ATM Virtual Circuit and Path Flashcards
What mode does an ATM network operate in?
Connection Oriented Mode
What is a PVC?
Permanent virtual circuit (provisioned by the network operator)
What is an SVC?
Switched virtual circuit (dynamically established using a signaling protocol)
What has to happen before data exchange can occur?
Pre-defined PVCs or dynamically established SVCs need to be established.
At what OSI Layer does ATM occur?
Layer 2: Data Link
What happens at the Data Link layer with ATM?
ATM uses logical paths and channels at this layer. The basic ATM protocol, in a 5-octet header of the cell, is also at this layer.
How is a particular physical port on the ATM switch identified? How is this similar to Frame Relay?
Two logical identifiers are used. These are equivalent to Frame Relay DLCI, which defines an end-to-end virtual circuit.
What is DLCI?
Data Link Connection Identifier.
What is VPI?
Virtual Path Identifier
What is VCI?
Virtual Channel Identifier
How is a VPI logical path identifier similar to X.25 logical channel over a physical circuit or DLCI on a Frame Relay access circuit?
It allows multiplexing of “logical” VPIs over one physical link.
How is a logical identifier defined?
A logical channel identifier VCI must be added to complete the full ATM logical assignment, which allows multiplexing of VCIs within a VPI.
T/F: every VPI in a single physical link can be multiplexed.
True.
What does the combination of VPI and VCI identify?
The VCC or Virtual Channel Connection.
What is VCC?
Virtual Channel Connection
Virtual circuits may be permanent (provisioned by network operator) or ________ (__________).
Switched (dynamically established).
What are PVCs and what do they do?
Permanent Virtual Circuits; provide connectivity and provide dedicated connections in the network
What are SVCs and what do they do?
Switched Virtual Circuits; provide dynamic establishment of logical connections across ATM network
How does customer equipment use VCIs?
Uses them to identify the virtual circuit over which data is to be transmitted
How does having a VPI field increase performance?
The network uses the VPI field to bundle VCIs together between source and destination, which decreases switching time (less to examine)
T/F: VCIs have local significance only while VPIs have significance across a wider network.
F. Both have local significance only.
T/F: VPI and VCI values can change even for the same cell.
True. The ATM switch has to track these.
What are Tx and Rx
Transmit side and Receiver side
What is an NMS?
Network Management System
T/F: VPI/VCIs are unidirectional: however, a full duplex PVC/SVC can be constructed using two pairs of each.
True
What identifies a VCC?`
Virtual Channel Connection is identified by the combination of VPI/VCI
Who uses VCIs and for what?
Customer equipment uses VCIs to identify the virtual circuit over which data is transmitted
Who uses the VPI and for what?
Used by the network to bundle VCIs together between same source and destination
T/F: VCIs/VPIs have local significance only.
True
T/F: a pair of “user” VPI/VCIs is unidirectional.
True
How do a pair of user VPI/VCIs have to be defined?
On a per-port basis
What typically configures UE and network nodes?
centralized control and management system
VPI is to what on the ATM airport? (VPI = 23)
Flight number on specific airline (AC 1290). Local significance!
Airlines deal with flights, not individual cells/passengers
VCI is to what on the ATM airport? (VCI=305)
Seat assignment on a specific flight (22A). Local significance! However, VCIs actually apply to a stream of cells, rather than an individual cell.
VCC is to what on the ATM airport?
All of the flight and seat numbers that get you to your destination
A VPI is a bundle of ___ all going the same direction.
VCIs
T/F: All VCIs in the same VPI get the same grade of service.
True
ATM switch is to what in the ATM airport?
Airport terminal
