Allowing More Time for Digit Entry with the SIP First Digit Entry Timer

The "first digit timer" controls the time between when a phone is taken off hook until the first digit is dialed. Increasing the timer gives users more time between going off-hook to enter digits to make a phone call. It is different to the T302 (inter-digit) timer. The "Off Hook to First Digit Timer" is configured under the SIP profile and applied to the physical IP handset. The default profile cannot be modified - the profile must be copied and then applied to specific phones.

The first digit timer comes into play whenever a new line is seized. For example:

  • When the receiver is taken off-hook
  • When the speaker button is pressed
  • When "Transfer" is pressed and the party performing the transfer searches for the destination party (for example, ...

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Unauthorized SIP Messages and Authorization Failure in CME

Username configuration and authentication against the SIP registrar is absolutely critical in order for phones to register in CME when running SIP. Take a sample voice register pool configuration.

voice register pool 1
id mac 001B.D4A0.9BA0
type 7941
number 1 dn 1
dtmf-relay sip-notify
codec g711ulaw

Notice that a username has deliberately not been configured. Now, configure debug ccsip media. Observe the first message, where the IP phone attempts to regiser. CME responds with a 401 "Unauthorized" message, since authentication has failed.

======= IP Phone Registration Request =======

Jan 21 11:13:00.323: //-1/xxxxxxxxxxxx/SIP/Msg/ccsipDisplayMsg:

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Configuring CME for SIP to Allow Phones to Register

The command set using SIP is actually quite similar to SCCP - there are some subtle differences, mainly to do with entering the CME sub-configuration mode(s). This article considers the minimum steps to configure 2 x IP phones and enable calling from Phone A to Phone B.

Firstly, allow calls from SIP to SIP endpoints, and setup the SIP registrar.

voice service voip
  allow-connections sip to sip
  sip
   registrar server expires max 1200 min 300

Next, configure the global parameters; at a minimum, the following must be configured:

  1. Mode (CME)
  2. Maximum DN's (based on hardware platform - i.e. 192 in a 2821)
  3. Maximum pool, or IP phones (again, based on hardware platform)
  4. Specify ...

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