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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