Overview of POS Interfaces
A POS interface uses SONET/SDH as the physical-layer protocol and provides a high-speed, reliable, and P2P IP data transfer.
Introduction to POS
A POS interface uses SONET/SDH to transfer IP data in MAN and WAN. The POS uses the link-layer protocol (FR, PPP and HDLC) to encapsulate IP packets, uses the service adapter at the SONET/SDH channel layer to map the packets to the payload of SONET/SDH signals, then uses the SONET/SDH transport layer and section layer to add a path overhead and segment overhead and encapsulate the payload in a SONET/SDH frame, and finally transmits it on the optical network.
The device provides POS interfaces with two rates and their signal level are OC-3/STM-1 (155 Mbit/s) and OC-12/STM-4 (622 Mbit/s).
SONET and SDH Overview
- In electrical signal, the basic rate is called level-1 Synchronous Transport Signal (STS-1).
- In optical signal, the basic rate is called level-1 Optical Carrier (OC-1).
ITU-T, based on SONET, develops a worldwide standard synchronous digital hierarchy (SDH), which is mainly used in Europe.
The basic rate of SDH is 155.52 Mbit/s, which is called STM-1. This rate equals the OC-3 rate in SONET.