Adtran ISU 128 User Manual

Chapter 7. Protocol Options

61202.029L2-1

ISU 128 User Manual

The DSU 57.6 ASYNC or DSTOP protocol allows the ISU 128 to communicate 
asynchronously at 57.6 kbps with ADTRAN 2- and 4-wire Switched 56 DSU 
products.  In addition, the ISU 128 will communicate with other ISUs over dial 
and leased connections using this protocol.  Figure 7-1 illustrates the menu 
path for setting the DSU 57.6 ASYNC protocol.

The T-Link protocol allows the ISU 128 to communicate with 2-wire Switched 
56 DataPath Data Units (DUs) such as the ADTRAN DSU III 52W.  The T-Link 
protocol performs two functions:

•

The T-link protocol adapts DTE data subrates of 64 kbps to the 64 kbps 
bandwidth of the ISDN bearer channel.

•

For asynchronous and synchronous DTE rates up to 19.2 kbps, T-Link 
transmits the status of the DCE-DTE EIA leads to facilitate flow control 
and maintenance.

In addition to 2-wire Switched 56 DataPath DUs, the ISU 128 can communicate 
with any other device that uses the T-Link protocol.  Figure 7-1 shows the 
menu path for selecting T-Link.

Simple ADTRAN Protocol (SAP) is a rate adaption method providing DTE 
service between ISU 128 units at a sub 64 kbps ISDN bearer channel rate.  Se-
lecting this menu item causes the ISU 128 to use SAP protocol.  

The primary usage for SAP is general purpose asynchronous rate adaption in 
a dial-up or leased environment.  SAP only operates on a 64 kbps data link.   
See Figure 7-2 for the menu path to select SAP.