I deal mostly with Layers 1 2 and 3 of the OSI Model
What I do or work with can be understood by following these links Frame Relay forum ATM Forum FDDI (Pretty close to TLS(Translan Service))
IP/VPN Internet Protocol/Virtual Private Network. This is fairly new in the telco world though I think it should have been out there years ago. IP/VPN allows us to let our customers use any service at each site and connect them seamlessly. ATM talking to ISDN talking to Frame Relay talking to SMDS(Switched Multi mega bit data service) and on and on it goes. SMDS
Now the OSI modle is just that, a model. Each layer much be covered.... let me back up.
Each service I work with has it's own protocol stack. They each cover all of the layers in the OSI modle but do not have all the same layers. For example TCP/IP is a prtocol stack but dose not have 7 layers as the OSI model dose. http://www.uwsg.iu.edu/usail/network/nfs/network_layers.html
TCP/IP has 4 layers. But these four cover everything the seven suggested layers cover. If anyone is intrested I can break this out further.
I need to have a pretty good understanding of bandwidth in my job.. No big
A T-1 has 24 channels each is 64kbs. Some of you would say no 56kbs. Wrong!!!! 64kbs. The phone company robs you the customer of the least needed bits for management pourposes, i.e. dial tone, troubleshooting and so forth.
There are 28 T-1's in a T-3. each T-1 is 1.5443mbs A T-3 is basically 45mbs. Then you have Sonnet. An OC3 is 3 T-3's bunnddled together. An OC12 is 12 T-3's bunndeled together. See a pattern here? An OC24 is 24 T-3's
Now all Sonnet lines go out on fiber. so all OC class lines leave our switch and CO on fibber. so you have lets say an OC 3. and a switch has let say 30 of these coming out of it. 30 pieces of fibber? Nope! You can mux all 30 on to a single piece of fiber. different bands of light or different colors will not affect each other. last I checked we can mux 256 various colors of light into on strand of fiber. That is a good start, but I think we can do more on the photon level in the future.