Single Path Signalling Technologies
Entry posted by ccbrennan
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Single path signaling solutions
This blog aims to outline the options for single path signaling.
To avoid continuous repetition of “network polling, alarms, UDL, diagnostics etc this document will refer to these features as “ATS functions”.
Network polling is the transmission of data between a transmitter located at the protected premises and the alarm receiving centre for the purposes of identifying the loss of an end to end route over the network.
Alarms are events generated by either pin/channels or SIA events from the security system (intruder or fire).
UDL refers to Upload/Download of data to and from the security system or transmitter for the purposes of management and maintenance.
Diagnostics refers to troubleshooting security system, transmitter or network problems remotely over the network.
Technologies
There are 5 methods used to provide single path signaling today using standard, non proprietary communications methods.
Standard PSTN (Public Switched Telephone Network)
Dial up (Digi modem)
Modem data over wireless
GSM (Global System for Mobile Communications)
IP over fixed line
xDSL/fibre/other (Digital Subscriber Line - Asymmetrical, Symmetrical upstream and downsream options)
IP over wireless
GPRS/3G/other (General Packet Radio System, 3rd Generation, LTE (Long Term Evolution)
Billing
Each technology incurs communications costs (not including ARC monitoring fees). In the security application costs are incurred by network polls, alarm delivery and remote service.
With certain technologies the cost is paid by the end user to the telecoms service provider. Other technologies are billed via the ARC by the ATS provider.
Some ATS providers do enable the end user to procure their own SIM for either GSM data or GPRS, however in general:
Standard PSTN
End user pays
Proprietary PSTN
ATS provider charge via ARC
Modem data over wireless
ATS provider charge via ARC
IP over fixed line
ATS provider charge via ARC
IP over wireless
ATS provider charge via ARC
Costs
Because single path signaling is generally only considered for low risk premises the end users expectation is for low cost/low functionality.
Summary
PSTN
Dedicated line provides best functionality/security
Dedicated lines are expensive
Calls are expensive
Security reduced by reducing call frequency
Security reduced by implementing on shared line
Test call and power fail should be configured at all times
GSM data
Less expensive than PSTN
More expensive than GPRS and ADSL
Same dial in security issues as PSTN
Test call and power fail should be configured at all times
GPRS data
Very low cost support for all ATS functions
More secure than PSTN and GSM (firewalled etc)
Test call and power fail should be configured at all times
Remote UDL has increased security
Remote UDL can operate in internet/private APN modes
Private APN is more elegant for any time access
Private APN includes fixed IP address for SIMs
Costs of APN/fixed IP is close to zero for ATS providers
xDSL
As a shared service cost of ATS functions is close to zero
High polling frequency means anytime UDL possible
High polling frequency means network reporting time can be reduced to identify power failure/faults more quickly, without undue stress on ARC
More secure than PSTN and GSM
Operates in dynamic or fixed IP address modes
Detail
PSTN
PSTN is a point to point service, operating only one application to a dialed destination at any time (or inbound call).
In the security context the most reliable and secure implementation is to use a dedicated PSTN line. A dedicated PSTN line can efficiently support all ATS functions, though generally at a lower frequency than other proprietary or IP based systems.
Using a dedicated line ensures that the security service is not interruption by other dial up applications or compromised by “off hook” scenarios (which can also occur undetected during the Open and Set periods).
However dedicated lines are expensive, prone to disconnection by finance departments because of their low useage profile and the trend in price remains on the increase.
Because of the cost of PSTN lines and call charges many installers and end users have reduced the number of test calls and alarm traffic sent. This further reduces security and devalues the application.
The potential trend for these systems, even without the network issues which occur from time to time, is for end users to cancel the services.
Using shared PSTN lines reduces the line rental costs, but introduces the off hook risks. For installers that want to use remote UDL there is also the issue of the inbound call being answered (by fax or person) or that the line is busy.
Generally the remote UDL over PSTN is insecure. There are very few measures to restrict a system dialing into a site (such as a firewall). Dial in/dial back for UDL does provide some security, but data is sent by the digi unencrypted and many installers enable dial in/common engineering codes for efficiency/simplicity.
Modem data over wireless
Sending ATS functions over GSM data networks removes the cost of a dedicated land line and is significantly cheaper. However GSM data useage is expensive compared to GPRS and xDSL services.
GSM can be remotely dialed by the UDL package, but the security risks remain the same as PSTN dial up. GSM can be dialed just as PSTN is if you know the telephone number of the SIM. See security issues above for PSTN.
GPRS
During the past 8 years GPRS costs have dropped dramatically and it’s functionality has improved. Because GPRS is a “packet” based system which uses shared local access and network resources it is charged on a useage basis i.e the amount of bandwidth you use per month. M2M GPRS is procured on a contract basis and there are many commercial options open to ATS providers including pooled bandwidth, fractional billing, line rental with inclusive bandwidth etc.
GPRS is suitable for all ATS functions and it has added security and encryption over GSM dial up data. Because the GPRS service uses IP technology to transport data the SIM/service is behind the network provider’s firewall systems.
If the SIM is not sending data to a server (e.g. a receiver) it is not possible to send data directly to the SIM over GPRS when behind the public internet firewall. For single path ATS systems, if the remote device is polling very infrequently (e.g. every 24 hours) then remote connectivity for UDL is not possible.
Other methods can be used to make the SIM send data to initiate two way communications, however they add (minor) cost and the UDL package may time out during the process.
To maintain the security of the GPRS system (when used as a single path system) and allow anytime access for ATS functions, the most elegant solution is to provide the SIM with a Fixed IP address. To achieve this the ATS provider procures a dedicated APN/IPSEC tunnel(s) from the mobile provider. This creates a closed network group for the SIMs, fixed IP addressing etc.
The cost of APN/IPSEC tunnels has reduced dramatically over the past 3 years making the cost implications to a volume ATS provider negligible/zero.
xDSL
Fixed line broadband internet connections are designed for high speed, shared application use. The cost of transmission is effectively zero (when operating on a shared circuit).
The firewall does restrict unsolicited inbound access, providing a higher level of security than PSTN. This is overcome by ATS providers using network polling as the transport for all ATS functions.
In the case of xDSL based systems, there is no need for a dedicated APN/IPSEC tunnel from the service provider because the bandwidth used is provided by the end user (at almost zero cost). Therefore the polling frequency on fixed line IP systems can be far higher than GPRS, enabling any time access all the time.
ARC costs
Digi modems communicate directly with the ARC into a receiver rack. PSTN/ISDN lines modems/terminal adapters are required and contention is high (we have seen digis contending 100-1 for ARC based resources). (PSTN traffic from ATS providers is generally delivered by a hosted system over IP connections or, in some cases, legacy kilostream services).
GPRS and fixed line IP services are delivered into the ARC using high speed internet connections. These are more scalable and less contended than the PSTN infrastructure. (Statement holds for hosted or direct connections from ATS providers).
Pros and cons of each technology
Four elements effect the choice of single path signaling; frequency of polling, frequency of unconfirmed network faults reported, network maintenance and the affect of loss of power to the ATS communication/communications equipment/line.
Network polling frequency
Any single path system is compromised by the fact that an interruption in service cannot be detected quickly without high speed polling. Using dial up PSTN and GSM services, high speed polling can be expensive.
Network fault reporting
The downside of high speed polling is that short term network faults can be reported to the operator. Dependent on the technology used polling the network incurs cost.
Network maintenance
Every service is affected by network maintenance by the communications service provider, or the end user. In general maintenance outages are very short. Whilst the actual work may take some time, the implementation of the upgrade/work takes a few minutes whilst systems reboot. Signalling standards take care of this with a minimum 3 minute reporting time at Grade 4 and much longer at the lower Grades (3 and 2). The majority of network equipment either local or remote to the premises can be worked open without interrupting operation with the reboot taking less than 3 minutes.
Power
A loss of power can also stop a communications service operating.
Loss of power using a Digi modem or GSM/GPRS system
PSTN systems which use a copper path include a line voltage, driven by power at the exchange. However, the digi modem will only operate for the battery backup time of the alarm panel, hence the requirement to back up the panel for 24 hours using a battery.
Once expended the modem will fail, but the line will stay in operation. The same power backup times apply to the operation of a GSM/GPRS modem.
For systems which monitor power it remains possible to transmit a “Power failure” message to the ARC, but only if this has been configured in the panel or via a channel.
If this alarm is not configured the ARC will be made aware only when the battery backup of the panel fails and the test call from the modem is not received, if the test call has been configured to be sent.
Loss of power using fixed line or wireless IP single path systems
Power loss will result in the loss of broadband and the ability to signal. Because of the fast polling times a fault can be recognized by the receiver quickly. The majority of power failures are short, but installers can choose from Grade 2 (24 hour), Grade 3 (5 hours) and Grade 4 (3 minute) reporting times. Some ATS providers enable a hybrid reporting time of 30 minutes to an hour, which is both logical and statistically proven to be a reasonable time to enable either a single path wireless or fixed line system to recover from the majority of network faults, maintenance or power outage issues. Additional reporting can employed to report a power fail over PSTN in either instance, creating an IP+PSTN or GPRS+PSTN solution.
The use of VoIP for digi modems
Many xDSL routers support the connection of an analogue modem. The router will convert the modem analogue signal to packet, but at the receiving end a router will need to convert the data stream back to analogue for receipt by a modem.
The process is complex and in the security environment can introduce kiss off issues with the alarm panel – which is the very problem many ARCs are attempting to avoid.
The future
Fixed line
Fixed line technologies such as fibre are already available. Changes the users will see are that transmission and download speeds will become faster and more symmetrical. Services will continue to converge applications over a single line at faster speeds of transmission and access giving remote control a continually improved “real time” feel.
IPv6 introduces the concept of a fixed IP address for every device, this has advantages in terms of reducing the configuration required.
Firewalls will remain a key element in protecting devices from malicious, unsolicited in bound attack, even when every device has it’s own IP address.
Wireless
The major changes to communications will be in wireless. 3G has been available for several years nationally, however the price of 3G hardware has restricted use of this technology in security.
When 3G hardware costs reduce this will enable a more elegant solution for Imaging and CCTV transmission over wireless because of its increased upstream speed when compared with GPRS.
LTE frequency auctions start in 2013. Networks will roll out during 2014. Speeds will be very high, but the technology will come with the same price of hardware/power consumption issues at first. This will then decline to be affordable/reliable/efficient in line with other digital technology trends.
In general the wireless communications solutions will continue to evolve to a point where the airborne traffic is as fast and affordable as the fixed line traffic – eventually delivering a symmetrical service over any path, both operating at the same/very similar speeds.
Coverage will continue to improve, but wireless will always be prone to signal strength issues due to geographical location, physical construct of the building and installation location within the premises.
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