- VT1.5
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 andJapan , the VT1.5 is the most common virtual tributary because it can carry 1.728 Mbit/s; just enough room for a DS1/T1 signal. InEurope , 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.External links
* [http://www.commsdesign.com/showArticle.jhtml?articleID=56700123 "Understanding Sonet VTs: A Tutorial"]
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