On Fri, 25 Feb 2005, Per Gregers Bilse wrote:
You generally need a router or something else acting as store-and-forward. E1/T1 and other plesiochronous circuits are just that, near synchronous, and certainly not asynchronous. Things cannot be transmitted or received without clocks on both sides being in synch, which may or may not be the case if you try to hook up two arbitrary lines. Moreover, assuming both are terminated towards you, both will be driving clock for your router ("terminal equipment") to pick up, and they are not going to be in phase. Then there's the issue of different options for framing and various control bits, etc. You might get lucky if you could convince one of the circuit providers to take clock from you (which would then come from the other circuit), but you would probably still need to deal with signal level, framing, and other issues (ie, have a box of sorts). All in all, an old cisco 2500 is probably the cheapest and most troublefree solution.
In every case I've dealt with when setting up a back-to-back connection of T1 or E1 circuits, the appropriate crossover connection between transmit and receive (1,2 - 4,5 on 8-pin jacks, swap Tx and Rx on co-ax) and setting one side to supply internal clock and the other side to recover clock from line works just fine. -- Jay Hennigan - CCIE #7880 - Network Administration - jay@west.net WestNet: Connecting you to the planet. 805 884-6323 WB6RDV NetLojix Communications, Inc. - http://www.netlojix.com/