The difference between EPON / GPON

A friend asked about the difference between EPON and GPON. Today we will look at the comparison between them.

The application and difference between EPON and GPON

1. Introduction to PON

1. What is PON

PON (passive optical network) technology (including EPON, GPON) is the main implementation technology for the development of FTTx (fiber-to-the-home), which can save backbone fiber resources and network layers, and can provide bidirectional high-bandwidth capabilities under long-distance transmission conditions. There are a variety of access services, and its remote management capability and passive optical distribution network structure can greatly reduce operation and maintenance costs, and can support a variety of application scenarios.

2. PON technology development

Since the emergence of PON, it has been developed for many years, and a series of concepts, specifications and product sequences such as APON, BPON, EPON, and GPON have been formed.

APON (ATMPON)

ATM is a transport protocol based on cells. 155Mb/s PON system technical specifications, ITU-TG.983 series standards;

BPON (Broadband PON)

The APON standard has been strengthened later to support a transmission rate of 622Mb/s, and functions such as dynamic bandwidth allocation and protection have been added at the same time.

EPON (Ethernet PON)

GPON (Gigabit PON)

3. Optical fiber access technology

2. Introduction of EPON

1. What is EPON?

EPON (Ethernet Passive Optical Network) is a point-to-multipoint network structure, passive optical fiber transmission mode, based on high-speed Ethernet platform and TDM (time division multiplexing) time-division MAC media access control mode, providing multiple A broadband access technology for integrated services.

The EPON system adopts WDM technology to realize single-fiber bidirectional transmission.

2. The principle of EPON

In order to separate the incoming and outgoing signals of multiple user pairs on the same optical fiber, the following two multiplexing techniques are used.

a. The downstream data flow adopts broadcasting technology.

b. The upstream data flow adopts TDMA technology.

3. The principle of EPON - downlink

a. Assign a unique LLID after ONU successfully registers.

b. Add an LLID before the start of each packet, replacing the last two bytes of the Ethernet preamble.

c. When the OLT receives data, it compares the LLID registration list. When the ONU receives data, it only receives frames or broadcast frames that match its own LLID.

4. The principle of EPON - uplink

a. The OLT compares the LLID registration list before receiving the data.

b. Each ONU sends a data frame in the time slot uniformly allocated by the office equipment.

c. The allocated time slot compensates the distance difference between each ONU and avoids the collision between each ONU.

5. Working process of EPON system

Operation of the OLT

a. Generate a timestamp message for the system reference time.

b. Assign bandwidth through MPCP frame 3. Perform ranging operation.

c. Control ONU registration.

ONU operation

a. The ONU synchronizes with the OLT through the time stamp of the downlink control frame.

b. The ONU waits for the discovery frame

c. The ONU performs discovery processing, including: ranging, specifying a physical ID and bandwidth.

d. The ONU is waiting for authorization, and the ONU can only send data at the authorized time

6. Design of EPON network management system

EPON network management system is divided into four modules according to network management functions: configuration management, performance management, fault management and security management.

7. Realization of EPON network management system

a. The realization of EPON network management system includes the realization of management station network management software and agent station software.

b. Management station The network management system is a control entity that provides users with a friendly interactive interface and uses the SNMP protocol to manage the agent process.

c. The realization of SNMP in the agent station mainly includes the realization of agent process software and the design and organization of MIB.

3. Introduction to GPON

1. What is GPON?

GPON (Gigabit-CapablePON) technology is the latest generation of broadband passive optical integrated access standard based on the ITU-TG.984.x (ITU TG.984.x) standard, with high bandwidth, With many advantages such as high efficiency, large coverage area, and rich user interfaces, it is regarded by most operators as an ideal technology for realizing broadband and comprehensive transformation of access network services.

2. GPON principle

GPON downlink - broadcast transmission

GPONS uplink - TDMA mode

The network topology of passive optical fiber transmission is mainly composed of OLT (Optical Line Terminal), ODN (Optical Distribution Network), and ONU (Optical Network Unit).

ODN provides optical transmission means for OLT and ONU. It is composed of passive optical splitter and passive optical combiner. It is a passive device connecting OLT and ONU.

3. GPON principle - uplink

a. The transmission of uplink data is uniformly controlled by the OLT.

b. The ONU transmits user data according to the time slot allocated by the OLT to avoid data transmission conflicts generated by the ONU.

c. The ONU inserts uplink data into its own time slot according to the time slot allocation frame, realizing the sharing of uplink channel bandwidth between multiple ONUs.

4. GPON networking mode

The main networking methods used by GPON are FTTH/O, FTTB+LAN and FTTB+DSL.

a. FTTH/O is fiber to the home/office. After the optical fiber enters the optical splitter, it is directly connected to the user ONU. One ONU is only used by one user, with high bandwidth and high cost. It is generally aimed at high-end users and business users.

b. FTTB+LAN is fiber to the building, and then different services are connected to multiple users through a large-capacity ONU (called MDU). Therefore, multiple users share the bandwidth resources of one ONU, and each person occupies a lower bandwidth and lower cost. , generally aimed at low-end residential and low-end commercial users.

c. FTTB+ADSL is fiber to the building, and then the business is connected to multiple users in the form of ADSL, and multiple users share one ONU. The bandwidth, cost and customer base are similar to FTTB+LAN.

Four, GPON and EPON technology comparison

According to the different characteristics of GPON and EPON technology, the following analysis can be made on these two technologies.

1. GPON supports a variety of speed levels, and can support asymmetric uplink and downlink speeds. GPON has a greater margin in the selection of optical devices, which can reduce costs.

2. EPON only supports ODN levels of Class A and B, while GPON can support Class A, B and C, so GPON can support a split ratio of up to 128 and a transmission distance of up to 20km.

3. Compared with the protocol alone, because the EPON standard is based on the 802.3 architecture, compared with the GPON standard, its protocol layering is simpler and the system implementation is easier.

4. ITU has continued to use many concepts of the APON standard G.983 in the process of formulating the GPON standard, which is more complete than the EPON standard formulated by EFM. Stipulating a high-efficiency TC layer mechanism will become a key point for ITU in formulating GPON standards.

5.The GPON standard stipulates that the TC sublayer can adopt two encapsulation methods, ATM and GFP, among which the GFP encapsulation method is suitable for carrying high-layer protocols based on packets such as IP/PPP.