PM8611-BIAP PMC [PMC-Sierra, Inc], PM8611-BIAP Datasheet - Page 262

• Manufacturer Part Number: PM8611-BIAP
• Manufacturer: PMC [PMC-Sierra, Inc]

13.3.1
13.3.2
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-2010883, Issue 2
Problem Description
The basic scheduling problem is to find the switch settings to properly route a set of connections.
This is more formally described using the definitions in the following paragraphs.
Port: an STS-12 input/output data stream. The serial ports on the SBSLITE devices and the
NSE-20G devices operate at STS-12 rates and utilize STS-12 frames. Since the intention of the
NSE-20G is to serve as a DS0-granularity switch, these STS-12 frames must be treated as
repeating on a cycle of 12*9*90 = 9720 octets. All connections considered by this algorithm are
octet connections. Higher aggregations of traffic are handled as collections of octets, and are
ignored for the purposes of describing this algorithm.
Timeslot: A specific octet location in the 9720 octet cyclic structure.
Spacetimeslot: A timeslot on a specific port, identified by a space component and a time
component: for example, octet 9 on port 3 of SBSLITE device 2
Connection: a mapping of an input spacetimeslot to an output spacetimeslot. Connections come
in two varieties, multicast and unicast. Unicast connections are a mapping of a single input
spacetimeslot to a single output spacetimeslot. Multicast connections are a mapping of a single
spacetimeslot to multiple output spacetimeslots. This algorithm is only concerned with the
unicast problem.
Naïve Algorithm
We begin by describing a simplified version of the algorithm, applied to a specific
SBSLITE/NSE-20G configuration. Figure 23 illustrates the application. Four SBSLITE devices
are connected by one port each to an NSE, which is likewise connected by one port to the egress
side of each SBSLITE device. Only four ingress/egress ports of 32 on the NSE-20G are in use in
this application, but the ideas generalize easily to larger fabrics.
Information flows from left to right. Each edge connects an egress port (on the left) to an ingress
port (on the right); each such edge has a capacity of 9720 timeslots.
For present purposes, we consider the SBSLITEs to be supporting a single P-SBI port (eight bits
at 77.76 MHz, or STS-12). Also, we ignore the “standby” LVDS port. This reduces the
SBSLITE from a multi-ported Memory switch (which it in fact is) to a simpler two-ported (P-SBI
and Active S-SBI) Time switch. This reduction in complexity makes the following discussion
more straightforward, but does not reduce the algorithm’s ability to deal with the more complex
cases introduced by the use of the four slower P-SBI ports, or by concurrent use of the standby
LVDS port. The nature of switching in this application is illustrated by Figure 19. The two
dimensional 4-X-4 matrices represent octet slots in both space (vertical) and time (horizontal).
We trace through the switching processing in the following steps:
Reconnection requests may be made individually in which case an incremental connection-
setting algorithm is desired, or as complete batches in which case a batch algorithm may be
desirable.
Reconnection requests may be pre-computed for fast protection fall-over mechanisms.
SBSLITE™ Telecom Standard Product Data Sheet
Preliminary
261