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Speed of interfaces on Cisco's devices.

NetworkingGeek1
Beginner
Beginner

Hello,

I know this topic has been discussed many times, but I didn't find clear anwer yet. 

Let's say speed of interface of the swith is 1Gbps. Does it mean that theoretically this interface can transmit and receive data at the time with the speed of 1 Gbps? Meaning 1Gbps transmit and 1Gbps receive at the same time.

Thank you!

2 Accepted Solutions

Accepted Solutions

Hello,

check the link below (the explanation under Figure 2.7).

" Full-duplex offers 100 percent efficiency in both directions (transmitting and receiving). This results in a 200 percent potential use of the stated bandwidth."

https://www.ciscopress.com/articles/article.asp?p=2181836&seqNum=5#:~:text=Full%2Dduplex%20communication%20improves%20the,also%20known%20as%20bidirectional%20communication.

View solution in original post

Joseph W. Doherty
Hall of Fame Master Hall of Fame Master
Hall of Fame Master

As noted by others, answer depends on whether interface is running in full duplex or half duplex mode.

With half duplex, one "bandwidth medium" is used to transmit and receive on, much like how a walkie talkie works, you can transmit or you can listen, cannot do both at the same time.

With full duplex, there's one "bandwidth medium" for transmission, and other different "bandwidth medium" for reception.  As there are two "bandwidth mediums" you can, concurrently, transmit and receive at the same time (at full rate).

So, if your 1 Gbps interface was in half duplex mode, you only have 1 Gbps of bandwidth, which you use for transmission or reception, but not at the same time.

And if, your 1 Gbps interface was in full duplex mode, you can send and/or receive 1 Gbps, at the same time, i.e. using 2 Gbps of bandwidth, but only 1 Gbps for transmission or reception.

View solution in original post

7 Replies 7

Leo Laohoo
VIP Community Legend VIP Community Legend
VIP Community Legend

@NetworkingGeek1 wrote:
Let's say speed of interface of the swith is 1Gbps. Does it mean that theoretically this interface can transmit and receive data at the time with the speed of 1 Gbps?

Combined/Total/Aggregate/Mixed-together/The-sum-of-which-is transfer and receive is 1 Gbps.  

Hello @Leo Laohoo  Thank you. So, it means that 1 Gbps is shared speed between transmit & receive for interface of the switch. Is there any oficial Cisco web page explained this?

Hello,

as far as I recall, if the port is set to full duplex, it can transmit and receive at a rate of 1Gbps, at the same time. So that means: 1Gbps transmit, and 1Gbps receive.

@Georg Pauwen  thank you. I didn't find any official information about this on Cisco web site. Could you please shaer if you have one?

Hello,

check the link below (the explanation under Figure 2.7).

" Full-duplex offers 100 percent efficiency in both directions (transmitting and receiving). This results in a 200 percent potential use of the stated bandwidth."

https://www.ciscopress.com/articles/article.asp?p=2181836&seqNum=5#:~:text=Full%2Dduplex%20communication%20improves%20the,also%20known%20as%20bidirectional%20communication.

Thank you Georg. It's strange there is only one official source about this. I didn't find anyting about this from other official resources (like Cisco website, for example).

Joseph W. Doherty
Hall of Fame Master Hall of Fame Master
Hall of Fame Master

As noted by others, answer depends on whether interface is running in full duplex or half duplex mode.

With half duplex, one "bandwidth medium" is used to transmit and receive on, much like how a walkie talkie works, you can transmit or you can listen, cannot do both at the same time.

With full duplex, there's one "bandwidth medium" for transmission, and other different "bandwidth medium" for reception.  As there are two "bandwidth mediums" you can, concurrently, transmit and receive at the same time (at full rate).

So, if your 1 Gbps interface was in half duplex mode, you only have 1 Gbps of bandwidth, which you use for transmission or reception, but not at the same time.

And if, your 1 Gbps interface was in full duplex mode, you can send and/or receive 1 Gbps, at the same time, i.e. using 2 Gbps of bandwidth, but only 1 Gbps for transmission or reception.

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