Wireless Options | Wide Area Network Technology Options

George Gilder, a well-known champion of "infinite bandwidth," says the [wireless] spectrum is infinite, ubiquitous, instantaneous, and cornucopian. Current industry trends certainly support his hyperbole. Wireless Internet services, low earth orbit satellite services, Bluetooth, fixed wireless, and many other permutations of communications over the air are providing services that were either not available or prohibitively expensive in the past.

Following are some of the technologies and applications that have the potential to streamline operations or to serve as less-expensive, ersatz landlines.

VSAT and Geosynchronous Satellites

In the 1950s and 1960s, many organizations maintained private, point-to-point networks of terrestrial lines, often with multiple "drop-off points" in more remote areas. It was expensive and arduous to maintain this cobbled together network. For a network manager dealing with locations in the hundreds of thousands, it meant maintaining contacts with many small local exchange carriers (e.g., Bob and Pat's Telephone Company) and a relatively high level of downtime (for specific sites).

As commercial satellites began to be deployed in numbers during the 1970s, the use of VSAT (very small aperture terminals) networks increased significantly. Exhibit 1 shows a simplified diagram of a VSAT network.

Exhibit 1: Typical VSAT Configuration

By using a satellite to transmit all traffic within a large geographic region (e.g., Canada, the United States, and Mexico), the need for terrestrial lines is eliminated except for the backhaul (high-capacity terrestrial circuit from the commercial satellite hub to the organization's headquarters location).

Following are advantages and disadvantages of VSAT systems versus traditional terrestrial networks:

• Advantages:

  • Less expensive for data communications. Satellite systems become less costly per site as the number of sites increases. The cost differential is most significant in rural areas where terrestrial access lines (e.g., for Frame Relay) are costly.

  • Less expensive for video communications. Terrestrial lines with the bandwidth to support video are expensive (typically requiring a minimum of 384 kbps for good quality). VSAT can deliver one-way video for a fraction of the cost of a terrestrial solution (point-to-point solutions or ATM).

  • Known, reliable technology. VSAT technology has been around for decades, with the dishes progressing from type I to the current type III technology. In many areas of the world, including oil rigs in the ocean, VSAT communications is the only practical alternative. Over time, techniques to optimize common protocols such as TCP/IP over higher delay satellite networks have been developed.

  • Much quicker to deploy. In some remote areas, the local telephone company can take months to install a data circuit. In some cases, the LEC may not be willing to incur the up-front cost. VSAT equipment, on the other hand, can be set up relatively quickly — in a week or two. The only requirements are that electrical power be available and that the satellite be within the VSAT dish line-of-sight (proper angle).

  • Available in remote and underdeveloped areas. VSAT technology functions well in northern Alaska, Pitcairn Island, and Tierra del Fuego.

• Disadvantages:

  • Only moderately high uptime. Satellite communications cannot provide an extremely high uptime, such as 99.999. Providers such as Hughes will typically quote numbers such as 99.5 to 99.8 percent uptime. Unavoidable events such as extremely heavy rain, sunspots, and even solar transit outage cause the signal to degrade and thus interrupt transmission. In some cases, interference from improperly configured ground stations (bad polarity, for example) from other carriers can weaken the signal.

  • Transmission (propagation) delay. Because the signal must go up 22,300 miles from the VSAT and down the same distance to the hub (ground station), there is a noticeable lag time for interactive systems (0.25 second one way, 0.5 second round trip). This reduces the popularity of VSAT for traditional voice communications, although it can work in a "take your turn … Roger … over" mode.

  • High initial cost. VSAT equipment will cost an initial $6 to $8K per site, plus any monitoring equipment that the organization chooses to use. Also, satellite contrasts are lengthy, generally five years.

  • Limited uplink bandwidth. While large volumes of data can typically be downloaded from the satellite (e.g., for video), uplink from a single VSAT dish is typically less than 128 kbps.

  • Single point of failure. Satellites have a limited life (a 15-year-old satellite is an antique) and are subject to limited fuel to keep them in proper orbit, electrical breakdowns, meteors, being hit by other satellites, and other sources of destruction. For example, PanAmSat lost its Galaxy-IV satellite in 1998, resulting in widespread loss of paging services across the United States for a few days. To mitigate this risk, organizations can obtain rights to use a backup satellite from their provider. If the primary satellite fails, VSAT dishes must be repositioned to point to the backup satellite. Repositioning can take anywhere from a few days (best case) to several weeks for a large number of sites.

An important economic consideration for an organization with a large VSAT network is hub ownership. Firms with a smaller number of sites typically use their provider's hub and receive all communications via a dedicated leased line from the provider to their headquarters site. However, even at a cost of roughly $1 million, at some point hub ownership becomes a viable option. Only organizations committed to VSAT over a relatively long time period should consider this option, because the technical staff and expertise to operate a satellite hub are considerable.

Comparison of terrestrial network costs to comparable satellite numbers depends on a number of factors, such as:

• Number of sites

• Uplink and downlink bandwidth

• Service level agreements and disaster recovery requirements

• Price of the VSAT equipment

• Maintenance costs of the equipment (dish, RF equipment)

In one recent study, the cost of supplying comparable bandwidth to 1000 sites was found to be approximately $400 to $450 per site with Frame Relay and $150 per site using VSAT services (Global VSAT Forum, http://www.com-sys.co.uk/vsatind.htm). The authors have seen similar figures for other firms. Including video in the mix would make the cost disparity even greater.

Low Earth Orbit Satellite

The economics of wireless communications are not always suited to broad generalizations. Each business case must be considered individually. As an example, consider energy firms that use pipelines to transport natural gas across the United States. The pipelines must constantly be monitored for signs of rust to ensure that a gas rupture does not occur. One engineering technique long used by pipeline companies is cathodic protection, in which a metal rod is attached via wires to the pipelines and serves as a "sacrificial anode" to keep a correct electrochemical balance. In effect, the expendable rod rusts instead of the pipeline itself.

Because the metal rod eventually rusts out, inspections and replacements must occur on a regular basis. Trips to the more remote sites may require hours of "windshield time;" that is, a service technician driving a truck a hundred miles to spend a few minutes inspecting and possibly replacing the anode. Attaching an inexpensive transmitter to each site and then sending appropriate telemetry data to low earth orbit satellites can eliminate many of these inspection trips. The satellites, in turn, transmit to an Earth station. From there, the data is sent to a data acquisition center where appropriate maintenance reports are created.

Whether the above scenario makes economic sense depends on a number of factors: people costs, time on the road, unit capital costs (for the remote field transmitter), and system maintenance costs. Low earth orbit, or LEO, satellite transmission is relatively expensive on a per-packet basis. However, if the application requires only a small quantity of data per month (as in the previous example), LEO technology may be a good fit. Exhibit 2, courtesy of Orbcomm and Leocell, illustrates a typical implementation.

Exhibit 2: Low Earth Orbit Transmission Example

Bluetooth

For selected environments and applications, a radio-frequency, personal area network may be superior to its wired counterpart. Bluetooth is a popular, open standard for wireless transmission over a relatively short range (10 to 100 meters). It enables functions such as:

• Wireless LAN access

• Synchronization of PDAs and laptops

• Midrange bandwidth for connection to the Internet (up to 720 kBps): any Bluetooth-enabled device, such as a mobile phone, can link to the Internet if within range of a suitable access point

• Conferencing functionality: documents and business cards can be quickly exchanged among the participants

• Faxing

• Facilitation of electronic paper transmission: for example, a sales rep could fill out a form using a Bluetooth-enabled pen that records the motion of the pen on paper and transmits the order to appropriate servers via a nearby access point or receiving PDA

To some extent, Bluetooth competes with the older Wi-Fi wireless LAN specification. However, Wi-Fi is intended as a cable system replacement and has a higher bandwidth than Bluetooth. Wi-Fi does not fill the same market space.

From a cost perspective, implementation of wireless solutions depends on the organization's workforce. Some car rental companies, for example, use CDPD (wireless) to check out returning customers. Hospitals track patient records using secure wireless technologies as well.

Fixed Wireless Broadband

The slow speed of narrowband wireless communications such as cellular voice transmissions, CDPD, infrared, etc., reinforces the general perception that "wireless" denotes slow and error prone. In fact, there is no theoretical reason why fixed wireless systems cannot transmit very large quantities of data with extremely low error rates. For example, one of the networks discussed below, LMDS (local multipoint distribution services), tops out above OC-3 (155 Mbps) and is typically deployed at 45 Mbps downstream and 10 Mbps upstream. These networks use high-frequency radio connections to send and receive voice, data, and video; from the user's perspective, the result is no different than what would be expected from a copper- or fiber-based solution.

Fixed wireless solutions can often be a lower-cost alternative for broadband access, particularly in rural/low-density areas within the United States. Internationally, fixed wireless is increasingly popular due to its quick deployment, avoidance (from the carrier's perspective) of heavy infrastructure development, and, for some very poor nations, the absence of copper wires, which are sometimes stolen.

From an architectural perspective, broadband wire line access methods, such as xDSL and cable modem, compete with fixed wireless solutions. All these solutions are targeted toward solving the "last mile" problem — getting broadband to the customer's premises. When reviewing options, an organization should consider the following issues:

• Advantages:

  • Fixed wireless can be the lowest-cost alternative.

  • The technology is quick to deploy. In some U.S. rural or international locations, wired broadband access can take several months (T1 drops can take up to nine months in some areas). Fixed wireless antennas and services can sometimes be implemented in weeks.

  • Coverage increases are incremental (just add more receivers/transmitters).

  • Legal/governmental regulations are much easier to address. For example, easements or special licenses are not usually required from the end customer.

  • Under certain circumstances, fixed wireless can deliver more bandwidth than xDSL or cable.

• Disadvantages/concerns:

  • Some technologies require line-of-sight from transmitter to receiver.

  • Tall buildings, mountains, and heavy rainfall can interfere with signals for some of the networks.

  • Standards for equipment have not yet crystallized, resulting in uncertainty in the marketplace and a smaller number of equipment vendors creating the equipment.

  • Economies of scale are still needed to achieve lowest pricing to the end user.

Listed below are the most common broadband access options using fixed wireless.

LMDS (Local Multipoint Distribution Services)

Operating in the 28-GHz range of the spectrum, LMDS provides transmission rates exceeding OC-3 (155 Mbps). A typical deployment provides 45 Mbps downstream and 10 Mbps upstream. Well suited for urban areas, LMDS can be considered "ersatz fiber" when installed with sufficient cell overlap to reduce the effects of heavy rain. One limitation is that line-of-sight is required and wireless links (transmitter and receiver) must be less than 2.5 miles from each other.

MMDS (Multichannel Multipoint Distribution Services)

Although it has been used for more than 25 years to transmit television signals, MMDS is now finding a new niche in the high-speed Internet access service world. It does not require line-of-sight transmission and can work effectively over 35 miles. At 10 Mbps, downstream speed is considerably less than LMDS but its lower frequency range makes it less susceptible to weather interference.

After gaining an understanding of the technologies available and the financial consequences of options within each technology, the next step is to perform a comprehensive review of the existing network.

Frame Relay | Wide Area Network Technology Options

In the 1970s and 1980s, IBM mainframes were so dominant that the comment "no one ever got fired for buying IBM" became a cliché. Frame Relay now appears to have a similar cachet — the service is low cost, almost ubiquitous in the United States and reliable. Also, contrary to general perception, Frame Relay is expandable well beyond T1 speeds and, in fact, has no specific bandwidth limit (e.g., Verizon offers speeds up to 44 Mbps). So any organization considering a WAN deployment should include Frame Relay as a priority option.

Why Frame Relay rather than traditional circuits (e.g., T1s or ISDN)? Frame Relay costs less for the same throughput because it more efficiently uses bandwidth. As the successor to the hoary X.25 standard, ^[1] Frame Relay allows multiple customers to share the bandwidth of a physical connection by taking advantage of the bursty nature of data transmissions (bandwidth on demand). It supports applications such as host-to-host/LAN-to-LAN links, telecommuting, multiple user Internet access, PBX-to-PBX communications, and passable voice/video communications.

The cost for Frame Relay service usually includes three elements:

1. PVC (private virtual circuit), which is usually related to the CIR (committed information rate)

2. Port charges

3. Access to the premises

It would seem that with only three major cost elements, comparing service offerings would be straightforward. Unfortunately, there are a number of factors that complicate the analysis. Following are key factors to consider.

Port Size, CIR, and Discard Eligible Flag

A rough rule of thumb that some network designers use is to set the CIR at half the port size (e.g., a PVC with a port size of 512 kb might have a CIR of 256 kbps). A better approach is to understand the bandwidth requirements of the organization's users and applications and set port size and CIR at optimum levels.

Assume, for example, a Portland field office is connected to the New York headquarters building. Portland has low bandwidth requirements but needs to be able to connect at any time (and not be subject to bottlenecks during busy times of the day). Portland might have a port speed of 128 kbps and a CIR of 64 kbps. In addition, there are six other field offices that transmit to headquarters, with the same specifications. The headquarters port speed is set at 256 kbps, with a CIR of 128 kbps. Clearly, headquarters is seriously oversubscribed. That is, if all sites transmit at once, headquarters will not be able to handle the volume. If the business environment is such that the network designer knows all six will not be transmitting at once, this can be a practical way to minimize costs.

If the network designer also knows that users in field offices can tolerate some transmission delay, further savings can be obtained by reducing the CIR, maybe even down to zero. At zero CIR, all packets are marked as "discard eligible" and are marked for a later transmission.

Asymmetric PVCs

Some carriers, such as AT&T, allow PVCs to be configured with CIRs (committed information rates) that are not equal in both directions. For example, assume a firm's corporate office is in Knoxville, Tennessee, and one of its field offices is in Houston, Texas. Data transmission from Houston to Knoxville may require a CIR of 64 kbps, whereas Knoxville to Houston may only require a 16-kbps CIR. If the carrier permits asymmetric PVCs, they should be considered because many times traffic is unequal between sites. Because the CIR is one factor driving Frame Relay charges, use of this technique can drive down costs with no decrease in service levels to the organization. Many WANs using Frame Relay have been implemented without fine-tuning for unequal traffic.

Multi-Carrier Networks

Many Frame Relay networks are single vendor from the IXC (interexchange carrier) POP to the destination. The local access link may be provided by the LEC, but the Frame Relay network itself is all one vendor. An alternative and more economical solution is to use a LEC Frame Relay network to concentrate traffic to a hub within an intraLATA area, and then transmit to major sites using IXC Frame Relay facilities. The critical factor is the access link. There are two disadvantages to this approach: (1) additional time is required to negotiate and manage separate vendors, and (2) some network management information is lost when Frame Relay packets cross vendor boundaries.

Exhibit 1 illustrates the multi-carrier approach. This solution only makes sense if the organization's topology fits the scenario — smaller locations in relatively close proximity to a hub location (within an intraLATA boundary). The alternative to this approach is to connect each site directly to the IXC POP.

Exhibit 1: Multi-Carrier Frame Relay Configuration

PVC versus SVC

Initially, carriers set up Frame Relay circuits with dedicated, permanent virtual circuits (PVCs) that required an always-up access circuit to the POP. However, switched virtual circuits (SVCs) are now available for organizations that need (1) less frequent access to the network, or (2) more dynamic connection requirements. An SVC is started by the user, then the data is sent and the connection is torn down as in a traditional telephone call. SVCs are less expensive than PVCs up to a point (similar to traditional dial-up per-minute charges versus a dedicated circuit). Aside from lower transmission costs for limited duration sessions, SVCs offer other potential benefits:

• Reduced equipment costs (FRADs ^[2] and router serial ports) relative to a complete PVC implementation, particularly as the network grows in a highly meshed configuration.

• Inexpensive disaster recovery capability. Ongoing backup PVC costs are not incurred and regular database updates for backups can be scheduled as appropriate.

• Temporary, any-to-any connections. These limited-duration links eliminate the need for PVCs between sites that only occasionally communicate with each other.

• Simplified administration. Preconfiguring and managing PVC changes are time-consuming. For highly meshed networks, SVCs can reduce network configuration maintenance.

The above advantages are contingent on the availability of SVCs from the carrier and on user requirements. Also, at certain volumes of traffic, SVCs are no longer economical — sites should be periodically reviewed for appropriate technology. Unfortunately, many carriers do not offer SVCs.

Frame Relay over DSL

Increasingly, CLECs are offering Frame Relay via a DSL link (FRoDSL). Combined with the increased ability of providers to monitor commercial DSL and provide service-level guarantees, this option can provide significantly lower access costs.

Voice Communications Networking

Voicemail

Voicemail, which became widespread in the 1980s, was originally considered a substitute for a live person at the other end of the line. More recently, however, a shift in usage toward intentional messaging has occurred. Where there is no need for dialogue, voice messages can be recorded and sent quickly to an individual extension or distribution list.

Most major voicemail vendors have long provided the ability to transfer voicemail messages from one location to another over dedicated lines or the PSTN (public switched telephone network). For example, Avaya's Audix system can forward messages to another Audix server or to a different vendor's voicemail system using the AMIS (Audio Messaging Interchange Specification).

More recently, a new standard called VPIM (Voice Profile for Internet Messaging) has been developed, which allows voice messages to be packetized and sent over IP networks (or the public Internet). Most major voicemail vendors, including Avaya, Nortel, Siemens, and others, are implementing this standard into their voice messaging products. VPIM provides both economic and functional benefits:

• Conserves bandwidth. The message is packetized and compressed to one half its original size.

• Simplifies distribution. As more voicemail systems become VPIM compatible, distribution to multiple locations is easier.

• Improves efficiency of message broadcast. The older AMIS system sent messages one at a time, even if many users at a distant location were receiving the same message. VPIM sends a single message, which is then addressed to multiple recipients, resulting in both a quicker and more efficient (i.e., less bandwidth) transmission.

• Integrates easily with unified messaging. Sending and receiving voicemail messages in VPIM format is more straightforward, because the transmission is treated as a special, multimedia e-mail.

Exhibit 2 illustrates the use of VPIM for voicemail message transmission.

Exhibit 2: Transfer of Voicemail Messages Using VPIM Protocol

Virtual Private Network (VPN)

The term "virtual private network" has become closely linked with substitution of an IP-based public network (usually the Internet) for dedicated or leased facilities. Instead of leasing a T1 or Frame Relay circuit to link office A to a distant office B, an encrypted "tunnel" can be established across the Internet to securely transport data packets. Originally, carriers such as AT&T used the concept of VPN (called SDN by AT&T) to describe a logical private network for each customer using the service. The term "virtual" was used because the actual hardware, software, and circuits are shared among all the carrier's customers, but the end customer perceives the service as a dedicated facility.

VPNs reduce long-distance communications costs — particularly for international sites — by eliminating much of the IXC expense. However, there are start-up and maintenance charges that can make a VPN implementation uneconomical for certain volumes of traffic. Also, VPNs that use the public Internet are subject to the vagaries of events on the Net — congestion, irregular quality of service, etc.

Exhibit 3 shows a typical VPN configuration. The example shown is for data communications only. Although voice over the public Internet may yet have its day, currently the quality of service (QoS) on the Internet is not adequate for most enterprises. Voice-over-IP, using private transmission facilities with guaranteed QoS, is discussed in another section of this chapter.

Exhibit 3: VPN/Firewall Deployment with Security and Monitoring

Generally, most medium to large organizations that have multiple, dispersed sites can use VPN technology to supplement (rarely to completely eliminate) their existing wide area networks. The likelihood of a good fit increases dramatically if the organization incurs a large dialup (800 number) bill, typically associated with a RAS (remote access service) implementation. Indeed, organizations such as PricewaterhouseCoopers, having thousands of professionals on the road, have saved hundreds of thousands of dollars annually by sharply reducing long-distance dialup minutes.

When considering implementation of a VPN, there are a number of financial, business, and security issues to consider:

• Advantages:

  • Replace some dedicated lines, such as T1s, with transmission over the Internet (e.g., backup T1s could be eliminated). The organization must be aware of the caveats, such as the potential for Internet congestion and poor quality of service.

  • Eliminate some or most RAS dial-up charges. While ISPs may charge a per-hour charge for users tunneling through a VPN, those charges are significantly less than IXC per-minute charges. For example, a large organization might negotiate a $1-per-hour ISP connect time charge, whereas the same charge for an hour of toll-free dial-up could be $5.00.

  • Enable quick bandwidth increases by adding additional ports (compared to lead-times of two to eight weeks for new T1/T3 services).

  • Facilitate extranets for customers, suppliers, and partners, and provide additional E-commerce functions.

  • Make secure intranets available to field offices around the world (at a reasonable cost).

  • Provide high-speed services to telecommuters who have broadband access in the home/small office. For example, VPNs can operate over cable modem lines or DSL. With this capability, some jobs can be accomplished off site that might otherwise require office space/equipment.

  • Reduce management costs of a WAN by using a fully integrated, secure VPN solution, in contrast to the traditional plethora of network access gear.

  • Reduce the number of access lines for some field offices. If the office has a separate line for Internet access and data communications (e.g., for Frame Relay), VPN can eliminate one access line.

  • EDI (electronic data interchange) communications costs can be reduced by establishing an extranet using a VPN and eliminating use of a value-added network (VAN).

• Disadvantages/concerns:

  • VPNs are more complex to manage. Some organizations outsource the management of the VPN network.

  • VPN is not always the answer. For example, a small network with low bandwidth requirements may be better served via a Frame Relay solution (less expensive edge equipment, less maintenance).

  • The public Internet occasionally suffers congestion. Although this may someday change with the introduction of MLPS, ^[3] for the moment it is a significant concern for organizations that must have extremely high uptime. Some vendors offer fail-over capabilities that allow traffic to be sent over an alternative link (e.g., dial-up ISDN) if the Internet is congested.

  • The level of available VPN encryption, while certainly adequate for any domestic U.S. commercial needs, may not be available for some international traffic due to government restrictions. However, this may be changing, at least for some countries. France, for example, has long required that encryption be no stronger than that afforded by a 40-bit key. Recently, the maximum permitted length has been increased to 128 bits, a considerable increase in security levels.