"Richard E. Brown" wrote: > > Folks: > > There's a controversy about the amount of traffic that a T1 circuit can carry. > Obviously, it can send, or receive, 1.544 Mbps per second. > > But can it send *and* receive 1.5 Mbps simultaneously? Or does the total data > carried (send plus receive) max out at 1.5 Mbps? > > I've heard people who ought to know give both answers. So I'll open the question > to the world's experts and ask this list.
I've seen others that have essentially answered the question, but I suspect the "real" question is that of bandwidth and utilization. Then there are two answers, depending on if you are in marketing or you are an end-user :-) Yes, a T1 can send and receive 1.544Mbps simultaneously. End-user: a T1 has 1.544Mbps capacity Marketing: a T1 has 3.088Mbps capacity You are downloading a huge file, and ideally, downloading at 100% efficiency, it won't go any faster. End-user: the T1 is at 100% utilization Marketing: the T1 is at 50% (plus fudge for acks) In short, the T1 is full-duplex. The real question is how to quantify half-duplex and full-duplex when discussing "bandwidth", or especially in terms of "utilization". For half-duplex, utilization can be stated as either: (a) ((Rx + Tx) / Bx) * 100 (b) (max(Rx, Tx) / Bx) * 100 For full-duplex, the values are similar: (a) ((Rx + Tx) / 2Bx) * 100 (b) (max(Rx, Tx) / Bx) * 100 For full-duplex operation, Intermapper seems to use the (b) rule to report %utilization. Cisco's Traffic Director, on the other hand, uses the (a) rule, and report the link bandwidth as 2Bx. The routers themselves report Rx and Tx separately. But back to the original 1.544Mbps T1 issue, this is the physical data rate of a raw T1, B8ZS encoding, ESF formatting, non-channelized. A channelized T1 is 1.536Mbps, 24*DS0s usable, the missing 8Kbps being the signalling channel. (Likewise the 56Kbps vs 64Kbps depends on bonding the 8K voice band with the 56K data band). European standards are E1 (32*DS0) rather than T1 (24*DS0). To get actual data bandwidth, you have to peel off the layers: * encapsulation (PPP, HDLC, SDLC, etc) * IP framing/checksums * TCP framing/CRC * MTU size etc Jeff ____________________________________________________________________ Note: To unsubscribe from this mailing list, please send email to: <mailto:[EMAIL PROTECTED]> Thanks!
