Download Network Troubleshooting

SECTION II
TROUBLESHOOTING LOCAL-AREA NETWORKS
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ATM
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tions are set up dynamically over individual transmission sections using signaling protocols:
UNI<>NNI
Signaling from an end system into an ATM network that consists of
several networked switches (user-to-network)
NNI<>NNI
Signaling within an ATM network that consists of several networked switches (network-to-network)
Meta-signaling is not used in practice because the use of the reserved signaling
virtual channel, VCI 5, has been found to be sufficient even in large ATM
networks.
Virtual Path Connections (VPCs)
Virtual path connections are a hierarchical level above virtual channel connections. In other words, a virtual path can contain several virtual channels (note,
however, that in terms of the layered model, the VC is above the VP in the stack).
VPCs have the same properties as VCCs. Path connections can likewise be set up
manually as permanent virtual paths, or on request by means of signaling
processes or network management functions. One aspect of VPC worth noting
is that, while the VPI of a VPC changes at every switching node in the network,
the VCI values of all VCs within the VP are preserved end-to-end.
10.1.7.3
Quality-of-Service (QoS) Parameters
In ATM networks, services with widely differing communication requirements
are transported concurrently. Real-time applications with varying bit rates are
much more exacting with regard to average cell delay, for example, than simple
data transfers at a constant bit rate. For this reason, the ATM layer assigns each
connection QoS parameters that specify certain characteristics of the connection when the connection is set up. ITU-T Recommendation I.356 defines seven
cell transfer performance parameters:
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Cell Error Ratio
Severely Errored Cell Block Ratio
Cell Loss Ratio
Cell Misinsertion Rate
(the proportion of cells with a valid but incorrect header)
• Cell Transfer Delay
• Mean Cell Transfer Delay
• Cell Delay Variation