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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical switching versus routing ATM redux
Wading thru the flood in the past two days, I was wondering why Carmen Hillenburg <[email protected]> is answering Richard Irving <[email protected]> email? And why, with all the terminology being flung around, they don't realize that the term "Broadband ISDN" came years before "ATM"? The former is Engineering Speak, the latter Marketing Speak. FYI, they are confused. BRI ISDN is "baseband", not "narrowband". 10-base-2, 100-base-T, and gigabit ethernet are also "baseband". Cable TV channels (6 Mbps) are "broadband". Old 2400 bps satellite links are also "broadband". And why cannot either of them tell the difference between measured RTT of a ping and measured RTT using a real IP hop measurement tool, such as is available from LBL? And why there is any argument about forwarding latency, since by definition the last bit of the last ATM cell is not going to arrive any sooner than the last bit of a packet containing any IP datagram? Measuring the first bit arrival of cut-thru-switching is a waste of time. Processing of the IP datagram at the destination will not occur any sooner than the last bit.... And we all know that the task switch in the source and destination dominates the end-to-end timing (especially of non-fast-path ICMP messages like ping). A good ATM switch will buffer the entire packet anyway, to avoid wasting downstream bandwidth when one of the cells is dropped. No different than a router. By definition, there is much more link overhead (at least 2 ATM headers) and forwarding overhead (at least 2 ATM cell switches per SDH hop) for an IP/ATM/SDH datagram than an IP/PPP/SDH datagram (1 small header and 1 packet switch per SDH hop). Thus, ATM takes more bandwidth (is slower) and more cell switches (is slower), cumulatively at every hop. Slower is slower is slower.... And, on another thread, I was pretty sure that NetStar cum Ascend had a 622 Mbps OC-12c (STM-4) IP/PPP/SDH card long before Cisco. They were engineering it nearly 2 years ago. Did they not sell any? At the time, both Cisco and NetStar had very talented engineers on the OC-3 and OC-12 projects (and I'm not easily impressed), but the Cisco folks were hampered by the speed of their backplane and buffering on their card. NetStar had the backplane bandwidth and plenty of buffering, but had routing software instability. Reports on this list were that they were fixed. [email protected] Key fingerprint = 17 40 5E 67 15 6F 31 26 DD 0D B9 9B 6A 15 2C 32 [email protected] Key fingerprint = 2E 07 23 03 C5 62 70 D3 59 B1 4F 5E 1D C2 C1 A2 |