As the two main members of optical network access, EPON and GPON each have their own merits, compete with each other, complement each other, and learn from each other. The following will compare them in various aspects.
Rate
EPON provides fixed uplink and downlink 1.25 Gbps, adopts 8b/10b line coding, and the actual rate is 1Gbps.
GPON supports a variety of rate levels, which can support asymmetric uplink and downlink rates, 2.5Gbps or 1.25Gbps for downlink, and 1.25Gbps or 622Mbps for uplink. The uplink and downlink rates are determined according to actual needs, and the corresponding optical modules are selected to increase the rate-price ratio of optical devices.
Split ratio
The split ratio is how many ONUs (user terminals) are carried by an OLT port (central office).
The EPON standard defines a split ratio of 1:32.
The GPON standard defines the following split ratios: 1:32; 1:64; 1:128.
In fact, technically EPON systems can also achieve higher split ratios, such as 1:64, 1:128, and the EPON control protocol can support more ONUs. The split ratio is mainly limited by the performance index of the optical module, and a large split ratio will cause the cost of the optical module to rise substantially.
GPON provides multiple options, but the cost advantage is not obvious. Maximum transmission distance The maximum physical distance that the GPON system can support. When the optical splitting ratio is 1:16, it should support a maximum physical distance of 20km; when the optical splitting ratio is 1:32, it should support a maximum physical distance of 10km. EPON is the same as this, but it is equal in general.
Service quality
The Ethernet protocol itself does not have the ability to handle QoS. Therefore, in order to enable EPON to serve users, a concept of virtual local area network is proposed. VLAN proposes that the priority identification of received frames can be modified to lay the foundation for QOS, but because VLAN is implemented manually, which is extremely costly. And GPON has its own excellent QoS service capabilities.
EPON and GPON link layer comparison
Compared with GPON, EPON is simpler and more direct. In pure Ethernet transmission, the two encapsulation methods and ATM support of GPON will not play a big role.
However, in access network services, EPON is only suitable for data transmission services, while GPON can provide three-in-one services.
EPON is an all-Ethernet solution that fully complies with the characteristics, performance and performance of the Ethernet protocol, while GPON uses synchronous optical network/synchronous digital system technology and general framing protocol for Ethernet transmission.
EPON and GPON have their own advantages and disadvantages. In terms of performance indicators, GPON is superior to EPON, but EPON has advantages in time and cost. GPON is catching up. Looking forward to the future broadband access market, it may not be who replaces others, but coexists and complements each other.For customers with high bandwidth, multi-service, QoS and security requirements, and ATM technology as the backbone network, GPON will be more suitable. For cost-sensitive customer groups with low QoS and security requirements, EPON has become the dominant one.