HP 200 Series Services And Applications page 35

Architecture and Technology
Software Data Flow Architecture
Drivers
A driver controls the data-link-layer (layer two) and physical-layer (layer
one) protocols. The functions performed by a receiving driver include
accepting packets from the network. The functions performed by a
transmitting driver include accepting packets from the circuit group
manager to forward onto the appropriate LAN or WAN link.
Data-Link Service
The data-link service performs the messaging, resource management, and
flow control necessary to move a packet from a source link to a destination
link through a routing or bridge module. The functions of the data-link
service include demultiplexing incoming packets from the driver, managing
internal flow control, and providing transparent access to multiple
redirectors concurrently.
Redirectors
Each HP router can support the simultaneous operation of multiple routing
and bridging services. Each software module representing one of those
services is known as a redirector. Redirectors are responsible for forwarding
packets from one circuit group to another. They receive packets from the
data-link service. Table lookups result in subsequent modification of the
packet header's address and control fields. Redirectors then transmit the
modified packets through the data-link service to the specified driver and
device(s).
It should be noted that the spanning tree protocol, routing protocols (such
as RIP or AppleTalk RTMP), and router management protocols (such as
SNMP) are not a part of the performance data path. The routing protocols
only collect and maintain the routing information used by the network-layer
data-path modules shown in figure 6. The flow of routing information is
shown in the next section.
Circuit Group Manager
The circuit group manager manages the circuits and network interfaces
(circuit groups). The circuit group manager is responsible for selecting the
best circuit from a circuit group using the circuits database. It handles the
load sharing and automatic backup functions. The circuits database contains
up-to-date metrics about all of the router's circuits.
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