ONU hardware design based on PAS6301

ONU hardware design based on PAS6301

With the rapid development of the Internet, user Ethernet is widely used. For this reason, in December 2000, Ethernet equipment suppliers proposed a standard research plan for using PON Ethernet for access networks. This type of Ethernet using PON is called EPON. EPON (Ethernet Passive OpTIcal Network, Ethernet passive optical network) is a new type of optical fiber access network technology, which uses a point-to-multipoint structure, passive optical fiber transmission, and provides multiple services over Ethernet. It uses PON technology at the physical layer, Ethernet protocol at the link layer, and Ethernet access using the PON topology. Therefore, it combines the advantages of PON technology and Ethernet technology: low cost; high bandwidth; strong scalability, flexible and rapid service reorganization; compatibility with existing Ethernet; convenient management and so on.

1 ONU function introduction in EPON system

A typical EPON system consists of OLT, ONU, ODN, as shown in Figure 1. OLT (OpTIcal Line Terminal) is placed in the central computer room, and ONU (OpTIcal Network Unit) is placed near the user equipment or integrated with it. The optical distribution network ODN (OpTIcal Network Unit) is composed of optical fibers and one or more passive optical splitters and other passive optical devices, providing optical channels between the OLT and the ONU. According to the different location of the ONU in the access network, the EPON system can have several types of network applications: fiber to the junction box (FT-TCab), fiber to the building / distribution box (FTTB / C), fiber to the home user (FTTH), fiber to the company / office (FTTO).

The types of services that the EPON system may carry include Ethernet / IP services, voice services, TDM services, and CATV services, among which TDM services are E1 circuit simulation services. According to the IEEE802.3ah standard, the ONU serves as the user access device of the EPON system. The main functions can be described as:

◆ Select to receive broadcast data sent by OLT.
◆ Response to registration and ranging commands issued by OLT.
◆ Cache the user's Ethernet data, report the buffer queue status to the OLT and send the buffered data in the upstream sending window allocated by the OLT.
◆ According to the OAM frame sent by the OLT, perform the corresponding OAM function.
◆ Other related Ethernet functions.

2 ONU hardware system design

As shown in Figure 2, the basic hardware modules of ONU mainly include: PAS6301 chip, Ethernet switching module, FLASH, SDRAM, EEPROM, optical transceiver module.

2. 1 PAS6301 module

The PAS6301 chip is the latest EPON optical network unit (ONU) and optical path terminal (OLT) chip introduced by PMC-Sierra. The new devices include those used for user equipment. The combination of PAS6301 ONU and PSA5201 OLT for central office equipment can provide an end-to-end EPON solution that can support the algorithms and functions defined by China Telecom Group for the Chinese telecommunications market. The PAS6301 chip provides a solution to the key functions of EPON ONU based on the 802.3ah standard. It integrates a serial / parallel converter and an ARM922 processor, etc. Its goal is to achieve fiber-to-the-home (FTTH), and can also be used as an upstream physical layer device in the fiber-to-the-rack (FTTCab). Accompanying the PAS6301 chip is a complete software development platform and board-level support package that can help developers build a comprehensive ONU solution. PAS6301 also integrates Media Access Control (MAC) and protocol management functions, including upgraded IP address and UDP / TCP advanced packet classification engine (advanced packet classification engine), a 10/100/1000 Ethernet User interface, as well as analog-to-digital conversion and additional 10/100 Ethernet interface for exchange management.

2. 2 PAS6301 internal module introduction

As shown in Figure 3, the chip is mainly divided into five modules: EPON MAC module, packet processing engine, user network interface (UNI, User Network Inter-face), embedded subsystem and operation, management and maintenance module (OMA, Opera- tion, Administration & Maintenance). The functions of each module are as follows:

(1) MAC module

The EPON interface and MAC provide all the components and functions needed for transmission and reception.

(2) Packet processing engine module

EPON's packet processing engine function group serves as a bridge between the EPON protocol and the Ethernet protocol, and it is further divided into upstream service flows and downstream service flows. In addition to the upstream and downstream service flow data interfaces, it also has an external memory interface that provides the PACKETBUFFER function, and a special queue interface including PON queue and UNI to the CPU.

(3) UNI module

The UNI functional group provides a 10/100 / 1,000 Mbps Ethernet connection to the switching equipment, using the GMII interface.

(4) Embedded subsystem module

The PAS6301 subsystem function group monitors the configuration of all wake-up or management request modules on the device. This also includes monitoring and maintaining the status of all interfaces. In general, the embedded subsystem module monitors and executes real-time processes including clearing buffer memory and counting. It also implements the OAM protocol defined by the EPON system.

(5) OMA module

Based on the IEEE 802.3ah standard, PAS6301 provides comprehensive OAM functions for EPON systems. OAM support is implemented on an API that receives OAM messages with the ONU's own MAC address as the destination address.

3 Ethernet switch module

In this design, we use Marvell88E6045 from Marvell. It is connected with PAS6301 through GMII interface, as shown in Figure 4. Marvell 88E6045 is a 2GE + 4FE Ethernet switching chip, and its two GE ports are Port9 and Port1O which include serial / parallel conversion interfaces. The serial / parallel conversion interface can be used to connect 10/100/1000 copper PHY (Physical Layer) equipment at 3 times speed, 1000BASE fiber module or other switching equipment of Marvell. Port9 does not support GMII, so we use Port10, which can be connected to MII or GMII, to expand Port10 port, providing users with 4 FE interfaces and 1 GE interface.

4 Storage module

4.1 FLASH

We use S29GL032M90 chip as Flash memory. It uses the MirrorBit technology of 0.23 μm, the access time is up to 90 ns, and only 3 volts are required for reading and writing. When the voltage changes, its low voltage detector will automatically prevent write operations to protect hardware data. The main pins of FLASH and PAS6301 are connected as shown in Figure 5. The related functions include: RY_NBY pin input CPU interrupt signal to MEM_IRQO; A [1:22] receives the CPU interface address signal of MEM_AD [1:22]; CPU passes D [0 : 15] and MEM_D [0: 15]