Specifications

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Cisco IGX 8400 Series Provisioning Guide, Release 9.3.3 and Later Releases
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Chapter 4 Cisco IGX 8400 Series Trunks
IGX Trunk Configuration
Bandwidth on IMA Trunks and Lines
The transfer and receive rates for an IMA trunk or line is the sum of all physical lines minus the overhead
used by the IMA protocol. The overhead used by the IMA protocol is defined in the following rules:
• If the IMA trunk or line group consists of 1-4 physical lines, the IMA protocol overhead is 1 DS0.
• If the IMA trunk or line group consists of more than 4 physical lines, the IMA protocol overhead is
2 DS0.
For example, using an IMA line group defined as 8.1–4 with T1 lines, the following total bandwidth is
possible:
TX (transfer) rate = RX (receive) rate = 24 x 4 DS0s – 1 DS0 = 95 DS0s
For an IMA line group defined as 8.1–5 with T1 lines, the following total bandwidth is possible:
TX rate = RX rate = 24 x 5 DS0s – 2 DS0s = 118 DS0s
If a physical line fails and the retained links threshold has not been reached, the switch automatically
adjusts the total bandwidth downward to compensate for the failed physical line.
See Table 4-7 for available port speeds with different combinations of T1 or E1 interfaces for an IMA
trunk or line group.
.
Table 4-7 Available Trunk Speeds for IMA Trunk or Line Groups
Interface Trunk Speed (DS0) Trunk Speed (cps)
8xT1 T1/190 28697
7xT1 T1/166 25056
7xT1 T1/142 21433
6xT1 T1/118 17811
5xT1 T1/95 14339
4xT1 T1/71 10716
3xT1 T1/47 7094
2xT1 T1/23 3471
T1 T1/24 3622
8xE1 E1/238 35924
7xE1 E1/208 31396
6xE1 E1/178 26867
5xE1 E1/148 22339
4xE1 E1/119 17962
3xE1 E1/89 13433
2xE1 E1/59 8905
1xE1 E1/29 4377
E1 E1/30 4528