It's ATM day. | Consider the following configuration | ________ _______________________ ________ | | Router | loop A | | loop C | Router | | | A |=========| Wide-Area ATM Service |========| C | | |________| |_______________________| |________| | | | | local loop B | | | ________ | | Router | | | B | | |________| Consider the following configuration: Ra----fibrepath2----------RbRc------fibrepath2--------Rd or the following: Ra---ll1---[IXCi]---ll2---RbRc---ll3---[IXCii]---ll4--Rd I wonder what the distribution is, in terms of number of backbones, of each of the three models. (You may choose to imagine easy extensions like Ra and Rd really being two routers, with physical connectivity between Ra' and Rd') In terms of designing Internet backbones, do you see any issues other than cost when choosing between your version and either one of my versions? Also, does this change when there are, say, twenty-odd routers at each of the three locations? Sean.