TDM Service Protection

TDM transport is the basis for many corporate applications, including the interconnection of telephone switchboards, or PBX. TELNET is aware of this critical importance and we’ve developed several products and topologies that guarantee levels of service that are unprecedented on the market. This application note covers some of the most important ones to introduce them to you.

E1 protection with two TDM networks

In this first scenario, two PBXs are connected over two independent networks or TDM E1 circuits. The goal is to interconnect both PBXs over both routes; it’s important to note that each PBX only has one E1 interface.

As shown in the previous figure, TELNET’s Switch TDM 4xE1 module allows two TDM networks to be used and offers a single E1 to each PBX; in other words, each telephone switchboard is connected with two different routes. This switch monitors both routes at the signal level (LOS) and frame level (LOF), and if any anomalies are detected, it switches the service over to the most optimum route. Switching time is not more than 50ms, guaranteeing the stability of the telephone service.

The Switch TDM is available in two configurations: one for four E1 interfaces (Switch TDM 4xE1) and another with eight, Switch TDM 8xE1. Both products are transparent to the traffic carried over them, so they can work with any type of frame, signaling, or service.

Protection of E1 and Gigabit traffic over two optical fibers

TELNET has developed the MediaMUX module for projects in which Gigabit services have to be carried on a single optical fiber along with E1 channels. MediaMUX allows the simple, economical, and transparent interconnection of up to 8 E1s and one local network at Gigabit speed over one optical fiber.

In this scenario, TELNET’s proposed configuration includes the use of two fiber-optic routes in the connection of two MediaMUXs between two centers. To do this, TELNET has the AO GbE 1+1 optical adapter to manage the two fiber-optic routes.

The AO GbE 1+1 receives the output from the MediaMUX card, and according to the policies configured by the user, routes traffic over one of the two optical fibers. In parallel, the AO GbE 1+1 card constantly monitors traffic in search of errors in the signal or in the frame. In response to an error or deterioration of the signal, MediaMUX reroutes the traffic over the second fiber. This switch time is not more than 50ms, so the voice and data services will not be affected by the event. .

Protection of E1 and Gigabit traffic with two point-to-point xWDM networks

This application is similar to the one described earlier, except that here, there are two xWDM networks in a point-to-point configuration. 

In this scenario, the modularity of the AO GbE 1+1 adapter facilitates the use of SFP optical parts with different wavelengths. This means that the laser that is properly suited to the CWDM or DWDM lambda plan will be installed.  Of course, all of the fault detection capabilities and quick-switchover to the backup xWDM network or route are guaranteed in this topology.

Protection of E1 and Gigabit traffic with an xWDM ring

In this last scenario, a fiber ring topology is used to connect a number of Branch Offices with one Central Office over two different routes, which topologically correspond to each direction of the ring.

In designs based on optical rings, the OADM (Optical Add&Drop Multiplexer) plays an essential role. As shown here, this component is located in each one of the Branch Offices, which allows one or more wavelengths to be extracted or inserted to the interior of the office. All of the other lambdas pass transparently. The previous example allows Branch Office 2 to maintain one connection with the Central Office over the South route (Office 2-Office 1- Central Office) and another backup in the North direction (Office 2 – Office 3 – Central Office).