PM8611 Datasheet, PDF (264/292 Pages) PMC-Sierra, Inc – SBSLITE™ Telecom Standard Product Data Sheet Preliminary

SBSLITE™ Telecom Standard Product Data Sheet
Preliminary
Figure 24 Time:Space:Time Switching in one NSE-20G and four Single-Ported SBSs
I
Time
0123
0
1
α
2
3
β
II
Time
0123
0
1α
2
3
β
Space Switching
by NSE
III
Time
0123
0α
1
β
2
3
IV
Time
0123
0
α
1β
2
3
α: (S=1, T=2) => SBSLITE => (S=1, T=0) => NSE => (S=0, T=0) => SBSLITE => (S=0, T=3)
β: (S=3, T=2) => SBSLITE => (S=3, T=3) => NSE => (S=1, T=3) => SBSLITE => (S=1, T=0)
Consider a request to route an octet from ingress port i to egress port j, where i and j range from
0 to 3, over four ports corresponding to the four SBSLITE devices. To make this connection, we
must find a timeslot in the NSE-20G which can accept an octet from the ingress SBSLITE and
send an octet to the egress SBSLITE. If the NSE-20G has these two slots free in the same
timeslot, then the SBSLITEs must also have the corresponding slot free. The actual routing of the
sample is accomplished in several steps. The octet is:
• Mapped to the free timeslot by the ingress SBSLITE port
• Picked up by the NSE-20G in that timeslot on the port from the ingress SBSLITE and
mapped to the port which leads to the egress SBSLITE
• Picked up by the egress SBSLITE in the expected timeslot
It may not be possible to find a free time which connects the ingress SBSLITE to the egress
SBSLITE, even though both SBSLITE devices have unused capacity into the NSE-20G core (the
ingress SBS may have a free timeslot at time i and the egress SBSLITE may have a free timeslot
at time j, but i ~= j). Such cases require a more complex algorithm which is capable of
disconnecting and reconnecting other connections to make space for the new i to j connection.
(Disconnection and reconnection of other connections is done hitlessly by NSE/SBSLITE
fabrics.) This more sophisticated algorithm is described in the remainder of this section.
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
263
Document ID: PMC-2010883, Issue 2