(HA) is a feature that ensures the availability of resources in a computer
system, in case of component failures in the system. The unique hardware and
software architecture of the Cisco ASR1000 Series, Cisco ISR G2 and Cisco ISR
4000 Series routers is designed to maximize router uptime during any network
event, and thereby provide maximum uptime and resilience within any network
Figure 1. CUBE High
The diagram above
illustrates the CUBE's HA feature that allows active calls to be preserved when
a CUBE router experiences an outage.
provides a brief overview of the different types of high availability (HA)
options on the Cisco routers for the CUBE Enterprise edition.
Refer to the next section in this
document. For detailed information about inbox and box-to-box redundancies,
refer to the chapter titled “Stateful Switchover Between Redundancy Paired
Intra- or Inter-box Devices” in the
Cisco Unified Border Element Configuration Guide.
Route Processor Redundancy (RPR)
allows you to configure a standby RP. When you configure RPR, the standby RP
loads the Cisco IOS software on bootup and initializes itself in standby mode.
In the event of a fatal error on the active RP, the system switches to the
standby RP, which reinitializes itself as the active RP. In this event, the
entire system is rebooted, so the switchover with RPR is slower than with other
High Availability switchover features such as Nonstop Forwarding/Stateful
(SSO) provides media preservation of calls and post-switchover teardown of
calls, in case of active RP failure. This means that the CUBE calls would
continue to be active even after the active RP card goes down (provided a
redundant RP is present). The standby RP would become active and service new
CUBE(ENT) calls. The context of the CUBE (ENT) calls that were switched over
from the Active card would be present on the new active card. Hold/Resume or
any other supplementary services will work after switchover. In SSO, both media
and signaling session context are preserved on failover.
The terms failover and switchover are used interchangeably.
Nonstop forwarding (NSF) helps to
suppress routing flaps in devices that are enabled with stateful switchover
(SSO), thereby reducing network instability. NSF allows for the forwarding of
data packets to continue along known routes while the routing protocol
information is being restored after a switchover. Non Stop Forwarding (NSF)
works together with SSO and allows the routing protocols to reestablish their
routing information by requesting their network neighbors to resend all of the
routing information when a switchover occurs.
to the facility or architecture to implement stateful switchover (SSO). It
provides the mechanisms to help synchronize state data between the active and
standby route processors or chassis in a consistent, repeatable, and
From Cisco IOS
Release 15.6(1)T and Cisco IOS-XE Release 3.17S onwards, checkpointing
mechanism is enhanced to provide support for multimedia endpoints with larger
SDP up to 6000 bytes. With the new enhancement, CUBE supports preservation of
media up to a maximum of 6 m-lines/streams (audio, video, and application).
CUBE HA is enhanced
to support the preservation of Record-Route and Contact header information.
After SSO, all subsequent midcall SIP messages will be routed based on the
correct Record-Route and Contact headers.
The CUBE HA
implementation supports full stateful failover for active SIP-to-SIP calls.
This means both media and signaling session information is preserved after
switchover. The Cisco Unified Border Element (CUBE) provides three types of
high availability (HA) options:
Figure 2. Inbox
Figure 3. L2 Box-to-Box
Routing Protocol (ISR-G2 Devices)
The Cisco Unified
Border Element (CUBE) provides high availability (HA) using box-to-box
redundancy configurations when implemented on a Cisco ISR-G2 platform. CUBE
box-to-box redundancy on ISR-G2 is based on the Hot Standby Routing Protocol
(HSRP) router technology, and HSRP is specific to ISR-G2.
provides high network availability by routing IP traffic from hosts on networks
without relying on the availability of any single router. HSRP is used in a
group of routers for selecting an Active router and a Standby router. HSRP
monitors both the inside and outside interfaces—if any interface goes down, the
whole device is considered down, the standby device becomes active and takes
over the responsibilities of the active router. Box-to-box high availability is
supported using virtual IP addresses for the signaling and media. For more
information about HA support using virtual IP addresses, refer to the section
titled “Stateful Switchover Between Redundancy Paired Intra- or Inter-box
Devices” in the
CUBE Configuration Guide.
On the ASR,
box-to-box redundancy option (introduced in the previous section) uses the
Redundancy Group (RG) Infrastructure to form an Active/Standby pair of routers.
The Active/Standby pair share the same virtual IP address (VIP) and continually
exchange status messages. CUBE session information is check-pointed across the
Active/Standby pair of routers enabling the Standby router to take over
immediately all CUBE call processing responsibilities if the Active router
should go out of service. This redundancy option is supported on the ASR
1001/1002-X/1004 platforms, and with Cisco IOS XE 3.11S, it is also supported
on ASR 1006 with a single route processor and an Embedded Services Processor
(ESP). ASR 1006 supports both box-to-box and inbox redundancy, and you cannot
switch between these two modes dynamically.
redundancy requires two identical ASR platforms on the same physical LAN.
Redundancy Group (RG) Infra component provides the box-to-box communication
infrastructure support between the two ASRs and will negotiate the final stable
redundancy state. The RG Infra component provides:
- An HSRP-like protocol that
negotiates the final redundancy state for each router by exchanging keepalive
and hello messages between the two ASRs in pair (using the control interface).
mechanism for checkpointing the signaling and media state for each call from
the ACTIVE to the STANDBY router (using the data interface).
Configuration/management of the virtual IP (VIP) interface for the traffic
interfaces (multiple traffic interfaces can be configured using the same RG).
implications and configuration details are not covered in this chapter. For
information about HA, refer to the High Availability section in the CUBE
Choosing an HA Configuration
When considering HA design, the
following VoIP aspects apply:
Media preservation of active
Calls that are currently being signaled
Signaling protocol state preservation for active calls
(supplementary services will work after switchover)
Calls using software MTP on the CUBE
H323-to-SIP and H323-to-H323 calls