H3C Technologies H3C SR8800 - Manual (Page 53)

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Terms
• Multiplex unit—A basic SDH multiplex unit includes containers (C-n), virtual containers (VC-n),
tributary units (TU-n), tributary unit groups (TUG-n), administrative units (AU-n), and administrative
unit groups (AUG-n), where n is the unit level sequence number.
• Container—Information structure unit that carries service signals at different rates. G.709 defines
the criteria for five standard containers: C-11, C-12, C-2, C-3 and C-4.
• Virtual container (VC)—Information structure unit supporting path level connection of SDH. It
terminates an SDH path. VCs are divided into lower-order and higher-order VCs. VC-3 in AU-3 and
VC-4 are higher-order VCs.
• Tributary unit (TU) and tributary unit group (TUG)—TU is the information structure that provides
adaptation between higher-order paths and lower-order paths. TUG is a set of one or more TUs
whose locations are fixed in higher-order VC payload.
• Administrative unit (AU) and administrative unit group (AUG)—AU is the information structure that
provides adaptation between the higher-order path layer and the multiplex section layer. AUG is a
set of one or more AUs whose locations are fixed in the STM-N payload.
• Optical carrier (OC)—OC is a series of physical protocols (including OC-1, OC-2, and so on)
defined for optical transmission over an SONET network. The number in an OC level corresponds
to a rate for STS frames. The base rate is 51.84 Mbps (OC-1), the rate of OC-3 is 155.52 Mbps, and
so on.
E-CPOS
The low-speed tributary signals multiplexed to form an SDH signal are called channels. A channelized
POS (CPOS) interface makes full use of SDH to provide precise bandwidth division, reduce the number
of low-speed physical interfaces on network devices, enhance their distribution capacity, and improve
the access capacity of dedicated lines.
The basic functions of enhanced CPOS (E-CPOS) interfaces and CPOS interfaces are the same but their
port rate hierarchies and channelization levels are different. For more information, see “
Configuring the
operating mode of an E-CPOS interface/channel .”
Channelized and unchannelized
• A channelized POS interface uses the low-speed tributary signals of STM-N to transmit multiple
streams of data independent of one another over an optical fiber. Each data stream shares
separate bandwidth and has its own start point, end point, and monitoring policy. They are called
channels.
• An unchannelized POS interface uses all STM-N signals to transmit a stream of data over an optical
fiber. The transmitted data has the same identifier, start point, and end point, and is regulated by
the same monitoring policy.
When multiple streams of low-speed signals are to be transmitted, channelization can make better use of
bandwidth. When a single high-speed stream of data is to be transmitted, the unchannelized mode is
recommended.
Operating modes of E-CPOS interfaces
An E-CPOS interface can operate in channelized mode or concatenated mode:
• In channelized mode, a higher-order STM-N frame is regarded as being formed by four lower-order
STM-N frames through time-division multiplexing. In this case, a higher-order STM-N frame will be
demultiplexed into multiple lower-order STM-N frames for processing.