Network Applications of ETH PWE3
8.2 Native TDM
In Native TDM, TDM frames are directly encapsulated to GPON GEM frames in TDMoGEM mode. This mode features simple encapsulation, small network cost, and guaranteed link quality.
8.2.1 Introduction
Definition
By using the standard 8 kHz (125μm) frames, the GPON GTC layer is synchronous in nature.
Therefore, GPON can support the TDM service. This is called Native TDM.
In Native TDM, TDM frames are directly encapsulated to GPON GEM frames in TDMoGEM mode. This mode features simple encapsulation, small network cost, and guaranteed link quality.
Purpose
Currently, the circuit switched network is evolving to the packet switched network. During the deployment of the packet switched network, the method to provide traditional circuit switching service over the packet switched network must be taken into consideration. In a GPON network deployment, the traditional TDM service can be delivered over the PSTN network through the Native TDM mode.
8.2.2 Specifications
l Each TOPA board provides 16 E1 upstream ports or two STM-1 ports.
l Each TOPA board provides 2 STM-1 ports and supports processing the Native TDM service based on packet transmission.
l Up to 63 TDM service streams can be configured on each STM-1 upstream port.
l The STM-1 port supports 1+1 protection.
l The STM-1 port supports the system clock, line clock, and recovery clock.
l Each TOPA board supports two STM-1 ports, with each STM-1 port supporting creation of up to 63 TDM service virtual ports. Therefore, each TOPA board supports creation of up to 126 TDM service virtual ports.
l The 24-hour BER of the TDM service is 0.
l The delay of the TDM service transmission from the E1 port on the ONT to the upstream STM-1 port on the OLT must be shorter than 1.5 ms.
8.2.3 Reference
The following lists the reference documents of Native TDM:
l ITU-T G.984.1 General characteristics for Gigabit-capable Passive Optical Networks (GPON)
Module
Feature Description 8 Layer 2 VPN
l ITU-T G.984.2 Gigabit-capable Passive Optical Networks (GPON): Physical Media Dependent (PMD) layer specification
l ITU-T G.984.3 Gigabit-capable Passive Optical Networks (GPON): Transmission convergence layer
l ITU-T G.984.4 Gigabit-capable Passive Optical Networks (GPON): ONT management and control interface specification
8.2.4 Availability
Hardware support
The Native TDM feature needs the cooperation between the TOPA board and the GPBC or GPBD board.
License support
The Native TDM feature is the basic feature of the MA5600T/MA5603T. Therefore, no license is required for accessing the corresponding service.
Limitation
l The E1 ports of the ONU/ONT must support the Native TDM mode.
l The E1 service traffic is processed as the unstructured data stream in a unified way. The structured channel mode is not supported.
l The STM-1 port does not support the OC-3 mode.
8.2.5 Principle
Basic Principle
The MA5600T/MA5603T supports E1 and STM-1 upstream transmission mode. The following section uses E1 upstream transmission as an example.
NOTE
The application of STM-1 upstream transmission is similar to the application of E1 upstream transmission.
The only difference lies in that different daughter boards are attached to the TOPA boards in two applications. When the TOPA board provides STM-1 ports, STM-1 frames are generated. One STM-1 frame can encapsulate and multiplex up to 63-channel E1 service signals (One STM-1 frame contains one VC4, one VC4 maps 63 VC12s, and one VC12 maps one-channel E1 service signal).
In the TDMoGEM mode, the TDM frame is directly encapsulated to the GPON GEM frame so that the TDM service can be transmitted in a GPON network. Figure 8-39 shows the basic principle of Native TDM.
Module
Feature Description 8 Layer 2 VPN
Figure 8-39 Basic principle of Native TDM
输入TDM 业务
Input buffer
GEM frame TDM byte buffer
Poll each frame to confirm the sent
bytes Input of TDM
service
PLI
Payload:TDM field PortID
PTI HEC
TDM data
Mapping of the TDM service to the GEM frames allows variation of the GEM frame length based on frequency offset of the TDM service. The length of the TDM field is specified by the PLI field.
In the adaptation process of the TDM source, the input data enters a queue in the input buffer.
When a frame arrives (namely for every 125 µs) there, the multiplexing entity of the GEM frame records the number of bytes to be sent in the current GEM frame. In general, the PLI specifies a fixed byte count based on the TDM nominal rate. But it happens that the bytes larger or smaller than the fixed byte count are sent, which are reflected in the PLI field.
The TDMoGEM mode does not distinguish whether it is a structured service such as the voice and PBX access services, or an un-structured service such as private line service. All services are handled as un-structured services. GPON access transparently delivers only the E1 service without performing the refined service processing. In other words, GPON access provides the long-haul E1 transmission.
In general, the private line service has an independent clock, which is asynchronous with the GPON line clock. The jitter and frequency difference exist between the two clocks. Therefore, the E1 service traffic can be transmitted only after the E1 rate adjustment occurs at the ONU.
The bit asynchronous mapping mode of SDH is adopted while the GPON line clock or system clock is used as the reference clock. Through the bit adjustment, the E1 service traffic is mapped to the payload section of the tributary unit to form a standard VC12 virtual channel, which is delivered in the GEM frame. At the receiver end, de-byte adjustment is adopted to recover the original clock and the E1 service traffic.
Application
Figure 8-40 shows the TDMoGEM network application. The E1 ports of the ONU/ONT access the TDM traffic from the base stations and enterprises. The ONU/ONT sends both the Ethernet traffic and the TDM traffic to the OLT. The OLT differentiates the Ethernet traffic and the TDM traffic, and sends the traffic to the IP network and the SDH network, respectively.
Module
Feature Description 8 Layer 2 VPN
Figure 8-40 Native TDM network application
E1 GPON
Ethernet Ethernet
E1
Ethernet E1
Ethernet E1
TDMoGEM ONU
ONU
ONU
GPON
SDH Base station
Business center
OLT
Business center
8.3 Glossary, Acronyms, and Abbreviations
This topic provides the glossary, acronyms, and abbreviations of the Layer 2 tunnel emulation feature.
Glossary
None
Acronyms and Abbreviations
Table 8-4 Acronyms and abbreviations of the Layer 2 Tunnel Emulation feature Acronym/Abbreviation Full Spelling
PWE3 Pseudo Wire Emulation Edge-to-Edge
TDM Time-Division Multiplexing
SAToP Structure-Agnostic Transport over Packet
CESoP Circuit-Emulation Service over Packet
MPLS Multi-Protocol Label Switching
LDP Label Distribute Protocol
LSP Label Switching Path
Module
Feature Description 8 Layer 2 VPN
Acronym/Abbreviation Full Spelling
BTS Base Transceiver Station
BSC Base Station Controller
Module
Feature Description 8 Layer 2 VPN