TDC 461/Session 5
Data Communications and the PSDN
- Announcements
- Reminder: Exams are due Friday, 7 August, at 5:00pm.
- Voice Processing
- Overview and Review
- Touch Tone and Voice Recognition
- Automated Attendant
- Automatic Call Distributors--5 main duties
- Prioritize calls
- Route the call to the appropriate agent
- Deliver any announcements, queue
- Direct busy calls to announcements
- Handle messages for call backs
- Voice Mail
- Interactive Voice Response
- Computer Telephony Integration
- Data Communications--Big Concepts:
- 6 Steps to Data Com
- Select and Deal with transmission media
- Use communicating devices that will preesnt the proper signal to the line
- Set up or abide by already-accepted rules (protocols)
- Use a pre-established alphabet that the devices can understand
- Ensure the integrity of information before, during, and after transmission
- Deliver information to the receiving device
- Big Concept #1: Standards
- =d->definition or description of a technology
- de facto
- de jure
- De facto standards often become de jure standards later down the line.
- Big Concept #2: Architectures
- =d->a coordinated set of guidelines that together constitute a complete description of one approach to building a communications environment.
- Big Concept #3: Protocols
- =d->provide the rules for communication between counterpart components on different devices.
- Protocols are usually written into software, but there are two notable hardware protocols, asynchronous and synchronous.
- Asynchronous Transmission Protocols: clocked or synchronized one byte at a time. Each byte is framed by one start bit, at least one stop bit, and an error checking bit (partity bit). 7-bit bytes (like ASCII) or 8-bit bytes (EBCDIC) require 10-11 bits for successful transmission.
- Asynchronous transmission has high overhead
- Nominal speed calculation-9600 bps/10 bits per byte=960 characters per second, in the best of all worlds
- Clocking is controlled by data terminal equipment(DTE) (PC)
- Most PCs and Minicomputers use asynchronous transmission
- Serial interfaces can only handle asynch transmission
- Synchronous Transmission Protocols
- clocked on blocks of bytes rather than a single byte
- bytes are sent in contiguous groups (blocks) of varying size
- much lower overhead than asynchronous transmission
- clocking is controlled by data communications equipment (DCE) (Modem)
- 2400+ bps modems are really synchronous "over the wire"
- Big Concept #4: Error Detection
- 3 modes of error control
- Recognition and Flagging
- Recognition and Retransmission
- Recognition and Forward Error Correction
- Echo Checking=>echoes sent signal back to sender’s monitor for checking
- Parity Checking/Vertical Redundancy Checking=>
- Odd Parity=>
- Even Parity=>
- No parity=>
- Longitudinal Redundancy Checking
- Cyclic Redundancy Checking
- Big Concept #5: Plexing--Review
- Simplex
- Half Duplex
- Full Duplex
- Big Concept #6: Multiplexing
- Space Division Multiplexing
- Frequency Division Multiplexing
- Time Division Multiplexing
- Big Concept #7: Compression
- Why compress?
- Formatting
- Redundant Characters
- Commonly Used Characters
- Commonly used strings of characters
- Big Concept #8: Standards
- Public Switched Data Network
- Brief History
- 1950s
- 1960s
- 1970s
- 1980s
- 1990s
- WAN/MAN development
- Dataphone Digital Service
- Switched 56 Kbps (Digital Switched Access)
- Circuit-switched digital service applicable to same applications as DDS
- Digital Carrier Systems and Networks
- Carrier Systems
- =>systems that derive multiple logical channels from a single physical communications path, thereby supporting multiple communications.
- Digital Carrier
- introduced in 1957 in Newark, NJ.
- T-carrier (trunk carrier) refers to a specific set of cable pairs and digital repeaters every 6000 feet, for twisted pair. Much less for fiber.
- T-carrier concept
- Uses:
- Advantages:
- Channelized T-carrier
- Unchannelized T-carrier
- Fractional T1
- Encoding
- Framing
- Hardware
- Channel Service Units and Digital Service Units=>
- Multiplexers
- Nodal multiplexers=>
- X.25 (Packet-Switched) Networks
- Concept of packetization
- Concept of packet-switching
- ISDN
- SS7 protocol
- Basic-Rate Interface (BRI) ISDN
- Primary-Rate Interface (PRI) ISDN
- Applications of ISDN