The 3174 Model 21L is a rack-mounted local channel controller that supports the System/370-architecture channel interface for SNA and non-SNA attachment. The Model 21L supports up to sixty-four 3270 devices and twenty-four ASCII devices.

The IBM 3174 is an Establishment Controller that provides a broad range of connectivity options, workstation and host attachment possibilities, network asset management capabilities, and expandability features. In addition to options that allow host connections via both local channel and remote communication link connections, the 3174 can connect to the IBM Token-Ring Network or Ethernet LAN Networks (IEEE 802.3 and Ethernet DIX Version 2). The 3174 can connect to an ASCII host, an AS/400, APPN as well as provide the 3270 display controller function. The IBM 3174 ISDN Basic Rate Interface Adapter is available to enable attachment to ISDNs.

Terminal Attachment

The 3174 Establishment Controllers offer a wide variety of terminal attachments. They can be configured to connect terminals directly, via 3299 Terminal Multiplexers, via optional Terminal Multiplexer Adapters (#3103) and via optional Telephone Twisted Pair Terminal Multiplexer Adapters (#3105), or by a combination of these attachments.

The 3174 has an integrated four-port terminal adapter which permits up to four terminals to be directly attached, or by using one of the following, up to a maximum of 32 terminals can be attached:

• One to four 3299 Terminal Multiplexers
• One to four Terminal Multiplexer Adapter optional features (#3103)
• Any combination of up to four 3299 Terminal Multiplexers and Terminal Multiplexer Adapter optional features.
• One Telephone Twisted Pair Terminal Multiplexer Adapter (#3105)

Channel Attachment

The 3174 Model 21L and 21H attaches to a byte multiplexer, block multiplexer, or selector channel of the processors listed above. The channel cable may be up to 122m (400 ft) long, under the conditions described in S/370 channel architecture. The Model 21L also attaches to the IBM 3044 Fiber Optic Channel Extender Link. Single-tag interlocked and two-tag High-Speed-Transfer channel operational modes are supported, for data rates up to 1.25MB per second. When attached to 4361 high-speed channels via an IBM 3044 Fiber Optics Channel Extender Link, the Models 21H and 21L must be configured for Single-tag interlocked mode. The Model 21L may be channel attached to an ES/9000 Model 120, 130, 150 and 170 processor via the internal channel cables.

The 3174 Model 21L and 21H with Configuration Support-B Release 2 or later or Configuration Support-C installed, supports Data streaming. Data streaming is supported at 1.25 or 2.5 MBytes per second data rates. It operates in SNA environments where the 3174 is connected to a 9370 or 3090 block multiplexer channel.