T1 Details And Connections
A T1 Line is difficult to understand, but is very handy in your big or small business. It is a great way to get a fast internet connection. Before your look into this, you need to make sure that you have a good T1 connection, by finding a good t1 cost, and a good t1 provider. It is also an intelligent to research some details about t1 connections in order to make sure that you are getting a good deal.
To start, there are some technical strategies that can be found when you are looking to T1 connections. To start, a two wire bus called 'U', with a minimum wire size of 26 AWG, links the Telco switch with the customer premise.
The box into which the U bus terminates is called NT1 and you can think of it as the 'ISDN BRI modem'. From the NT1, a four wire full duplex bus called T goes into another box called NT2. The NT2 can be your PBX a bridge, a multiplexer, etc. Out of NT2 another 4 wire bus called S connects to the ISDN stations or terminals.
Up to eight TEs maybe connected to the same NT1 and BRI in what they call a 'passive bus arrangement' in a multipoint configuration.
Only two of the eight devices can talk over the two B channels at a time; the others have to wait patiently for their turn.
Each BRI or PRI can get one or more phone numbers; if one is supplied, then the telco switch treats the B channels as part of what they call a 'hunt group' and the incoming calls are allocated the first available B channel. Each attached device is also allocated an extension called a TEI or 'Terminal Equipment Identifier'. ISDN-capable ones are called TE1.
The other type includes things that you and I use daily, such as PCs, dumb terminals and plain old telephones that cannot signal over the D channel and cannot transmit at a rate of 64 Kbps. Those are called TE2. To hook up to the S bus, they need a special standalone box or a card inserted in the PC, called a TA.
The interface between the TE2 and TA is known as the R interface. When a TE wishes to place a call, it does so over the D channel by sending a message named 'Call Request' in a language very similar with X.25. Then, the switch in the Telco forwards the message to its attached STP computer.
Then, if accepted, the calling device receives a Connected Indication packet, and it can start transmission over the allocated B channel. Otherwise, the call will be rejected and a code with the reason for the rejection will be provided to the calling TE by the switch. Additionally, if one has a terminal adapter that can 'speak' packet X.25, it can do so via the D channel while no signaling is in progress, and while using the circuit-switched B channels for other calls.
Simultaneously, the power company can control the meters and the usage of electricity over the same D channel through a process called telemetry. ISDN tariffs are written so that one can signal the network via the D channel to request more bandwidth for a connection.
When available, the network assigns additional B channels to the call. The connecting equipment combines the B channels to create H channels. There are many possibilities, the most common ones being 384 Kbps, 768 Kbps and 1,536 Mbps. This way, full motion video can be accommodated over several such channels combined into a larger bandwidth pipe. Although these details sound overwhelming they are easily understood once you look into them a little bit.
