Circuit Emulation
Circuit Emulation (CEM) is a technology that provides a protocol-independent transport over IP/MPLS networks. It enables proprietary or legacy applications to be carried transparently to the destination, similar to a leased line.
CEM provides a bridge between a Time-Division Multiplexing (TDM) network and a Multiprotocol Label Switching (MPLS) network. The router encapsulates the TDM data in the MPLS packets and sends the data over a CEM pseudowire to the remote Provider Edge (PE) router. As a result, CEM functions as a physical communication link across the packet network.
The router supports the pseudowire type that utilizes CEM transport: Structure-Agnostic TDM over Packet (SAToP) and Circuit Emulation Service over Packet-Switched Network (CESoPSN).
L2VPN over IP/MPLS is supported on the interface modules.
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We recommend that you configure the controller in the administratively up mode. Configuration under the administratively down mode is not recommended and it might cause configuration errors. |
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The default behaviour of the CEM pseudowire is always UP irrespective of the controller alarms. |
Structure-Agnostic TDM over Packet
Structure-Agnostic TDM over Packet (SAToP) encapsulates Time Division Multiplexing (TDM) bit-streams as pseudowires over public switched networks. It disregards any structure that may be imposed on streams, in particular the structure imposed by the standard TDM framing.
The protocol used for emulation of these services does not depend on the method in which attachment circuits are delivered to the Provider Edge (PE) chassis. For example, a T1 attachment circuit is treated the same way for all delivery methods, including copper, multiplex in a T3 circuit, a virtual tributary of a SONET circuit, or unstructured Circuit Emulation Service (CES).
In SAToP 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 out transparently as a part of a bit stream.
CEM pseudowire Scale
Effective from the 16.12.1 release,
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21504 CEM pseudowires without protection (with SONET)
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10752 CEM pseudowires with protection
is supported on the router.
Currently the Cisco A900-IMA3G-IMSG support a maximum of 1344 CEM pseudowires.
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The 21K CEM pseudowire’s can be achieved on the router by using the combination of the Cisco A900-IMA1Z8S-CX and A900-IMA3G-IMSG interface modules in multiple slot combinations. |
Restrictions for pseudowire Scale Increase
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CEM pseudowire scale is supported only on the SONET mode.
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When configured for scale beyond 21504 CEM pseudowire, a syslog is printed as:
Cannot allocate CEM group, maximum CEM group exceeded, but the configurations will not be rejected. For example, when a 215xxth CEM pseudowire is configured, the configuration fails even though the CLI is not rejected with the mentioned syslog notification.
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While performing ISSU with 21504 CEM pseudowire, sufficient delay must be provided for each interface module.
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After SSO and successful bulk sync, run the show platform software tdm-combo cem ha-stray-entries command. If the output of this command displays no entries, then the next SSO can be performed. You must wait until show platform software tdm-combo cem ha-stray-entries has no entries.