Telco Basics, Convergence, and Total Network Connectivity Flashcards
Goal of Security
Confidentiality Integrity Availability (authentication) (nonrepudiation)
Tip and Ring
Old fashioned way of saying “plus” and “minus” or ground and positive in electrical circuits
Derive their names from the operator’s cordboard plug.
Today, tip refers to the first wire in a pair of phone wires, ring is the second wire. Together they constitute the circuit that carries speech or data.
The Step-by-step (or Strowger, the name of the undertaker who invented the switch) switch
connects pairs of telephone wires by progressive step-by-step operation of a series of switches.
Replaced the manual switchboard
Common Control
A method of switching in which the control equipment is responsible for routing calls through the network (as opposed to step device responsible only for the next step in the connection).
Depends on a crossing or intersection of two points to make a connection. The switching matrix, or crosspoint array, depends on energizing a vertical line and a horizontal line and the point where they intersect represents the connection made.
ESS
Electronic Switching System
ESS (Electronic Switching System)
Early electronic switches were still analog (the “reed switch”), now replaced with digital switches.
Use stored program control as the next step to common control. Systems are much more fault tolerant.
Tremendous increase in speed of switching with the new digital switches.
PABX
Private Automatic Branch Exchange. Another name for PBX.
PBX
Private Branch Exchange
Private Branch Exchange
A privately owned (usually scaled-down) switching system for a company.
Transmission Media
Conducted
Copper wire, coax, fiber optic
Radiated
Microwave, satellite
PCM
Pulse Code Modulation (PCM) is the most common method of encoding an analog voice signal into a digital bit stream.
Sampling –
records the voltage level in time intervals along an analog wave.
Quantizing –
rounding to the nearest discrete value
Encoding –
Converting the numeric amplitude voltage levels into binary 8-bit code
Decoding –
Converting the 8-bit code into the voltage level
Reconstruction –
reproduces the original analog wave from the voltage levels
Filtering –
strips noise out.
The process of combining many signals into one composite signal – thus several calls can be transmitted at once over a single line.
Multiplexing
FDM
Frequency Division Multiplexing
- Limited to analog transmissions.
TDM
Time Division Multiplexing
STDM
Statistical Time division multiplexing
Blue Boxes
Blue boxes are nothing more then a device to generate pairs of tones, and a single 2600 Hz tone.
Benefits of Voice Over Network
You may save some money
You may achieve some benefits of managing a voice and data network as one network
If you have IP phones, moves, adds, and changes will be easier and cheaper
Added, and integrated, new services including
Integrated messaging
Bandwidth on demand
Voice emails
Terminal
A terminal, or a client, is an endpoint where H.323 data streams and signaling originate and terminate. It may be a multimedia PC with a H.323 compliant stack or a standalone device such as a USB (universal serial bus) IP telephone. A terminal must support audio communication; video and data communication support is optional.
Gateway
A gateway is an optional component in a H.323-enabled network. When communication is required between different networks a gateway is needed at the interface. It provides data format translation, control signaling translation, audio and video codec translation, and call setup and termination functionality on both sides of the network.
H.323 Components
IP Telephony Architecture includes Terminal, Gatekeeper and Gateway. (Also Routers)
Gatekeeper
A gatekeeper is a very useful, but optional, component of an H.323-enabled network. Gatekeepers are needed to ensure reliable, commercially feasible communications. When a gatekeeper exists all endpoints (terminals, gateways, and MCUs) must be registered with it.
What services does a Gatekeeper provide?
Address translation
Admission and access control of endpoints
Bandwidth management
Routing capability
MCU
A multipoint control unit (MCU) enables conferencing between three or more endpoints. Although the MCU is a separate logical unit it may be combined into a terminal, gateway, or gatekeeper. The MCU is an optional component of an H.323-enabled network.
The multipoint controller provides a centralized location for multipoint call setup. Call and control signaling are routed through the MC so that endpoints capabilities can be determined and communication parameters negotiated.
H.225
Performs the signaling for call control
Uses H.245 to establish and terminate individual logical channels for communication
Five Phases of Signaling Process
Call setup
Initial communications and capability exchange
Establishment of audiovisual communication
Call services
Call termination
Why Converge?
Save Money
- Eliminate long distance toll charges
- Eliminate duplicate infrastructures
- Increased competition in the industry
Enhancement of current applications and development of new applications
Collaborative tools
The industry has been heading there for a while now anyway…
Broadcast networks –
no intermediate switching nodes, each station communicates over a shared medium Packet radio networks Satellite networks Local networks E.g. bus or ring
Basic premise is that an uninterrupted connection exists between the endpoints (Circuit Switching)
Constant bandwidth dedicated to this session
Resources for this session reserved for the entire duration of the call
Blocking is possible as a circuit may not be available
Initial connection requires considerable work but once established, minimal to maintain it
The PSTN is a circuit switched network
Packet Switching
Bursty Traffic
In packet switched network, data is fragmented into discrete units (packets)
Each packet contains information about its source and destination
A complete message may consist of 1000’s of packets
Packets may actually take different routes and may arrive out of order, or not at all
Packet switched networks do not reserve bandwidth for each connection
Addressing is organizationally based
Why are digital transmissions preferred over Analog?
Digital equipment cheaper to produce
Digital signals provide higher quality communication
Digital less susceptible to ‘noise’
Digital signals easy to compress to reduce required bandwidth
ISDN
Integrated Services Digital Network - Based on idea that not everyone will talk at the same time on phone.
CATV
Community Antenna Television (CATV)
DSL
Digital Subscriber Lines
ADSL
Asymmetric Digital Subscriber Lines takes advantage of the fact that the majority of traffic is downstream not upstream and provides greater downstream data rates.
CTI
Computer Telephony Integration - The software and hardware elements that allow a computer to manage telephone calls and integrate additional features beyond those offered by the PBX
PSTN
Public Switched Telephony Networks
