|
North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: MCI
>> > > > > What kinds of routers can route at near wire speeds a bunch of ports at > > > > 155Mb ATM? > > > > > > None right now. Gigarouter can handle it theoretically, but... > > > > > > I'm being picky, but it's a moot question since doing wirespeed OC3c using > > > ATM is impossible in of itself. Hell, mapping of > > > SONET framings to ATM cells take off about 6 mbps right there. > > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > > By the way, I did not post the above.. Oops. Replied to the right thread but wrong author. > [email protected] (Shikhar Bajaj) wrote: > > A couple of minor corrections here. ATM cells are mapped into SONET frames and > > not the reverse. Also, I presume that the 6 Mbps that you are talking about is that > > the ATM bit rate over an OC-3 is 149 Mbps as opposed to the OC-3 pipe > > rate of 155 Mbps. Those 6 Mbps are taken up by the SONET management overhead > > (section, line, and path) in the frame. This is independent of whatever goes in the > > SONET payload envelope and has nothing to do with ATM. > > > It seems to me that Sonet OC-3 is often taken as transport for 3 DS3s, > which would reduce 155.530 Mbps to 134.208 Mbps (3 x 44.736 Mbps), less > than the 149 Mbps you cite above. The 149 Mbps assumes that you have a native ATM/OC-3 interface where the SONET transport is STS-3c ('c' for concatenated). Here, a single connection can use the full bandwidth of the pipe. In your example, a DS-3 gets mapped into an STS-1 and then 3 STS-1s get muliplexed into an STS-3. The multiplexing is for trunking purposes and there is no relation between any of the STS-1's (other than they are byte multiplexed). Thus, the maximum bandwidth available for any single connection is 51 Mbps (or DS-3 in this case). Routers with ATM/OC-3 interfaces do STS-3c framing. > Do you have a good recommendation for Gordon Cook, TCP/IP direct over Sonet? I've heard rumblings about such work going on but I am not personally familiar with any of it. The only thing I can think of is some work that the IETF did for PPP over SONET (RFC 1619). I *think* it became an Internet Standard. Shikhar
|