Interface Configuration Guide 7705 SAR Interfaces
Edition: 01 3HE 11011 AAAC TQZZA 77
The interface deals with links that are added or deleted, or that fail. The higher layers
see only an IMA group and not individual links; therefore, service configuration and
management is done using IMA groups, and not individual links that are part of it.
The IMA protocol uses an IMA frame as the unit of control. An IMA frame consists of
a series of 128 consecutive cells. In addition to ATM cells received from the ATM
layer, the IMA frame contains IMA OAM cells. Two types of cells are defined: IMA
Control Protocol (ICP) cells and IMA filler cells. ICP cells carry information used by
the IMA protocol at both ends of an IMA group (for example, IMA frame sequence
number, link stuff indication, status and control indication, IMA ID, Tx and Rx test
patterns, version of the IMA protocol). A single ICP cell is inserted at the ICP cell
offset position (the offset may be different on each link of the group) of each frame.
Filler cells are used by the transmitting side to fill up each IMA frame in case there
are not enough ATM stream cells from the ATM layer, so a continuous stream of cells
is presented to the physical layer. Those cells are then discarded by the receiving
end. IMA frames are transmitted simultaneously on all paths of an IMA group, and
when they are received out of sync at the other end of the IMA group link, the receiver
compensates for differential link delays among all paths.
3.2.5 Network Synchronization on Ports and Circuits
The 7705 SAR provides network synchronization on the following ports and CES
circuits:
• Network Synchronization on T1/E1, Ethernet, GPON, and DSL Ports
• Network Synchronization on SONET/SDH Ports
• Network Synchronization on DS3/E3 Ports
• Network Synchronization on DS3 CES Circuits
• Network Synchronization on T1/E1 Ports and Circuits
3.2.5.1 Network Synchronization on T1/E1, Ethernet, GPON, and
DSL Ports
Line timing mode provides physical layer timing (Layer 1) that can be used as an
accurate reference for nodes in the network. This mode is immune to any packet
delay variation (PDV) occurring on a Layer 2 or Layer 3 link. Physical layer timing
provides the best synchronization performance through a synchronization
distribution network.
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