Passive Optical Network (PON) Standards
| There are two important gigabit line rate PON standards, the IEEE 802.3ah Ethernet in the First Mile standard and the ITU-T G.984 GPON standard. |
IEEE 802.3ah GE-PON or EPON - Gigabit Ethernet PON
GE-PON, also called EPON, is deployed widely in Japan and provides for a symmetrical 1.0 Gbps data rate in both directions, upstream and downstream. It is the first gigabit PON technology to achieve high volume deployment.
One of the most important advantages of GE-PON is the use of native Ethernet transport protocols. Low-cost asynchronous Ethernet has been deployed in the extended data network for years and there are significant economies of scale associated with gigabit Ethernet components such as optical interfaces. The asynchronous nature of Ethernet enables Ethernet-based network equipment to be much lower cost than comparable clock-synchronous ATM or SONET-based equipment.
IEEE 802.3ah - Key Facts- Ratified by the IEEE in June of 2004
- Combines Ethernet transport protocols with point to multipoint PON network topologies
- Also called Ethernet in the First Mile or EFM
- 1.0 Gbps symmetrical upstream and downstream bandwidth
- Includes mechanisms for network Operations, Administration and Maintenance (OAM)
- Supports Class of Service (CoS) operation for time-sensitive transport of data payloads such as video where video frames must be delivered in sequence and in time to prevent visible glitches
- Supports TDM using circuit emulation services
- Supports voice services with Voice over IP (VoIP)
ITU-T G.984 GPON - Gigabit PON
GPON has received a lot of attention since the ITU introduced the ITU-T G.984 recommendation in 2003. But the recommendations are still in flux with details still being updated. As a result, GPON is not yet widely deployed. GPON is based on the previous ITU BPON standard but has many similarities to GE-PON.
Introduced in 2003 as ITU-T G.984, GPON uses a new native Generic Encapsulation Method (GEM) transport layer that supports multiple "non-native" transport protocols including ATM, Ethernet, and TDM. The original intention was to broaden support and market acceptance by supporting multiple protocols, but the effect has been to add complexity to those systems not requiring additional protocol support. A key characteristic is the 2.5 Gbps downstream data rate and the 1.25 Gbps upstream data rate. GPON operates in a very similar fashion to GE-PON when supporting Ethernet as its primary transport protocol. But since Ethernet, gigabit Ethernet and 10Gb Ethernet do not support a 2.5 GHz clock rate, unlike GE-PON, GPON does not benefit from the availability of low-cost Ethernet optical components.
ITU-T G.984 - Key Facts- Recommendation from ITU-T in January of 2003, revisions in process
- Uses Generic Encapsulation Method (GEM) protocol layer to support Ethernet, ATM and TDM over point to multipoint PON network topologies
- 1.25 Gbps upstream and 2.5 Gbps downstream bandwidth
- Includes mechanisms for network Operations, Administration and Maintenance (OAM)
- Supports Class of Service (CoS) operation for time-sensitive transport of data payloads
- Supports TDM using circuit emulation services or transport over GEM
- Supports voice services with Voice over IP (VoIP)
GE-PON and GPON In the Market
Lacking the economies of scale and with the specifications still being updated, GPON deployment has lagged behind that of GE-PON. Nonetheless, with the backing of FSAN, the Full Service Access Networks organization, a group of worldwide carriers who play an important role in the ITU standards body, and the prospect simplifying protocol support to focus on Ethernet, GPON has garnered a great deal of interest in North America and other geographic regions seeking to adopt a gigabit PON standard for FTTH deployment.
