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Packets Are Lost During the GE Service Interconnection of the OSN7500 EGS4 Board

Publication Date:  2012-07-25 Views:  125 Downloads:  0

Issue Description

Sites A and B use the EGS4 boards of the OSN7500 to deploy the broadcast service. Site A uses the following configuration: port 1 - VCTRUNK1, 7×VC4 services; port 2 - VCTRUNK2, 3×VC4 services. Site B uses the following configuration: 2 VBs, VCTRUNK1, port 1, port 2, VCTRUNK2, port 3, port 4; the services are normal. When the channel capacity of vctrunk2 is expanded to 7×VC4, packets are discarded on port 1 at site B. 

Alarm Information


Handling Process

1. Expand the capacity of the EGS4 boards.
2. Reduce the channel capacity. 

Root Cause

1. Broadcast limit of the VBs.
The chip has limited multicast and broadcast forwarding capabilities. The transmit rate of each multicast or broadcast port cannot exceed 9/X Mpps, where X is the number of ports connected in the multicast or broadcast domain. Note that even the source port must also participate in bandwidth allocation, although the multicast or broadcast service packet should not be forwarded to the source port. The transmit rate of each port cannot exceed 9/(number of port)*8*(packet length) Mbit/s. The actual test results may slightly deviate from the results of theoretical calculation using the calculation formula.
2. When a packet enters the board from an Ethernet interface or a VCG interface, the board splits the packet into fixed-length segments. The theoretical rate of the board during the processing of these segments is about 2.9 G bit/s to 5.8 Gbit/s bidirectionally or up to 2.5 Gbit/s unidirectionally. Therefore, the bandwidth varies with the packet length. In practical networks, long packets do not appear only at the time when the chip’s processing efficiency is the lowest and thus the bandwidth can be more than 2 Gbit/s.
In sum, broadcast packets at a rate of 900 Mbit/s cannot simultaneously enter port 1 and port 2 at site A. The total bandwidth of port 2, port 3, and port 4 at site B will reach 3.6 Gbit/s.