"Just Daisy Chain"



  • I work for an isp that has equipment in a telco environment.  The fun thing about this stuff is that it all runs on -48V most of the time instead of the more common 120.   One of the problems I've been having lately is that the vendors don't make -48 volt GigE switches.  They will happily sell me a 10/100 switch to plug my gigE  DSLAM into but as you can guess that doesn't provide me the needed speed when each user can have 24MB each (adsl2+) or 100M each (Vdsl2).  When queried on this one of our vendors gave me the following reply:

    "Each VDSL DSLAM has two Ethernet ports if you need to daisy chain."



  • I'm not a network person, but how does daisy chaining slow(er) devices make it faster? Did they mean to imply you can have parallel data streams to give the effect of a faster device?

     Just guessing here, but a single feed split into two slower feeds doesn't yield net faster speed, or am I totally barking up the wrong tree?



  • Well, for starters, doesn't "daisy-chaining" usually refer to hooking multiple devices into each other end-to-end (i.e., in a chain) rather than splitting anything into multiple paths?  So the guy in the story here was just speaking nonsense (while trying to appear that he was giving a real solution) to our dear OP.



  • @snoofle said:

    I'm not a network person, but how does daisy chaining slow(er) devices make it faster? Did they mean to imply you can have parallel data streams to give the effect of a faster device?

     Just guessing here, but a single feed split into two slower feeds doesn't yield net faster speed, or am I totally barking up the wrong tree?

     

    Each DSLAM has two GigE network ports and it's quite standard for them to have a sort mini switch inside that connects them.  The proposed solution would involve pluging my uplink to the first DSLAM , the second DSLAM into the first, the third into the second  etc.

    The downsides:
    If I have to remove something from the middle the whole network breaks.

    I can forget about any sort of QOS packet quing to make sure everything gets it's fair share of the uplink.

    This setup will get VERY complicated if I have to use extended networking options like VLAN (virtual network) 

     



  • @Saladin said:

    Well, for starters, doesn't "daisy-chaining" usually refer to hooking multiple devices into each other end-to-end (i.e., in a chain) rather than splitting anything into multiple paths?  So the guy in the story here was just speaking nonsense (while trying to appear that he was giving a real solution) to our dear OP.

    You have a good point. I was thinking of what was done in the office where my brother works. They needed extra USB ports, so they added a port-splitter into the last slot on the first port splitter. It was daisy chained, but created multiple (logical) parallel paths, even though it was all ultimately only one USB port off of the PC. I was trying to draw a parallel with the proposed daisy chained network solution, and was thinking that yielding several slower paths hanging off of one main line doesn't speed things up.

    Or is my (admittedly simple) analogy off base?



  • If you can afford 2U, http://www.tsipower.com/DC-to-AC-Inverter.htm may be useful. As for daisy chaining... the vendor should be consigned to maintaining a thinnet installation.



  • When I worked at the superb Australian carrier Telstra, -48V was the most common supply voltage in the exchanges.  Of course, Telstra isn't normal, so I don't know if that counts elsewhere.



  • -48V (DC) is very common in telcos all over.  They use the 48V batteries that run the phone system to power other stuff too.
     



  • @reptar said:

    When I worked at the superb Australian carrier Telstra, -48V was the most common supply voltage in the exchanges.  Of course, Telstra isn't normal, so I don't know if that counts elsewhere.

    -48V is pretty standard - along with big banks of batteries.

     

    IIRC running at -48v helped reduce corrosion on the earth contacts... 



  • Never rely on features that the OEM added "just because they could".

    I had a Nortel CVX (1800 modems in 12U IIRC) which could allegedly speak OSPF... the stupid thing flooded the network with an OSPF route for EVERY SINGLE MODEM and overloaded the poor old routers sat in the middle.

    Treat the DSLAM as a DSLAM and nothing else, get a switch to be a switch and a router to be a router, and that way you'll have less chance of your manager convincing you to log in to a back-door serial port server re-configuring routers via your PDA while you're on holiday.

     

    Not that I'm bitter... 


     


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