Alcatel-Lucent 1643 AMS User's Operation Manual page 390

Traffic provisioning
and the Ethernet switch on the LAN unit. The WAN port is the internal port between
the Ethernet switch and the part of the LAN unit where the Ethernet frame is mapped
into or de-mapped from SDH payloads.
VLAN trunking
VLAN trunks carry the traffic of multiple VLANs over one single Ethernet link and
allow handling off aggregated LAN traffic from multiple end users via one single high
capacity Ethernet link (Fast Ethernet or Giga Ethernet) to data equipment in a Central
Office or an IP Edge Router, IP Service Switch, or an ATM Switch. The main benefit
of VLAN trunking is that TransLAN cards can hand off end user LAN traffic via one
high capacity LAN port instead of multiple low speed LAN ports.
Advantages of VLAN trunking are:
• it does not require the assignment of CID tags
• it permits different 802.1 tagged frames to share the same physical LAN port
• it gives additional flexibility for egress logical WAN port assignment
• it permits successfully routing via an aggregation function.
Learning bridges
To increases the efficiency of the network, it can be separated into segments. A bridge,
which may have several parts, passes packets between multiple network segments. By
noting at which port an Ethernet packet with a certain source address arrives, the
bridge learns to which ports a packet with a certain destination address must be sent. If
the port does not know the destination address, then it will send it to all the ports
except the port where it comes from. The tables which the learning bridge uses to pass
the Ethernet packets to its ports are not shown to the user by the management systems.
MAC-Bridges perform automatic address learning based on the source MAC-address
present in each frame.
• In this process an unknown SA of a frame is stored together with the port number
over which the frame entered the Bridge to be used when frames with that DA
need to be forwarded
• Addresses that are not refreshed (relearned) within the so-called MAC address
ageing time, are removed.
In case more different source address than there is memory space are passing in a
specific interval, the MAC address ageing time, addresses are prematurely flushed and
possibly need to be re-learned
The MAC address ageing time is not stable. Ageing time can vary between 240s up to
420s.
This causes some excess traffic as unlearned traffic is broadcasted. Too much
unlearned traffic can also affect the learned traffic (because of the broadcasting).
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Ethernet over SDH
365-312-807R7.2
Issue 4, May 2007