Characterizing transmission of data segments within a switch fabric using multiple counters for each destination node

#1. Field of the Invention

#The invention relates to packet-based switching fabrics, and more particularly to a load balancing method and apparatus for selecting an appropriate next-stage module for transmission of a data packet of variable size.

#2. Description of Related Art

#The invention will be described with respect to specific embodiments thereof, and reference will be made to the drawings, in which:

#FIGS. 1, 1A, 1B, 1C and 1D are functional block diagrams of various fabrics of FIG. 2.

#FIG. 2 is a functional block diagram of pertinent components of a switching system incorporating features of the invention.

#1. System Overview

#FIG. 2 is a block diagram of a modular switching system 200 incorporating the invention. The system of FIG. 2 has three stages: an ingress stage 210, an intermediate stage 212 and an egress stage 214. The switching system 200 is shown in a folded topology, in which each egress node shares an integrated circuit chip with a corresponding ingress node in a one-to-one correspondence. Because of the folded nature of the topology of FIG. 2, each node 216 performs both ingress functions and egress functions. A node 216 therefore may be referred to herein variously as an ingress node 216, an egress node 216 or an ingress/egress node 216, whichever is most appropriate in the context of the discussion. Any or all of the nodes can implement its switching function internally by using a crossbar switch, one or more recursive levels of 3-stage sub-networks, or by any other structure. The ingress stage 210 of the system has v ingress/egress modules 216, numbered P(1) through P(v). The system also includes v bidirectional line cards 222, numbered LC(1) through LC(v). Each ingress/egress module 216 has one bidirectional I/O port adapted for exchanging data with one corresponding line card 222. In practice the data path between a line card and its corresponding ingress/egress module includes four closely matched data links, each carrying one-fourth the total data rate of the port (10 Gbps each for a total of 40 Gbps in each direction per port). Not every line card needs to use all four data links, in which case the total system utilization will be less than the maximum that it can handle.

#The intermediate stage 212 has w nodes 100, numbered F(1) through F(w). Each ingress/egress module 216 has q 10 Gbps bidirectional link(s) to each intermediate stage node 100, across a backplane 224. In general, there is no requirement that the data rates of any of the routes through the system be the same. The intermediate stage nodes 100 have multicast capability, but that is not required in a different embodiment.