Does anyone know if I can use a coax cable to extend my existing network?

Ob

You cannot. You need at least 2 pairs to have ethernet work.

~Matt

This is true if you are using twisted-pair based ethernet (10baseT, 100baseT, 1000baseTX), but remember that the original 10mb ethernet was based on a single coax cable bus running between stations, tapped at each location.

Coax is not used for new installations, but it is still out there. It's generally considered to be obsolete, but it still works if you don't expect high performance.

Coax based ethernet is 10mb/sec, shared media, half-duplex, unlike 10baseT which uses dedicated tx/rx paths, and can be full-duplex if connected to switches.

Coax based ethernet comes in two types. ThickNet (10base5) uses a thick 50ohm coax similar to RG8/RG213/RG214 type. Normally yellow or orange in color, tapped with vampire taps, or N connectors. Maximum segment length 500m before a repeater or bridge is required. Each end must be terminated with a 50ohm terminator.

ThinNet (10base2) uses RG58A/U type 50ohm coax, with a maximum segment length of 185m. BNC connectors and T's are used at each station. Each end must be terminated with a 50ohm terminator, which may be built-in to a hub.

Note that these are both 50ohm coax types, not the 75ohm coax used for tv/sat/video.

If you are using a 10mb hub with a BNC connector on it, you can use RG58A/U to extend the network to other hubs.

You still use that junk? I figured 2 things when answeing this question: He isnt going to want to buy a bunch of obsolete junk to make that work, and he is probably talking about RG6. However - good point techie.

Hey Obsaleet, Can you use the existing coax to pull in a cat5 cable.

~Matt

Thanks guys,
I don,t 10mb is gonna cut it. I have an sub building that was wired in 1969. Someone has run coax to it. The old phone lines have been spliced many times from what I can see. All is direct buried about 200'. We tried a new product that is like a DSL but I think there is to much impedance on the phone lines due to the splices. It did not work. The wireless is not reliable and security is now becoming an issue do to change in use. I 'm working up a price to get a 2" pvc coduit out there and due it proper. I'm getting concerned about distance thou as the trench will have to go the long way around(about 280"). As usual the budget is tight.

Ob

Sounds like you are going to want to run fiber..

I support a small network that has a run of thicknet out to a remote communications shelter to support a pc and a multiport terminal server used to interface to a antenna positioning system.
The distance is too far for twisted-pair, and thicknet cable was readily available, as were 10mb hubs and utp-to-coax media converters. The required bandwidth is low.

Around here, getting your hands on obsolete 10mb hardware is easy.. you just take a run down to Weird Stuff, or any of the other surplus places in the valley.

Oh.. didnt see where you were. You talking about the one on Caribbean Dr? I have been to that one and their first location as well.. the newest place seems to be the biggest warehouse they have. I live in antioch.

You must know of halted too then, right? That place always beat weird stuff imo.

~Matt

Thats the one..

HSC has a better selection of some things, but Weird Stuff has more computer stuff. HSC always seems a bit overpriced..

The one I miss is Haltek, which had a great selection of small hardware (screws, etc) and linear power supplies. (they had a large stack of Lambda supplies..), but they closed a number of years ago.

The other good place to get parts, although they are not a surplus house, is HDB in Redwood City. There is a good taco stand down the street as well.

Techie,
It was my understanding that 300' would be the cutoff. I would expect that even if we are close we will just have less bandwidth. Witch compaired to what is going on now would be a hughe improvment.


ob

The specified maximum distance for a cat5 segment is 100m.
This includes 90m of structured wiring, and 10m of patch cables. The 100m segment will support the full bandwidth.

People have successfully exceeded 100m with full duplex links between switches, but it is not recommended as a standard practice.

If you are running a link between buildings, it is recommended that you run fiber to eliminate any possible differential in ground voltages between endpoints.

If the link fails, it won't be a "just have less bandwidth" failure--it will fail by having a high error rate, which results in dropped packets, which results in end-to-end retransmissions. This is a Very Bad Thing(tm).

However, 285' shouldn't be a problem. As techie pointed out, the maximum length of a 100 megabit Cat5 segment is 100 meters, or around 330'. Assuming that the everything is installed properly, that should work with no problem.

Using Cat6 cable will probably provide you a bit of extra insurance, but isn't really necessary, because the connection is designed to operate flawlessly across 100m of Cat5 cable.

To expand a bit on one of techie's comments, 100m is a hard limit for a half-duplex link. This is because of the "slot time" built into the Ethernet retransmission algorithm. If you make the length longer than that, you will have collisions that aren't detected, resulting in lost packets. Full duplex, on the other hand, doesn't use use the collision detection and backoff algorithm, so there isn't a hard limit as there is with half-duplex. So one can stretch beyond the 100m spec, but it is definitely not recommended practice.

I note that normally hubs are half-duplex, and switches are full-duplex.

techie, I agree that fiber isn't a bad idea between buildings. However, the original Ethernet installation at PARC saw around a 90V difference in ground potential from one end of the coax to the other, so we specified something like 2000V isolation in the coupling transformers when we wrote the standard. This isolation was carried over into the BaseT specs. So there really shouldn't be any problem using copper between two buildings, unless there might be more than 2000V difference in ground potential between the buildings. (In which case you have much, much larger problems to worry about...)

You CAN get over 100 Mbps at 300m on coax using Moca adapters. This may get pricey as the technology is pretty new.

http://www.mocalliance.org/en/index.asp

The issue with all networking technologies is that you will almost certainly be violating the ANSI/CSA/UL 60950-1 listing when you run between buildings. The interface ports of most networking equipment are classified SELV and as such they are not subject to the overvoltage testing (power line cross) that is required in the US and Canada. In other coutries you will only be violating circuit separation clauses of the safety standard. When you run these indoor circuits outside, this make the interface a "cable distribution system" (rather than jsut a SELV circuit that happens to connect to coax) which adds testing requirements that may not have been considered during the NRTL investigation.

If I was uncertain of the conditions of the product Listing (and unable to stop myself from proceeding with the installation anyway), I would install the equipment on and over a non-flamable surface and/or locate it inside a fire enclosure. I only say this cuz I know some people are just going to run stuff outside anyway. May as well make some effort to encourage them to do it the least wrong way possible.

Ethernet will have the same violation of Listing issue.

Ethernet can run up to 500m on a half-duplex link (thick coax). There is a limit for the total network diameter to ensure that collisions are still detected, but there's no way you're going to exceed it with a single twisted pair link.



Hubs are always half-duplex. Switches can be either half or full duplex according to either the port settings or autonegotiation. One of the most annoying problems I've encountered is admins forcing the ports to full-duplex which breaks autonegotation. The end result of this is terrible performance unless you set the network card in the PC to also run in full-duplex.

Unmanaged switches will not allow you to change the port duplex settings manually. They are autonegotiation-only.

I should have clarified that the 100 meter limit is for 100 megabit and gigabit Ethernet. For 10 megabit Ethernet the limit is 500 meters per backbone segment, but you can go something like 2500m (IIRC) end-to-end, through repeaters. It was designed so that you could have a 1500m fiber segment bridging between two "ethers."


Yes, you are quite correct that switches can support half-duplex. I was thinking in terms of going switch to switch for the OP's situations, but I did omit that most switches can operate either way.

Actually, the 100 meter limit is for all twisted pair based Ethernet, 10baseT, 100baseT, and 1000baseT.

(the following is mostly of historical interest, since no one actually builds shared networks of this size any more.)

For 10base5 (Thicknet) the limit is 500 meters per segment. For 10base2 (Thinnet) the limit is 185 meters per segment.

The 5-4-3 rule applies. Between any two stations in a shared Ethernet network, you may have up to 5 segments, with 4 repeaters (hubs are considered multi-port repeaters), but only 3 segments may be populated with stations. If you are using 10base5, this means that there can be a maximum of 3000 meters between end stations before a router or bridge is required. 3000 meters is based on 5x 500m 10base5 coax segments, and 10x 50m AUI transceiver cables (ie: [HOST]-50m-(X)-500m-(X)-50m-[REPEATER]-50m-(X)-500m-(X)-50m-[REPEATER]-50m-(X)-500m-(X)-50m-[REPEATER]-50m-(X)-500m-(X)-50m-[REPEATER]-50m-(X)-500m-(X)-50m-[HOST]

If you need to extend the network beyond these limits, you need to segment the collision domain with a router or a bridge (a switch is essentially a multi-port bridge).

A DEC remote repeater uses up to 1000 meters of fiber optic cabling to connect two network segments. FOIRL (Fiber Optic Inter Repeater Link) also has a 1000 meter limitation. 10base-FL, which replaces FOIRL, has a 2000 meter limit.

I believe that you are allowed to replace one segment with a fiber optic remote repeater, based on the old DEC configuration guidelines.

Hi Guys Thanks for all your help! I installed two cat 5e cables Fri and it works great measured 290 feet to new switch. The IT guy is very happy!


Ob

For 100baseT, there is apparently a hard 100 meter limit that is due to collision timing issues, in addition to signal strength issues.

For 10baseT, the 100 meter limit is due to signal strength issues ONLY. Modern cat5e cable has less attenuation than does the cable for which 10baseT was originally speced (which is not even cat3 cable, but just plain old telco grade twisted pair, like what might have been used to wire a Merlin phone phone system in 1985) and therefore it is apparently possible to run 10baseT up to 150 meters on cat5e cable without issue.

For 100baseT as a shared media (ie: using a hub), there is a hard limit due to timing. There is also a limitation on the number of hubs in the network, again due to timing issues.

The basic problem is that the frame must be able to reach the furthest point in the network and return before the originating station has finished transmitting the frame. The timing is based on the minimum frame size of 64 bytes.

The rules effectively limit a shared 100baseT network to a single hub driving 100m segments, or two "class II" hubs driving 100m segments, separated by up to 5m of cable linking the hubs.

I should mention that ethernet has been tested successfully over short lengths of barbed wire.

I should amend my posting above. IEEE 802.3 notes that the non-populated link segments are supposed to be full-duplex (twisted pair or fiber), and the length of the AUI cables used with fiber transceivers is 25m.