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12/10/09

2148T-1GE - Latency Tests

The Nexus 5000 is marketed as a low latency switch, specifically 3.2 microseconds between 2 ports.  What happens to the latency when you're not traveling between 2 ports on a Nexus 5000, but between two 2148T fabric extenders that connect to a 5000?  After scouring CCO and finding no mention of FEX latency numbers, I decided to mock up a simple topology and run some tests.  The topology is quite simple, there are two 2148 fabric extenders, each with (1) 10G uplink to a 5020.  A traffic generator is connected to port 1 on each FEX.

Please note:
    1. Latency values are listed in microseconds
    2. Frame sizes do not count the Inter Frame Gap and MAC Preamble


Frame Size Load % Min Latency Max Latency
64 10 8.3 8.6

20 8.3 9.4

30 8.3 9.2

40 8.3 10.2

50 8.3 9.6

60 8.3 9.1

70 8.3 9.0

80 8.3 10.6

90 8.3 9.9




250 10 9.8 10.1

20 9.8 10.1

30 9.8 10.1

40 9.8 11.0

50 9.8 10.3

60 9.8 10.1

70 9.8 11.0

80 9.8 10.4

90 9.8 10.6




500 10 11.8 12.1

20 11.8 12.1

30 11.8 12.1

40 11.8 12.1

50 11.8 12.1

60 11.8 12.1

70 11.8 12.1

80 11.8 12.1

90 11.8 12.1




1000 10 15.8 16.1

20 15.8 16.1

30 15.8 16.1

40 15.8 16.1

50 15.8 16.1

60 15.8 16.1

70 15.8 16.1

80 15.8 16.1

90 15.8 16.1




1518 10 19.9 20.2

20 19.9 20.2

30 19.9 20.2

40 19.9 20.2

50 19.9 20.2

60 19.9 20.2

70 19.9 20.2

80 19.9 20.2

90 19.9 20.2

As a point of reference, if you go between (2) WS-X6748-GE-TX (DFC3C) cards in a Catalyst 6500, the latency will range between 8 and 14 microseconds when tested at 90% load for similar frame sizes.

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