• High-bandwidth business connectivity
• Enterprise/campus PON
• Wireless 4G/5G Xhaul
• Hospitality/MDU offerings
• Incremental pluggable growth model

When Juniper’s pluggable OLT is paired with our ACX Series routers, service providers gain more network control and automation. We supply a PON Manager Web interface that gives providers direct access to all PON components and visualizations. Fully customizable, it’s provided through the Juniper MicroClimate Management System (MCMS) and can help with three important areas of passive optical networking:

PON management

Through a browser-based graphical user interface (GUI), MCMS gives network operators virtual control and management of active PON components.

Northbound interface

Uses standard NETCONF protocols and published YANG data models.

Distributed PON control

Facilitates ONU Management Control Interface (OMCI) and operations, administration and management (OAM) communications from the OLT to PON Manager and supports scalable deployments with external servers. It can also be integrated to our ACX Series routers with our unified Junos operating system.

The Junos OS provides high levels of performance, orchestration, and security. It also runs on all Juniper technology platforms, so you don’t have to learn and support multiple operating systems as is often the case with other vendors.