Can a Tahoe 681 modem (G.shdsl/Ethernet) be connected to a Tahoe 635 (G.shdsl/V.35) or a Tahoe 671 (G.shdsl/G.703)?
No. Tahoe 681 and 682 modems use ATM encapsulation on the DSL link. This means that the transmitted data are placed in ATM cells. The Tahoe 635 modem will synchronise with the Tahoe 681, but the data stream sent to the V.35 interface will be unintelligible to the connected external router, which will expect a data stream conforming to the HDLC protocol.When using a single-pair modem (Tahoe 681), is there any benefit in using a two-pair line (connected in parallel to reduce its resistance)?
Connecting two lines in parallel does reduce their combined resistance, but it increases the capacitance and may introduce phase shifts and additional signal reflections. Such a connection may therefore sometimes increase, but may also decrease, the achievable throughput. What will actually happen can only be determined by testing the modems on the specific line.
To make full use of two copper pairs and increase the range or throughput of the modems, two-pair modems such as the Tahoe 682 should be used. They contain two separate transmission circuits - as if they contained two separate modems. As a result, the aggregate throughput is twice the throughput achievable on a single line.Will modems or routers operating in bridge mode forward IPX packets?
Yes, modems and routers operating as a bridge work at the hardware layer and operate independently of the higher-layer protocol - it may be IP, IPX or anything else. A bridge works on the same principle as an Ethernet switch.How do Tahoe modems perform on lines fitted with attenuators?
The attenuators that some companies install on leased lines restrict the transmitted bandwidth so that HDSL modems cannot achieve a throughput higher than that specified by the line provider. Consequently, HDSL modems will achieve a throughput at most 10-20% higher.
G.shdsl+ modems (Tahoe 635, 671, 681, 682), on the other hand, use the highly efficient TCPAM32 modulation, which reduces the occupied frequency band by a factor of two and a half. Therefore, on a line with an attenuator these modems achieve throughputs 2-3 times higher than HDSL modems.