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Platform Redundancy

The SBC 5000/7000 series platforms support 1:1 box level redundancy through the communication paths provided by the external High Availability Ethernet (HA) ports.

Types of platform redundancy include:

  • Server—The Server modules provide 1:1 redundancy with automatic switchover and no interruption to stable calls.
  • Power—The SBC has no common power supplies; each server module is connected to both redundant AC or DC power feeds and handles its own DC conversion.
  • Cooling—The SBC 5000 series has three fan modules and the SBC 7000 series four fan modules. The SBC can operate indefinitely if one fan module fails.

For more information on installing the HA pairs, see Installing SBC Application Software.

Geographical Redundancy

The Sonus SBC Portfolio supports High Availability geographic redundancy using Master Trunk Resource Manager (MTRM) server/client logic spread across multiple SBCs where each MTRM consists of a server to which a set of clients are registered. If an SBC server becomes unreachable from a client's perspective (for example, the server is down or completely isolated), the client contacts a secondary server which then learns about the current resource usage of each client. From that moment onwards, call processing functions the same as with the original server. If the Primary server comes back up, the clients connect back to the Primary server. See CAC Management Using MTRM for additional feature details and example configurations.

Additionally, SBC HA servers may be deployed to different geographical locations to meet various disaster recovery requirements. The SBC Active and Standby servers can tolerate a round-trip link delay up to 100 milliseconds between HA ports in a geographic redundancy configuration. The following table compares SBC 5000 series and SBC 7000 series High Availability link delays per HA pair.

Table : SBC 5000/7000 Series HA Link Delays



Maximum HA Link
Round-Trip Delay

Call Rate

Call Capacity

Delay After Switchover *

Mgmt Connectivity
Restoration Time

HA Restoration Time


110 ms

150 cps





60 ms

450 cps





20 ms

1350 cps




* Delay times are in minutes and seconds (mm:ss)

Non-Disruptive Fail-Over

In a Hig h Availability configuration with an active and standby (redundant) server where active server fails, switch-over is completely automatic preserving the integrity of stable calls.

A switch-over from active to redundant server can result in packet loss. Fax (and modem) calls are generally not tolerant to media interruptions. Despite the fact that some fax and modem calls may be preserved during a switch-over, it is not uncommon for fax machines and modems to terminate their transmissions as a result of a server switch-over.

SBC 7000 Port Redundancy and Link Detection

Port Redundancy Model

Each SBC 7000 series supports two primary (active) and two secondary (standby) 10 GigE media interfaces (packet ports). The standby port functionality provides redundant port protection for each of the active media interfaces. In an HA scenario, the backup CE has its own primary and secondary packet ports. See Figure 1 for a depiction of the HA port redundancy configuration.

For a depiction of media port interconnectivity in an HA configuration, see the Management and HA Port Connections diagram on page Connecting SBC 7000 Ethernet and Data Cables.

Figure : SBC 7000 HA Port Redundancy Model



  • Primary port: An Ethernet packet port that will attempt to become active if on an active CE. All four packet ports on the 52x0, the two packet ports on a 51x0 and two dedicated packet ports on the 7000 (MEDIA 0_P, MEDIA 1_P) are considered primary ports.
  • Secondary port: An Ethernet packet port designated as an alternate for a specific on-board primary port. The SBC 7000 series contains one secondary port for each 10 GigE primary port (SBC 5xx0 servers do not have secondary ports). The primary and secondary port roles are static and not modifiable by the user. 
  • Active port: An Ethernet packet port that is currently selected for use (e.g. for signaling, media, etc.); either a primary or secondary port on an active CE.

    A port which is in the active state does not necessarily imply that is "up".
  • Local standby port: A standby port on an active SBC 7000 series CE providing redundancy protection to the currently active port.

  • Standby port: A collective term for a local standby port on an active CE or any packet port on an inactive CE. Standby ports can provide protection for active ports.
  • Enabled or Disabled ports: A packet port may be administratively enabled or disabled. A port that is disabled cannot be an active port. Packet ports on an inactive CE do not have their own distinct administrative state. They share this configured element with their counterpart on the active CE.
A port's role (Primary/Secondary) is independent of the port's state (Active/Standby).

Link Detection Support

The Sonus SBC Portfolio supports the capability to perform link detection on standby and active Ethernet ports to facilitate determining the health of standby port before initiating a switchover/failover. The intent is to allow simple connectivity checking to test the ability of SBC to send/receive Ethernet frames, connectivity to the adjacent switch/router, and the ability of the switches/router to do basic layer 2 receiving/forwarding/sending.

The following probing mechanisms are available on the SBC platforms:

Table : SBC Probing Mechanism Types

Probing MechanismSBC PlatformsAffected PortsPurpose
Physical link detection


All ports on both active and backup CEs
  • Detects the presence of the port cable and that the adjacent device is powered on (enabled by default on all physical ports configured by Link Monitor except for any ports administratively disabled or set out-of-service).
  • Reports any hardware failures to NRS and Link Verification Manager (LVM) tasks.
ICMP pingAllActive ports only

Checks two-way connectivity between SBC port and the configured destination (adjacent router) by sending ICMP Ping messages at configured intervals to the destination.

When destination IP address is configured in a Link Monitor, ICMP Ping is enabled along with physical link detection. By setting the destination IP address to NULL (, only physical link detection can be enabled. 
ARP ACD/ICMPv6 NUD*SBC 7000 only

Standby ports only

Performs active checking of two-way traffic through at least the local Ethernet interface, the cable, and the adjacent layer 2 switching function.

Checks are accomplished using ARP (for IPv4) or Neighbor Discovery (for IPv6) mechanisms to probe an arbitrary, operator-specified target IP address on a local IP subnet, typically an address of a router (Gateway IP address). Depending on the address family (IPv4/IPv6) of the gateway IP address configured, either ARP ACD or ICMPv6 NUD probing messages are sent in such a way that explicit assignments of IP addresses to the standby ports are not required.

Checks the link state between SBC port and the adjacent router.

*  Address Resolution Protocol - Address Conflict Detection / Internet Control  Message Protocol Version 6 – Neighbor Unreachability Detection

ARP ACD/ICMPv6 NUD Methods for Standby Ports


If the destination address configured is an IPv4 address, then IPv4 probing is initiated by sending ARP Probe requests and listening for the responses.

ARP Request probes are sent with:

  • Sender IP address of  The use of is compatible with rfc 5227 on IPv4 Address Conflict Detection. This is convenient to use on standby ports since IP addresses are not assigned for standby ports.
  • Sender hardware address containing the current local MAC address assigned to the sending port.
  • Target IP address containing the configured target IP address to be probed.
  • Target hardware address containing all zeros. The ARP request is sent on the LAN using L2 broadcast.

The target can be expected to respond with an ARP Response using L2 unicast. 


If the destination address configured is an IPv6 address, then IPv6 probing would be initiated using Neighbor Unreachability Detection mechanism (RFC 4861 section 7). This is based on Neighbor Solicitation and Neighbor Advertisement ICMPv6 messages.

Because these are IP packets, the SBC needs IP addresses to send/receive them. The SBC uses auto-generated link local IPv6 address from the current local MAC address.

Neighbor Solicitation messages are sent with:

  • IP source address containing auto-generated link local IP address
  • IP destination address containing configured target IP address
  • ICMP layer target address containing configured target IP address
  • ICMP layer source link layer address This field is left blank to prevent the target from learning our L2: L3 address binding from these probes.

The Neighbor Solicitation message is sent on the LAN via L2 unicast to the system with the target IP address.

The target can be expected to respond with a Neighbor Advertisement using L2 unicast. Received messages are validated per RFC 4861 section 7.1.2: Check that the S bit = 1 (solicited) and that the target address = our configured target IP address.

The SBC 7000 series may reduce the call accept rate when syncing from the active to the standby CE under full load causing some calls to get rejected with a 503 message even when the applied load is below the specified maximum call rate. This condition clears once the synchronization to the standby completes. Additionally, some calls may get rejected with a 503 message when synchronization occurs while the applied load is near the maximum specified.

The impact of a link or switch failure on SBC 7000 series is depicted in the diagram below.

Figure : SBC 7000 HA Port Status After a Link or Switch Failure