Telecommunications Networks: ISDN, ATM, Transmission Media, and Digital Switching Systems

Posted on Aug 1, 2024 in Computers

ISDN Networks

– Duplex Transmission of Signal (Echo Cancellation), Principle of Scrambler

– DEC (Digital Echo Cancellation): Simultaneous transmission in both directions by additive block, it adds incoming useful signal, parasitic reflected signal and compensation signal produced by transversal filter, which its adaptive regulated by control processor.

– Transmission of periodic sequences can negative affect function of echo compensator, so we have to use methods of signals scrambling:

  • Recovering of synchronization signal at receiver.
  • Equally spread the power of signal through whole frequency band.

ATM Networks

– UNI and NNI Structure of Cell (Short Characteristics)

ATM Networks

– Reference Model, Description of Layers (AAL, ATM, Physical)

– ATM is data link oriented, absolute address of terminal nodes doesn’t need to transfer during own communication but only relative information about virtual paths and channels.

– Reference model ATM three planes: User plane, control plane & management plane.

– Communication in ATM is proceeded through (3 nº):

1- AAL (ATM Adaptation Layer):

Receiving of data from higher layers and their serial and segmentation and vice versa.

– Types of adaptation:

  • AAL 1: Signals transfer in real-time with constant transfer rate, its possible to occupy next byte by pointer.
  • AAL 2: Signals transfer in real-time with variable transfer rate.
  • AAL 3/4: Data transfer in 44 bytes.
  • AAL 5: Data transfer in 48 bytes (simpler adaptation.).

– Services according to transfer rate: CBR, rt-VBR, nrt-VBR, ABR, UBR.

– Adaptation layer:

  • SVC: Is linked and its later cancelled for each connection.
  • Metasignalling: For formation, operating and cancelling of SVC through virtual channel MSVC (Meta-Signalling Virtual Channel), VPI=0/VCI=1.
  • Timing recovery: For signals transfer in real-time and emulation of circuit – reduction of jitter of signal– occasion to synch of RX and TX by:
    • — Transfer of RTS (Residual Time Stamp): Synchronization time stamp is carried by header, presence of reference networks frequency in terminal equipment is required condition, at transmitter side is measured difference derived from transmitters frequency and reference networks frequency (represented as number), at receiver sire is recovered from this difference (carried number) original frequency.
    • — Transfer of synchronization in information field of cell.

2- ATM Layer:

Supports assignment of header to information field of cell and all functions resulting from information included in header: VCI and VPI, mult and demul of various cells types provision of headers transm and others.

3- Physical Layer

Is especially used for control of bit pattern carry ATM cells by xDSL or LMDS.

Transmission Media

– Primary and Secondary Parameters of Conductions

– Primary parameters: Constants for specific type of conductions and freq: specific resistivity R [Ù/km], inductivity L [mH/km], capacity C [nF/km], conductivity G [ìS/km].

– Secondary parameters: For monitoring of transmission qualities of homogenous conduction:

  • Characteristic wave: Ratio between voltage U and current I).
  • Impedance Zc(|Zc| is modulus and phi is argument).
  • Specific wave propagation constant ganma: Relative alternation of voltage and current. Real part: á (specific (wave) attenuation [dB/km]), imaginary is â (specific phase shift [rad/km] or constant of wavelength).
  • Phase speed of propagation vp: Speed of expanding harmonic waves phase.
  • Group speed of propagation vgif group of harmonic waves with similar values.

Transmission Media

– Parameters Biasing Transfer Through Metallic Conductions

– Attenuation of conduction: A = Lm1– Lm2= α·x [dB; dBm, dBm; dB/ km, km] Lmx: Input absolute level of power Px; α: Specific attenuation of conduction; x: Length of conduction.

– Specific attenuation of conduction: [dB/km] [dB/km]

– Disturbing biases from surround:

  • Crosstalks: NEXT & FEXT (Near/Far End Cross Talk)
  • RFI (Radio Frequency Interference), affects all subscribers pairs in cable in whole frequency band with different intensity.
  • Pulsed jamming is caused by sources generated short transient performances.

Digital Switching Systems

– Characteristics of Particular Generations

– 1st gen: Paths control establishment, maintenance and cancellation of call – selector systems.

– 2nd gen: Partial centralization of control to register for receipt of selected numbers which are delivered to marker that links connection and serves to more paths. Czech: Systems with crossbar selectors.

– 3rd gen: Work with program control and space switching network.

– 4th gen: Work with program control and time switching network: Digital switching systems.