IBM 3745 Series, Hardware Maintenance Reference

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Introduction
The high performance transmission subsystem (HPTSS) is a combination of one or several high-speed
link scanners (HSSs) and NCP for the 3745.
The HSS is capable of clear channel, duplex, leased-line, HDLC/SDLC transmission using satellite,
Transfix, and any other transmission link (fiber, direct attachment of 3745, 3725, and so on) requiring
high-speed data transmission up to 2.048 Mbps. The HSS is also capable of operating with Frame Relay
traffic. Included are modifications on the NCP / ESS interface to improve the transmit and receive
command performance. This is referred to as the Frame Relay Performance Enhancement (FRPE).
This point-to-point non-switched connection can be attached to any network with the proper network
adapter like data communication equipment (DCE) or network communication terminal equipment (NCTE).
The HSS operates with the Network Control Program (NCP) and is transparent to the SDLC data traffic.
System Environment
Since the HSS is transparent to the data, the NCTE or DCE must conform to the network standards. The
HPTSS adapters (HSSs) can operate as secondary to the network clock connected to a network. When
operating as a secondary, the HSS operates with any clock speed up to 2.048 Mbps.
The HSSs can also be directly connected back-to-back without a network.
When directly attached to each other, the adapters can operate at any one of the three speeds set by the
NCP: 245.76 kbps, 1.47456 Mbps or 1.8432 Mbps. The connection to a 3725 is limited to 245.76 kbps.
The HSS provides two separate V.35 or X.21 interfaces to a network.
However, only one V.35 or X.21 interface to the NCTE or DCE can be active and enabled at a time.
HSS Packaging
The handling and management of such a high-speed data link is achieved by two cards:
Ÿ One communication scanner processor packaged on one card, the CSP card identical to those of the
low-speed scanner (LSS) but with a different CSP microcode load module (Refer to “CSP Microcode
Summary” on page 5-8).
Ÿ
One high-speed front-end scanner packaged on one card, the FESH card.
For board and card locations, refer to the Maintenance Information Procedures manual, SY33-2070.
┌────────┐ ┌────────┐
IOC Bus │ │ │ │ To High─Speed Data Link
%─────────────────┤ CSP ├──┤ FESH ├───────────────────────5
To CCU │ Card │ │ Card ├─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─5
│ │ │ │
└────────┘ └────┬───┘
DMA Bus │
%──────────────────────────────────┘
To Main Storage
Up to two HSSs (coupled CSP/FESH cards) may be installed on the basic board of the base frame, to
control up to two high-speed data links at one time.
On each FESH, a fan-out (standard feature) allows two high-speed data links to be connected at the tail
gate to that FESH. But only one of them must be active at a time.
Chapter 5. High Performance Transmission Subsystem (HPTSS)
5-5