
Chapter 3 System Features
User Interfaces
3-6
255-700-025
PacketStar
™
Access Concentrator 60 User Guide
, Issue 1
Release 6.3.0
HDLC Pass-through
The high-level data link control (HDLC) pass-through interface is a bit-
oriented, ITU-TSS (Telecommunications Standard Section) link layer protocol
standard for point-to-point and point-to-multipoint communication. In
HDLC, control information is always placed in the same position. Specific bit
patterns used for control are different from those used in representing data,
so errors are unlikely to occur. The following Access Concentrator I/O
modules support the HDLC Pass-through interface:
•
Channelized DS3
•
Channelized STS-1e
•
Enhanced DS1 module
•
Enhanced E1 module
•
Multi-Serial module
High-level data link control (HDLC) uses an ITU-TSS link layer protocol
standard for point-to-point and multipoint communication. Control
information is always placed in the same position, using specified bit patterns
dramatically different from data, reducing the likelihood of confusion.
Providers are using this option primarily in wireless TDMA applications with
ATM, finding that it is possible to save money by using ATM for backhauling
information between central office equipment and edge devices instead of
using time division multiplexing (TDM).
However, the process uses the new 5ESS switches that support a mixture of
inverted and standard HDLC pass-through interfaces. The new HDLC Pass-
through Bit Inversion option uses a software or firmware driver to reverse
the polarity of every bit, and communications ensues, but only over ATM
and only over this line.
Inversion will work for HDLC pass-through links at both 56 kbps and 64
kbps. Currently, bit inversion is available only with the Enhanced DS1 and
STS-1e modules. It remains a configurable option or a special firmware load
rather than a default.
The Interim Interswitch Signaling Protocol (IISP) Interface
Interim Interswitch Signaling Protocol, or IISP, was formerly known as PNNI
Phase 0. Building on ATM UNI 3.0/3.1, it uses static routing tables established
by the network administrator to route connections around link failures. IISP
is meant to be used pending completion of the PNNI Phase 1.
Private Network-Network (PNNI) 1.0 Interface
The private network-network interface, known as PNNI, is a link-state
routing information protocol that enables extremely scalable, full function,
dynamic multivendor ATM switches to be integrated in the same network. It
computes paths through a network by defining a method for distributing