8.0 ATM Measurement Mode
Background
: Asynchronous Transfer Mode (ATM) is a high speed Link Layer (Layer 2) network protocol and is used to provide
access to the ADSL physical layer, for higher layer protocols such as PPP and TCP/IP.
ATM cells
- are transmitted as cells of equal size where each cell has 53 bytes, of which the first 5 bytes are the cell
header, and the last 48 bytes are payload.
ATM channels
- an ATM network consists of a mesh of ATM switches that switch and direct cells according to their
destination using Virtual Channels (VC). All switches along the path have information about the VC, including the direction to
the next switch along the channel. Two parameters defining the VC, are logically bundled together into a virtual path.
Virtual Path Identifier (VPI)
- There are fewer Virtual Paths in the network than Virtual Channels. Core switches
forward cells on the basis of the VPI, looking the route up quickly in the relatively short list. There are fewer Virtual
Paths in the network than Virtual Channels so switches forward cells on the basis of the VPI
Virtual Channel Identifier (VCI)
- As a cell approaches its destination, switches forward it on the basis of its VCI
in order to get it to its own unique destination.
The
ATM Measurements
on the Home menu enables measurements related to the ATM layer and should be used only when
showtime or DSL link-up has been achieved.
BX100A/V Home Menu - ATM
Testing is made possible provided using the Operation, Administration & Maintenance (OAM) functions of ATM networks. OAM
controls the ATM alarm and circuit continuity and is important for monitoring ATM connections. OAM functions contain special cells
to test and monitor different aspects of ATM network performance. Continuity Check cells are used to ensure reliable path
connections while Loopback cells can be used to validate routing through a network. In an ADSL network or link, the ATM
endpoints are typically the ATU-R and the BRAS.
BX100A/V - ATM OAM TX setup
BX100A/V - ATM OAM TX result
BX100A/V e-Manual D07-00-001 Rev E01
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