ATM Virtual Circuit and Path

Question 1

What mode does an ATM network operate in?

Answer 1

Connection Oriented Mode

Question 2

What is a PVC?

Answer 2

Permanent virtual circuit (provisioned by the network operator)

Question 3

What is an SVC?

Answer 3

Switched virtual circuit (dynamically established using a signaling protocol)

Question 4

What has to happen before data exchange can occur?

Answer 4

Pre-defined PVCs or dynamically established SVCs need to be established.

Question 5

At what OSI Layer does ATM occur?

Answer 5

Layer 2: Data Link

Question 6

What happens at the Data Link layer with ATM?

Answer 6

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.

Question 7

How is a particular physical port on the ATM switch identified? How is this similar to Frame Relay?

Answer 7

Two logical identifiers are used. These are equivalent to Frame Relay DLCI, which defines an end-to-end virtual circuit.

Question 8

What is DLCI?

Answer 8

Data Link Connection Identifier.

Question 9

What is VPI?

Answer 9

Virtual Path Identifier

Question 10

What is VCI?

Answer 10

Virtual Channel Identifier

Question 11

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?

Answer 11

It allows multiplexing of “logical” VPIs over one physical link.

Question 12

How is a logical identifier defined?

Answer 12

A logical channel identifier VCI must be added to complete the full ATM logical assignment, which allows multiplexing of VCIs within a VPI.

Question 13

T/F: every VPI in a single physical link can be multiplexed.

Answer 13

True.

Question 14

What does the combination of VPI and VCI identify?

Answer 14

The VCC or Virtual Channel Connection.

Question 15

What is VCC?

Answer 15

Virtual Channel Connection

Question 16

Virtual circuits may be permanent (provisioned by network operator) or ________ (__________).

Answer 16

Switched (dynamically established).

Question 17

What are PVCs and what do they do?

Answer 17

Permanent Virtual Circuits; provide connectivity and provide dedicated connections in the network

Question 18

What are SVCs and what do they do?

Answer 18

Switched Virtual Circuits; provide dynamic establishment of logical connections across ATM network

Question 19

How does customer equipment use VCIs?

Answer 19

Uses them to identify the virtual circuit over which data is to be transmitted

Question 20

How does having a VPI field increase performance?

Answer 20

The network uses the VPI field to bundle VCIs together between source and destination, which decreases switching time (less to examine)

Question 21

T/F: VCIs have local significance only while VPIs have significance across a wider network.

Answer 21

F. Both have local significance only.

Question 22

T/F: VPI and VCI values can change even for the same cell.

Answer 22

True. The ATM switch has to track these.

Question 23

What are Tx and Rx

Answer 23

Transmit side and Receiver side

Question 24

What is an NMS?

Answer 24

Network Management System

Question 25

T/F: VPI/VCIs are unidirectional: however, a full duplex PVC/SVC can be constructed using two pairs of each.

Answer 25

True

Question 26

What identifies a VCC?`

Answer 26

Virtual Channel Connection is identified by the combination of VPI/VCI

Question 27

Who uses VCIs and for what?

Answer 27

Customer equipment uses VCIs to identify the virtual circuit over which data is transmitted

Question 28

Who uses the VPI and for what?

Answer 28

Used by the network to bundle VCIs together between same source and destination

Question 29

T/F: VCIs/VPIs have local significance only.

Answer 29

True

Question 30

T/F: a pair of "user" VPI/VCIs is unidirectional.

Answer 30

True

Question 31

How do a pair of user VPI/VCIs have to be defined?

Answer 31

On a per-port basis

Question 32

What typically configures UE and network nodes?

Answer 32

centralized control and management system

Question 33

VPI is to what on the ATM airport? (VPI = 23)

Answer 33

Flight number on specific airline (AC 1290). Local significance! Airlines deal with flights, not individual cells/passengers

Question 34

VCI is to what on the ATM airport? (VCI=305)

Answer 34

Seat assignment on a specific flight (22A). Local significance! However, VCIs actually apply to a stream of cells, rather than an individual cell.

Question 35

VCC is to what on the ATM airport?

Answer 35

All of the flight and seat numbers that get you to your destination

Question 36

A VPI is a bundle of ___ all going the same direction.

Answer 36

VCIs

Question 37

T/F: All VCIs in the same VPI get the same grade of service.

Answer 37

True

Question 38

ATM switch is to what in the ATM airport?

Answer 38

Airport terminal