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)

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

• 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.

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>

• Define Dial Peer for PSTN

dial-peer voice 1 pots
  destination-pattern 9.T
  port 0/1/0:15

• Enables overlap receiving on ISDN interfaces
• Has to be enabled in countries with open numbering plans

interface serial0/1/0:15
  isdn overlap-receiving [T320 ms]

• Configure interdigit timeout

call-manager-fallback
  timeouts interdigit <sec>

• 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]

call-manager-fallback
  dialplan-pattern 1 5215553... extension-length 4

• 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

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>

• Configures COR on dial peers associated with directory numbers (ephone-dn)
• Max COR list = 20
• Examples

• Define COR list
• These lists will be used as lock to be placed on outgoing dial peer

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

• These list will be used as keys assigned to phones

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

• Assign COR list (keys) to phone(s)
• cor {incoming | outgoing} <cor-list-name> [<cor-list-number> <start-num> - <end-num> | default]

call-manager-fallback
  cor incoming phone1 1 3001
  cor incoming phone2 2 3002
  cor incoming phone3 3 3003

• Assign COR list (locks) to dial-peer

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
!