On 5/28/20 9:10 AM, James Knott via talk wrote:
On 2020-05-28 08:30 AM, Alvin Starr via talk wrote:
Generally speaking fiber is still more expensive than copper wiring but the difference is not nearly as bad as it once was. The biggest thing is the price of CAT-5,6,7... is way down the price curve due to volume and the fact that most of us can afford the hardware to terminate copper cable. The cost of fiber termination is still way up there.
The cost of fibre patch cords isn't that far from copper: https://www.fs.com/c/fiber-optic-cables-209?gclid=Cj0KCQjwwr32BRD4ARIsAAJNf_...
SFP modules will set you back less than $10. Compare that to the cost of a Cisco switch or router and you'll find the difference is trivial.
There's also the advantages such as immunity from electrical interference, shock hazard, no longer limited to 100M (in fact, it's possible to cross the Atlantic, without repeaters). Unbelievable bandwidth (theoretical maximum 2.5 petabit, IIRC), less volume (important with larger cables) and more. Absolutely. There are some real advantages to fiber and I did not say that fiber did not have its advantages just that it is still a little more expensive
FS.com is a good source of inexpensive patch cables and networking products. But still a 1M OM3 cable is ~$5 and a 1M CAT5e is ~$2.5. Not a huge difference but if you need a thousand of them it starts to add up. I am sure a Cisco SFP is more than $10 from Cisco If your doing the cabling then the cost of the termination and testing equipment can become a stumbling block.\ There is also the cable prep and cleaning that is needed with optical fiber which is not part of the CATx than CATx.
Redundant networks over the same cable(bundle) is not really redundant.
Who said anything about being in the same bundle?
True. That was my bad. I made an assumption from your comment about the cable being along the LRT right of way. But that being said all cable along a single right of way is in essence a single point of failure( think back hoe ). Multiple fiber bundles does not make that problem go away.
Ethernet is not a real-time protocol. There are a number of ways to cover that shortcoming but Ethernet networks will never have deterministic throughput. For most things this is OK but if you need microsecond level timing then your looking at some other protocol.
Token ring was deterministic, in that there was a maximum time, before a device could transmit. This compared with half duplex Ethernet (coax or hub), where there's a random factor. However, that difference doesn't exist with switches, where you can assign priority, scheduling and more. The limiting factor with Ethernet is something called "funneling", where packets from multiple sources are all heading to the same port, which will cause a backup. VLAN tags can be used to provide priority, as well as ToS in IP. So, it all boils down to proper engineering of the network.
Still Ethernet is not real-time. There are a lot of things that can be done to make it more amenable to human scale real-time but hard real-time operation is just not part of the mix. Once you hit a switch it gets worse. There may be some switches out there with deterministic queuing but I don't know of them.
Throwing out real-time response and using CSMA/CD half duplex operation made the initial Ethernet hardware much cheaper than its competitors.
When's the last time you saw half duplex Ethernet? Also, most of that gear ran at 10 Mb, with a small amount capable of 100 Mb. However, switches killed half duplex. Of course, 100 Mb was left in the dust years ago, with 100 Gb, or more, now used in many applications. https://en.wikipedia.org/wiki/Terabit_Ethernet Yesterday. I still have some thinnet hardware in my junk pile.
The design choices early on have effects on the uptake of a technology. Cheap Ethernet cards made for more people using the technology and more people using the technology leads to more companies developing hardware to extend the technology. Rinse and repeat. The openness or propritaryness of the protocols may have also played into those cost calculations. I remember a time when it looked like ATM might take take a chunk out of the Ethernet installed base but the cards never came down in price enough to make it happen. I did have a friend who made a lot of money by selling his ATM card startup to Cisco. Losing a manufacturer may have help in the demise of cheap ATM cards.
As for IP. It is best described as resilient and not redundant. The protocols on top of IP make for a very robust network that will generally route around failures. But they are even further from deterministic.
IP and Ethernet are best effort. Then again, so was token ring. They all rely on some end to end protocol, such as TCP to provide protection against data loss. You'd have to go back to X.25 (yes, I've worked with that too) to get such protection on a per hop basis.
As I mentioned, almost my entire career, going back to 1972 has been in telecom, computers and networks, so I do have some idea about what I'm talking about.
I was there also and around the same time along with dealing with aircraft avionics where there are some hard real-time and redundancy requirements. I also know a little about this. I did not suggest that you did not know what you were talking about I was just pointing out some subtler points. -- Alvin Starr || land: (647)478-6285 Netvel Inc. || Cell: (416)806-0133 alvin@netvel.net ||