Cisco Unified Border Element (SP Edition) Configuration Guide: Unified Model
SIP Timer
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SIP Timer

Table Of Contents

SIP Timer


Information About SIP Timer

How to Configure SIP Timer

Configuring SIP Timer

SIP Timer

The SIP Timer feature allows the user to configure a number of Session Initiation Protocol (SIP) timers that were hard-coded in the previous releases of Cisco IOS software. The ability to configure SIP timers enables users to improve the interoperability and performance of their devices and network environment.

Note For Cisco IOS XE Release 2.4 and later, this feature is supported in the unified model only.

Cisco Unified Border Element (SP Edition) was formerly known as Integrated Session Border Controller and may be commonly referred to in this document as the session border controller (SBC).

For a complete description of the commands used in this chapter, refer to the Cisco Unified Border Element (SP Edition) Command Reference: Unified Model at:

For information about all Cisco IOS commands, use the Command Lookup Tool at or a Cisco IOS master commands list.

Feature History for SIP Timer Functions


Cisco IOS XE Release 2.4

This feature was introduced on the Cisco IOS XR along with support for the unified model.


This module contains the following sections:

Information About SIP Timer

How to Configure SIP Timer

Information About SIP Timer

The SIP timer feature allows the user to configure some of the SIP timers that were hardcoded to default values in the previous releases of Cisco IOS software. In the previous releases, Cisco Unified Border Element (SP Edition) used the default SIP timer values recommended by RFC 3261. See Table 43.

Table 43 Default Values of the Timers 



500 ms default

round-trip time (RTT) estimate


4 s

The maximum retransmit interval for non-INVITE requests and INVITE responses


5 s

Maximum duration a message will remain in the network

Timer A

initially T1

INVITE request retransmit interval, for UDP only

Timer B

64* T1

INVITE transaction timeout timer

Timer C

> 3 min

Proxy INVITE transaction timeout

Timer D

> 32 s for UDP
0 s for TCP/Stream Control Transmission Protocol (SCTP)

Wait time for response retransmits

Timer E

initially T1

non-INVITE request retransmit interval, UDP only

Timer F

64* T1

non-INVITE transaction timeout timer

Timer G

initially T1

INVITE response retransmit interval

Timer H

64* T1

Wait time for ACK receipt

Timer I

T4 for UDP
0 s for TCP/SCTP

Wait time for ACK retransmits

Timer J

64* T1 for UDP
0 s for TCP/SCTP

Wait time for non-INVITE request retransmits

Timer K

T4 for UDP
0 s for TCP/SCTP

Wait time for response retransmits

Cisco Unified Border Element (SP Edition) allows the user to modify T1, T2 and Timer D, using the udp-first-retransmit-interval, udp-max-retransmit-interval, and udp-response-linger-period commands. You can also use the invite-timeout command to choose how long SBC should wait for the remote SIP endpoint to respond to the SBC's outgoing INVITE or Timer B in an outgoing transaction.

In addition to the SIP protocol-level timers, Cisco Unified Border Element (SP Edition) also allows modification of transport-related timer commands: tcp-connect-timeout (how long TCP SYN will wait for the reply) and tcp-idle-timeout (how long TCP connection should stay active while idle). Although these timers are transport-level values, Cisco IOS XE Release 2.4 supports these timers in SIP only, but not in H.323, nor H.248.

Note The incorrect configuration of the SIP timer values may lead to unexpected behavior in certain cases.

How to Configure SIP Timer

This section contains the steps for configuring SIP timers.

Configuring SIP Timer


1. configure

2. sbc service-name

3. sbe

4. sip timer

5. tcp-connect-timeout interval

6. tcp-idle-timeout interval

7. invite-timeout interval

8. udp-first-retransmit-interval interval

9. udp-max-retransmit-interval interval

10. udp-response-linger-period interval

11. end

12. show sbc service-name sbe sip timers


Command or Action

Step 1 



Router# configure

Enables global configuration mode.

Step 2 

sbc service-name


Router(config)# sbc mysbc

Enters the mode of an SBC service.

Use the service-name argument to define the name of the service.

Step 3 



Router(config-sbc)# sbe

Enters the mode of the signaling border element (SBE) function of the SBC.

Step 4 

sip timer


Router(config-sbc-sbe)# sip timer

Enters the mode of the SIP timer function of the SBC.

Step 5 

tcp-connect-timeout interval


Router(config-sbc-sbe-sip-tmr)# tcp-connect-timeout 3000

Configures the time (in milliseconds) that SBC waits for a SIP TCP connection to a remote peer to complete before failing that connection. The default timeout interval is 1000 milliseconds.

Step 6 

tcp-idle-timeout interval


Router(config-sbc-sbe-sip-tmr)# tcp-idle-timeout 30000

Minimum time (in milliseconds) a TCP socket has not processed any traffic, before it is closed. The default is 2 minutes.

Note The value for this command might not be precise since the idle timers are checked every 12 seconds.

Step 7 

invite-timeout interval


invite-timeout 60

Configures the time (in seconds) that SBC waits for a final response to an outbound SIP INVITE request. The default is 180 seconds. If no response is received during that time, an internal "408 Request Timeout" response is generated and returned to the caller.

Step 8 

udp-first-retransmit-interval interval


Router(config-sbc-sbe-sip-tmr)# udp-first-retransmit-interval 1000

Configures the time (in milliseconds) that SBC waits for a UDP response or ACK before sending the first retransmission of the relevant signal.

If SBC keeps getting no responses, it doubles subsequent retransmission intervals each time until they reach the udp-max-retransmit-interval duration. SBC ceases retransmitting the request and time out the signal if 64 times this duration passes without the receipt of a response/ACK.

The default first UDP retransmission interval is
500 milliseconds.

Step 9 

udp-max-retransmit-interval interval


Router(config-sbc-sbe-sip-tmr)# udp-max-retransmit-interval 8000

Configures the maximum time interval (in milliseconds) at which SBC will retransmit (see Step 9, udp-first-retransmit-interval above). The default maximum UDP retransmission interval is 4 seconds.

Step 10 

udp-response-linger-period interval


Router(config-sbc-sbe-sip-tmr)# udp-response-linger-period 10000

Configures the time (in milliseconds) for which SBC will retain negative UDP responses to INVITE requests.

All subsequent retransmitted responses received within this time will be answered with a negative ACK. Thereafter, any further retransmitted responses are ignored.

The default UDP response linger period is 32 seconds.

Step 11 



Router(config-sbc-sbe-sip-tmr)# end

Exits the sip timer mode and returns to Privileged EXEC mode.

Step 12 

show sbc service-name sbe sip timers


Router# show sbc mysbc sbe sip timers

Shows the currently configured SIP-related timers.