Asymmetric digital subscriber line#Interleaving and fastpath

FastPath is the name for an option to reduce the latency for ADSL connections.

Benefits are a better response time for online games or terminal connections (eg SSH), a lower speech delay and better echo suppression in Internet telephony and a slightly smoother web experience. In rare cases, this may adversely affect the effective rate of transmission.

Technology

FastPath is realized by turning off interleaving, a tool for error correction, on the route between the DSL modem and the transfer point to the telephone network operator (DSLAM ). When interleaving the data blocks are transmitted interleaved to certain data error, so-called burst errors caused by transient electrical noise on the telephone line better correct, can. This nesting means that the round-trip transmission time of data packets ( so-called ping time ) with an average of 60 ms is relatively high. FastPath the option the data packets are transmitted and not nested the latency is reduced to about 15 to 25 ms.

Possibly the increasing occurrence of transmission errors can be handled in protocols based on TCP, for connectionless protocols ( for example, UDP use ) go bad packets inevitably lost. The shutdown of interleaving can be problematic if the DSL connection, depending on the line quality and length, already at the limit of their capacity (see also signal -to-noise ratio). This is checked prior to activation of FastPath through the telephone network operator.