by The Cavalier
Society for the Freedom of Information
March 11, 1992
With the telephone network's complexity growing exponentially as the
decades roll by, it is more important than ever for the telecom enthusiast to
understand the capabilities and function of a typical Central Office (CO)
switch. This text file (condensed from several hundred pages of Northern
Telecom documentation) describes the features and workings of the Digital
Multiplex Switch (DMS)-10 digital network switch, and with more than an average
amount of imagination, you could possibly build your own.
The DMS-10 switch is the "little brother" of the DMS-100 switch, and the
main difference between the two is the line capacity. The DMS line is in
direct competition to AT&T's ESS line (for the experienced folks, the features
covered are the as those included in the NT Software Generic Release 405.20 for
the 400 Series DMS-10 switch).
Table of Contents
~~~~~~~~~~~~~~~~~
I. OVERVIEW/CPU HARDWARE SPECS
II. NETWORK SPECS
1. Network Hardware
2. Network Software
3. Advanced Network Services
III. EXTERNAL EQUIPMENT SPECS
1. Billing Hardware
2. Recorded Announcement Units
3. Other Misc. Hardware
IV. MAINTENANCE AND ADMINISTRATION
1. OAM
2. Interactive Overlay Software Guide
V. SPEC SHEET
VI. LIMITED GLOSSARY
The DMS-10 switch is capable of handling up to 10,800 lines, and was
designed for suburban business centers, office parks, and rural areas. It can
be installed into a cluster configuration to centralize maintenance and
administration procedures and to increase combined line capacity to 50,000
lines. It is capable of functioning as an End Office (EO), an Equal Access End
Office (EAEO), and an Access Tandem (AT), and is a known as a Class 5 switch.
It supports up to 3,408 trunks and 16,000 directory numbers. It can outpulse
in DP (Dial Pulse), MF (Multi-Frequency), or DTMF (Dual-Tone Multi-Frequency),
insuring compatibility with new and old switches alike (translation -- the
switch is small, by most standards, but it has massive bounce for the ounce).
Hardware Specifications
The DMS-10 switch itself is a 680x0-based computer with 1 MB of RAM in its
default configuration. The processor and memory are both duplicated; the
backup processor remains in warm standby. The memory system is known as the
n+1 system, meaning that the memory is totally duplicated.
II. NETWORK SPECS
Network Hardware
The DMS-10 network hardware consists mostly of PEs, or Peripheral
Equipment trunk and line packs. The PEs take the incoming analog voice
signals, digitalize them into 8 bit PCM (Pulse Code Modulation) signals, and
feed it into the main transmission matrix section of the switch. There, it is
routed to another trunk or line and converted back into an analog signal for
retransmission over the other side of the call. Note that manipulating voice
in the digital domain allows the signal to be rerouted, monitored, or
retransmitted across the country without any reduction in signal quality as
long as the signals remain in PCM format. <Hint!>
Network Software
The DMS-10 has a variety of software available to meet many customers'
switching needs. A good example of this software is the ability of several
DMS-10 switches to be set up in a cluster (or star configuration, for those of
you familiar with network topologies). In this arrangement, one DMS-10 is set
up as the HSO (Host Switching Office) and up to 16 DMS-10s are set up as SSOs
(Satellite Switching Offices), allowing all billing, maintenance, and
administration to be handled from the HSO. Additionally, all satellites can
function on their own if disconnected from the HSO.
Another feature of the DMS-10's network software are nailed-up
connections, commonly known as loops. The DMS-10 supports up to 48 loops
between any two points. The connections are constantly monitored by the switch
computer, and if any are interrupted, they are re-established.
Meridian Digital Centrex (MDC) is the name given to a group of features
that enable businesses to enjoy the benefits of having PBX (Private Branch
Exchange) equipment by simply making a phone call to the local telco.
Advanced Network Services (ANS)
If the DMS-10 is upgraded with the 400E 32-bit RISC processor, the switch
will be able to handle 12,000 lines, enjoy a speed improvement of 80%, support
a six-fold increase in memory capacity, and, perhaps most importantly, will be
able to run NT's Advanced Network Services software. This software includes
Common Channel Signaling 7 (CCS7), Advanced Meridian Digital Centrex, DMS
SuperNode connectivity, and ISDN. CCS7 is the interswitch signaling protocol
for Signaling System 7, and the concept deserves another text file entirely
(see the New Fone eXpress/NFX articles on SS7).
III. EXTERNAL EQUIPMENT SPECS
Billing Format Specifications
The DMS-10 can record AMA (Automatic Message Accounting) billing data in
either Bellcore or Northern Telecom format, and it can save this data in one of
several ways:
- by saving onto a 9-track 800 BPI (Bits-Per-Inch) density tape drive
called an MTU (Magnetic Tape Unit)
- by saving onto a IOI (Input/Output Interface) pack with a 64 MB SCSI
(Small Computer System Interface) hard drive, and transferring to 1600
BPI tape drives for periodic transport to the RAO (Regional Accounting
Office)
- by transmitting the data through dial-up or dedicated telephone lines
with the Cook BMC (Billing Media Converter) II, a hard drive system that
will transmit the billing records on request directly to the RAO. The
Cook BMC II supports six different types of transmission formats, listed
below:
* AMATS (BOC) [max speed: 9600 bps]
Call records are stored using the Bellcore AMA format and polled
using the BX.25 protocol. Two polling ports are provided with one
functioning as a backup.
* BIP Compatible [max speed: 9600 bps (2400*4)]
Call records are stored using the Bellcore AMA format and polled
using the HDLC Lap B protocol. Four polling ports are provided
that can function simultaneously for a combined throughput of 9600
bps. This specification is compatible with GTE's Billing
Intermediate Processor.
* Bellcore AMA w/ BiSync polling [max speed: 9600 bps]
Call records are stored using the Bellcore AMA format and polled
using the IBM BiSync 3780 protocol. One polling port is provided.
This option is intended for operating companies who use independent
data centers or public domain protocols for data processing.
* Bellcore AMA w/ HDLC polling [max speed: 9600 bps]
Call records are stored using the Bellcore AMA format and polled
using the HDLC (High-level Data Link Control) protocol. One port
is provided.
* NT AMA w/ HDLC polling [max speed: 9600 bps]
Call records are stored using the Northern Telecom AMA format and
polled using the HDLC protocol.
* NT AMA w/ BiSync polling [max speed: 4800 bps]
Call records are stored using the Northern Telecom AMA format and
polled using the BiSync protocol.
- by interfacing with AT&T's AMATS (Automatic Message Accounting
Teleprocessing System)
- by interfacing with the Telesciences PDU-20
All of the above storage-based systems are fully fault-tolerant, and the
polled systems can store already-polled data for re-polling.
Recorded Announcement Units
The DMS-10 system may be interfaced to one or more recorded announcement
units through two-wire E&M trunks. Some units supported include the Northern
Telecom integrated Digital Recorded Announcement Printed Circuit Pack (DRA
PCP), the Cook Digital Announcer or the Audichron IIS System 2E.
The DRA PCP is integrated with the DMS-10 system, as opposed to the Cook
and Audichron units, which are external to the switch itself. It provides
recorded announcements on a plug-in basis and offers the following features:
- Four ports for subscriber access to announcements
- Immediate connection when pack is idle
- Ringback tone when busy until a port is free
- Switch-selectable message lengths (up to 16 seconds)
- Local and remote access available for message recording
- Memory can be optionally battery-backed in case of power loss
- No MDF (Main Distribution Frame) wiring required
Other External Hardware
The DMS-10 can also support the Tellabs 292 Emergency Reporting System,
the NT Model 3703 Local Test Cabinet, and the NT FMT-150 fiber optic
transmission system. More on this stuff later, perhaps.
IV. MAINTENANCE AND ADMINISTRATION
OAM
---
OAM, or Operations, Administration, and Maintenance functions, are
performed through an on-site maintenance terminal or through a remote
maintenance dial-in connection. The DMS-10 communicates at speeds ranging from
110 to 9600 baud through the RS-232C port (standard) in ASCII. There can be up
to 16 connections or terminals for maintenance, and security classes may be
assigned to different terminals, so that the terminal can only access the
programs that are necessary for that person's job. The terminals are also
password protected, and bad password attempts result in denied access, user
castration and the detonation of three megatons of on-site TNT. <Just kidding>
The software model for the DMS-10 consists of a core program which loads
overlays for separate management functions. These overlays can be one of two
types: either free-running, which are roughly analogous to daemons on Unix
environments, which are scheduled automatically; or interactive, which
communicate directly with the terminal user.
The major free-running programs are the Control Equipment Diagnostic
(CED), the Network Equipment Diagnostic (NED), the Peripheral Equipment
Diagnostic (PED), and the Digital Equipment Diagnostic (DED). The CED runs
once every 24 hours, and tests the equipment associated with the CPU buses and
the backup CPU. The NED runs whenever it feels like it and scans for faults in
the network and proceeds to deal with them, usually by switching to backup
hardware and initiating alarm sequences. The PED is scheduled when the switch
is installed to run whenever the telco wants it to, and it systematically tests
every single trunk and line connected to that central office (CO). The DED
tests the incoming line equipment that converts analog voice to digital PCM.
Now, for interactive programs (a.k.a. interactive overlays), I'm going to
list all of their codes, just in case one of you gets lucky out there. To
switch to an overlay, type OVLY <overlay>. To switch to a sub-overlay, type
CHG <sub-overlay>. Keep in mind that NT has also installed help systems on
some of their software, accessible by pressing "?" at prompts. Here we go:
Overlay Explanation and Prompting Sequences
------- -----------------------------------
ALRM Alarms
ALPT - Alarm scan points
SDPT - Signal distribution points
AMA Automatic Message Accounting
AMA - Automatic Message Accounting
MRTI - Message-rate treatment index
PULS - Message-rate pulsing table
TARE - Tariff table
AREA Area
CO - Central Office Code
HNPA - Home Numbering Plan Area
RC - Rate Center
RTP - Rate Treatment Package
CLI Calling Line Identification
CNFG Configuration Record
ALRM - Alarm System Parameters
AMA - Automatic Message Accounting parameters
BUFF - System Buffers
CCS - Custom Calling Services
CCS7 - Common Channel Signaling No. 7
CDIG - Circle Digit Translation
CE - Common Equipment Data
CLUS - Cluster data
COTM - Central Office overload call timing
CP - Call processing parameters
CROT - Centralized Automatic Reporting of Trunks
CRTM - Central Office regular call processing timing
CSUS - Centralized Automatic Message Accounting suspension
DLC - Data Link Controller assignment for clusters
E800 - Enhanced 800 Service
FEAT - Features
GCON - Generic Conditions
HMCL - Host message class assignment
IOI - Secondary input/output interface pack(s)
IOSF - Input/Output Shelf Assignment
LCDR - Local Call Detail Recording
LIT - Line Insulation Testing parameters
LOGU - Logical Units Assignments
MOVE - Move Remote Line Concentrating Module
MTCE - Maintenance Parameters
MTU - Magnetic Tape Unit Parameters
OPSM - Operational Measurements
OVLY - Overlay scheduling
PSWD - Password Access
SITE - Site assignments
SSO - Satellite Switching Office Assignments
SUB - Sub Switch
SYS - System parameters
TRB - Periodic trouble status reporting
VERS - Version
CPK Circuit Pack
ACT - AC Testing Definition
DCM - Digital Carrier Module
LPK - Line Concentrating Equipment line packs
PACK - Peripheral Equipment packs
PMS - Peripheral Maintenance System pack
PSHF - Peripheral Equipment Shelf
RMM - Remote Maintenance Module
RMPK - Remote shelf
RSHF - Remote Concentration Line Shelf
SBLN - Standby line
SLC - SLC-96
SLPK - SLC-96 pack
DN Directory Number
ACDN - Access Directory Number
CRST - Specific Carrier Restricted
ICP - Intercept
RCFA - Remote Call Forwarding appearance
ROTL - Remote Office Test Line
STN - Station Definition
EQA Equal Access
CARR - Carrier Data Items
CC - Country Codes
HUNT Hunting
DNH - Directory Number Hunting
EBS - Enhanced Business Services hunting
KEY - Stop hunt or random make busy hunting
LAN Local Area Network
LAC - LAN Application Controller
LCI - LAN CPU Interface
LSHF - Message LAN Shelf
ACT - AC Testing definition
D1PK - DS-1 interface pack (SCM-10S)
DCM - Digital Carrier Module
1FAC - Interface packs
LCM - Line Concentrating Module
LPK - Line Concentrating Equipment line packs
NWPK - Network packs
PACK - Peripheral Equipment packs
PMS - Peripheral Maintenance System packs
PSHF - Peripheral Equipment Shelf
RCT - Remote Concentrator Terminal
REM - Remote Equipment Module
RSHF - Remote Shelf
SBLN - Standby line
SCM - Subscriber Carrier Module
SCS - SCM-10S Shelf (SLC-96)
SLC - SLC-96
SLPK - SLC-96 Line Packs
SRI - Subscriber Remote Interface (RLCM)
ODQ Office Data Query
ACDN - Access Directory Number
CG - Carrier group
CNTS - Counts
DN - Directory Number
DTRK - Digital Trunks (line and trunk)
LINE - Lines (line and trunk)
PIN - Personal Identification Number
STOR - Memory Storage
TG - Trunk Group
TRK - Trunks (line and trunk)
DP - Dial Pulse. A form of signaling that transmits pulse trains to indicate
digits. Slow compared to DTMF and MF. Made obsolete by DTMF. Old
step-by-step switches use this method, and there are still quite a few
subscriber lines that use DP, even though DTMF is available.
In-band Signaling - Transmitting control signals in the 300 - 3300 hz voice
band, meaning that they're audible to subscribers.
Out-of-band Signaling - Transmitting control signals above or below the 300 -
3300 hz voice band. See SS7, CCS7.
DTMF - Dual Tone Multi-Frequency. A form of in-band signaling that transmits
two tones simultaneously to indicate a digit. One tone indicates the
row and the other indicates a column. A fast, technically simple way of
dialing that is in use almost all over the United States. White boxes
generate DTMF tones, a.k.a. "Touch Tones" or Digitones. See DP, MF.
MF - Multi-frequency. A form of in-band signaling similar to DTMF, except the
signals are encoded differently (i.e., the row and column tones are
different, because the keypad for MF tones isn't laid out in a rectangular
matrix). These are the "operator tones." Blue boxes generate these
tones. See DTMF, In-band signaling.
CCS7 - Common Channel Signaling 7. Part of the Signaling System 7
specification, CCS7 transmits control signals either above or below the
voice band to control switch equipment, so control signals may be
transmitted simultaneously with voice. See SS7.
SS7 - Signaling System 7. An inter-switch signaling protocol developed by
Bellcore, the RBOCs' research consortium. Relatively new, this protocol
can be run only on digital switches. See CCS7, CLASS.
CLASS - Custom Local Area Signaling Services. Several subscriber-line features
that are just being introduced around the United States at the time of
this article. See SS7, CCS7.
Centrex - A scheme that turns a switch into an off-site PBX for business users.
It can usually co-exist with existing lines.
If anyone has any more questions, contact me at WWIVNet THE CAVALIER@3464.
Thanks to Northern Telecom (the nicest sales staff in the world of switch
manufacturers, with a killer product to boot!), Pink Flamingo, Taran King,
Grim, and the crew who supported the NFX in "days of yore."
