Inline Power : Cisco and 802.3af

by | Mar 10, 2010 | Non classé, Uncategorized, Written Theory | 0 comments

There are 3 ways to power up a device:

The external power supply unit

Power over Ethernet (PoE) from a switch

A Midspan power injector/inline power patch panel (a device that sits between a switch and an IP Phone)

Both the Cisco proprietary and IEEE 802.3af provide power to connected devices over switch port pins 1,2,3,6. When using midspan power injectors/inine power patch panels, power is sent to the connected device using pins 4,5,6,7

Reminder : For the Cisco proprietary method, the switch sees a coming back FLP and for 802.3af, the switch see a resistance of 25K ohms on a voltage applied (-2,8 to -10V)

DNS : Quick Definition

by | Mar 10, 2010 | Non classé, Uncategorized, Written Theory | 0 comments

DNS is the tool which associate an IP Address with a name, an URL. So using name instead IP Address can also introduce failures because if your DNS down , you can’t resolve anymore IP addresses. But it can be very helpful in the case of a DR mode ( where you need to point the server to a different IP address)

Network Address Translation – NAT

by | Mar 10, 2010 | Non classé, Uncategorized, Written Theory | 0 comments

To work correctly with your voice flows, a NAT device must inspect Layer3 and Layer4 protocol ,port information and sometimes the embedded payload.

Cisco IOS NAT ALG can support the following voip protocols :

  • H323v2
  • H225
  • H245
  • RAS
  • SIP
  • SCCP

So if you change the default port number of these protocols, then you have to change it also in the configuration with the following command ip nat service <<protocol>> tcp port <<port-number>>.

Pay attention also that NAT doesn’t support voice signaling encryption

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