Sonet Switching - Cisco ASR 900 Series Configuration Manual

Configuring SONET

SONET Switching

SONET Switching is achieved on optical interface modules by circuit emulation. Circuit Emulation (CEM)
is a way to carry TDM circuits over packet switched network. CEM embeds TDM bits into packets, encapsulates
them into an appropriate header and then sends that through Packet Switched Network (PSN). The receiver
side of CEM restores the TDM bit stream from packets.
Modes of CEM:
• Structure Agnostic TDM over Packet (SAToP) (RFC 4553) – Structure-Agnostic TDM over Packet
• Circuit Emulation Service over Packet (CEP) (RFC 4842) - CEP mode is used to encapsulate SONET
Table 4: Modes of CEM
Mode
STS-48C
STS-12C
STS-3C
STS-1
DS3
DS3-T1
VT 1.5
VT DS1
(SAToP) mode is used to encapsulate T1 or T3 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 VT1.5 or VT2 or STS-1 or STS-Nc over packet switched networks. 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.
CEM
CEP
CEP
CEP
CEP
SAToP
SAToP
CEP
SAToP
1 port OC48/ 4 port OC12/OC3 + 12 port T1/E1 + 4 port T3/E3 CEM Interface Module Configuration Guide, Cisco IOS

SONET Switching

Ports
OC-48, OC-192
OC-12, OC-48, OC-192
OC-12, OC-48, OC-192
OC-3, OC-12, OC-48, OC-192
OC-3, OC-12, OC-48, OC-192
OC-3, OC-12, OC-48, OC-192
OC-3, OC-12, OC-48, OC-192
OC-3, OC-12, OC-48, OC-192
XE Fuji 16.7.x (Cisco ASR 900 Series)
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