Ethernet Connection Daisy Chain - Page 1
Forum section: electronics / projects

author: cRash1001
author_rank: Contributor
timestamp: March 30, 2016, 03:29:32 pm
content: I want to implement a Daisy Chain for connecting RJ45 Ethernet Connection. It would be used to transfer tokens and data between various PCB. I would like to know what kind of Ethernet transceiver they use in VOIP phone where you have a ethernet in and a ethernet out. I want to use this to eliminate the use of switches. So guys is Daisy Chaining Ethernet RJ45 any good and how do i do this. What IC would in need to use?Thanks.

author: nctnico
author_rank: Super Contributor
timestamp: March 30, 2016, 03:50:43 pm
content: Hint: a VOIP phone has an internal ethernet switch.

author: stmdude
author_rank: Frequent Contributor
timestamp: March 30, 2016, 04:12:25 pm
content: First off, there's no such thing as "daisy chaining" Ethernet.There's the concept of hub and switches. Hubs are basically a distribution-box, allowing everything connected to the hub hear everything everyone else is transmitting. If you want to transmit something, but someone else is transmitting already, you'll have to wait. If you both start transmitting at the same time, the packet it lost, and both transmitters needs to back off a "random" time, and try again (CSMA/CD).Downsides (except the whole everyone can hear everyone else) is that they're also limited to half-duplex, and the maximum aggregated bandwidth cannot exceed the performance of the slowest port.However, they're stupid simple to build, if you're not concerned with getting it absolutely perfect. An example:http://www.zen22142.zen.co.uk/Circuits/Interface/pethhub.htmThe next step up is "Switches". They're intelligent, and implement a store-and-forward method, i.e, they buffer the incoming packets, look at the destination address, and only forward it to the port where the recipient is located. This means that they can do full-duplex, and the aggregate bandwidth is usually enough to have all ports running at full blast at the same time.However, this would require the use of an ethernet switch chip, as well as transceivers/PHYs.As cRash1001 mentioned, VoIP phones have a switch chip in them. A three-port switch. One for "in", one for "out", and one internal that that phones CPU is using.The reason for them marking them "in" and "out" when they in (flawed) theory could be used interchangeably is that most VoIP phones uses Power-over-ethernet (POE), and only the "in" port can accept the 48V (or so) that POE delivers.

author: Fgrir
author_rank: Regular Contributor
timestamp: March 30, 2016, 04:23:20 pm
content: Quote from: stmdude on March 30, 2016, 04:12:25 pmI miss my old10BASE2.

author: cRash1001
author_rank: Contributor
timestamp: March 30, 2016, 05:01:43 pm
content: What i want is a device which has two embedded Ethernet ports which function as an Ethernet switch, as well as an interface to the local device. This allows information to flow to the device, or flow through the ports to other devices in the daisy-chain. Devices in the chain are cabled together in series using standard Ethernet cable, similar to legacy fieldbus but without the need for additional Ethernet switches.(http://iebmedia.com/index.php?id=5968&parentid=74&themeid=255&hft=49&showdetail=true&bb=1)I have been asked to develop an Ethernet-based device that should be connected in a daisy chain network. So, the Ethernet connection is can it be implemented in an embedded design in daisy chain topology?

author: Monkeh
author_rank: Super Contributor
timestamp: March 30, 2016, 05:03:22 pm
content: What you want is.. drumroll please.An ethernet switch.

author: mariush
author_rank: Super Contributor
timestamp: March 30, 2016, 05:08:43 pm
content: for communication between some boards..You could easily program basic 8 bit microcontrollers with two hardware uart/spi/i2c modules to work in a chain, one module as input, one module as output and loop the last board's output to the first board's input ... give each chip an unique id and then each chip takes turns sending data in the chain or telling the next chip in line to take control of communication.Even $1.5 or cheaper PIC microcontrollers in theory can do 15-25 mbps when they run at 32-40Mhz (with built in oscillator so no external parts required).Your data packets can have 1-2 bytes to tell which boards are supposed to receive it and if a board receives the data packet it can check if the packet is meant for itself and then optionally check the following bits to see if other boards in the chain are meant to receive it and then send it along to next board otherwise stop there and give control to next board in chain.I guess it depends on the data packets and their size, if they're small packets they can be stored in mcu's sram or some attached memory chip until each board's "brains" can actually retrieve the information and process it.

author: jc101
author_rank: Frequent Contributor
timestamp: March 30, 2016, 05:09:18 pm
content: Do you mean something like one of these?http://www.microchip.com/DevelopmentTools/ProductDetails.aspx?PartNO=AC320004-4This is an add-on board for a PIC32 dev board, but it is in effect a 3 port switch, two physical and one internal that connects to the PIC32. Schematics are available from the link, perhaps this will give you a starting point?

author: Kjelt
author_rank: Super Contributor
timestamp: March 30, 2016, 05:12:08 pm
content: You can do a LAN tap, only downside is that due to the capacitive coupling the bitrate is reduced from 1Gb to 100Mb. Very handy tool to monitor multiple connections for instance between two switcheshttp://hackerwarehouse.com/product/lan-tap-kit/

author: wkb
author_rank: Super Contributor
timestamp: March 30, 2016, 05:54:49 pm
content: Quote from: Fgrir on March 30, 2016, 04:23:20 pmBah.. far too modern:https://en.wikipedia.org/wiki/10BASE5I still have the tool to drill the holes for a vampire tap on BASE5.

author: cRash1001
author_rank: Contributor
timestamp: March 30, 2016, 06:08:16 pm
content: Quote from: jc101 on March 30, 2016, 05:09:18 pmHey, finally found an IC from microchip like the one i needed. KSZ8852 and KSZ8842. These are industrial capable Ethernet switches, providing integrated communication for a range of Industrial Ethernet and general Ethernet applications.These support daisy-chained topologies preferred for industrial Ethernet networks. C A flexible 8- or 16-bit general bus interface is provided for interfacing to an external host processor.

author: stmdude
author_rank: Frequent Contributor
timestamp: March 30, 2016, 07:09:04 pm
content: Quote from: Fgrir on March 30, 2016, 04:23:20 pmAw, crap, how could I have forgot (repressed?) good old BNC based ground-fault devices?

author: chickenHeadKnob
author_rank: Super Contributor
timestamp: March 30, 2016, 11:01:23 pm
content: Quote from: wkb on March 30, 2016, 05:54:49 pm**** cough **** ethercat ***cough ****https://www.ethercat.org/en/technology.html

author: CM800
author_rank: Frequent Contributor
timestamp: March 31, 2016, 01:13:29 pm
content: Quote from: chickenHeadKnob on March 30, 2016, 11:01:23 pmEtherCAT is lovely for some things, but the complexity of implementing it is painful, the only chips that have it integrated have a reference manual of 2000+ pages (going on 3000), the Sitara range from TIthe other option is the custom chips from Beckoff which cost about 20 EUR in medium quantity each.

author: Howardlong
author_rank: Super Contributor
timestamp: March 31, 2016, 05:23:34 pm
content: Going a bit higher up the stack, typically VoIP phones also offer VLAN segregation, so they encapsulate the PC traffic in a different IP network to that of the phone's, so they aren't typically just basic switches or hubs. They will also offer PoE, and so will need a switch that supports both VLAN tunnelling and PoE.

author: madires
author_rank: Super Contributor
timestamp: March 31, 2016, 05:49:39 pm
content: BTW, the maximum number of daisy chained switches supporting STP (Spanning Tree Protocol) is 7.

author: technix
author_rank: Super Contributor
timestamp: March 31, 2016, 07:08:36 pm
content: I would really suggest against such kind of networking as one device in the chain offline mean all devices downstream offline. People deprecated the daisy chained 10BASE2 and 10BASE5 in favor of a star topology for a reason - in the previous implementations each node is a SPOF, but in the new implementation there is only one SPOF at the center of the network: the Ethernet switch.

author: nctnico
author_rank: Super Contributor
timestamp: March 31, 2016, 07:15:55 pm
content: Quote from: technix on March 31, 2016, 07:08:36 pmUnfortunately that is not always an option. In many existing buildings (think an apartment building) there is no physical room to pull an extra cable from a central room to each apartment so daisy chaining is the only option. Having a switch built in makes life a lot easier. For one of my previous employers I designed a box which was an ethernet switch, an RFID based lock and some other functions in one. This device was supposed to be daisy chained as well.

author: technix
author_rank: Super Contributor
timestamp: March 31, 2016, 09:29:22 pm
content: Quote from: nctnico on March 31, 2016, 07:15:55 pmIn such scenarios it may be a better idea to use wireless instead of wired network, despite the obvious existence of wires in the wall. Use short patch cables (almost impossible to fail unless physically damaged) to short out sockets in rooms where no wireless access points are placed, and daisy chain those access points. This will significantly reduce your points of failure (as one wireless access point will cover a few rooms) and the possible points of failure are specifically designed against such failure from happening (purpose-built networking hardware instead of a board someone cooked up from their lab.)

author: theoldwizard1
author_rank: Regular Contributor
timestamp: April 01, 2016, 03:13:54 pm
content: Quote from: stmdude on March 30, 2016, 04:12:25 pmActually, there is ! Or perhaps I should say "WAS" !Before many if you here were born, there was something call Thinwire Ethernet, 10Base2. Yes, it was only 10 Mbit, and it actually used RG58 cable with "tees" for daisy chaining. It was a very cost effective solution for a local area network !

author: stmdude
author_rank: Frequent Contributor
timestamp: April 01, 2016, 03:23:37 pm
content: Quote from: theoldwizard1 on April 01, 2016, 03:13:54 pmActually, I'm old enough to have been shocked _many_ times by those ground-fault inducing little b*****ds. Seems I had repressed those memories. Perhaps due to the shocks I received.