Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
Frame. A TDM Frame is simply a sequence of ingress and egress reservations. The length (number of cell
times) of a TDM Frame is configurable up to a maximum of 1024 cells. The TDM Frame repeats after a
certain fixed time. All ports are synchronized to the start of the TDM Frame, and operate
cell-synchronously with respect to each other. Thus, at any cell time, every ETT1 port knows whether it has
made a reservation to send or receive a TDM cell. See the application note “LCS-2 TDM Service in the
ETT1 and TTX Switch Core”, available from PMC-Sierra, Inc.
Figure 5 illustrates the idea of a TDM Frame. The TDM Frame has N slots (N is 1024 or less) where each
slot is one 40ns cell time. The TDM Frame is repeated continuously, but adjacent TDM Frames are
separated by a guard band of at least 144 cells.
Figure 5. The TDM Frame Concept
40ns
N
1
One TDM Frame
Guard band
All of the ETT1 ports must be synchronized with respect to the start of the TDM Frame. This
synchronization information is distributed via the Scheduler. The Scheduler can generate the
synchronization pulses itself, or it can receive “Suggested Sync” pulses from a ETT1 port which can in turn
receive synchronization signals from a linecard. The linecards do not need to be exactly synchronized to
either the ETT1 core or the other linecards. The LCS protocol will compensate for the asynchrony between
the linecard and the ETT1 core.
1.2.6 Subport Mode (2.5 Gbit/s Linecards)
An ETT1 switch core can have up to 32 ports. Each port supports a linecard bandwidth in excess of
10 Gbit/s. This bandwidth might be used by a single linecard (for example, OC-192c), or the ETT1 port can
be configured to share this bandwidth among up to four ports, each of 2.5 Gbit/s. This latter mode,
specifically four 2.5 Gbit/s linecards, is referred to as subport mode, or sometimes as quad OC-48c mode.
A single ETT1 switch can have some ports in ‘normal’ mode, and some in subport mode; there is no
restriction. The four levels of prioritized best-effort traffic are available in all configurations. However, there
are some important differences between the two modes. One difference is that the LCS header must now
identify the subport associated with each cell. Two bits in the LCS label fields are used for this purpose, as
described below.
A second difference is that the EPP must carefully manage the output rate of each subport, so as not to
overflow the buffers at the destination linecard, and this is also described below.
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
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PMC [ PMC-SIERRA, INC ]
