====== SRST ======

===== Basic SRST =====
  * Supports up to 720 SCCP IP phones
  * Supports Cisco Voice Gateway 248 Analog Phone Gateway
  * Supports secure voice fallback during SRST fallback service
  * No hunt-group feature during SRST
  * No MWI during SRST 

**Failover**
  * If WAN link fails, IP phone lose contact with CUCM
  * IP Phones register with local gateway
  * Gateway queries/asks IP phones for configuration and autoconfigures itself
    * Using the Simple Network Auto Provisioning technology (SNAP)
{{cucm-srst1.png|}}

**SRST Mode**
  * Calls between remote-site phones survives switchover
  * Remote-site calls using the local non-MGCP gateway survive switchover
  * Phone will continue to send keep-alive to CUCM.

**Fail Back**
  * Won't attempt to re-register right away. Will wait for a timer to make sure the CUCM is stabled typically 120s
  * Immediate
  * Graceful
    * After all the call is completed
  * Delay
    * After a certain preconfigured time

**Timing**
  * If there are multiple CUCM in the group, it may take a while before cutting over to SRST because of multiple tries to register to CUCM
  * This time can be shorten by adjusting the Station Keep Alive Service Parameter
{{cucm-srst2.png|}}

===== Configuration =====

==== SRST ====
  * Enable SRST
  * Configure IP and port. This must matches configuration on CUCM
  * Specify max dn and ephones. Default is zero.
  * Dual-line - allows transfer, conferencing features
  * (Optional) Limit DN for models of phone. Default is 6.
  * (Optional) Keepalive sent to router by IP phones. Default is 30s.
<code>
call-manager-fallback
  ip source-address <ip> [port 2000]
  max-dn <number> [dual-line]
  max-ephones <number>

  ! *** Optional ***
  limit-dn {7910 | 7935 | 7940 | 7960} <max-lines>
  keepalive <secs>
</code>

==== Dial Peer ====
  * Define Dial Peer for PSTN
<code>
dial-peer voice 1 pots
  destination-pattern 9.T
  port 0/1/0:15
</code>

===== Optional =====
  * Enables overlap receiving on ISDN interfaces
  * Has to be enabled in countries with open numbering plans
<code>
interface serial0/1/0:15
  isdn overlap-receiving [T320 ms]
</code>

  * Configure interdigit timeout
<code>
call-manager-fallback
  timeouts interdigit <sec>
</code>

  * Configure global prefix that can be used to expand the extension numbers of inbound and outbound calls into E.164 numbers
  * Translate called number of incoming PSTN call - reduced to extension-length to match local extension
  * Translate calling number of outgoing PSTN call - expand local extension to extension-pattern 
  * dialplan-pattern 1 <pattern> extension-length <length> [extension-pattern <extension-pattern>] [no-reg]
<code>
call-manager-fallback
  dialplan-pattern 1 5215553... extension-length 4
</code>

  * Configure translation rule
  * Configure and add rules translation profiles 
  * Assign to SRST
  * Can be used to translate called number to Central Site to Full E.164 number
<code>
voice-translation-rule <number>
  rule 1 /match-pattern/ /replace-pattern/ [type {<match-type> <replace-type} [plan {<match-type> <replace-type>}]]
!
voice-translation-profile <name>
  translate {called | calling | redirect-called | redirect-target} <translation-rule-num>
!
call-manager-fallback
  translation-profile {incoming | outgoing} <name>
! *** OR apply on dial peer ***
dial-peer voice 2000 pots
  translation-profile {incoming | outgoing} <name>
</code>

===== COR =====
  * Configures COR on dial peers associated with directory numbers (ephone-dn)
  * Max COR list = 20
  * Examples
{{cucm-srst3.png|}}

  * Define COR list
  * These lists will be used as lock to be placed on outgoing dial peer
<code>
dial-peer cor custom
  name internal
  name pstn
  name pstn-intl
!
dial-peer cor list internal
  member internal
!
dial-peer cor list pstn
  member pstn
!
dial-peer cor list pstn-intl
  member pstn-intl
</code>

  * These list will be used as keys assigned to phones
<code>
dial-peer cor list phone1
  member internal
  member pstn
  member pstn-intl
!
dial-peer cor list phone2
  member internal
  member pstn
!
dial-peer cor list phone3
  member internal
</code>

  * Assign COR list (keys) to phone(s)
  * cor {incoming | outgoing} <cor-list-name> [<cor-list-number> <start-num> - <end-num> | default]
<code>
call-manager-fallback
  cor incoming phone1 1 3001
  cor incoming phone2 2 3002
  cor incoming phone3 3 3003
</code>

  * Assign COR list (locks) to dial-peer
<code>
dial-peer voice 9 pots
  corlist ougoing pstn
  destination 9T
  port 1/0:23
!
dial-peer voice 9011 pots
  corlist ougoing pstn-intl
  destination 9011T
  port 1/0:23
  prefix 011
!
dial-peer voice 2000 pots
  corlist outgoing internal
  destination 2...
  port 1/0:23
!
</code>