ASR 9K perfomance question

[Alexey Stytsenko]

Good day!

Recently i viewed in one presentation from Cisco Expo Moscow slide with routers ASR9K series characteristics:

And question arised what those digits mean - lets consider on example "Megatron"

Max. Linecard Bandwidth - 360 Gbps. It can be assumed that some top linecard can contain 18  10G ports, what will give us 360 Gbps.

Max. Slot Bandwidth - 1.2 Tbps. Here problems begins. What does it mean - that slot has such powerfull connection to fabric, that current line cards can`not utilize it fully?

Chassis Bandwidth - 48 Tbps. Here doubts about my knowledge of math arised - 20 slots* 1.2 Tbps = 24 Tbps, but here result is twise greater.

Can smb clarify how those values get/calculated?

[Joseph W. Doherty · Accepted solution]

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Posting

First realize when "bandwidth" is given, it's sometimes provided unidirectional and sometimes bidirectional (if full duplex is supported).  For example, a "gig port", full duplex, might be described as 2 gig.  Bidirectional bandwidth is often what's provided for fabric bandwidths.  Slot bandwidths, today, are often provided as unidirectional bandwidths.

The foregoing might explain how 20 x 1.2 Tbps (unidirectional) per slot (24 Tbps) = chassis 48 Tbps (bidirectional - 2x unidirectional).

Regarding max line card bandwidth vs. max slot bandwidth, that could be simply there's no line card, today, that uses more than 360 Gbps.

When the 6500-Es were first put out, you might find mention in the initial documentation that they (the chassis) would support more bandwidth per slot.  However, at the time, the most any 6500 line card would use was 40 Gbps.  When the sup2t was announced, it was also announced it supported 80 Gbps per slot, even on the 6513-E.  Besides the -E chassis and the new supervisor, new line cards were announced that could utilize the 80 Gbps.  In other words, for a couple of years the 6500-E series actually supported 80 Gbps per slot but there wasn't a supervisor or line card (yet) to take advantage of the design bandwidth of the 6500-E chassis.

It might be similar for the ASR9K, and if so, Cisco is just making clear what's the potential (for bandwidth growth) for the ASR9K.

[Alexey Stytsenko]

First realize when "bandwidth" is given, it's sometimes provided unidirectional and sometimes bidirectional (if full duplex is supported).  For example, a "gig port", full duplex, might be described as 2 gig.  Bidirectional bandwidth is often what's provided for fabric bandwidths.  Slot bandwidths, today, are often provided as unidirectional bandwidths.
The foregoing might explain how 20 x 1.2 Tbps (unidirectional) per slot (24 Tbps) = chassis 48 Tbps (bidirectional - 2x unidirectional).

I haver thought about this, but this is common practice for now to count bandwidth as bidirectional, any way it seems weird to adduse bandwidth of slot and card as uniderectinal but chassis as biderectional.

BTW it seems to be right assumption cos there are 36 10G ports line cards for asr 9k - A9K-36x10GE-SE, which will provide with 360 Gbps unidirectional bandwidth.

[Alexey Stytsenko]

Today I found other weird slide in other ASR 9k presentation, smth wrong with those devices

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Actually, what you've highlighted, I believe, conforms with what I believe is how Cisco is representing the bandwidth.

120 Gbps "bi-directional" (or duplex) sums (2x 120 Gbps) to 240 Gbps one the chassis.

[Alexey Stytsenko]

Oh, you right, i get that bi-derectional already mean summ of two directions.