Synchronous Optical Network (SONET) is an American National
Standards Institute (ANSI) specification format used in transporting digital
telecommunications services over optical fiber.
Channelized SONET provides the ability to transport SONET frames
across multiplexed T3/E3 and virtual tributary group (VTG) channels.
SONET uses Synchronous Transport Signal (STS) framing. An STS is
the electrical equivalent to an optical carrier 1 (OC-1).
A channelized SONET interface is a composite of STS streams,
which are maintained as independent frames with unique payload pointers. The
frames are multiplexed before transmission.
When a line is channelized, it is logically divided into smaller
bandwidth channels called
paths. These paths carry the SONET payload. The sum of the
bandwidth on all paths cannot exceed the line bandwidth.
When a line is not channelized, it is called
clear channel, and the full bandwidth of the line is
dedicated to a single channel that carries broadband services.
The T3/E3 channels can be
channelized into T1s, and the T1s can be channelized further into DS0 time
Channelizing a SONET line consists of two primary processes:
You configure the controller first by setting the mode of the
When the mode is specified, the respective controller is
created, and the remainder of the configuration is applied on that controller.
For example, mode T3 creates a T3 controller. The T3 controller can then be
configured to a serial channel, or it can be further channelized to carry T1s,
and those T1s can be configured to serial interfaces.
Depending on the support for
your installed SPA, each STS path can be independently configured into T3s,
E3s, or VTGs, and so on.
The following level of SONET channelization modes are supported
in CEoP SPA:
OC3->STS-1->VTG-> VT1.5 -> Unframed T1
OC3->STS-1->VTG-> VT1.5 -> T1 -> DS0
This figure shows the VTG paths that can be configured.
Only VTG paths are supported on the Cisco 1-Port Channelized
OC-3/STM-1 SPA on the
Cisco ASR 9000 Series Router.
Figure 1. SONET VTG Channelized Paths
Synchronous Digital Hierarchy
(SDH) is the international equivalent of SONET.
SDH uses Synchronous
Transport Mode (STM) framing. An STM-1 is the electrical equivalent to 3
optical carrier 1s (OC-1s). A Synchronous Transport Module (STM) signal is the
Synchronous Digital Hierarchy (SDH) equivalent of the SONET STS, but the
numbers are different for each bandwidth. In this guide, the STM term refers to
both path widths and optical line rates. The paths within an STM signals are
called administrative units (AUs).
A summary of the basic
terminology differences between SONET and SDH is as follows:
SONET STS is equivalent to SDH administrative unit (AU)
SONET VT is equivalent to SDH tributary unit (TU)
SDH basic building blocks are STM-1 (equivalent to STS-3) and
STM-0 (equivalent to STS-1)
An administrative unit (AU)
is the information structure that provides adaptation between the higher-order
path layer and the multiplex section layer. It consists of an information
payload (the higher-order virtual container) and an administrative unit
pointer, which indicates the offset of the payload frame start relative to the
multiplex section frame start.
An AU can be channelized into
tributary units (TUs) and tributary unit groups (TUGs).
An administrative unit 3
(AU-3) consists of one STM-1.
An administrative unit group
(AUG) consists of one or more administrative units occupying fixed, defined
positions in an STM payload.
This table shows the commonly used notations and terms in SONET
standards and their SDH equivalents.
Table 1 SONET and SDH Terminology Equivalencies
The following levels of SDH
channelization are supported on the CEoP SPA:
This figure shows an example of SDH AU-3 paths that can be
configured on the CEoP SPA.
Figure 2. SDH AU3 Paths
This figure shows the SDH AU4 paths that can be configured on
the CEoP SPA.