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ForeRunner
ATM Switch Network Configuration Manual
Configuring an Emulated LAN
3.3.3 Data Transfer
When LEC1 receives a network-layer packet from a higher layer protocol to transmit to some
destination MAC address (for example, LEC2), LEC1 initially does not know the correspond-
ing ATM address of the destination. Consequently, LEC1 transmits an LE_ARP request to the
LES.
NOTE
The example shown in Figure 3.2 assumes that
LEC2 has already registered with the LES, and
that connections similar to those described for
LEC1 already exist.
While waiting for the LES to respond, LEC1 forwards the packet to the BUS. The BUS broad-
casts the packet to all LECs on the ELAN. This is done to avoid data loss, and to minimize con-
nection set-up latency (due to the LE_ARP process) that may not be acceptable to some
network protocols.
If the LE_ARP response is received, LEC1 establishes a data-direct connection
➏
to the desti-
nation address of LEC2. This path will be used for subsequent data transfers. Before LEC1
begins to use this connection, it first sends a “flush” packet via the BUS to the destination,
LEC2. When LEC2 acknowledges receipt of this packet, signifying that the BUS path is empty,
only then does LEC1 begin to use the data-direct connection
➏
for data transfer. This process
ensures that the network protocol’s frames arrive in the proper order.
If no response is received to the LE_ARP, LEC1 continues to send data via the BUS, while con-
tinuing to LE_ARP until a response is received and a data-direct connection to LEC2 is estab-
lished.
If LEC1 already has a data-direct connection to a MAC address it wishes to reach, it need not
go through the LE_ARP process again. Instead, it continues to use the current connection. This
is possible because each LEC maintains a cache of MAC address to ATM address mappings
that it receives in response to the LE_ARPs it has sent. Entries in this cache are “aged” out over
a period of time. Data-direct connections are also cleared if they remain inactive for a period of
time.
Summary of Contents for forerunner series
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Page 16: ...TOC 10 ForeRunner ATM Switch Network Configuration Manual Table of Contents ...
Page 20: ...LOF 4 ForeRunner ATM Switch Network Configuration Manual List of Figures ...
Page 22: ...LOT 2 ForeRunner ATM Switch Network Configuration Manual List of Tables ...
Page 30: ...viii ForeRunner ATM Switch Network Configuration Manual Preface ...
Page 144: ...3 58 ForeRunner ATM Switch Network Configuration Manual Configuring an Emulated LAN ...
Page 180: ...6 12 ForeRunner ATM Switch Network Configuration Manual ATM Forum PNNI ...
Page 220: ...9 6 ForeRunner ATM Switch Network Configuration Manual Configuring Timing ...
Page 300: ...D 24 ForeRunner ATM Switch Network Configuration Manual Configuring FramePlus Modules ...
Page 308: ...Acronyms 8 ForeRunner ATM Switch Network Configuration Manual Acronyms ...
Page 346: ...Glossary 38 ForeRunner ATM Switch Network Configuration Manual Glossary ...
Page 352: ...Index 6 ForeRunner ATM Switch Network Configuration Manual Index ...