TDMoE over DSL

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TDMoE over DSL

Postby edo » Sun Oct 30, 2005 1:58 am

it's possible run TDMoE over DSL link (VDSL or SHDSL)?
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Postby WillKemp » Sun Oct 30, 2005 2:16 am

I'd never even heard of TDMoE until you mentioned it, but i'd say it's guaranteed that it can't be done - because it requires a synchronous transmission medium and DSL is asynchronous.

Even though TDMoE is carried over ethernet, it has to be a point to point ethernet connection - i.e., not via a switch. And i think it has to be done over raw ethernet, not via IP over ethernet - which is probably the most common way ethernet is used.

TDMoE is a very interesting application though.

Have you read:

http://www.voip-info.org/wiki/view/Asterisk+TDMoE
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Postby edo » Sun Oct 30, 2005 3:03 am

WillKemp wrote:Even though TDMoE is carried over ethernet, it has to be a point to point ethernet connection - i.e., not via a switch.
i think any traditional ethernet equipment (hub, switch, fiber media converter) must be ok:
Note that this does NOT allow routing the data over the internet, it only functions on a single Ethernet segment.


but dsl can be a trouble - it add some delays.
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Postby WillKemp » Sun Oct 30, 2005 3:53 am

edo wrote: i think any traditional ethernet equipment (hub, switch, fiber media converter) must be ok:

It may be, but i doubt that, because the switch will intefere with the timing - which is crucial to reassembling the bits of channel at the other end.

Note that this does NOT allow routing the data over the internet, it only functions on a single Ethernet segment.

I take "single ethernet segment" to mean a single cable connection - i.e., from one NIC to another. If there's a switch in the middle, that's two segments - i.e., from NIC to switch and from switch to other NIC.
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Postby dufus » Sun Oct 30, 2005 7:45 am

I've played a bit with TDMoE.

When I put it across any Ethernet connectivity equipment, every now and then I'd have problems. Lost/dropped packets and network collisions are very problematic, and messed with both ends of the link.

What I have done (and quite successfully) is use TDMoE between Asterisk boxes on individual Ethernet connections that are joined only by a crossover Ethernet cable. It makes a very good connection. I highly reccomend this configuration if you're planning a multiple server solution. (Even for Asterisk Real Time or something like that.)

Issues I did run into include making sure that both NICs were full duplex. Also the link worked best when the two cards were from the same manufacturer.

When you put one or two calls across the link it wasn't really a problem but when you fully loaded the link, having a full duplex connection from the same manufacturer made a noticeable difference. Packets arrived very reliably, and very immediately.
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Postby edo » Sun Oct 30, 2005 8:36 am

:(

i need connect to E1 port, located on some distance (1km) from asterisk server.
i can add small server with one E1 card (like Wildcard TE110P) and connect it to the main server via VDSL (cheap) or fiber.

it's possible use TDMoE in this configuration?
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Postby dufus » Sun Oct 30, 2005 9:06 am

I would doubt it. Really. Ethernet isn't a real time method of delivering information. It simply wasn't designed to be.

TDM (time divisional multiplexing) is, as it's name suggests very time sensitive.

Timing sources have to be the same at both ends, (to prevent slips) and losses are very noticeable.

You NEED low latency for TDM connections, and I don't think you'll get that from a DSL line.

My suggestion would be to call the telco, and have a point to point E1 put between the Asterisk box and the distant E1 port. No, it's not as cheap as a DSL solution, but with higher service quality, you should expect higher costs.

If you happen to have fiber (as you suggest) go buy a fibermux for each end. You can just run an E1 through that natively.

Don't go trying to re-invent the wheel. It's just not worth it. TDM solutions will always have a place in any voice installation, and I would think it's appropriate here.
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Postby edo » Sun Oct 30, 2005 10:09 am

dufus wrote:My suggestion would be to call the telco, and have a point to point E1 put between the Asterisk box and the distant E1 port. No, it's not as cheap as a DSL solution, but with higher service quality, you should expect higher costs.
classical E1 solution is shdsl or fiber modem with E1 interface, but i don't like cost ;)

exist any way run TDMoE over 1km link?
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Postby WillKemp » Sun Oct 30, 2005 2:02 pm

Ethernet over cat5e (or better) cable should work up to about 1km. Try and get the whole distance in one cable - rather than joining it - if you can. If not, solder the joints or use a proper krone block - not plugs and sockets - and make a good job of it to increase your chances of it working.

Alternatively, set up an Asterisk server at the remote end and use IAX2 trunking to connect the two over DSL.
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Postby dufus » Sun Oct 30, 2005 5:20 pm

edo wrote:classical E1 solution is shdsl or fiber modem with E1 interface, but i don't like cost


It doesn't matter if you don't like the cost. It's not likely you will get TDMoE to work across DSL. You will have to use it.

I would disagree with my colleague WillKemp. I don't believe that you will get Cat 5 to work across a 1km distance. The specified limit for Cat 5 wiring is 100m. It is unlikely that it will work across a distance 10 times that which it was designed to operate.
Last edited by dufus on Mon Oct 31, 2005 8:17 am, edited 1 time in total.
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Postby WillKemp » Mon Oct 31, 2005 4:53 am

dufus wrote:I would disagree with my colleague WillKemp. I don't believe that you will get Cat 5 to work across a 1km distance. The specified limit for Cat 5 wiring is 100m. It is unlikely that it will work across a distance 10 times that which it was designed to operate.

Yeah, of course! I'm not sure how that extra zero got into my head! ;-)
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