ATM Option System Reference - Comtech EF Data

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• Another difficulty is that resources allocated to a PVC are guaranteed. This
means that even if the PVC is not being used the resources must be reserved by
the network, which detracts from overall network efficiency.
End System A
ATM SW2
PVC1 (VPI=1, VCI=1)
ATM SW1
VPI=1 & VCI=1 ->ATM SW5
ATM SW4
With SVCs, configuration of the virtual connections is pushed to the end system, greatly
simplifying VC management for network providers.
• SVC parameters are configured on the end system (the NetPerformer), and are
used whenever a connection is established.
• The ATM switch uses these parameters to determine whether it can satisfy the
end system requirements, such as bandwidth and QoS. If the resources are unavailable,
the switch can reject a request to establish an SVC.
• Each end system is assigned a unique ATM address, which is used by other end
systems to establish a VC with this node. This is similar to using a telephone
number to place a phone call. ATM addresses are discussed further on See “ATM
Addressing” on page 9..
1.2.6 User to Network Interface (UNI)
UNI (User-to-Network Interface) is the generic name for the various processes responsible
for the exchange of information between an ATM end system and an ATM switch. UNI is
responsible for controlling ATM SVCs. Two components are required to implement
SVCs:
• UNI signaling (see next section)
• ILMI (Integrated Local Management Interface), described on See “Integrated
Local Management Interface (ILMI)” on page 8..
UNI Signaling
ATM SW3
Figure 1-1: ATM PVCs in the Network
ATM SW5
VPI=2 & VCI=2 ->ATM SW1
End System B
PVC2 (VPI=2, VCI=2)
UNI Signaling is responsible for establishing and tearing down SVCs. It is similar in
function to the D-Channel in ISDN.
NOTE: The ITU-T Q.2931 specification, from which the various UNI implementations
are derived, is based on the ISDN specification, ITU-T Q.931.
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