Usually SFP's adhere to standards like 1000BASE-SX or 10GBASE-LR or special types like BiDi, BX, ER, ZR which describes several requirements like wavelength, type of led/VCEL/laser used to transmit signals and more. All SFP's of the vendors then comply with these standards so a switch from vendor A will successfully make a connection to another switch/router/server's SFP module. Usually in ethernet standards you have ports running a single speed like 1 Gbps and only support SFP modules. But you also have dual speed ports like 1/10Gbps SFP+ ports. And even beyond 40/100Gbps ports. If your customer has an old fiber plant you'll need to stick to 1 Gbps links but you could bundle 2 or 4 or 8 links to upgrade your inter switch bandwidth that way.
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