AMPS (Advanced Mobile Phone System) is a
somewhat ironic name for the original cellular system authorized
in the United States. It uses an analog FM radio link and it is
very easy to eavesdrop on it. AMPS is particularly inefficient in
use of spectrum compared to any of the digital standards.
Generally AMPS still has the best coverage of any of the standards
(solely due to its ten year head start on buildout), but that's
about the only thing it has going for it. Sound quality is
generally worse than any of the digital standards.
Bit within the context of CDMA is distinct
from chip and refers to a payload binary digit. Each bit is
represented by many chips. Bits contain information and are
subject to the laws of Information Theory.
CDMA stands for Code Division Multiple
Access and refers to a technology for the radio link which
utilizes spread spectrum communication with very tightly
controlled power levels by all participants. There is currently
(2/2000) only one commercial system which uses CDMA, covered by
the specifications IS-95 and J-STD-008, and thus the term CDMA is
often used to refer to that system. In future, other systems will
adopt a CDMA air interface. CDMA was designed by Qualcomm in the
US.
Cellular is a word used to mean a lot of
different things. According to the FCC, cellular refers to any
portable phone system which operates in the 800 MHz band allocated
for use by portable phone systems. This includes AMPS, IS-136 and
IS-95. At one time, only AMPS existed, and in some contexts
cellular is used as a synonym for AMPS. (In particular, a
"cellular ready modem" usually refers to one which works in AMPS
mode, and often only in AMPS mode.) In some contexts it is used
generically to refer to any portable phone system which relies on
a grid of service provider antennas, and thus the term is used
sometimes to includePCS.
Chip in the context of CDMA is distinct
from bit and refers to binary digits transmitted over the RF link.
The chip rate in IS-95 is 1.2288 MHz (thus allowing adequate guard
bands to permit the carriers to be spaced 1.25 MHz apart). Each
bit is represented by many chips, and if a majority of the chips
get through then the bit can be reconstructed properly. The number
of chips representing each bit varies depending on the bit rate.
When using an 8K Vocoder (such as EVRC) there are 128 chips for
each bit. Chips as such don't contain data because both the sender
and receiver know the spreading pattern used to create them from a
bit, and as such are not directly subject to the laws of
Information Theory. Though there are many phones simultaneously
using a single frequency to transmit full chiprate, that means
that the channel is not saturated unless the bitrate approaches
the bandwidth of the carrier.
Codec (pronounced CO-deck, short for
compressor/decompressor) refers to a device inside the phone (and
at the cell system) which takes digitized voice and compresses it
prior to transmission to the cell, and which takes compressed
voice received from the cell and decompresses it prior to playing
it out the speaker of the phone. Codec algorithms are extremely
sophisticated and are designed specifically around the
characteristics of human voices and human ears. There are three in
common use in IS-95, called "8K", "13K" and EVRC. GSM and IS-136
have their own codec standards.
ESN (Electronic Serial Number) is a unique
number assigned to the phone by the phone manufacturer. No two
phones will ever have the same ESN. It is against the law to try
to change the ESN in a phone.
EVRC (Enhanced Variable Rate Codec) is a
new codec being rolled out as this is written (2/2000) for IS-95
and J-STD-008 systems. It uses 8Kbps bandwidth but sounds nearly
as good as the standard 13K codec. Because of this, when the
majority of phones can use EVRC the cell systems will have more
capacity without having to deploy more equipment. This should
yield better service.
Forward link refers to the radio link from
the cell to the phone.
Frame is the name of a CDMA digital voice
packet duration. Frames are 20 milliseconds long. IS-95 transmits
50 frames per second, with each frame containing sufficient
information to reproduce 20 milliseconds of sound. It should be
pointed out that it may not require the whole 20 milliseconds to
transmit the frame. The IS-95 codecs can generate "half-rate",
"quarter-rate" and "eighth-rate" packets if the sound in that 20
milliseconds is sufficiently simple to require fewer bits to
represent. A half rate packet only requires 10 milliseconds to
transmit. An eighth rate packet only requires 2.5 milliseconds to
transmit.
GPS stands for Global Positioning System
and it is a system where a receiver can capture signals from
orbiting satellites which permit it to determine the time very
precisely, and also its location very precisely. CDMA cell systems
use fixed GPS receivers to determine the time very precisely. This
is needed to synchronize the long code and short code in the
infrastructure.
IS-95 is a standard which describes a cell
system which uses a CDMA link and operates at 800 MHz. Sometimes
the term is also used to describe 1900 MHz CDMA, though that
properly is covered by J-STD-008. The two standards are similar
and as time has gone on they have been migrating towards each
other and have become more similar.
J-STD-008 is a standard which describes a
cell system which uses a CDMA link and operates at 1900 MHz. It is
similar to, but not identical to, IS-95.
GSM (Global System for Mobile
communications) is a sophisticated cellular system used. It uses a
TDMA air interface.
Idle handoff in CDMA is when the phone
moves from one sector or cell to another while not in a call. If
it moves from one zone to another it will register. If the new
cell or sector is part of the same zone, it does not need to
register.
LiIon (Lithium Ion) is a rechargeable
battery technology which utilizes the metal Lithium. They are the
preferred form of batteries for cell phones at this time (2/2000).
Long code in CDMA is a chip sequence which
is 240 chips long, which repeats every 41.4 days. Its primary
purpose is to assist in spreading the signal, to make spread
spectrum work more efficiently. The Long code used on the reverse
link is usually modified using the phone's ESN when in a call. See
Long Code Mask.
Multipath refers to a common phenomenon in
RF where the signal arrives multiple times at the receiver at
slightly different times. If you've used a TV with an old-style
rabbit-ear antenna, you've sometimes seen ghosting, where the
video seems to have echos of itself extending to the right. This
is due to multipath. Usually the strongest path is nearly direct
from the transmitter to the receiver. However, the signal can
reflect off of other objects (large buildings are particularly
good at this) and that signal arrives somewhat later, since it
follows a somewhat longer path. For most kinds of RF multipath is
a form of interference and degrades the signal. CDMA is unique
among cellular transmission standards in that it actually uses
multipath to its advantage by using fingers in the rake receiver.
As a result, CDMA performance is actually improved by multipath.
NiCad (Nickel Cadmium) is a rechargeable
battery technology which utilizes the metals Nickel and Cadmium.
Generally they don't have as much energy storage capacity as newer
technologies like NiMH or LiIon and are not generally used for
cell phones anymore.
NiMH (Nickel Metal Hydride) is a
rechargeable battery technology which utilizes the metal Nickel.
They tend to be heavier than LiIon and are not used much any more
for cell phones. (In other contexts, it stands for National
Institute of Mental Health.)
Noise floor in CDMA refers to the part of
the incoming signal which is unusable. The primary component of
the noise floor on the forward link is signals being sent by the
cell to other phones in the same sector, and to a lesser extent
other nearby cells and sectors transmitting to their phones. The
primary component of the noise floor on the reverse link is other
phones transmitting to this cell or to others nearby.
Orthogonal ("composed of right angles") is
a technical term referring to a certain special characteristic of
the long code, the short code and the Walsh codes. It refers to
the fact that, for instance, if you take any two Walsh codes and
XOR them together, the result will be 32 1's and 32 0's. But if
you XOR a Walsh code with itself, the result is 64 0's. The short
code and long code are orthogonal to themselves at different
offsets. What this means is that if two short codes are
synchronized, then the XOR of them is all 0's. If they are offset
from each other, by any amount, then the XOR of them is about half
1's and about half 0's. The long code is also orthogonal to
itself. This was done deliberately and without it CDMA wouldn't
work. This fundamental characteristic of the long code, short code
and Walsh codes is what makes it possible for the rake receiver to
separate out the chip sequence intended for this phone from the
ones being sent to all the other phones.
A Page is a message sent by the cell
system on the paging channel to a particular phone which says that
there's an incoming phone call. When the phone receives a page, it
sends a message to the system requesting a traffic channel, and
when it is granted one it then rings to tell its owner that a
phone call is waiting.
Paging channel in CDMA is
a channel used by the cell to send pages, which indicate incoming
calls, to the phone. The Paging channel also carries other
information, such as indications of voice mail, SMS indications,
plus housekeeping information such as the PN Offsets of all nearby
cells and sectors.
PCS stands for personal communication
system and according to the FCC it refers to any portable phone
system which operates in the 1900 MHz band allocated for such
systems. Among others, this includes J-STD-008, GSM and IS-136.
Some phone companies have used this term as a synonym for
"portable phone", so they have sometimes referred to 800 MHz
phones as being "PCS". This is a misuse of the term.
Pilot channel in CDMA is a special channel
which the cell transmits constantly. It is not modulated using the
long code and it uses Walsh code channel 0, which is all 0's, and
it transmits a bit pattern of all 0's. That means that what it
contains is the short code at the phase being used by the cell.
System acquisition by the phone begins by locating the pilot
channel, and this permits the phone to synchronize its short code
with the cell. After this, the phone looks for the sync channel.
Power control bits in CDMA are chips which
are altered in the forward link to permit the cell to adjust the
transmit power of the mobile phone on the reverse link while in a
call. They are transmitted 800 times per second and cause the
phone to increase or decrease its transmit power by a small
increment.
PRL stands for Preferred Roaming List
Rake receiver is the
digital section of a CDMA receiver which permits the phone (or
cell) to separate out the relevant signal from all the other
signals. The relevant signal will be encoded with a known Walsh
Code and a known phase of the Short code, and the rake receiver
can do this because the Walsh codes are orthogonal and the Short
code is orthogonal to itself at different offsets. The rake
receiver is capable of receiving multiple signal sources and
adding them together using multiple fingers, each of which has the
ability to use a separate phase of the short code and long code
and a separate Walsh code if necessary. Different fingers might
track multiple signals from the same cell (arriving at slightly
different times due to multipath) or might track separate cells
due to soft handoff.
Registration in CDMA is a process where
the phone turns its transmitter on briefly and sends a packet on
the paging channel which identifies the phone to the cell system.
The phone does this when it first acquires the system. On most
systems, it does this periodically (at a time interval selected by
the cell system, typically every ten or twenty minutes). The
registration message contains part of the phone's NAM, which the
phone system uses to look up the phone's ESN. (If you are roaming,
the roaming system asks your home system to look up the ESN.) The
phone also registers if it changes zones, and can be challenged by
the system to register.
Reverse link in CDMA refers to the radio
link from the phone to the cell. RF stands for "Radio Frequency"
and is a commonly used acronym to refer to a radio link, e.g.
"goes over RF to the cell".
Searching in CDMA is a process where the
phone scans the phase space of the short code looking for valid
signals. Depending on when and how this is done, it may be looking
for valid pilots, or it may be looking directly for valid paging
channels. In a dual-band or dual-mode phone this may also involve
attempt to find an AMPS system.
Sector refers to the fact that a typical
cell divides its circular coverage into several slices, sort of
like a pie. The number of sectors supported is variable, but it's
common for there to be three. Each sector in CDMA will use a
different PN Offset. From the point of view of the phone, there's
no difference between moving between sectors and moving between
cells.
Short code is a chip sequence which is 215
chips long which repeats every 26.666 milliseconds. Different
cells and cell sectors all use the same short code, but use
different phases of it, which is how the phone differentiates them
from each other. The phase is known as the PN Offset. The moment
when the Short code wraps around and begins again is called a PN
Roll. (PN stands for Pseudo-Noise.) The chip sequence is designed
to be orthogonal to itself at different phases.
Signal strength refers to the total amount
of power of RF received by the receiver. This is divided into
useful signal, referred to as EC/I0, and the noise floor which is
useless.
Soft handoff refers to a feature of CDMA
where a phone can communicate simultaneously to two or more cells,
or in some cases with two sectors on the same cell. This often
happens when the phone is about halfway between the cells or on
the dividing line between sectors, and permits the call to
continue even though the signal from any one cell would not be
strong enough to keep the call up. No other phone standard has
this ability.
SMS (Short Messaging Service) is a
mechanism which allows brief text messages to be sent to the
phone. Several of the major phone standards support it. In CDMA
systems, this is controlled by TIA/EIA-637-A.
Sync channel is a special channel which is
always transmitted by the cell. It is not modulated by the long
code. It repeatedly transmits a sync channel message which
contains information about the cell and the phone system, and also
contains information which permits the phone to determine the
absolute wall clock time. The phone looks for the sync channel as
the second step of system acquisition, and uses it to synchronize
its long code generator. Once the sync channel message has been
processed, the phone has sufficient information to begin to
process the paging channel and to register.
TDMA (Time Division Multiple Access)
refers to a digital RF link where multiple phones share a single
carrier frequency by taking turns. Each phone gets the channel
exclusively for a certain time slice, then gives it up while all
the other phones take their turn. TDMA is also used sometimes to
refer specifically to the standard covered by IS-136, which is a
source of confusion because GSM also uses a TDMA air interface, as
does IDEN, and neither of those systems are compatible with
IS-136.
Traffic channel in CDMA is a channel which
carries a phone call. When a phone wants to set up a call, it
makes a request to the cell on the paging channel and the cell
system sends back a message telling it which traffic channel to
use (in other words, which Walsh Code to use).
Walsh code is one of 64 chip patterns
which are 64 chips long. CDMA channels are differentiated by which
Walsh code they use. They are carefully chosen to be orthogonal to
each other.
A B C D E F G H I J
K L M N O P Q R S T U V W X Y Z
A
ASIC |
: |
Application-specific integrated circuit |
ACD |
: |
Automatic Call Distributor |
ABR |
: |
Area Border Router |
ADM |
: |
Add-Drop Multiplexer |
APON |
: |
ATM Passive Optical Network |
ARP |
: |
Address Resolution Protocol |
AS |
: |
Autonomous System |
ASBR |
: |
Autonomous System Boundary Router |
ASP |
: |
Active Server Pages |
ASIC |
: |
Application Specific Integrated Circuits |
ATM |
: |
Asynchronous Transfer Mode |

B
BGP |
: |
Border Gateway Protocol |
BOOTP |
: |
Boot Protocol |
BER |
: |
Bit Errror Rate |

C
CAT 5 |
: |
Category 5 (Cable Type) |
CDMA |
: |
Code Division Multiplexing Access |
CD-ROM |
: |
Compact Disc Read Only Memory |
CIDR |
: |
Classless Inter Domain Routing |
CLI |
: |
Command Line Interface |
CLIP |
: |
Calling Line Identification Presentation |
CMS |
: |
Call Management Services |
CPE |
: |
Customer Premise Equipment |
CPU |
: |
Central Processing Unit |
CRF |
: |
Customer Registration Form |
CRM |
: |
Customer Relationship Management |
CR-LDP |
: |
Constraint-Based Routing - Label Distributed Protocol |
CSMA/CD |
: |
Carrier Sense Multiple Access / Collision Detect |
CSU/DSU |
: |
Channel Service Unit / Data Service Unit |
CTI |
: |
Computer Telephony Integration |
CUG |
: |
Closed User Group |
CD |
: |
Chromatic Dispersion |

D
DARPA |
: |
Defense Advanced Research Projects Agency |
DCN |
: |
Data Communication Network |
DHCP |
: |
Dynamic Host Configuration Protocol |
DNR |
: |
Dynamic Network Routing |
DNS |
: |
Domain Name System |
DSCP |
: |
DiffServ Code Point |
DSP |
: |
Digital Signal Processor |
DSN |
: |
Database Source Name |
DVMRP |
: |
Distance Vector Multicast Routing Protocol |
DWDM |
: |
Dense Wavelength Division Multiplexing |
DXC |
: |
Digital Cross-Connect |
DLD |
: |
Domestic Long Distance |

E
EGP |
: |
Exterior Gateway Protocol |
EIGRP |
: |
Enhanced Interior Gateway Routing Protocol |
ERP |
: |
Enterprice Resource Planning |
ETSI |
: |
European Telecommunications Standards Institute |
ECS |
: |
Enhanced Communication Services |
EMS |
: |
Enhanced Messaging Services |

F
FDD |
: |
Floppy Disk Drive |
FEC |
: |
Forward Equivalence Class |
FR |
: |
Frame Relay |
FTP |
: |
File Transfer Protocol |
FDDI |
: |
Fiber distributed Data Interface |
FSP |
: |
Fixed Line Projects |

G
GMPLS |
: |
Generalized Multiprotocol Label Switching (Multiprotocol
Lambda Switching) |
GSM |
: |
Global System for Mobile Communication |
GMMI |
: |
Gigabit Media Independent Interface |

H
HTML |
: |
HyperText Markup Language |
HTTP |
: |
HyperText Transfer Protocol |
HVAC |
: |
Heating, Ventillation and Air-Conditioning |

I
IAP |
: |
Internet Access Point |
IDC |
: |
Internet Data Centre |
IDS |
: |
Internet Data Services |
IEEE |
: |
Institute of Electrical and Electronic Engineering |
IETF |
: |
Internet Engineering Task Force |
IG |
: |
International Gateway |
IGMP |
: |
Internet Group Management Protocol |
IGP |
: |
Interior Gateway Protocol |
IFG |
: |
Interframe Gap |
IGRP |
: |
Interior Gateway Routing Protocol |
IN |
: |
Intelligent Network |
IP |
: |
Internet Protocol |
IPv4 |
: |
Internet Protocol version 4 (Addresses) |
IPv6 |
: |
Internet Protocol version 6 (Addresses) |
ISDN |
: |
Integrated Services Digital Network |
ISO |
: |
International Standard Organization |
ISP |
: |
Internet Service Provider |
ISUP |
: |
ISDN User Part |
ITU-T |
: |
International Telecommunication Union Telecom |
IXP |
: |
Internet Exchange Point |

L
LAN |
: |
Local Area Network |
LANE |
: |
LAN Emulation |
LCD |
: |
Liquid Crystal Display |
LDP |
: |
Label Distribution Protocol |
LED |
: |
Light Emitting Diode |
LER |
: |
Label Edge Router |
LMP |
: |
Link Management Protocol |
LQM |
: |
Link Quality Monitoring |
LSP |
: |
Label Switched Path |
LSR |
: |
Label Switching Router |
LASER |
: |
Light Amplification By Stimulated Emissions Of Radiation |

M
MAC |
: |
Media Access Control |
MGCP |
: |
Media Gateway Control Protocol |
MIB |
: |
Management Information Base |
MLS |
: |
Multi-Location Services |
MPLS |
: |
Multiprotocol Label Switching |
MPOA |
: |
Multiprotocol over ATM |
MSA |
: |
Master Services Agreement |
MMS |
: |
Multimedia Messaging Service |

N
NIC |
: |
Network Interface Card |
NAP |
: |
Nodal Access Point |
NAT |
: |
Network Address Translation |
NMS |
: |
Network Management Service |
NOC |
: |
Network Operation Center |
NTP |
: |
Network Time Protocol |
NZDSF |
: |
Non Zero Dispersion Shifted Single Mode Fiber |

O
OSI |
: |
Open System Interconnection |
OSPF |
: |
Open Shortest Path First |
OXC |
: |
Optical Cross-Connect |
OFC |
: |
Optical Fiber Cable |

P
PC |
: |
Personal Computer |
PCB |
: |
Printed Circuit Board |
PDH |
: |
Plesiochronous Digital Hierarchy |
PIM |
: |
Protocol Independent Module |
PoP |
: |
Point of Presence |
POS |
: |
Packet over Synchronous Optical Network |
PPP |
: |
Point to Point Protocol |
PSTN |
: |
Public Switched Telephone Network |
PVC |
: |
Permanent Virtual Circuit |
PBX |
: |
Private Branch Exchange |
PMD |
: |
Polarization Mode Dispersion |
PIM |
: |
Personal Information Management |

Q
QA |
: |
Quality Assurance |
QoS |
: |
Quality of Service |

R
RADIUS |
: |
Remote Authentication Dial-in User Service |
RARP |
: |
Reverse Address Resolution Protocol |
RAS |
: |
Remote Access Server |
RFC |
: |
Request for Comment |
RIP |
: |
Routing Information Protocol |
RMON |
: |
Remote Monitoring |
RSVP |
: |
Resource Reservation Protocol |

S
SDCA |
: |
Short Distance Charging Area |
SDH |
: |
Synchronous Digital Hierarchy |
SIP |
: |
Session Initiation Protocol |
SLIP |
: |
Serial Line Internet Protocol |
SLA |
: |
Service Level Agreements |
SMS |
: |
Short Messaging Service |
SMTP |
: |
Simple Mail Transfer Protocol |
SNMP |
: |
Simple Network Management Protocol |
SONET |
: |
Synchronous Optical Network |
SPF |
: |
Shortest Path First |
SQL |
: |
Structured Query Lanugae |
SSA |
: |
Secure Server Access |
STM |
: |
Synchronous Transport Module |
STP |
: |
Shielded Twisted Pair |
SS7 |
: |
Signaling System 7 |
SSH |
: |
Secure Shell |
SVC |
: |
Switched Virtual Circuit |
SES |
: |
Severely Errored Seconds |

T
TACACS |
: |
Terminal Access Controller Access Control System |
TAX |
: |
Trunk Automatic Exchange |
TCP |
: |
Transmission Control Protocol |
TCP/IP |
: |
Transmission Control Protocol / Internet Protocol |
TDM |
: |
Time Division Multiplexing |
TE |
: |
Traffic Engineering |
TEC |
: |
Telecom Engineering Center |
TFTP |
: |
Trivial File Transfer Protocol |
ToS |
: |
Type of Service |
TTL |
: |
Time to Live |
TIR |
: |
Total Internal Reflection |

U
UBR |
: |
Unspecified Bit-Rate |
UDP |
: |
User Datagram Protocol |
UTP |
: |
Unshielded Twisted Pair |

V
VAS |
: |
Value Added Services |
VMS |
: |
Voice Mail Services |
VLAN |
: |
Virtual Local Area Network |
VoIP |
: |
Voice over Internet Protocol |
VPN |
: |
Virtual Private Network |

W
WAN |
: |
Wide Area Network |
WDM |
: |
Wavelength Division Multiplexing |
WRED |
: |
Weighted Random Early Detection |
WWW |
: |
World Wide Web |

X
XTACACS |
: |
Extended Terminal Access Controller Access Control
System |
|