3Com S7902E, Configuration Manual

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The configuration of prioritizing high-priority packets and that of the downlink bandwidth limit take
effect only when the downlink bandwidth allocation policy is enabled.
The configured downlink bandwidth limit takes effect only on known unicasts, but not on unknown
unicasts, multicasts, or broadcasts.
The sum of the minimum uplink bandwidths configured for all the existing ONU ports under an OLT
port cannot exceed 921600 kbps, namely, 900 Mbps.
Enabling Related Protocols on an ONU
You can use an OLT to remotely enable RSTP, DHCP snooping, DHCP snooping Option82, and
PPPoE+ on an ONU through extended OAM packets.
RSTP
Enabling RSTP on an ONU can eliminate the loops between the UNIs or in the user networks by
blocking redundant links.
DHCP Snooping
After DHCP snooping is enabled on an ONU, a DHCP snooping table will be generated on the ONU to
record the IP address and user MAC address information that the DHCP client obtains from the DHCP
server, with each record being an entry in the DHCP snooping table.
DHCP Snooping Option82
With DHCP snooping Option82 enabled on an ONU,
For DHCP request messages with Option82 fields, the ONU replaces the Option82 fields with the
local one before broadcasting the DHCP request messages;
For DHCP request messages without Option82 fields, the ONU adds the Option82 field (which
contains ONU MAC addresses, number of the UNI connected to the DHCP client, and the VLAN to
which the UNI belongs) into the request messages when the DHCP client connected to the ONU
sends DHCP request messages to the DHCP server. This allows the DHCP client addresses to be
recorded in the DHCP server.
PPPoE+
The Point-to-Point Protocol over Ethernet (PPPoE) technology interconnects large numbers of hosts
through Ethernet, allowing the hosts to access the Internet through a far-end access device, and
implementing control and accounting functions on each connected host. Operating in the client/server
mode, PPPoE encapsulates PPP packets into Ethernet frames, and provides PPP connection over
Ethernet.
PPPoE+, also known as PPPoE Intermediate Agent, is designed for broadband users using PPPoE
mode authentication. PPPoE+ allows for user port identification by adding user port information into the
PPPoE packets.
After PPPoE+ is enabled on an ONU, when a PPPoE client sends a request packet: