T1/T3

• T1, or tier 1, of service is sometimes referred to as a DS-1, or Digital Service tier 1.
• You specify the tier of service that you require when ordering service as a T1.
• The T1 provides 1.544 Mbps of bandwidth.
• A T1 is a group of 24 channels of serial data.
• A channel of data = DS0
• We use a special device called a channel service unit/data service unit (CSU/DSU) to convert the channels back into a stream of data.
• If each channel is 64 Kbps and we have 24 channels, in total we have 1.544 Mbps of bandwidth.
• Channels can be used for voice or data.
• We can even divide T1 so that some of the channels are for the PSTN and some are for data.
• We can even purchase only a few channels of data; that is called a fractional T1.
• A T3, or tier 3, of service is sometimes referred to as a DS-3.
• The T3 is the next step up from T1, when you need more bandwidth.
• T2 existed at some point, but T1 and T3 became the popular ordering standard.
• A T3 is 28 T1. connections, or 672 DS0 channels, combined together to deliver 44.736 Mbps of bandwidth.