CCNA Voice Summary – Part 4

Circuit Switched Network

Involves 2 nodes that establish a dedicated circuit in order to communicate. The channel remains up during the whole conversation. PSTN is the largest Circuit switched network in the world. The PSTN uses SS7 signaling.

Advantages: Dedicated Channel; Excellent quality; delay and bit rate is constant

Disadvantages: Not always enough available channels; bitrate is limited – there is little chance for newer technologies to increase the sound quality; To enable Video, we need to bond channels together. e.g. h.320

 Packet Switched Network

Digital network that transmits data into packets irrespective of the data. Layer 3 devices encapsulate the data into layer 2 frames. Each device makes decisions for the packet independent of the previous device. Good Example is the Internet

Advantages: Constant bitrate; newer technology can improve sound, Easier to increase bandwidth for features. QoS overcomes all disadvantages

Disadvantages: No dedicated connection; Packet loss; Not always enough available bandwidth but can be added; Packet delay – latency; Jitter – delay variance.
Voice Packet Requirements

  • smooth bandwidth demand
  • minimal impact on other traffic
  • Small packets (60 – 200 bytes)
  • Delay intolerant
  • drop intollerant
  • UDP priority

Data Packet Requirements

  • varied bandwidth demand
  • can tolerate some delay
  • can tolerate high drop rates
  • use TCP for retransmission

Video Packet Requirements

  • bursty and greedy for bandwidth
  • impacts other traffic
  • Delay intolerant
  • drop intollerant
  • UDP priority

Unified Communication Networks

Everything flows over the same network as standard data. QoS keeps UC packets prioritized. They Include: Voice Calls, Conferences. VoiceMail, Presence and IM, Directory Services and phone based applications

 Public Providers

UCSystems can connect to both the old PSTN network and the Newer VoIP Network (SIP, H323, and ITSP – Internet Service Provider).

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