Differences between EPON and GPON
Nowadays, optical network technologies are becoming more and more popular. When it comes to optical networks, EPON and GPON technologies are the most discussed. This post will briefly describe the differences between these two technologies.
Ethernet Passive Optical Network (EPON) is an Ethernet-based PON technology. It adopts the point-to-multipoint structure and passive optical fiber transmission and provides multiple services over the Ethernet.
The EPON technology is standardized by the IEEE802.3 EFM working group. The IEEE802.3EFM working group released the EPON standard, IEEE802.3ah, which will be incorporated into the IEEE802.3-2005 standard. In this standard, Ethernet and PON technologies are combined.
The PON technology is used at the physical layer and the Ethernet protocol is used at the data link layer. The PON topology is used to implement Ethernet access.
The GPON technology originated from the ATM PON technology standard gradually formed in 1995.
The GPON(Gigabit-Capable Passive Optical Network) was first proposed by the FSAN organization. Based on this, ITU-T formulated ITU-T G.984.1 and G.984.2 in March 2003.
Later, G.984.3 was gradually standardized. In this way, the GPON technical standard is finally formed.
EPON provides fixed upstream and downstream 1.25 Gbit/s, and adopts 8b/10b line coding. The actual rate is 1 Gbit/s.
GPON supports multiple rate levels and supports asymmetric upstream and downstream rates, such as 2.448 Gbit/s or 1.244 Gbit/s in the downstream direction, 1.224 Gbit/s or 622 Mbit/s in the upstream direction.
According to the EPON standard, the split ratio is 1:32 and 1:64.
According to the GPON standard, the split ratio is 1:32, 1:64, and 1:128.
Comparison between GPON and EPON protocol stacksEPON adopts a simple Ethernet data format and uses MPCP point-to-multipoint control protocol to realize the functions of bandwidth allocation, registration, and ranging in the EPON system.
GPON uses a brand-new transmission convergence (TC) layer, defines ATM encapsulation and GFP encapsulation, and provides diversified services and more powerful functions.
Please refer to the following table to understand the differences between the two.
QOS (Quality of Service)
EPON network adds a 64-byte multipoint control protocol (MPCP) to the Ethernet header at the MAC layer. MPCP controls access to the P2MP P2MP topology through messages, state machines, and timers, implementing DBA dynamic bandwidth allocation.
MPCP involves the allocation of ONU transmit timeslots, automatic discovery and joining of ONUs, and reporting of congestion to the upper layer for dynamic bandwidth allocation.
MPCP provides basic support for the P2MP topology architecture. However, MPCP does not classify service priorities. All services compete for bandwidth randomly. GPON has a more complete DBA and provides excellent QoS service capabilities.
In GPON, service bandwidth allocation modes are classified into fixed bandwidth, assured bandwidth, non-assured bandwidth, and best-effort bandwidth in descending order. The DBA further defines a traffic container (T-CONT) as an upstream traffic scheduling unit, and each T-CONT is identified by an Alloc-ID. Each T-CONT can contain one or more GEM port IDs.
T-CONTs are classified into 5 types. Different types of T-CONTs have different bandwidth allocation modes to meet different QoS requirements for different service flows, such as delay, jitter, and packet loss ratio.
- T-CONT type 1 is characterized by fixed bandwidth and fixed timeslots, corresponding to fixed bandwidth (Fixed) allocation. T-CONT type 1 is suitable for delay-sensitive services, such as voice services.
- T-CONT type 2 is characterized by fixed bandwidth but uncertain timeslots, corresponding to assured bandwidth allocation. T-CONT type 2 is applicable to fixed bandwidth services that have low jitter requirements, such as video on demand (VoD) services.
- T-CONT type 3 is characterized by the minimum bandwidth guarantee and dynamic sharing of surplus bandwidth. In addition, T-CONT type 3 has the restriction of the maximum bandwidth and corresponds to the non-assured bandwidth allocation. T-CONT type 3 is applicable to services that require service assurance but have large burst traffic, such as downloading services.
- T-CONT type 4 feature is Best Effort and has no bandwidth guarantee. T-CONT type 4 is applicable to services that have low requirements on delay and jitter, such as web browsing services.
- T-CONT type 5 is a combination type. After the assured and non-assured bandwidths are allocated, the extra bandwidth requirements are allocated as best as possible.
When you configure the line profile on the OLT, you can find that the T-CONT cannot be configured in the EPON line profile.