ALPS / Point-to-Point Protection

Problem
You have critical data which is transported between two or more locations. You cannot afford to have the system out of service. How can you protect your T1 data without a lot of expensive and complicated switching equipment or a costly stand-by (seldom used) T1 lines?

Solution
Coastcom's D/I Mux III in ALPS mode allows data to be switched automatically from one T1 path to a secondary T1 path when a transmission failure occurs. The voice, data, and video connections to the D/I Mux III do not change, only the transmission path changes.

How Does It Work?
Figure s13 indicates that when the primary transmission path fails, a receiver on D/I Mux III B detects the failure and sends out a code on the secondary direction or path. When D/I Mux III A receives the switching code or loses input on T1-1, the channel data (voice and/or data circuits) is switched to the secondary direction.

Figure s13. ALPS Point-to-Point Application

What Actually Occurs?
A single T1 line runs between each D/I Mux. In normal operation all information is carried on 2 of the 4 conductors in the T1 lines. We refer to this as the primary ring. Channel traffic is sent in a clockwise direction and received from the clockwise direction.

The primary and secondary transmission paths take opposite physical routes around the loop. If one of the paths T1s fails then the opposite path takes over.

For example, when a work crew accidentally cuts the T1 cable between A and B, the system automatically detects the failure and reroutes the T1 traffic to the backup ring. The backup ring is the second pair of conductors in the T1 cable. Back up traffic travels counter-clockwise on the ring.  The switching will not be detectable by voice circuits but will cause a data hit, a few millisecond break in digital data which makes retransmission necessary.

How Do You Set It Up?
On the D/I Mux III control terminal, enter the shelf configuration SC screen to select ALPS operation and the source of shelf timing. In an ALPS point-to-point network, one of the D/I Mux IIIs is the timing source and the other D/I Mux III is synchronized to it. Select Local Shelf Timing to be the timing source and select Loop Shelf Timing to synchronize to the local timing source.

In ALPS operation, channel card circuits are mapped in only the T1-1 direction. The ALPS mode takes care of the special transmission paths for both normal ring and protection switching operation.

In Figure s13, the transmission paths are shown as arrows around the ring to better explain the operation of ALPS. Notice that all the D/I Mux III's T1-1 ports are connected to the T1-2 port of the next D/I Mux III down the line.

ALPS is used exclusively for high reliability private networks. It is important to remember that in private networks the receive and transmit paths between multiplexers are directed by the T1 cables. A rollover cable is required to connect the transmit of one system to the receive of another. This is different from connecting to the PSTN where a straight through cable connects to the network.

Figure s14. Private Ring Network Protection

What Do You Order?
ALPS operation requires minor hardware upgrades compared to a standard D/I Mux. Only the LIU's differ between ALPS and non-ALPS systems.

For ALPS systems, order LIUs 30309-105 and 30309-115. All D/I Mux feature cards operate normally in an ALPS system as do the controllers, CCU (30305-101 or 30305-108) and AMCU (40305-104).

ALPS/Automatic Loop Protection Switching on a Private Ring Network

Problem
Your network consists of many sites. The information which is transported on your network has to be delivered because it is critical to your business's operation. If the communications network goes down, processes stop until it is operational again. How can you protect your network without expensive, complicated, and redundant equipment?

Solution
Coastcom's D/I Mux III in ALPS mode protects your network from a transmission failure. ALPS mode uses two communications rings in a single T1 span: one primary ring for normal operation and one secondary ring should a transmission link fail. ALPS switching protection is an automatic process which is not detectable by end users.

How Does It Work?
Voice and/or data circuits are carried on the primary ring during normal operation. When the two D/I Mux IIIs in the primary ring network detect a loss of framing, they switch the channel data to the backup ring. The switching will not be detectable by voice circuits but may cause a data hit, a brief break in digital data, which makes retransmission necessary.

Application 1
The New West Oil Refinery has an extensive communications network to monitor refinery processes, pipe transport systems, and levels in storage tanks. It is a private network which covers many square miles at one site.

When a pipe fails between a refinery cooking tank and a storage tank, the refinery control computer detects an abnormality and goes into alarm. The computer operator knows where the problem area is because of the data detected. The computer operator then calls a work crew to the area.

As the work crews hurry to replace the broken section of pipe, the communications line is cut between the cooking tank and storage tank. The ALPS system automatically redirects the transmission path around the break. The ALPS protection switching keeps the communications system on line and the refining processes can continue.

The communications crew has avoided an emergency situation and repairs the cable while the network is still running. After the cable is repaired the system automatically switches back the primary ring, normal operation.

Figure s15. Private Ring Network Protection

How Do You Set It Up?
On the D/I Mux III control terminal, enter the shelf configuration SC screen to select ALPS operation and the source of shelf timing for each of the D/I Mux IIIs in the network. In an ALPS ring network, one of the D/I Mux IIIs is the source of timing and the others are synchronized to it. Select Local Shelf Timing to be the source of timing and select Loop Shelf Timing to synchronize to the network.

In ALPS operation, channel card circuits are mapped in only one direction on the T1-1 map. The ALPS mode takes care of the special transmission paths for both normal ring and protection switching operation.

What Do You Order?
ALPS operation requires minor hardware upgrades compared to a standard D/I Mux. Only the LIU's differ between ALPS and non-ALPS systems.

For ALPS systems, order LIUs 30309-105 and 30309-115. All D/I Mux feature cards operate normally in an ALPS system as do the controllers, CCU (30305-101 or 30305-108) and AMCU (40305-104).

ALPS / PSN Connection

Problem
You have several sites, each requiring a communications network. You need to build some type of redundancy into the networks because critical information is being carried. Communication also needs to take place between the network and the PSN. How can you achieve your network requirements without buying several types of equipment from a multitude of vendors?

Solution
The D/I Mux IIIs in ALPS mode creates a ring network with protected T1 transmission paths. The TTUs also allow an ALPS ring network to communicate to the PSN.

How Does It Work?
When running in ALPS mode the T1 is going in and out of nodes in a ring topology. The primary ring carries the information during normal operation. The second ring, which would normally be used for full duplex transmission, is held open and is called the backup ring. If a break occurs on the T1 span between two locations, the channel circuit information is rerouted on the backup ring as shown in Figure s16. In this manner all locations on the T1 loop are able to maintain contact with each other. This method of protection offers an inexpensive solution for maintaining circuit integrity without purchasing more expensive and complex redundant systems.

Figure s16. TTU Gateway to Public Network

Application 2
The Urban and Rural Water Company (URWC) has pumping stations located at key sites along a major tributary. Each pumping station fills water tanks in the evening when power rates are low for the next day's usage. The network is set up in a loop topology. A loop covers several pumping stations and water storage tanks. A TTU connects the sites to the PSN.

A break in the communications link could cause a critical loss of water service to households, businesses and services. The same figure shows how the data flow alters when a break in the T1 span occurs. For instance a construction project between two pumping stations could accidentally cut through a cable, or weather conditions could knock out a microwave link. If this occurs the two locations can still communicate. How is this done?

The D/I Mux III at the Marshland Storage Tanks normally receives data from the D/I Mux III at the Windy Hill Pumping Station. When the span is down, as shown by the red X on Figure s16, information is redirected onto the backup ring.

When the primary ring is fixed, the ALPS is capable of restoring to the normal ring topology without operator intervention. In the case of a single fault span error, there is virtually no loss of communication between sites.

How Do You Set It Up?
On the D/I Mux III control terminal, enter the shelf configuration SC screen to select ALPS operation and the source of shelf timing for each of the D/I Mux IIIs in the network. In an ALPS ring network, one of the D/I Mux IIIs is the source of timing and the others are synchronized to it. Select Local Shelf Timing to be the source of timing and select Loop Shelf Timing to synchronize to the network.

In ALPS operation, channel card circuits are mapped in only one direction on the T1-1 map. The ALPS mode takes care of the special transmission paths for both normal ring and protection switching operation.

The PSN is the source of timing in this network. The TTU is set to receive timing from the PSN. The Slot 2 Sync feature is then used to extract timing from the TTU and supply to the D/I Mux III. The D/I Mux III at the Hillview Station is then used as the master timing station.

What Do You Order?
ALPS operation requires minor hardware upgrades compared to a standard D/I Mux. Only the LIU's differ between ALPS and non-ALPS systems.

For ALPS systems, order LIUs 30309-105 and 30309-115. All D/I Mux feature cards operate normally in an ALPS system as do the controllers, CCU (30305-101 or 30305-108) and AMCU (40305-104).