Are the gigabit speed maintained over several switches?

Question

I want to understand the way data is sent between devices over several switches.

Let say I have this kind of setup (using consumer level switches).

Gbit Router > 16port Gbit switch > 16port Gbit switch

In theory, are all those ports at the switches end all going to have 1Gbit speed or only 1gbit/16 on first switch and 1Gbit/16/16 on second switch?

If I were to transmit 4K video of 50mbps bit rate from a PC using a Video Over IP (HDMI to LAN) device connected to the Gbit router, does all the port (32 total) be able to receive the data at full 50Mbps?

Are consumer level switches labeled Gigabit really transmit Gigabit the same quality/speed as the pro level Gigabit switches in this setup?

Thanks

Answer 1

Abstract

In the abstract, you'll generally be limited by your inter-switch links. You probably won't see maximum performance out of consumer grade hardware either. For example, the PCs probably can't sustain gigabit speeds reading and writing to their hard drives.

Time for maths

You'll need to find and compute several things to answer you questions. You'll have to consult with manufacturer specifications, and do some basic math.

Single Switch

If you only had one switch, you would only need to know the backplane speed of that switch. That will be your limiting factor of your network. If you have a nonblocking switch (see below), your nodes will be able to communicate at full speed.

Multiple Switches

If you have multiple switches, you'll need to find the backplane speed of all the switches. You want the backplane speed to be the number of ports times the speed times 2 (for full duplex) (For example, 8 ports x 1Gbps x 2 = 16Gpbs). Alternatively, you could look in its specs for the phrase "nonblocking" (wikipedia, DSL Reports, Cisco). Then, you'll need to create a network map of what nodes are communicating with what other nodes. You'll need to factor in the communications of all the devices of your network, and how they cross uplinks between the switches. If you exceed the rate of your uplink, that is a limiting factor, and your network becomes blocking. Professional switches usually have the next higher speed for their uplinks. For example, a 100mbit switch would have a gigabit uplink, and a gigabit switch would have a 10gigabit uplink.

An example of professionals referring to this with specific model numbers. Another example on Cisco's forum. Additional reading

Answer 2

Modern switches (for the last two decades or so) are only limited by port speed, this is also called non-blocking. Therefore, a 24-port gigabit switch can handle 1 Gbit/s ingress and egress on each port simultaneously.

Accordingly, interconnecting two gigabit switches allows 1 Gbit/s between any two ports. However, when the interconnect is limited to 1 Gbit/s, multiple flows across the interconnect will share this bandwidth.

This bottleneck can be widened by using faster ports on the interconnect or aggregating ports (with managed switches). Managed switches also allow you to control potential bottlenecks - which traffic is dropped first when the link capacity is exceeded (QoS) or how traffic is distributed over multiple links.