Overview
Packet over SONET (synchronous optical network)/SDH (synchronous digital hierarchy) is the serial transmission of data over SONET frames through the use of a protocol such as Point-to-Point Protocol (PPP).
POS is an ideal feature for networks that are built to provide IP data. It provides superior bandwidth utilization and efficiency compared with other transport methods. For expensive WAN links, POS can provide as much as 25 to 30 percent higher throughput than Asynchronous Transfer Mode (ATM)-based networks. By transporting frames directly into the SONET payload, you eliminate the overhead required in an ATM cell header for IP over ATM encapsulation.
E-series routers support PPP over SONET/SDH.
Features
POS supports the following features:
- Payload scrambling
- Clock source configuration
- Maximum transmission unit (MTU) size configuration
- Maximum receive unit (MRU) size configuration
- POS framing
- CRC checking
- Loopback configuration
SONET/SDH
SONET is an ANSI standard for transmitting bits over fiber-optic cable. SDH is the international standard defined by the ITU (International Telecommunication Union). SONET/SDH is the physical infrastructure of choice for carrier ATM networks operating at speeds above 50 Mbps.
SONET allows carriers to build high-speed international links without requiring conversion from one transmission protocol to another (for example, T1 to T3 or T1 to E3 conversion).
SONET transmission speeds start at 51.84 Mbps and are referred to as OC1. All other speeds are simply multiples of this base number.
Table 76 shows the speeds of the most common SONET/SDH implementations. The NMC-RX application supports OC3, OC3-POS, OC12-POS, and OC48-POS modules.