EPON Technology Overview
History on Access Networks
Access networks are part of a telecommunications network that connect users to their providers. Historically they were made out of twisted copper wires for telephone access. These providers are known as “telcos”. Another type of access technology is Cable TV service which is delivered through a coaxial cable, TV was the only service offered in the early days.
Over time the access network became capable of delivering other services, like high speed data, video, and voice.
-This created the need for more bandwidth. Technologies like xDSL for telcos or DOCSIS 3.0 and 3.1 in the cable world have increased bandwidth over the years, keeping the existing networks alive. Regardless, these technologies are not enough to deliver multigigabit/s service to residential and commercial subscribers today.
Fiber to the rescue!
Unlike twisted copper pairs or coax cable, optical fiber is capable of delivering today symmetric 10Gbps of data, voice, and video services at distances equal or beyond 20 kilometers from a central location to a subscriber.
-This is known as Fiber to the x (FTTx) service, where x = Home, Business, Premises, etc. Fiber can be deployed in the local access network using a point-to-point (P2P) or point-to-multipoint (P2MP) topology, with dedicated fiber runs from the HUB to each end-user (subscriber). One cost effective way of delivering FTTH service is with the use of Passive Optical Networks (PON).
What exactly is a PON?
Definition of PON（Passive Optical Network）
– Is a point-to-multipoint, Fiber-to-the-Premises (FTTP) network architecture.
– Is called “passive” because unpowered optical splitters are used to enable a single optical fiber to serve multiple premises, typically 16-128.
– It consists of Optical Line Terminals (OLT), and more than one Optical Network Units (ONUs) and connected through the Optical Distribution Network (ODN).
– The ODN is an optical access network without any active electronic devices between OLT and ONU.
Components in a PON Network
Different standard groups created different PON standards:
What is EPON？
• EPON（Ethernet Passive Optical Network） was initially chosen by MSOs as the preferred PON architecture based on several high level factors:
– Simple Protocol based on Ethernet Framing instead of more expensive and complicated GPON specification (ATM) which affects future pricing
– Momentum already made toward a DOCSIS based provisioning model
– 10G specification was completed in 2009, with product available today
• In collaboration with CableLabs, MSO’s have spent 5+ years working with contributing vendors to develop specifications for DOCSIS Provisioning of EPON (DPoE). DPoE focuses on the following concepts:
– Multi-vendor interoperability
– Metro Ethernet services functionality for commercial services
– Multigigabit IP/HSD residential service
– Capable of provisioning millions of devices
– Use of existing MSO back office systems
• Simplified provisioning and access network speeds of 10Gbps are key differentiators for MSOs against existing and new service providers.
• Minimizes fiber deployment and number of transceivers in the field compared to CWDM (lower CAPEX).
• No active devices in the field (lower OPEX).
EPON as Universal Fiber Access Architecture
• All Service Types
– Cellular backhaul
• All Configurations
• All Data Rates
– 1Gb/s (802.3ah 2004)
– 10/1 and 10/10 (802.3av 2009)
• All supported on the same
• outside plant (ODN)
EPON Technology Roadmap
EPON standard evolution:
– 802.3ah: 1G/1G specification (2004)
– 802.3av: 10G/10G specification (2009)
– DPoEv1: DOCSIS Provisioning over EPON (2011)
– DPoEv2: (2012)
– SIEPON: Service Interoperability in Ethernet Passive Networks (2013)
– NG-EPON: IEEE already working on next generation EPON for speeds of 40 or 100Gbps.
A typical EPON system is composed of an OLT, several ONUs and an ODN.
– The OLT (Optical Line Terminal) resides in the MSO’s hubs, or sometimes in a MDU, it connects the optical access network to the core. OLTs can be a switch or router and contain EPON interfaces. It’s the optical equivalent of a CMTS.
– The ONU (Optical Network Unit) is located at the end-user location (customer premises), it has an optical transceiver and provides services such as voice, data and video. It’s the optical equivalent of a Cable Modem.
– The ODN (Optical Distribution Network) connects the OLT and ONU. In the ODN one fiber carries the DS and US signals using WDM. Fibers are then split to serve individual ONUs. The optical splitter is a simple passive device.
EPON US/DS Wavelengths
An EPON system uses Wavelength Division Multiplexing (WDM) in order to achieve two way communication on a single fiber.
EPON Architectures Models
-Tree topology (a) is typically used in China, US and Europe for residential and business customers with no physical layer resiliency requirements
-Bus topology (b) is typically used in Japan (where most fiber is deployed in aerial bus-type architecture)
-Ring topology (c) used typically for networks with high resilience (tree / trunk protection under SIEPON)
-The EPON protocol works on any ODN (optical distribution network) architecture
Optical Power Levels
802.3ah (1Gig EPON)
• TX Wavelength: 1480 to 1500nm
• TX: +2 to +7dBm
• RX: -6 to -27dBm
• TX Wavelength: 1260 to 1360nm
• TX: -1 to +4dBm
• RX: -3 to -24dBm
802.3av (10Gig EPON)
• TX Wavelength: 1575 to 1580nm
• TX: +2 to +5dBm
• RX: -6 to -28dBm
• TX Wavelength: 1260 to 1280nm
• TX: +4 to +9dBm
• RX: -10 to -28.5dBm
OLT broadcasts data to every ONU
• ONUs receive a Logical Link ID (LLID) upon registration (can be more than one LLID). This is similar to a cable modem receiving a pair of service flows (US/DS) in DOCSIS.
• ONU only forwards traffic to its own set of active LLIDs.
• To broadcast data to all ONUs the OLT uses TDM (Time Division Multiplexing)
• During ONU registration the OLT calculates the time delay (distance) from ONU and instructs it to adjust its transmission parameters.
• Each ONU only transmits during the assigned timeslots from OLT
• Transmission from each ONU arrives at the OLT without collisions
• To provide multiple access to a single fiber link for all connected ONUs, Time Division Multiple Access (TDMA) architecture is implemented for the Upstream channel