Released
PMC-Sierra, Inc.
PM9311/2/3/5 ETT1™ CHIP SET
Data Sheet
PMC-2000164
ISSUE 3
ENHANCED TT1™ SWITCH FABRIC
Figure 26. The Queueing Structure
ETT1 Core
Linecard
ETT1 port
ETT1 port
Linecard
Ingress
TDM
Egress
TDM
Egress
TDM
queue
queue
queue
Ingress
TDM
queues
LCS credits
Figure 26 also highlights some important points with respect to the TDM service:
•
•
•
The linecard may also require a TDM ingress and egress queue. Unless the arrival of TDM cells at
the linecard is synchronized with the start of the TDM Frame, the linecard will need to buffer those
cells until the appropriate time.
There is no backpressure from the ETT1 egress TDM queue. Backpressure is not meaningful for a
TDM service within the ETT1 core. The egress linecard must accept TDM cells that are sent to it
(or else discard them).
The normal LCS credit mechanism is used for ingress TDM cells.
1.5.2 TDM Reservation Tables
The TDM service operates by enabling ports to reserve bandwidth through the ETT1 crossbar at specific
times. Each port has two logically separate tables; one for sending and one for receiving TDM cells. The
Send and Receive tables are physically implemented in a single table called the TDM table. This TDM
table has 1,024 entries, although fewer entries can be used if the Frame length is less than 1024. Each
entry is of the form shown in Table 2.
Table 2. TDM Reservation Table
Field
Size (bits)
Meaning
Input VLD
Input Tag
1
1 if the input side TDM entry is valid
Tag for incoming cells (TDM flow ID)
10
PROPRIETARY AND CONFIDENTIAL TO PMC-SIERRA, INC., AND FOR ITS CUSTOMERS’ INTERNAL USE
55
PMC [ PMC-SIERRA, INC ]
