ForeRunner
ATM Switch Network Configuration Manual
4 - 13
MPOA
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4.3.4.3 Flow Analysis
On a LEC/MPC’s host or edge device, IP packets with destinations within the host’s subnet
are sent using LANE 1.0 methods; i.e., the client puts on its LEC “hat” and works directly with
its ELAN’s services to connect with local destinations. Packets destined for remote subnets
cause the LEC/MPC to put on its MPC “hat.” This client is then referred to as an “ingress
LEC/MPC.”
Ingress LEC/MPCs associate destination IP addresses with shortcut circuits. Ingress
LEC/MPCs use configurable parameters called flow descriptors to determine whether and when
to trigger creation of shortcut circuits. The ingress LEC/MPC also monitors the most recent
use of a shortcut circuit to determine when to tear down the shortcut. Specifically, when an
ingress LEC/MPC sends a packet:
1.
If a shortcut circuit already exists to the IP destination, the LEC/MPC sends the
packet over this circuit.
2.
If no shortcut circuit exists, the LEC/MPC determines whether shortcuts to this IP
address are allowed. If shortcuts to the destination IP address are not allowed, the
LEC/MPC sends the packet to the gateway router.
3.
If no shortcut circuits exist, and shortcuts to the IP address are allowed, the
LEC/MPC determines if the packet traffic flow exceeds the shortcut enable trigger
value (set by the flow descriptors) for the destination IP address’s flow. If the flow
exceeds the trigger value, the LEC/MPC tries to establish a shortcut circuit to the
destination LEC/MPC (called the egress LEC/MPC). If the flow does not exceed
the trigger value, the ingress LEC/MPC simply sends the packet traffic to the gate-
way router.
4.3.4.4 Making a Shortcut
When the ingress LEC/MPC determines that the packet traffic flow exceeds the shortcut-
enable trigger value, the ingress LEC/MPC tries to establish a shortcut circuit to the egress
LEC/MPC. The following describes how a shortcut is set up:
1.
The ingress LEC/MPC initiates the shortcut creation process by sending an MPOA
resolution request to the MPS it uses as a gateway router (this MPS is called the
ingress MPS). The MPS converts the request to a next hop resolution protocol
(NHRP) request. This NHRP request includes the destination’s IP address and asks
for the corresponding ATM destination address.
2.
This request is passed along hop-by-hop until it reaches the final MPS (called the
egress MPS) on the route to the destination IP address.
3.
The egress MPS sends a cache imposition request to the egress LEC/MPC. The
egress LEC/MPC sends a cache imposition reply, which is converted to a NHRP
response by the egress MPS. The ingress MPS converts the NHRP response to an
MPOA resolution response and transmits it to the ingress LEC/MPC.
Summary of Contents for forerunner series
Page 6: ......
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 ...