OC3port Plus
Users Manual
5-22
Background Traffic Option
There are two types of cells that you can specify for use as background traffic: idle
and unassigned. An idle cell is defined as one with a five-byte ATM header set to
00 00 00 01 52 (hex), and an unassigned cell is defined as one with a five-byte
header of 00 00 00 00 55 (hex). Both types of cells are used in the ATM cell
stream to fill unused bandwidth.
To specify which type of cell to use as background traffic, follow these steps:
1.
Press the
ATM
key. The
ATM SELECTIONS
menu is displayed.
2.
Press the
Down Arrow
key until
ATM Options
is on the selection line. Press
ENTER
. The
ATM OPTIONS
submenu is displayed.
3.
Press the
Down Arrow
key to move the
Bckgrnd Traffic
option to the selection
line, as in:
ATM OPTIONS:
Correction Algr OFF
Bckgrnd Traffic UNA
Header Type UNI
za075f.eps
There are two settings for this option:
UNA
(unassigned) and
IDL
(idle).
4.
Press the
Left
or
Right Arrow
key to select the desired setting.
The OC3port Plus is now set up to use as background traffic the setting you
selected.
Header Type Option
Two different header schemes are used for ATM cells: one for
UNI
(User Network
Interface) and one for
NNI
(Network-to-Network Interface). UNI is an interface
that connects ATM users with a private ATM switch that is managed locally, such
as within the same corporate network. NNI, on the other hand, is an interface that
connects ATM users with an ATM switch deployed in the public
telecommunications network. NNI is typically more global or far-reaching, and
capable of spanning long distances such as that between two countries.
Both UNI and NNI cells use five-byte headers. The header format of UNI cells and
NNI cells is identical, except that for NNI cells the GFC field is replaced by an
additional four bits of VPI, resulting in a 12-bit VPI. Figure 5-1 illustrates the
differences in structure between the UNI and NNI cells.
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