IP linking creates new options and benefits for one-way paging
This base station linking method offers enhanced link bandwidth use, immediate fault reporting, instantaneous remote access to base station equipment and seamless link redundancy, all with the opportunity for cost savings.
The basic architecture of paging infrastructure has changed little during the past 20 years. At a central location, paging control terminals (PCTs) house the subscriber database, accept and process incoming calls from the telephone network, and encode pages for transmission. At distributed locations, radio transmitter and control equipment make up the paging base station. Pages are initiated by a call to the PCT. Pages are batched and encoded at a central location then transported via the “linking” system to the base stations. Finally, pages are sent out over the air by the transmitters.
With the introduction of two-way narrowband personal communications service (NPCS), this model has changed somewhat. A network of receivers is now required to receive transmissions from the pagers. This new model prompted the use of a new communications links between the encoding site and the base stations. Two-way paging requires two-way communication between central locations and base stations. This is served best when using digital packet network-based links.
Packet network linking, also known as IP (Internet protocol) linking, is now also available for conventional one-way paging systems. Glenayre’s GL-C2010 transmitter controller is equipped with IP linking interfaces, and it communicates with the encoder using the TCP/IP (transmission control protocol and Internet protocol) suite of protocols_hence the name, IP linking. This opens up a world of options for paging carriers and can provide increased flexibility, efficiency gains and cost reduction.
Paging systems linking Traditional one-way linking, which carries paging data and, in some cases, configuration and control commands, is available in a number of forms, as shown in Figure 1 below. Broadcast wireless technologies, as well as point-to-multipoint terrestrial links, can be used. Broadcast technologies are typically either one-way satellite links or radio links. Terrestrial links include wireline links, microwave links or both. All of these options provide either digital or analog communications channels. Typically, each of these alternatives provides a unidirectional data path, from the encoder to the base stations.
Critical to the operation of a modern paging network is the ability to change and to maintain equipment configuration, and for operators to be alerted of system faults, especially from remote base station sites. Consequently, there is a need to transfer information from the base stations to a central location where network management is performed. This can be accomplished by sending network management information out over the paging transmitter. Most often, however, in today’s high-speed paging networks, this is done using a dial-up telephone line connected to equipment at each transmitter site. A connection with the public switched telephone network (PSTN) at the site permits both the base station equipment to automatically dial out to report faults and network operators to dial in to check equipment status and change configuration.
Using this architecture, two separate communications channels connect to the paging base station, which increases operating costs for the paging carrier. Another disadvantage of this design is that the forward channel links do not efficiently accommodate redundant links. If an operator considers back-up links critical to business success, implementation may require additional equipment at the base station to manage the feature. Any solution will still incur the loss of paging data during switch-over time.
Dial-up links for fault reporting and base station access can be time-consuming. Establishing the link requires time, due to dialing and connection delays. If a base station dials in to report an alarm, it must complete the task and disconnect before an operator can dial back to investigate. Alarm reporting may be delayed if multiple base stations try to report at the same time. An operator can connect only to one base station at a time. These possible drawbacks can limit the paging carrier’s ability to deliver a maximum number of pages, a critical success factor of any paging carrier.
Packet networks What exactly are packet networks? In packet networks, streams of digital data are split into blocks. These blocks of data are encased in framing and address information and injected into a transmission network for delivery to a specific destination or destinations.
Physically, packet networks can be switched or built on dedicated lines. A switched network is often a telecommunications network whose owner offers data delivery services. In a switched network, multiple paths will be between any external equipment serviced by the network, perhaps hundreds or thousands of paths. Under this topology, subsequent packets from a single source bound for the same destination may be switched through different paths. Public Frame Relay and X.25 networks are types of packet networks.
Private, dedicated lines can also be used to build a packet network. The lines can be duplex digital lines or dedicated analog lines equipped with modems at each end. The topology of the network can be a ring, a bus, a star, a branched network or combinations of any of these.
A third, relatively new, example of a packet network is two-way VSAT (very small aperture terminal) satellite services. Vendors now offer this service, mixing data from numerous subscribers on the satellite carrier. Router equipment at each satellite receiver delivers forward channel data to appropriate customer equipment. The reverse channel is managed using a CSMA/CD (carrier sense multiple access and collision detection) protocol, making the service essentially a big Ethernet in the sky. This is a bus topology; logically, each terminal device is connected to the same data conductor.
One advantage of packet networks is the ability to connect separate networks of differing types using off-the-shelf equipment. Bridges, gateways, routers and switches manage the networks and facilitate interconnection.
IP linking and the transmitter controller How can IP packet networks be used for paging links, and what advantages do they offer? IP linking for paging systems provides a single integrated communications channel for paging data, fault reporting, configuration management and even equipment remote software upgrading, as shown in Figure 2 on page 30. The base station management connections are permanently established, and there is no congestion when multiple base stations report alarms. Alarms can even be reported to more than one network management system, and with the click of a mouse button, an operator can instantly access any base station. In fact, network operators can have live access to many base stations at the same time.
IP linking with our transmitter controller facilitates efficient use of the paging links. This is especially true of paging networks that serve many separate simulcast regions using a private, dedicated line, IP links. Packets can be addressed and routed such that, in a branch topology, on any segment of the network, only those packets that are destined for base stations served by that segment will be transported; base stations will no longer receive data not intended for them.
Our controller also provides a duplicate packet option for seamless redundancy. When in this mode of operation, all paging data packets are sent out of the encoder twice. One of the duplicate packets can be routed through a primary network and the second through a completely separate back-up network. Both packets arrive at the base station and are routed to the transmitter controller. The controller is able to recognize the duplicate packets and discard one. If one of the packets is corrupted or lost due to problems on one network, the transmitter controller will use the received or uncorrupted packet. Imagine: a massive link failure without a single lost page at any base station!
All of these features of packet network linking increase efficiency of the paging system operation. Link bandwidth use is maximized, faults are reported immediately, problem rectification is carried out sooner, and seamless redundancy is available_all with the opportunity for cost savings. For paging carriers, these advantages provide increased reliability of page delivery, which translates into greater customer satisfaction among their subscribers.
Markets Packet network telecommunications is being deployed on a global basis at a phenomenal rate. The Internet, for example, is built on thousands of interconnected packet networks. With newer technologies such as ATM (asynchronous transfer mode) circuit-switched networks, today’s telephone network is being replaced by packet networks where voice, video and data are seamlessly mixed into a single telecommunications network.
The availability and cost of public packet networks for use by paging operators vary significantly around the world. In regions with well-developed digital telecommunications infrastructure, public packet networks can be readily available and dedicated line private networks can be efficiently deployed. In other regions of the world, two-way VSAT is an available option and can be particularly well-suited for paging networks that cover a large geographic area.
A main benefit of packet networks is the ability to mix networks of different types within a single paging system. Urban areas may have readily available access to Frame Relay networks, whereas rural areas may not, although this does not present a problem for an IP-linked paging system. Urban base stations linked by Frame Relay can reside on the same virtual network as rural base stations linked using dedicated lines. IP linking will play a central role in the design and construction of new paging infrastructure on a global basis. For some paging operators, it is beneficial to swap-out their existing control system and link methods and convert to an IP-linked system to take advantage of the efficiency gains, added reliability and cost savings. Operators with Glenayre’s GL-C2000 controller, however, would require only an upgrade to realize the benefits of an IP-linked system.
The transmitter controller at work The GL-C2010 controller is equipped with a 10Base2 Ethernet port and an X.21 WAN (wide-area network) port. At the data link layer and the network layer, the transmitter controller uses the TCP/IP suite of protocols. Paging data are sent from the encoding point to the base stations in a User Datgram Protocol (UDP) multicast format. On the same network, a TCP connection is used by network management equipment to communicate with any C2010 controller.
Already, paging operators at locations around the world are realizing the benefits of IP linking and the transmitter controller. A paging operator in the United Kingdom has implemented a private packet network on its own E1 links. By using infrastructure that connects the company’s existing cellular telephone network, the marginal cost of the link network is low. At the same time, all the efficiency gains of the IP linking are realized. In the U.K. system, the transmitter controller connects to the network via its X.21 serial WAN port. Each base station is connected to a regional router using a single DS0 channel. Paging data branches out from the encoder site to regional routers, then on to the base stations. For this particular operator, this is a low-cost linking option that offers efficiency and reliability gains.
PageMart Wireless, Dallas, is testing a paging network based on the transmitter controller using two-way VSAT satellite linking. In this case, an IP linking network will be available to serve both one-way and two-way paging. The initial requirement for the IP network is for the two-way paging system. With the transmitter controller, the separate link systems and PSTN connections for the one-way equipment can be eliminated at the co-located base stations. Again, the result will be cost savings and efficiency gains. Paging providers in the largest and fastest-growing paging markets in the world, North America, South America and Asia, are planning two-way NPCS paging. There will be strong incentives for operators to combine one-way and two-way linking networks.
A major role in future networks Packet-network-linking systems are being deployed in many countries around the world. This type of paging system will play a major role in the design and construction of new paging networks and the modernization of existing ones. The need for this linking technology is being driven by several realities: increasing integration of one-way and two-way paging networks in North America; the importance of redundancy in Asia; and the growing demand from operators for more efficient, flexible and cost-effective networks. Expect to see the increasing use of IP linking in paging system design as more operators learn of the flexibility, conveniences and savings it offers.
