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Chapter 1 Overview
6 Avaya M770 M-ACCF/SF ATM Access Modules User’s Guide
Data VCCs
Data VCCs carry data frames between LECs and between a LEC and the BUS.
Unicast data is normally sent from one LEC to another LEC by data-direct VCCs.
Data direct VCCs are set up dynamically in a SVC environment by a transmitting
LEC after ascertaining the ATM LEC destination address for the packet to be
transmitted. Once established, a data-direct VCC remains in place for transmission
of subsequent traffic between the two LECs. However, a data direct VCC that
remains unused for VCC-Timeout-period is released by the LEC.
A multicast data VCC pair (multicast-send and multicast-forward) are established
between a LEC and the BUS in order to allow the LEC to send and receive multicast
data. In addition, initial unicast data (data whose LEC destination has not yet been
ascertained by the transmitting LEC) is sent on the multicast-send VCC to the BUS
which forwards it to all other LECs in the same ELAN. Characteristics of the data
VCCs are summarized in the following table:
Control-
distribute
LES==>LEC LES distributes
control traffic to
LECs, including
LE_ARP information
LES Membership
of LEC in
ELAN
Table 1.2 Data VCCs
VCC
Name
From/To
Information
carried
Initialize
d by
Duration
Data-
direct
LEC<==>LEC Point-to-point
Unicast data
between LECs
LEC Established by
need and released
when unused for
VCC-Timeout-
period
.
Multicast-
send
LEC<==>BUS LEC sends
multicast and
initial unicast
data to BUS
LEC Membership of
LEC in ELAN.
Multicast-
forward
BUS==>LEC BUS distributes
data traffic to
LECs
BUS Membership of
LEC in ELAN.
Table 1.1 Control VCCs (Continued)
VCC Name From/To Information carried
Initialized
by
Duration