Cisco ASR 9000 Series Configuration Manuallines page 115

Implementing Point to Point Layer 2 Services
SAToP addresses only structure-agnostic transport, i.e., unframed E1, T1, E3 and T3. It segments all
TDM services as bit streams and then encapsulates them for transmission over a PW tunnel. This protocol
can transparently transmit TDM traffic data and synchronous timing information. SAToP completely
disregards any structure and provider edge routers (PEs) do not need to interpret the TDM data or to
participate in the TDM signaling. The protocol is a simple way for transparent transmission of PDH
bit-streams.
• Structured mode is named CESoPSN (Circuit Emulation Service over Packet Switched Network)
Compared with SAToP, CESoPSN transmits emulated structured TDM signals. That is, it can identify
and process the frame structure and transmit signaling in TDM frames. It may not transmit idle timeslot
channels, but only extracts useful timeslots of CE devices from the E1 traffic stream and then encapsulates
them into PW packets for transmission.CEoP SPAs are half-height (HH) Shared Port Adapters (SPA)
and the CEoP SPA family consists of 24xT1/E1, 2xT3/E3, and 1xOC3/STM1 unstructured and structured
(NxDS0) quarter rate, half height SPAs.
Figure 14: Enterprise Data Convergence using Circuit Emulation over Packet
The CEM functionality is supported only on Engine 5 line cards having CEoP SPAs. CEM is supported on:
• 1-port Channelized OC3 STM1 ATM CEoP SPA (SPA-1CHOC3-CE-ATM)
CESoPSN and SAToP can use MPLS, UDP/IP, and L2TPv3 as the underlying transport mechanism.
This release supports only MPLS transport mechanism.
CEoP SPA supports these modes of operation:
• Circuit Emulation Mode (CEM)
• ATM Mode
• IMA Mode
L2VPN and Ethernet Services Configuration Guide for Cisco ASR 9000 Series Routers, IOS XR Release 6.3.x
Circuit Emulation Over Packet Switched Network
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