What does gigabit mean?

[Basshead]

So this may sound really dumb but I have a theoretical question. If a switch is called a gig switch, obviously we know that each port is limited to 1Gbps, but what about the inside? Can only one Gbps of data total travel inside the switch, or could port 1 be talking to port 2 at 1Gbps WHILE port 3 is talking to port 4 at 1Gbps?

[Needfuldoer]

"Giga" - prefix for billion

"bit" - One eighth of a byte

 

One billion bits per second. Giga-bit. Gigabit.

 

4 minutes ago, Basshead said:

Can only one Gbps of data total travel inside the switch, or could port 1 be talking to port 2 at 1Gbps WHILE port 3 is talking to port 4 at 1Gbps?

Switching capacity is entirely determined by the compute power the switch has. Even the cheapest modern Gigabit switches should let all the ports talk to each other at line speed, though you probably won't find that spec listed for low end and no-name switches. Enterprise grade rackmount managed switches usually have tons of available switching capacity, and their spec sheets and sales literature are more than happy to tell you all about it.

[Electronics Wizardy]

Typically a switch can have every port moving data at the line speed, so with a 8 port switch all 8 ports can send and receive at 1gb/s at the same time.

[da na]

Every port can "talk" at 1GBPS simultaneously. In practice you won't get exactly 1GbPS out of a switch but you'll get very, very close.

[Basshead]

12 minutes ago, Needfuldoer said:

"Giga" - prefix for billion

"bit" - One eighth of a byte

 

One billion bits per second. Giga-bit. Gigabit.

 

Switching capacity is entirely determined by the compute power the switch has. Even the cheapest modern Gigabit switches should let all the ports talk to each other at line speed, though you probably won't find that spec listed for low end and no-name switches. Enterprise grade rackmount managed switches usually have tons of available switching capacity, and their spec sheets and sales literature are more than happy to tell you all about it.

Thank you so much. I will be doing some research to see how off the shelf switches compare to one another especially in this way. I will post my findings.

[Kisai]

18 minutes ago, Basshead said:

So this may sound really dumb but I have a theoretical question. If a switch is called a gig switch, obviously we know that each port is limited to 1Gbps, but what about the inside? Can only one Gbps of data total travel inside the switch, or could port 1 be talking to port 2 at 1Gbps WHILE port 3 is talking to port 4 at 1Gbps?

Enterprise switches have number of ports *2 of switching capacity.

This is an UniFi 8 port 2.5GbE switch + 2 SFP So note the switching capacity is 8 x 10Gb. The 2 SFP ports are not included in this as they're usually not connected to "the switch" Now look at the "non-blocking throughput, this is how much can go across without inducing latency. So realistically there is enough bandwidth for full-duplex use if the SFP's aren't used. If the SFP's are used, then they might consume the bandwidth of a single port.

 

You'll find similar specifications on enterprise switches.

 

Now, consumer switches, like those on your router, are not the same. Realistically, you only ever see 4 or 5 ports, so the combined switching bandwidth is usually similar, however that doesn't include the MAC's of the "modem" side of the router (eg WAN port, or DSL or Copper/Fiber SFP) 

 

Like if you buy "just a switch", the best way to think of it is an X port-wide highway that has a traffic light at the end to do a U-turn onto another lane (for another port.)

 

If however you have a router, the "Switch" is eclectically connected as a single port. So if you have 8 10Gbe ports, but the SFP plugged in is 1GBe, then any traffic destined to the SFP only goes at the speed of the SFP. So if you have 40GBits of traffic flying around, that 40GBits may occasionally be interrupted by traffic from the SFP port.

 

If you look at a block diagram of a switch, vs a router, a router is simply a "switch" with one port connected to a computer. 

 

So each PHY in this case is 4 ports, and those are connected to another higher bandwidth switch.

 

Here's another example

https://www.eetimes.com/fpga-based-ethernet-switches-for-real-time-applications/

 

Now compare to a wireless router

https://www.eeworldonline.com/teardown-inside-the-tp-link-archer-c7-wireless-router/

It's actually really hard to find block diagrams of routers that don't look super complicated.

 

Basically routers are "computers" with an ethernet switch. Where as a switch is pretty much self-contained when it's unmanaged, and when it's managed it resembles a router.

 

Now the last thing to mention are "hubs" and "access points"

 

Ethernet "hubs" haven't really been a thing since 10Mbit. You may still find them. Unlike a switch, a hub only allows one connection to speak, and thus if two devices try to speak, they "Collide" and have to retry.  Hence why hubs are kinda useless unless everything you plug in is expected to listen (eg printers), not constantly communicate.

 

"Access points", basically look the same as a wireless router but lack the switch ports. Back before 802.11b took off, you usually had to buy an access point to plug into a 10/100 switch.

 

Presently 802.11n and later are usually integrated into ISP routers which basically whatever the ISP servers(DSL, Fiber, Cable, etc) on one MAC, The WiFi on another MAC, and then a 4 or 5 port switch.

 

So to answer your question is "only the devices plugged into the switch directly" have access to the full switching bandwidth. Like if you plug in two switches, eg one 4 port switch to another 4 port switch, the 3 devices plugged into the switch 1 can communicate through that 40Gbits of switch bandwidth, but if it has to talk to a device on the other switch, it will have to share that port's 10Gb with everything on both switches. This only gets worse when you add more switches.

 

Hence, you are better off buying a larger switch than you need if you will be using a lot of devices that will be communicating simultaneously. Such as file servers. If you're just worried about internet bandwidth, then the choke point will be the MAC connected to the internet. 

 

Most people will not need anything bigger than an 8 port switch, and if your ISP modem isn't as fast as you need it, you are better off buying an 8-12 port switch, and then plugging just one port on it into the ISP modem. This also gets into the "what happens if I plug in two ports from two switches", on enterprise switches, this doubles the bandwidth, but on consumer switches this isn't guaranteed since the switch logic is usually end-to-end, where as an enterprise managed switch is effectively routing it. 

 

At any rate. If you're just buying a switch to be able to connect everything in a room to your network, you can just do that, and you're fine. Only if you need to connect to specific devices (Eg file servers, media servers) do you need to consider the switching bandwidth, because Ethernet is slower than a directly attached storage device due to latency and software on either side.

[Alex Atkin UK]

19 hours ago, Basshead said:

Thank you so much. I will be doing some research to see how off the shelf switches compare to one another especially in this way. I will post my findings.

As mentioned, Gigabit switches will almost certainly allow full capacity.

 

Its multi-gig switches where it gets complicated, as sometimes they have multiple switches connected to each other so will have a bottleneck between them that wont allow full bandwidth of every port across that link.

[Blue4130]

20 hours ago, Basshead said:

Thank you so much. I will be doing some research to see how off the shelf switches compare to one another especially in this way. I will post my findings.

Or just head over to servethehome. He tests full throughput on every switch review.

 

example of a 8 port 2.5g with single 10g port.

[Alex Atkin UK]

7 minutes ago, Blue4130 said:

Or just head over to servethehome. He tests full throughput on every switch review.

 

example of a 8 port 2.5g with single 10g port.

Was trying to get the list up to post myself.

https://www.servethehome.com/?s=switch

 

Wish their YouTube channel was more organised, such as a playlist for just Switch reviews.

[Blue4130]

59 minutes ago, Alex Atkin UK said:

 

Wish their YouTube channel was more organised, such as a playlist for just Switch reviews.

Agreed. Great info, hard to find.

[Alex Atkin UK]

45 minutes ago, Blue4130 said:

Agreed. Great info, hard to find.

Some of the interesting videos have been the 2.5Gbit switches from Aliexpress.  Seemingly identical hardware but can be many watts differences in power consumption in the actual way they implemented that hardware.