The Surelink Family of reroute switches

ISDN backup for ADSL VPN's


surelink image


Surelink provides ISDN backup for ADSL VPN / VPN's and is a reliable backup solution for any IP based network connection. The Surelink VPN family of reroute switches, provide a complete end to end back-up solution for potentially unreliable VPN's based on ADSL. Get all the cost benefits of ADSL, with the knowledge that all essential traffic will be re-routed over your ISDN backup link in the event of an ADSL outage. Surelink provides the guaranteed connectivity associated with leased lines at a fraction of the cost, saving you thousands of pounds a year.


Migrating to ADSL

The Surelink ADSL re-route switch provides ISDN backup for ADSL VPN / VPN's and has been designed to support companies migrating from Leased line / ISDN solutions . Surelink combines the guaranteed connectivity associated with leased lines, with the significant cost savings associated with ADSL. Applications range from individual users who require guaranteed Internet connectivity, to SOHO environments using VPN tunnels across the public Internet to central corporate sites.

Surelink, Surelink Central and Surelink LAN

Surelink is available in two models, Surelink and Surelink Central, both models can support single and many to one client - server connections. For small scale solutions, Surelink can be used at both client and central server sites, to provide back up for a maximum of two client sites. Surelink Central is aimed at the central server site and larger scale solutions. It has provision to support the backup links of up to six client sites. However, many more client sites can be supported, by allowing clients to contend for the available back up connections. ISDN PRI solutions are avilable with Surelink LAN


Surelink is available with two Ethernet interfaces and one or two Serial interfaces. The Ethernet interfaces provide connectivity from the local LAN to the firewall / broadband ADSL device. The serial interfaces support internal ISDN BRI terminal adapters or external analogue modem / leased line interfaces to provide the backup network connections. Surelink LAN has two ethernet connection and connection to any type of ISDN



Network operation

Surelink sits between the local LAN and the Firewall and / or the ADSL router / modem. The Surelink client and server sides maintain keep-alive messages over the links between all connected sites. If the keep-alive fails, the back up process will be initiated. Depending on Surelink configuration, the back up can be initiated by either the client or the client and server. If initiated by the client, the client alone is responsible for establishing the link. The client and server then simultaneously re-route over the backup connection. If initiated by the client and server, the client and server sides contend for the back-up link and back off until one side establishes the link.

During the re-route process, user data is not lost. However, the user may see a short delay as the link sets up and thereafter notice a service speed degradation until the ADSL service returns. Whilst the re-route is in progress, the ADSL link is constantly tested, so that as soon as it becomes available, the user traffic is switched back through the ADSL service. The dial-up link is then disconnected. This happens automatically, without user intervention. The user is alerted to the failure of the primary link by e-mail or by an SNMP trap. A visual indication of the backup status is also present on the front panel.


Surelink and Surelink Central support ISDN BRI, PSTN and Leased line back up options. A bandwidth on demand facility provides a cost effective way of enabling extra bandwidth on the backup connection. When the bandwidth on a backup ISDN / PSTN call is exceeded, a second backup line can automatically be brought into service.

To make best use of this bandwidth, a Traffic filtering facility allows the user to define the type of traffic carried over the backup connection.

The unit can be configured to disable the re-route functionality during certain periods of the day / week e.g. evenings and weekends. This allows the user to save money on the dial-up services. If a re-route is in progress at the start of one of these periods, the call will be disconnected and automatically restarted as the time period finishes.

Surelink also supports configurable ADSL failure recognition parameters to correctly identify service outages. Software upgrades and configuration management can be carried out across the network using a web browser or SNMP based management system.

Web based interface

There is no software to be loaded. Surelink uses a standard browser and the simple web based interface is easy to use and configure.

Standard features

The following are supported as standard on the Surelink product range.

  • Web based interface
  • Automatic recognition of ADSL failure
  • Configurable failure recognition parameters
  • Automatic re-route over ISDN BRI / PSTN or Leased line on ADSL failure
  • Management and configuration via HTTP
  • Real-time statistics and event logging
  • Backup scheduler
  • Email / SMS
  • Serial port
  • User security

Custom software development

CubeRoot's software and hardware development team can offer a full range of project development and consultancy services. We can assist your R&D activities by providing embedded software and hardware solutions.

Call CubeRoot today to discuss your software, hardware requirements.

Technical specifications


MC68EC030 with 16 Mbyte DRAM 2 Mbyte FLASH






IP routing



Configuration Management

Multiple configuration / software images stored in Flash. Remote software upgrade via LAN or WAN


Local terminal




Browser support

Netscape 4.x or 6.x

Explorer 5.x +


2 x 10Base-T Ethernet

1 or 2 Serial

1 x Config

Serial interfaces


Transparent ISDN BRI

LAN interfaces


Power requirements

5 V DC nominal via mains adapter


Safety: EN60950 / IEC950

EMC: EN55022 Class B, IEC801-2, IEC801-3, IEC801-4.

Telecoms: CTR2/3/12

ISDN: A120368F, UK BABT/95/2258 AA605042, France 95350 B edition A dossier 73886 TD, Australia A95/79/0357.


200mm x 150mm x 30mm


1kg approx.

Temperature range

0 to +40 o C

20-80% Non-condensing


CubeRoot Ltd.

18 Melton Street,


LE1 3NB.

United Kingdom.

Tel: +44 (0) 116 2627370

Fax: +44 (0) 116 2628090



Copyright 2003 CubeRoot Ltd.