Cisco Systems PA-POS-2OC3, PA-POS-1OC3 manual SONET/SDH Overview, Sonet, SDH Equivalent

Chapter 1 PA-POS-1OC3 Overview

SONET/SDH Overview

Figure 1-1shows the PA-POS-1OC3 faceplate.

Figure 1-1 PA-POS-1OC3 Faceplate

		KLASSE			1	1					PA-POS-1OC3
							1	RX		TX ALARM
						CLASE
	DERDE		CLASSE
	PRODUCT			LASER
	LASER
ENABLED	1
	CLASSLASERPRODUKTPRODUIT PRODUCTO								POS 0	RCV	121578

SONET/SDH Overview

The POS specification addresses the use of PPP encapsulation over SONET/Synchronous Digital Hierarchy (SDH) links. SONET is an American National Standards Institute (ANSI) standard (T1.105-1988) for optical digital transmission at hierarchical rates from 51.840 Mbps (STS-1) to

2.5Gbps (STS-48) and greater. SDH is the international standard for optical digital transmission at hierarchical rates from 155.520 Mbps (STM-1) to 2.5 Gbps (STM-16) and greater.

Because SONET/SDH is by definition a point-to-point circuit, PPP is well suited for use over these links. PPP was designed as a standard method of communicating over point-to-point links.

SONET is an octet-synchronous multiplex scheme that defines a family of standard rates and formats. The basic rate for POS is that of STS-3c/STM-1, which is 155.520 Mbps. The available information bandwidth is 149.760 Mbps, which is the STS-3c/STM-1 Synchronous Payload Envelope (SPE), the payload portion of the SONET frame into which the octet-oriented user data is mapped. (Octet boundaries are aligned with the SPE octet boundaries.) For the SPE with the PA-POS-1OC3, section, line, and path overhead are removed.

The International Telecommunications Union Telecommunication Sector (ITU-T) defines a series of SDH transmission rates beginning at 155.520 Mbps, as follows:

SONET1	SDH Equivalent
STS-3c2	STM-12
STS-12c	STM-4c
STS-48c	STM-16c

1.ANSI-defined SONET specifications.

2.Supported by the PA-POS-1OC3.

Despite the name, SONET is not limited to optical links. Electrical specifications have been defined for single-mode fiber, multimode fiber, and CATV 75-ohm coaxial cable. The PA-POS-1OC3 allows transmission over single-mode and multimode optical fiber. Transmission rates are integral multiples of 51.840 Mbps, which can be used to carry T3/E3 bit-synchronous signals.

The following transmission multiples are currently specified and commonly used:

•STS-3c—155.520 Mbps (the PA-POS-1OC3 conforms to STS-3c)

•STS-12c—622.080 Mbps

•STS-48c—2,488.320 Mbps

PA-POS-1OC3 Single-Port Port Adapter Installation and Configuration Guide

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