MG-IP TDM Over IP Gateway Reference Manual
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TDM and Pseudowire Error Handling
This section describes the implementation of error handling in Olencom products’ TDM and
pseudowire interfaces. The document summarizes the requirements of relevant T1 and E1 standards, as
well as the Circuit Emulation IETF CESOP/SATOP drafts, the Docsis BSoD and the MEF-8 PDH
Implementation Agreement.
This section covers:
TDM defects and failures
Pseudowire defects
Failure reporting and transfer across the network
System Overview
A simplified system diagram is shown in Figure 29 below. A pseudowire is depicted as it heads
towards the TSP (TDM Service Processor) and is converted into a packet flow by the IWF
(Interworking Function). At the peer device, packets are received by the IWF and converted back to the
TDM interface at the TSP. A TSP may support one or more TDM interface ports (e.g. 4 x E1/T1 are
supported by the MG-IP-4). Similarly, an IWF may support one or more pseudowires. A description of
the mapping of TDM interfaces and pseudowires is beyond the scope of this document.
Defects and failures are detected on the TSP and IWF RX interfaces. Error conditions are signaled to
the peer TDM device on the TDM TX interface by transmission of AIS, RAI or idle signaling patterns.
Error conditions are signaled to the peer IWF across the PSN (Packet Switched Network) via the L, R
and M bits of the pseudowire packet flow’s Control word.
Figure 29: Point-to-multipoint TDM over Ethernet Pseudowire
RX
IWF
RX
TSP
Not all of the functionality described in this section will initially be implemented
in Olencom products. Some may be implemented gradually.
TDM Defects and Failures
The following defect definitions are specified in RFC3895, based on corresponding standard
documents.
TDM Defects
AIS Defect
AIS defect- for D4 and ESF links, the “all ones” condition is detected at a DS1 line interface upon an
unframed signal with a “ones” density of at least 99.9% being observed for a time equal to or greater
than T, where 3 ms <= T <= 75 ms (in the Dallas framer, this is set to 3 ms and is not configurable)
The AIS is terminated upon observation of a signal not meeting the configured “ones” density or the
unframed signal criteria for a period equal to or greater than T.
For E1 links, the “all ones” condition is detected at the line interface as a string of 512 bits containing
fewer than three zero bits.
TDM
Terminal
Equipment
TX
IWF
TX
TSP
TDM
Terminal/
Switching
Equipment