1-5
Cisco 6260 Hardware Installation Guide
OL-2365-02
Chapter 1 Product Overview
Introduction to the Cisco 6260 System
IMA breaks up the ATM cell stream, distributes the cells over the multiple physical links of an IMA
group, and recombines the cells into a single stream at the other end of the connection. The ATM cells
are distributed in a round-robin fashion over the physical links of the IMA group, recombined at the
receiving IMA group, and passed in their original form to the ATM layer (see
Figure 1-2
). Using the
multiple links of an IMA group increases the logical link bandwidth to approximately the sum of the
individual link rates. The physical links should be nominally the same length to avoid excessive
intragroup delay. We recommend that all of the links in an IMA group be bundled together between the
source and the destination.
Figure 1-2
Inverse Multiplexing and Recombining of ATM Cells Through IMA Groups
E1 I/O modules have eight ports. You can use the eight ports on the E1 I/O modules as independent ATM
links or in the IMA mode. The following bullets are examples of possible IMA groups, independent ATM
links, and mixed modes. In examples of IMA groups, two links are assumed per group.
•
Four IMA groups with any combination of eight links
•
Three IMA groups and up to two independent ATM links
•
Two IMA groups and up to four independent ATM links
•
One IMA group and up to six independent ATM links
•
No IMA group and up to eight independent ATM links
The E1 (1.544 Mbps) IMA port adapters provide network trunk or subtend connectivity and are used for
intercampus or wide-area links. The E1 IMA port adapters support unshielded twisted-pair (UTP)
connectors. The order of assignment of links to an IMA group is not restricted.
The IMA group interfaces use a naming convention different from those used by the other interfaces in
the system. IMA group interfaces are named with the convention
atm<slot>/ima<group>
, where
<slot>
is the slot number for the DS3+T1/E1 IMA NI-2 card and
<group>
is the IMA group number from 0 to
3.
Table 1-1
lists the interface naming conventions.
IMA group
PHY
Physical link 0
PHY
PHY
Physical link 1
Single ATM cell
stream from
ATM layer
Original cell
stream passed
to ATM layer
Physical link 2
IMA virtual link
IMA group
PHY
PHY
PHY
18092
