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Teaching models

Labs

These run in the browser. They do not log in to a cluster.

Codec bandwidth

Layer 3 is (payload + 40) 脳 8 脳 (1000 / ptime) / 1000. Add the layer-2 header you choose.

G.711 at 20 ms with an 18-byte Ethernet header is 87.2 kbit/s.

CSS order

Move Emergency above PSTN, then dial 911. Inside a partition the best match wins. Across partitions, order is searched as you list it. A 9.@ in an earlier partition can consume 911.

  1. PSTN 路 9.@
  2. Emergency 路 911
  3. Internal 路 directory numbers

SIP response

Type a code from the list.

  • 100 Trying
  • 180 Ringing
  • 183 Session Progress
  • 200 OK
  • 202 Accepted
  • 401 Unauthorized
  • 407 Proxy Authentication Required
  • 486 Busy Here
  • 487 Request Terminated
  • 488 Not Acceptable Here
  • 503 Service Unavailable

One-way checklist

  1. Is there a 200 OK on both SIP legs?
  2. Does each 200 that should carry an answer actually contain SDP?
  3. Is c= an address the other side can route to?
  4. Are RTP packets present in both directions after ACK?
  5. Only then look at DSCP and the jitter buffer.

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