METRObility Optical Systems R821-1S, Инструкция по установке и эксплуатации

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Radiance 10/100 Mbps Services Line Card
34
Upon receiving a Logical Services Loopback frame, the R821 services
line card performs the following operations, which are illustrated below:
•
Extracts the source MAC address from the incoming frame.
•
Inserts the source MAC address into the destination MAC address field
(shown in red).
•
Sets the new source address to the Loopback MAC address (shown in
blue).
•
Calculates the new Frame Check Sequence (FCS) and replaces the
existing FCS with the new value at the end of the frame, which is then
transmitted back to the sender.
The data remains unchanged. Logical Services Loopback operates at full
line rate with frames of any size. Normal data frames continue to be
received and transmitted without being dropped while Logical Services
Loopback is enabled.
Port
Management
By default, Port 2 is enabled to respond to management frames such as
ARP requests and SNMP commands. This feature is disabled on Port 1 by
default. Port management can be disabled on either port, however, it
cannot be disabled on both ports simultaneously. When management is
disabled on either port, the DIS LED turns green. A port with management
disabled discards all management frames, but data frames continue to be
received and transmitted normally.
Incoming (RX) Frame
Preamble
SFD
8 6
6
4 48+
Source
MAC Addr
FCS data
Dest
MAC Addr
Outgoing (TX) Frame
Preamble
SFD
Source
MAC Addr
FCS data
Dest
MAC Addr
Loopback MAC Address
bytes
Recalculated
Local R821
Services Line Card
Remote R821
Services Line Card
Access Access Network
Local
Device
Remote
Device