CVoice Chapter 1 Notes

For anyone reading/studying for Cisco’s CVoice exam, here are my notes from the exam cert guide chapter 1. WordPress kind of jacks with the formatting and I don’t feel like going back and correcting it. If you’d like a PDF version, then go here, fellow voice lover.

Chapter 1

• Signaling protocols generate control traffic/information between 2 endpoints
  • Peer to Peer
  • Client-Server
• Peer to Peer Signaling Protocols
  • H.323 – Umbrella of standards for voice, video, and data transmission
    • Includes the following protocols
      • H.225 Call signaling – establish a connection between 2 H.323 endpoints or and endpoint and a gateway
      • H.225 Registration, Admission, and Status – provides registration, admission, status, bandwidth changes, and disengage procedural messages between endpoints and gatekeepers
      • H.245 control signaling – provides end to end control messages about capabilities, opening/closing logical channels, flow control, general commands
  • SIP – Similar to http with URLs and status codes
    • Works with SAP (session announcement protocol) and SDP (session description protocol)
    • H.323 alternative
    • UAs (user agents) initiate sessions
    • SIP devices do not register with a call manager
• Client-Server Signaling Protocols
  • MGCP – protocol for PSTN gateway control
    • Controls VOIP gateways that are connected to call agents
    • Provides signaling for edge devices that do not have a full voice signaling protocol
    • All dial plan info resides on a separate call agent (not the CM)
    • Plain text protocol
    • Call manager knows of and controls individual voice ports on an MGCP gateway
  • SCCP – TCP skinny client control protocol between call manager and client
    • Cisco proprietary
    • Used between call managers and endpoints
    • All events cause traffic to the CM (the CM will tell the endpoint what to do in response to that event)
• Media Transmission Protocols
  • RTP – real time protocol
    • Communicates directly between endpoints
    • Uses multiplexing and checksum offered by UDP
    • Communicates on an even port, vs RTCP communicating on an odd port
  • RTCP – real time control protocol
    • Provides control info for RTP
    • Primary function is to provide feedback on the quality of service provided by RTP
      • Monitors traffic sent, jitter, feedback, delay and can signal the device to use higher compression codec if needed
  • cRTP – compressed RTP
    • RTP header is generally larger than the data it carries (40 byte header! – 20 IP bytes, 8 UDP, 12 RTP
    • Header compression results in 2-4 byte headers (the endpoints actually cache the header info and don’t necessarily compress it)
    • Useful on WAN links
  • sRTP – Secure RTP
    • Provides encryption, message authentication, integrity, and replay protection
    • sRTCP also
    • Uses AES encryption only
    • Uses HMAC-SHA1 for integrity and authentication – calculated for entire IP packet
• VOIP Gateways – connects VOIP systems to PSTN, PBX, or other TDM systems
  • Analog gateways provide connectivity from IPT to POTS or connect fax machines, etc. to VOIP systems
  • Analog trunks connect IPT to PSTN or PBX using FXO ports and E&M ports to connect to legacy PBX’s
  • Digital gateways connect IPT to PBX or PSTN using digital (PRI/BRI) trunks

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