Bandwidth limit of a port

[NIKHIL M K]

Hi Team

If a port supports only 1 Gbps and has an inbound traffic of 600 Mbps and outbound traffic of 800 Mbps, will it exceed its threshold? How will the 1 Gbps port behave? Will it handle 1 Gbps for both inbound and outbound simultaneously, or will it overrun the traffic?

Thank you

Nikhil M K

[Karsten Iwen]

We nowadays work with full duplex connections where we can simultaneously have inbound and outbound traffic. So, yes, both in and out. But this is only the port itself. The device also has to process this data. And at least with older devices (routers, firewalls), there were many that had Gigabit ports, but the processing power was not enough to forward a Gig in and out. 

[Joseph W. Doherty]

As @Karsten Iwen describes, if port is full duplex, in theory, it should be able to process full line-rate, tx and rx, concurrently.  As he further describes, some devices, generally using a CPU for their data plane, may be incapable of sustaining a port with a series of multiple frames, ingress and/or egress, back-to-back.  However some actual hardware designs may have the latter problem too, for rx, although that's unusual.  Also the latter problem might be due to sending or receiving hardware not being quite in conformance to spec.  (An example of the latter, would be an Ethernet Interpacket Gap being undersized.)

[M02@rt37]

Hello @NIKHIL M K 

A 1 Gbps port can handle up to 1 Gbps of traffic in each direction simultaneously, thanks to full-duplex operation. This means the port can manage 1 Gbps of inbound traffic and 1 Gbps of outbound traffic at the same time without exceeding its capacity.

In your scenario, with 600 Mbps of inbound traffic and 800 Mbps of outbound traffic, the port would not exceed its threshold. It can handle these traffic rates simultaneously because the combined usage of 600 Mbps inbound and 800 Mbps outbound falls within the 1 Gbps limit for each direction independently. Therefore, the port will operate efficiently and will not overrun the traffic, ensuring smooth data transmission without any loss or congestion due to capacity limitations.

[Joseph W. Doherty]

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M02@rt37 wrote:

Hello @NIKHIL M K 

A 1 Gbps port can handle up to 1 Gbps of traffic in each direction simultaneously, thanks to full-duplex operation. This means the port can manage 1 Gbps of inbound traffic and 1 Gbps of outbound traffic at the same time without exceeding its capacity.

In your scenario, with 600 Mbps of inbound traffic and 800 Mbps of outbound traffic, the port would not exceed its threshold. It can handle these traffic rates simultaneously because the combined usage of 600 Mbps inbound and 800 Mbps outbound falls within the 1 Gbps limit for each direction independently. Therefore, the port will operate efficiently and will not overrun the traffic, ensuring smooth data transmission without any loss or congestion due to capacity limitations.

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Actually, that's not guaranteed.

Interfaces always operate at either zero or 100 percent usage.  When we use terms like 600 Mbps or 800 Mbps, what that really means, for some time period, interface was active 60% or 80% of the time, respectively.  What we cannot tell, is how such a less than 100% usage was actually distributed during the measured time period and/whether traffic needed to be queued during the measured time period.

For example, if we had a gig interface that transmitted (or received) for 1 second, stopped for 1 second, and continued this cycle for a minute, our "measured" rate would be 500 Mbps.  But, the same, 500 Mbps, would be if the interface was active for 30 seconds and stopped for 30 seconds.  Those two different usage patterns can make a huge difference to whether the platform, or even its hardware, can process the "500 Mbps".