Operations Manual
115
Note that while a unique LES and BUS pair must exist for each ELAN/
VLAN, only one LECS is required in the network itself.
Connections
Each LEC has separate VCCs to control address resolution requests and
data traffic. While each VCC carries traffic for only one ELAN, the VCCs
form a mesh of connections between the LECs and the other LANE entities
including the LECS, LES and the BUS.
Control
Connections
LEC
↔
LECS.
A Configuration Direct VCC is a bi-directional VCC set up
by the LEC to be used to obtain configuration information such as the
address of the LES.
LEC
↔
LES/LEC
←
LES.
A Control Distribute VCC means VCCs will be
set up between a LEC and a LES. First, the LEC sets up a bi-directional
point-to-point VCC to the LES for sending control frames. In turn, the LES
may optionally set up a unidirectional point-to-point or point-to-multipoint
VCC for distributing control traffic from LES to LEC.
Data Connections
Data VCCs are used to carry data frames between LECs or between an LEC
and the BUS. These carry data frames as well as flush messages. Apart from
flush messages, data VCCs never carry control traffic.
LEC
↔
LEC.
A Data Direct VCC is set up to carry the unicast frames
between two LECs. When there are data packets to send, but the ATM
address of the destination MAC address is unknown, the LEC will forward
the packets to the BUS to broadcast them to all devices in the ELAN and, in
the meantime, query the LES of the ATM address for the destination
address.
If the LES does not have the ATM address of the MAC address, it will run an
address resolution protocol to resolve it. After receiving a reply with the
ATM address from the LES, the LEC sets up a point-to-point VCC to that
destination ATM address. After the data VCC is set up, all subsequent data
will be sent over the VCC to the LAN destination.
LEC
↔
BUS.
After obtaining the BUS’s ATM address from the LES, a VCC
LEC sets up a bi-directional Multicast Send VCC to the BUS.
