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Interfaces
When looking at interfaces the are a lot of misconceptions. Some times people call a connector an interface, while in a real interface is more then that. A complete interface consists of three parts:
Connector
Pin assignment
Electrical characteristics

Connector
The connector is defined by it shape, it"s size and the amount of pins it holds and of course the place the pins are mounted in the connector housing. Mostly it is built up of a shell (which contains the pins), the pins, the hood and something to mount it with like screw-locks or latches. Pin assignment
The pin assignment describes which pin is connected to which circuit and thus describes the actual function. Electrical characteristics
The electrical characteristics describe the voltages, currents and shapes of the signals.

DTE and DCE

The terms DTE and DCE are very common in the datacommunications market. DTE is short for Data Terminal Equipment and DCE stands for Data Communications Equipment. But what do they really mean? As the full DTE name indicates this is a piece of device that ends a communication line, whereas the DCE provides a path for communication.

Let"s say we have a computer on which wants to communicate with the Internet through a modem and a dial-up connection. To get to the Internet you tell your modem to dial the number of your provider. After your modems has dialed the number, the modem of the provider will answer your call and your will hear a lot of noise. Then it becomes quiet and you see your login prompt or your dialing program tells you the connection is established.
Now you have a connection with the server from your provider and you can wander the Internet.

In this example you PC is a Data Terminal (DTE). The two modems (yours and that one of your provider) are DCEs, they make the communication between you and your provider possible. But now we have to look at the server of your provider. Is that a DTE or DCE?
The answer is a DTE. It ends the communication line between you and the server. Although it gives you the possibility to surf around the glode. The reason why it is a DTE is that when you want to go from your provides server to another place it uses another interface. So DTE and DCE are interface dependend. It is e.g. possible that for your connection to the server, the server is a DTE, but that that same server is a DCE for the equipment that it is attached to on the rest of the Net.

Unbalanced
An unbalanced signal has a ground signal which is the common for all other signals and the actual signal voltage is measured in reference to this ground signal.
So if there is stated that the voltage for a signal is +12 Vdc for a one and -12 Vdc for a zero, that means that those voltages are measured in reference to the ground signal.

NOTE: Normaly the ground signal is said to be 0 Vdc, but it is possible that the line carries a voltage e.g. 220 Vac. What happens is that the signal voltages will then be superimposed on the 220 Vac, so the actual measured voltage at the receiver side is still only the signal voltage.

Balanced
A balanced signal has no ground reference. The measured voltage is defined as the voltage difference between two copper lines, normaly refered to as line A and B. So for every signal that needs to be transfered you will have two leads.
The signals can be defined in two ways:

  • The voltage difference between A and B can be an one when e.g. 12 volt and a zero when e.g. 6 volt.
  • The voltage difference between A and B can be an one when A>B or a zero when B>A.

Some terms and abbriviations

AC:
Access Control
ACE:
Automatic Calling Equipment
ACK:
ACKnowledge
ACR:
Abandon Call and Retry
ADSP:
Appletalk Data Stream Protocol
AEP:
Appletalk Echo Protocol
AFP:
Appletalk Filing Protocol
ARCnet:
Attached Resource Computer NETwork
ASP:
Appletalk Session Protocol
ATP:
Appletalk Transport Protocol
BN:
Bridge Number
BSA:
Basic Service Area
BSS:
Basic Service Set
CDDI:
Copper Distributed Data Interface
CMSA/CA:
Carrier Sense Multiple Access with Collision Avoidance
CP:
Continuation Pointer
CRC:
Cyclic Redundancy Check
CRQ:
Call Request
CSMA/CA:
Carrier Sense Multiple Access with Collision Avoidance
CSMA/CD:
Carrier Sense Multiple Access with Collision Detect
CTS:
Clear To Send
CUG:
Closed User Group
D:
Direction bit
DA:
Destination Address (MAC)
DAS:
Dual Attached Station
DCD:
Data Carrier Detect, officially known as Received Line Signal Detector
DCE:
Data Communications Equipment
DCLA:
DC Level Adjust
DDP:
Datagram Delivery Protocol
DID:
Destination IDentifier
DIX:
Digital Intel Xerox
DLO:
Data Line Occupied
DPR:
Digit Present
DR:
Date Rate
DSAP:
Destination Service Access Point
DSC:
Distant Station Connected
DSR:
Data Set Ready, officially known as DCE Ready
DSSS:
Direct Sequence Spread Spectrum
DTE:
Data Terminal Equipment
DTR:
Data Terminal Ready, officialy known as DTE Ready
ED:
Ending Delimiter
ELAP:
Ethernet Link-Access Protocol
ENQ:
Enquiry
EOT:
End Of Transmission
ESA:
Extended Service Area
ESS:
Extended Service Set
FBE:
Free Buffer Enquiry
FC:
Frame Control
FCS:
Frame Check Sequence
FDDI:
Fiber Distributed Data Interface
FHSS:
Frequency Hopping Spread Spectrum
FS:
Frame Status
GFI:
General Format Identifier
HDLC:
High level Data Link Control
IGRIP:
Interior Gatway Routing Information Protocol
IR:
Infrared
IRL:
Inter Repeater Link
IS:
Internet System
ISO:
International Standards Organisation
ISU:
Information Symbol Unit
ITT:
Invitation To Transmit
LAN:
Local Area Network
LAPB:
Link Access Procedure Balanced
LCN:
Logical Channel Number
LF:
Largest Framesize
LGN:
Logical Group Number
LLAP:
Localtalk Link-Access Protocol
LLC:
Logical Link Control
LTH:
Length
MAC:
Media Access Control
MDI:
Medium Dependent Interface
MII:
Medium Independent Interface
MPDU:
MAC Protocol Data Unit
Modem:
MOdulator DEModulator. A device for connecting two DTEs.
NAK:
Negative AcKnowledge
NBP:
Name-Binding Protocol
NIC:
Network Interface Card
NID:
Next IDentification
OSI:
Open Systems Interconnect
OSPF:
Open Shortest Path First
PAC:
Packet
PAD:
Packet Assembler/Disassembler
PAP:
Printer Access Protocol
PCM:
Pulse Code Modulation
PHY:
Physical
PLCP:
Physical Layer Convergence Protocol
PLP:
Packet Layer Protocol
PMD:
Physical Medium Dependent
PMI:
Physical Medium independent sublayer
PND:
Present Next Digit
PPP:
Point-to-Point Protocol
PSDU:
Physical Sublayer Data Unit
PTI:
Packet Type Identifier
PVC:
Permanent Virtual Circuit
RC:
Routing Control (16 bits)
RD, RxD:
Received Data
RDx:
Route Designator x
RI:
Routing Information
RII:
Routing Information Indicator
RIM:
Resource Interface Module
RIP:
Routing Information Protocol
RSU:
Reconfiguration Symbol Unit
RT:
Routing Type
RTMP:
Routing Table Maintenance Protocol
RTS:
Request To Send
SA:
Source Address incl. RII
SABM:
Set Asynchronous Balanced Mode
SABME:
SABM Extended
SAS:
Single Attached Station
SC:
System Code
SD:
Starting Delimiter
SDH:
Synchronous Digital Hierarchy
SFD:
Start Frame Delimiter
SGND:
Signal GrouND
SID:
Source IDentification
SN:
Segment Number
SNAP:
SubNetwork Addressing Protocol
SOH:
Start Of Header
SONET:
Synchronous Optical NETwork
SSAP:
Source Service Access Point
STP:
Shielded Twisted Pair
SVC:
Switched Virtual Circuit
TD, TxD:
Transmitted Data
THT:
Token Holding Time
TLAP:
Token ring Link-Access Protocol
TP-PMD:
Twisted Pair PMD
TRT:
Token Rotation Time
TTRT:
Target Token Rotation Time
UTP:
Unshielded Twisted Pair
WAN:
Wide Area Network
ZIP:
Zone Information Protocol


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