High Speed Link (HSL) refers to a single MTP2 link that uses the entire bandwidth of a trunk to transport MTP2 data.
The difference between a HSL MTP2 link and a Nx64/56kbps MTP2 link is that the Nx64/56kbps link uses many (N) independent timeslots, instead of all the timeslots. The HSL link and Nx64/56kbps link use a single HDLC receiver/transmitter that is not bound by a timeslot's normal 7/8 bit boundary like it is for a low speed link (LSL). The HSL can use the complete bandwidth of a channelized trunk to transmit data. All MTP2 links on channelized T1/E1 trunks can be switched via digital cross-connect equipment that can handle the timeslot level.