DCE - Data Communication Equipment
In the context of IBM mainframes and z/OS, Data Communication Equipment (DCE) refers to devices that establish, maintain, and terminate data transmission links between Data Terminal Equipment (DTE), such as a mainframe or a terminal, and a communication line. Historically, this often included modems, CSU/DSUs, and specialized communication controllers like the IBM 37x5 Front-End Processors.
Key Characteristics
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- Interface Conversion: DCEs convert data signals from the DTE into a format suitable for transmission over a specific communication medium (e.g., analog signals for telephone lines, digital signals for dedicated lines).
- Clocking and Synchronization: They provide timing signals (clocking) to synchronize data transmission between the DTE and the network, ensuring proper data flow and data integrity.
- Physical Layer Management: DCEs operate primarily at the physical layer (Layer 1) of the OSI model, managing the electrical, mechanical, procedural, and functional characteristics of the interface to the communication link.
- Connection Establishment and Termination: Responsible for initiating and terminating physical connections, such as dialing up a remote modem or establishing a dedicated line connection.
- Offloading Communication Tasks: Advanced DCEs, like communication controllers, could offload significant network processing from the mainframe's host CPU, improving overall system performance.
- Protocol Handling (Limited): While primarily physical, some sophisticated DCEs could handle lower-level communication protocols, especially within Systems Network Architecture (SNA).
Use Cases
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- Connecting Mainframes to Remote Terminals: A mainframe (DTE) would connect to a communication controller (a sophisticated DCE), which in turn connected to modems (other DCEs) to establish links with remote 3270 terminals (DTEs) over leased lines or dial-up.
- Interconnecting Mainframe Systems: DCEs facilitated communication between multiple mainframe systems, allowing for data exchange and distributed processing across geographically dispersed locations via dedicated or switched lines.
- SNA Network Backbone: Communication controllers (acting as DCEs) formed the backbone of traditional SNA networks, managing thousands of concurrent sessions and routing data between various network components.
- Legacy Application Access: Providing the necessary physical and data link layer connectivity for older applications running on z/OS that still rely on traditional communication protocols and hardware interfaces.
Related Concepts
DCEs are intrinsically linked to Data Terminal Equipment (DTE), where the DCE acts as the intermediary connecting the DTE to the communication line. In SNA, Front-End Processors (FEPs) like the IBM 37x5 series are prime examples of sophisticated DCEs, managing Systems Network Architecture (SNA) protocols and offloading communication tasks from the host z/OS system. They interact closely with VTAM (Virtual Telecommunications Access Method), which is the host software component responsible for managing network resources and sessions,