GEPON (Gigabit Ethernet PON) is a high-speed optical access technique standardized by IEEE802.3ah / EFM. In the beginning, this technology was called EPON but due to the effects of the service, it was known as Gigabit-EPON.
GEPON is a fiber optic network point-to-multipoint suitable for application to FTTH and FTTB, in which optical fiber is used to serve some customers. Architectural of PON consists of OLT (Optical Line Termination) on the provider side and one or several ONU (Optical Network Units) on the subscriber side. Such type of architecture is better than point-to-point architectural.
There are some basic GEPON principles, namely:
Communication between OLT and ONU
GEPON uses Ethernet packet encapsulation structure for communication on layer 2. Data is sent to the variable length data packets to a maximum of 1518 bytes according to 802.3ah standard, in which an OLT can be connected up to 32 ONU. All ONU share the bandwidth of 1Gbps via TDM, so that each ONU can provide maximum bandwidth to 1Gbps uplink and downlink.
GEPON does not require complicated protocol to transmit precise optical signals to the customers because signals from the customers can be transmitted centrally to OLT.
OLT sends multicast data to all the ONU through ODN (Optical Distribution Network). Network architecture is in the form of point-to-multipoint. ONU receives data according to its address. Other data that does not comply will be rejected by the ONU.
Each ONU share the bandwidth using TDMA (Time Division Multiple Access).
Upstream transmission of the ONU to OLT is done in multiple access, communicating first with point-to-point mode then multipoint-to-point mode after.
To control the optical network point-to-multipoint, GEPON uses MPCP (Multi-Point Control Protocol), which served to optimize the working bandwidth, bandwidth demand, auto discovery process, and range of process.
The figure shows the process of communication between the OLT and ONU. Within OLT, there is DBA (Dynamic Bandwidth Allocation) which serves to allocate bandwidth to each ONU. In GEPON, a bandwidth of 1Gbps is distributed to all ONU. A bandwidth allocation method sets the bandwidth to each ONU with a fixed value (static allocation) without considering the upstream traffic. This method causes a significant waste of bandwidth if bandwidth is still allocated even if there is no traffic. By using the DBA, the bandwidth is allocated according to the amount of the upstream traffic, making it more efficient.
There is a priority service that is set by the DBA. QoS (Quality of Service) is a concept that regulates a number of strategies in the transmission of network data traffic. Priority service refers to GEPON standard 802.1p with 8 priority level queue. Eight level of queues is classified in CoS (Class of Service) which focused on three priority service where bandwidth settings is performed by DBA. All three classes of service, namely:
1. High Priority
Used for fixed bandwidth services for applications sensitive to end-to-end delay or jitter, for example, voice service.
2. Medium Priority
Used for applications that are not too sensitive to end-to-end delay or jitter, but still requires guaranteed bandwidth.
3. Low Priority
Used for service with Best Effort traffic class that is not sensitive to end-to-end delay or jitter.
GEPON is designed for telecommunication purposes. Some advantages of GEPON are easy to integrate, flexible, easy to set up, and provides QoS function. In addition, GEPON can also replace the pre-existing DSL technology because GEPON is able to provide high bandwidth (up to 1Gbps) and also able to serve several needs at the same time.
GEPON provides connectivity for all types of IP or Ethernet communications packet, using layer 2 network that uses IP to carry voice, data, and video. Because the Ethernet device is readily available, the implementation of GEPON is quite cost efficient. In addition, GEPON also provides secure communications because there is encryption on both ends (upstream and downstream), so that information leakage can be minimized.
By using GEPON standard, there is no limit to the number of ONU used on the customer side. Large number of ONU and high speed networks can be applied to FTTH projects, such as IP-telephone access, broadband data, and IPTV.
GEPON is the right combination of Ethernet technology and passive optical network technology. With GEPON technology, the usage of active fiber optic components between the OLT and ONU can be reduced, thus saving costs and simplifying maintenance.