Avaya Configuring ATM and MPLS Services Uživatelský manuál stáhnout pdf (Strana 71)

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Understanding ATM, MPOA, ATM Router Redundancy, and OAM

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• Next Hop Resolution Protocol (NHRP)

NHRP is a sophisticated address resolution protocol that maps network layer

addresses (for example, IP addresses) to NBMA addresses (in the case of

BayRS, ATM addresses). For instructions on configuring an NHRP server, see

Appendix C, “Configuring NHRP for ATM Services.”

• Virtual router

A virtual router is a set of network devices and associated software that

collectively provides the functionality of multiprotocol routed networks.

Establishing a Network Cut-Through

MPOA components and elements function together to establish an SVC between a

source host and a destination host (Figure 1-14

A local MPC monitors traffic flow and maintains a count of packets addressed

over a specific interval to remote hosts. When the count exceeds a threshold

value, the MPC attempts to establish an SVC to the host.

To establish the virtual connection, the MPC needs the ATM address of the

host.

The MPS first checks a local address resolution cache to map the known

network layer address with an ATM equivalent.

If the cache search fails, the MPC issues an MPOA resolution request to the

local MPS function resident on the adjacent router.

The local MPS hands the resolution request to the MPOA router component.

The MPOA router generates an NHRP address resolution request for the ATM

address of the destination host. Standard routing protocols move the NHRP

request through the network toward the destination host. Eventually, the

NHRP request reaches the egress router, that is, the router that serves the host.

The egress router forwards the request to the remote MPS.

The remote MPS provides the ATM address of the destination host to the

remote MPOA router.

If the destination host is connected to a legacy LAN, the MPS provides the

ATM address of the router that connects to the legacy LAN. If the destination

host is ATM-attached, the MPS provides the ATM address of the destination

host.

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