Fiber Optic Wiki

The basic unit of transmission

September 20, 2011

The basic unit of framing in SDH is a STM-1 (Synchronous Transport Module level 1), which operates at 155.52 Mbps.

STS-3c/STM-1 which operates three times faster than STS-1

September 20, 2011

In packet-oriented data transmission such as Ethernet, a packet frame usually consists of a header and a payload. The header is transmitted first, followed by the payload (and possibly a trailer, such as a CRC). In synchronous optical networking, this is modified slightly. The header is termed the overhead and instead of being transmitted before the payload, is interleaved with it during transmission.

The STM-1 frame

September 20, 2011

The STM-1 (synchronous transport module level - 1) frame is the basic transmission format for SDH or the fundamental frame or the first level of the synchronous digital hierarchy. The STM-1 frame is transmitted in exactly 125 microseconds, therefore there are 8000 frames per second on a fiber-optic circuit designated OC-3 (Optical Carrier-3). The STM-1 frame consists of overhead and pointers plus information payload.

Transport overhead

September 20, 2011

The transport overhead is used for signaling and measuring transmission error rates, and is composed as follows:

Path virtual envelope

September 20, 2011

Data transmitted from end to end is referred to as path data. It is composed of two components:

SDH and relationship to 10 Gigabit Ethernet

September 20, 2011

Another circuit type amongst data networking equipment is 10 Gigabit Ethernet (10GbE). The Gigabit Ethernet Alliance created two 10 Gigabit Ethernet variants: a local area variant (LAN PHY) with a line rate of 10.3125 Gbps, and a wide area variant (WAN PHY) with the same line rate as OC-192/STM-64 (9,953,280 kbps).

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