Cem Overview - Cisco ASR 900 Series Configuration Manual

CEM Overview

VC
SDH supports a concept called VC. Through the use of pointers and offset values, VCs can be carried in the
SDH payload as independent data packages. VCs are used to transport lower-speed tributary signals. Note
that it can start (indicated by the J1 path overhead byte) at any point within the STM-1 frame. The start location
of the J1 byte is indicated by the pointer byte values. VCs can also be concatenated to provide more capacity
in a flexible fashion.
CEM Overview
Circuit Emulation (CEM) is a way to carry TDM circuits over packet switched network. CEM embeds the
TDM circuits into packets, encapsulates them into an appropriate header, and then sends that through Packet
Switched Network. The receiver side of CEM restores the TDM circuits from packets.
Modes of CEM
• Structure Agnostic TDM over Packet (SAToP) (RFC 4553) – SAToP mode is used to encapsulate
• Circuit Emulation Service over Packet (CEP) (RFC 4842) - CEP mode is used to encapsulate SDH
Table 4: SDH CEM Channelization Modes
SDH Modes
VC4-16c
VC4-4c
VC4
TUG-3-E3
TUG-3-T3
TUG-2-VC11
TUG-2-VC12
TUG-2-T1
TUG-2-E1
1-Port OC-192 or 8-Port Low Rate CEM Interface Module Configuration Guide, Cisco IOS XE Everest 16.7.x
(Cisco ASR 900 Series)
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T1/E1 or T3/E3 unstructured (unchannelized) services over packet switched networks. In SAToP mode,
the bytes are sent out as they arrive on the TDM line. Bytes do not have to be aligned with any framing.
In this mode, the interface is considered as a continuous framed bit stream. The packetization of the
stream is done according to IETF RFC 4553. All signaling is carried transparently as a part of a bit
stream.
payload envelopes (SPEs) like VC11, VC12, VC4, or VC4-Nc over PSN. In this mode, the bytes from
the corresponding SPE are sent out as they arrive on the TDM line. The interface is considered as a
continuous framed bit stream. The packetization of the stream is done according to IETF RFC 4842.
Configuring SDH on 1-Port OC-192/STM-64 or 8-Port OC-3/12/48/STM-1/-4/-16 Module
CEM
CEP
CEP
CEP
SAToP
SAToP
CEP
CEP
SAToP
SAToP
Ports
STM16, STM64
STM4, STM16, STM64
STM1, STM4, STM16, STM64
STM1, STM4, STM16, STM64
STM1, STM4, STM16, STM64
STM1, STM4, STM16, STM64
STM1, STM4, STM16, STM64
STM1, STM4, STM16, STM64
STM1, STM4, STM16, STM64