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Passive Optical LAN Tutorial

With Passive Optical LAN gaining traction all market verticals, now is the ideal time to learn more about this contemporary fiber-based networking technology.

Why install Passive Optical LAN?

Enterprise businesses that need to upgrade or replace existing telecommunications networks are looking for ways to improve energy efficiency and reduce capital and operating expenses. Technology managers are looking for solutions that furnish high bandwidth while increasing the security and reliability of their networks.

To meet these requirements, enterprises are turning to fiber-based Passive Optical Networks (PON) technologies. Passive Optical Local Area Networks (POL) provide enormous value to enterprises without forcing them to alter how they do business, while existing services provided by their networks remain the same with no change to core and end-devices connected.

Quick Facts

  • Fiber delivers better investment protection with superior extended life
  • Fiber infrastructure is significantly more environmentally sustainable
  • Fiber in buildings and outside plant is technology independent
  • Fiber technology offers graceful migration from gigabit to 100 gigabits
  • Fiber cabling is inherently more secure and reliable than copper
  • Fiber, such as Single Mode Fiber, has no known bandwidth capacity limits

How does Passive Optical LAN work?

Passive Optical LAN, or OLAN, is an IT infrastructure based on standards-based PON technologies (2.5G asymmetrical G-PON and 10G symmetrical XGS-PON) and standards-based advanced Ethernet technologies. The five (5) main pieces of an Optical LAN system include:

  1. Network Manager
  2. Optical Line Terminal
  3. Singlemode Fiber Cable
  4. Passive Optical Splitters
  5. Optical Network Terminal

Network Manager

The Passive Optical Network (PON) Manager (i.e. Element Manager) is the centralized intelligence and management of the passive optical network elements and subtended powered devices (i.e. powered devices). The PON Manager provides the one console and one screen control to orchestrate consist, repeatable, error-free IT policies and procedures through global profiles. This is the user interface that IT staff will access to perform faster network provisioning, configurations, moves, adds, changes and troubleshooting.

Optical Line Terminal (OLT)

The OLT is typically located in the building’s main data center and provides aggregation plus distribution of the enterprise network connectivity. A single OLT can be sized to support from 200 Ethernet connections to over 7,000 Ethernet connections from one location. It is the OLT that is connected to the Wide Area Network (WAN) and all internal resource servers through the core router. An OLT can be one rack unit in height (1 ¾ inches) to four rack units high (~ 6 inches) and even with the inclusion of powering equipment and fiber management typically all fits in one telco rack. Today's OLTs support both Passive Optical Networking service modules that allow XFP selectable ITU-T 984 G-PON 2.5G or ITU-T G.9807/G.987 XGS-PON symmetrical 10G connectivity down to the ONTs.

Singlemode Fiber (SMF)

SMF is the fiber optic cabling that runs throughout the building’s risers and pathways. It is the SMF that physically connects the OLT, splitters and ONTs. That said, it should be noted that there are options for operating PON over multimode fiber (MMF) and there are closet-based ONTs that can leverage the last 300’ of copper-cabling. There is also the choice of installing composite SMF cabling that includes two copper wires within the cabling jacket for remote powering of the ONTs.

Passive Optical Splitters

Optical splitters provide the point-to-multipoint connectivity between the OLT and the ONTs. The splitters offer flexible mounting in telecom closets, wall enclosures or ceiling enclosures. They offer split ratios from 1:2 up to 1:64 with the most common split ration being 1:32. Optical splitters also provide equipment, fiber and services protection through 2:X redundancy options. They are unmanaged, unpowered and highly reliable.

Optical Network Terminal (ONT)

ONTs enables optical to electrical conversion and Ethernet connectivity for voice, video, data, Wi-Fi and all other digital enterprise services and devices. ONTs are Power over Ethernet (PoE) enabled and subtend other powered devices (e.g. phones, cameras, wireless access points). ONTs themselves can be either locally powered from a nearby AC outlet, or remotely powered from a DC source. ONT mounting can be located above the desk, below the desk or can be nearly flush-mounted in the wall. They can also be mounted in zone boxes, with optional plenum brackets and in raised floors. Finally, there are also options for rack-mounted 48-port Ethernet ONTs that provide an economical one-to-one replacement of traditional closet-based Ethernet switches that can continue to utilize the last 300’ copper cabling drops inside a building.

Frequently Asked Questions

Q: Is fiber optic cable fragile, difficult to install and harder to test?

A: No. Singlemode fiber cabling is smaller, lighter, stronger, better bend radius, higher bandwidth capacity, longer reach, less susceptible to interference, faster connector solutions, longer life, more secure and less expensive.

Q: Do ONTs support Power over Ethernet?

A: Yes. ONTs commonly support 15 watts, 30 watts and 90 watts Power over Ethernet (PoE) to sub-tended powered devices by following IEEE 802.3 af/at/bt.

Q: Do industry ROI/TCOs for PON include the ONT power and cost?

A: Yes. Industry ROI/TCOs for PON do include the ONT power and cost calculations. This is how apples-to-apples cost comparisons are gathered that showcase great CapEx and even better OpEx savings for enterprise PON installations.

Q: Can PON be used to connect Wireless Access Points?

A: Yes. In fact, PON is an excellent choice for connecting Wireless Access Points (WAP) because the architecture positions the ONT close to the WAP where a economical multi-rate Ethernet connection can be made. Furthermore, with 10G XGS-PON and multiwavelength support for additional 10G XGS-PON wavelengths makes PON a very attractive design for modern Wi-Fi networks.

Q: Since PON shares bandwidth to ONTs, does that create traffic bottlenecks?

A: No. Many modern technologies share resources, like wireless and cloud-based services. PON ensures strict QoS is delivered end-to-end through centrally managed traffic segmentation, classification, rate limiting, policing, queue management, scheduling and shaping mechanisms.

Q: I heard that fiber optic cable infrastructure has higher costs than copper?

A: No. Single-mode fiber infrastructure solutions cost 25% to 50% less than copper. These savings have been realized in many PON deployments. Cost savings are spread across components, materials and labor.

Q: Is PON less reliable than legacy copper-based active Ethernet switched networks?

A: No. A single OLT connected by a single fiber to a single ONT can achieve five-nines availability (i.e. 99.999 network uptime, 5 minutes downtime per year) and reliability due to the carrier-class nature of the equipment. To configure a legacy Active Ethernet user for five-nines availability requires fully meshed connections between 2 core/aggregation routers and 2 access switches with 2 NIC cards installed in the computer. All of these components drive the cost of such a configuration skyward. Furthermore, Type-B PON Protection has enabled Optical LAN to achieve greater than seven-nines (99.99999%) availability, which means only about 30 seconds of unplanned downtime per port, per year.

Q: Does PON lack troubleshooting tools?

A: No. GUI-based element management software manages PON equipment. This is a more efficient method of managing a LAN than using only a craft user interface (CUI) at all the diverse, geographically challenged equipment location within an active Ethernet LAN. PON equipment utilizes an element management system (EMS) for easy management and troubleshooting, including user-friendly fault management (i.e., alarms, diagnostics and troubleshooting), configuration management (i.e., provisioning and upgrades), automation management (i.e., OSS, backups and restorations), performance management (i.e., reporting), security management (i.e., user roles and access controls) and inventory management.

Q: Does every end-point connected in an enterprise network require on ONT?

A: No. Each endpoint or desktop does not require an ONT, as many deployments share the multiple Ethernet port ONTs with multiple user locations. This approach optimizes the network architecture, lowers cost and reduces overall energy consumption significantly.

Q: What are the differences between the terms PON, G-PON, XGS-PON, POL and OLAN?

A: Passive Optical Networks (PON) references the overarching technology defined by FSAN and ITU standards bodies. PON is currently inclusive of G-PON (i.e. ITU-T G.984 that provides asymmetrical 2.4Gbps downstream and 1.2Gbps upstream capacity) and 10G XGS-PON versions (i.e. ITU G.9807.1 that provides symmetrical 10Gbps downstream and 10Gbps upstream capacity). Passive Optical LAN (POL) term is used when talking about PON use for enterprise applications inside local area networks (LAN) for connectivity inside buildings and across extended campus. POL vendors make tremendous investments in additional R&D to support advance Ethernet IEEE features to satisfy true enterprise LAN requirements (e.g. bridging, LAG, VLAN, ACL, PoE, LLDP, NAC, 802.1x, AS-SIP, PON protection, Change of Authorization, DAI, MAB, digital audio, etc…). Tellabs Optical LAN (OLAN) refers to the Tellabs’ branded solution.

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