VT1.5 is a type of virtual tributary in SONET.
SONET bandwidth is defined in multiples of an OC-1/STS-1, each of which can transport up to 51.84 Mbit/s. However, it is frequently desirable to address much smaller portions of bandwidth. To meet this need, sub-STS-1 facilities called Virtual Tributaries have been defined. In North America and Japan, the VT1.5 is the most common virtual tributary because it can carry 1.544 Mbit/s; just enough room for a DS1/T1 signal. In Europe, the VT2 (with a data rate of 2.304 Mbit/s) is used to transport E1s.
Some SONET manufacturers offer products that can switch at the VT1.5 level. Such equipment is able to re-arrange the data payloads so that inbound VT1.5s are placed into a completely different set of outbound STS's than the ones they arrived in. Among other things, this allows the bandwidth usage to be optimized and facilitates a cleaner network design.
The following is provided via Network Infrastructure/Design Student:
Four types of VT's defined in SONET
- VT 1.5 (DS-1: 1.544 Mbit/s)
- VT 2 (E-1: 2.048 Mbit/s)
- VT 3 (DS-1C: 3.152 Mbit/s)
- VT 6 (DS-2: 6.312 Mbit/s)
7 VT groups (VTG) per STS-1.
- Four DS-1s map into one VTG.
- One STS-1 frame can carry 28 DS-1s
- DS-3 Maps directly to STS-1. VT are not needed.
Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction