Over the years, memory, processor power, screens and wireless connectivity have become more robust, and the developer community has been busy producing many great applications that take advantage of all of these attributes. However, since there is now more power and real estate inside wireless devices and wireless networks are faster, the applications have been growing in size and their reliance on the wireless link has increased.
The assumption in the developer world and within the industry is that we have plenty of bandwidth for wireless connectivity and lots of speed. As a result, applications have become “chatty” across these connections, sending and receiving more data than ever before. IP Transport, which is where wireless broadband is heading with WiMAX and LTE, is not a wireless-friendly transport layer in and of itself. TCP/IP consists of two important layers in the Internet Protocol suite. The transport layer does not necessarily have to be TCP, it can be UDP and other protocols, some of which are more wireless-friendly. Even so, by and large, we start with a fairly inefficient method of transport as a basis for wireless broadband.
If we add security in the form of a Virtual Private Network and/or encryption, we are introducing additional overhead to the system, which reduces the amount of available bandwidth for the applications and data flow. Therefore, it is important to understand that, for a number of reasons, it is not safe to assume that every connection will be running at megabit speeds.
Even though we have 4G technology being deployed, these systems are in the process of being built and most networks are still made up of a combination of two or even three generations of wireless technologies. Second-generation systems (GSM and CDMA 1X) offer data speeds of up to about 120 Kbps downlink and slower uplink speeds. Third-generation systems (UMTS/HSPA and CDMA EV-DO) offer data speeds generally higher than 1 Mbps down and again, slower on the uplink side, and some of the newest releases of these systems offer data speeds in the range of 5 Mbps and higher. WiMAX delivers between 1 and 4 Mbps for the downlink, again slower on the uplink, and while we are not 100 percent certain of LTE’s capabilities, which will depend on the amount of spectrum in use per cell site, Verizon’s statements indicate that we can expect 5 Mbps to 12 Mbps on the downlink and between 1.25 Mbps and 3 Mbps on the uplink. While the industry as a whole believes Verizon’s stated speeds are conservative, in my research and discussions with the LTE vendor community, there is consensus that these are solid average speeds.
One more bit of information on data speeds is that even when connected to a WiFi hotspot capable of 5 Mbps or much more, such speeds will not always be available since the limiting factor for hotspots is how much bandwidth is available for the backhaul from the access point to the Internet. Most access points use T1 wired connections with a maximum data throughput of 1.544 Mbps. Thus, even with an 802.11 N access point, if the transport is a T1 line, the total bandwidth of the system will be limited to 1.544 Mbps.
Now that we know the data speeds we have to work with, there is another dimension to bandwidth that will further impact these speeds. All wireless systems provide bandwidth that is shared among users in a given area. In the case of a WiFi access point connected with a T1 line with a total available bandwidth of 1.544 Mbps, if there is a single user, that user gets all of the bandwidth all of the time. However, if there are ten users within range of the access point, the ten users share the bandwidth. This does not mean that each user only has one-tenth of the available bandwidth–the amount of bandwidth depends on the type of application or data that is being sent and received. If all ten users are emailing and surfing the Web, the perceived results will still be fast broadband connections. However, if five of the users are streaming video to their devices, the perceived speed for everyone will be much less, and those who come into the access point later will find it to be really slow for them.
This holds true for wide-area wireless systems as well. Each cell site is usually divided into three segments, each covering an area of 120 degrees from the site. Within this cell sector, the total available bandwidth is shared, and the further a user is from the center of the cell sector, the slower their data connection will be. This is one reason iPhone users were experiencing slow data rates in major urban areas; there were too many of them using too much data within a given cell sector. No matter how robust a network is, or how many cell sites are built, the result will be the same. If there are too many people within a given cell sector, data speeds will suffer.
Even though we have access to data rates of 1 Mbps or more, it makes sense to build applications that will perform well at the slower speeds. If you build an app that performs well on a 2G system, it will seem to scream on a 4G system and your customers will be happy. However, if you build an application that requires data speeds of 1 Mbps or more to perform well, a number of your customers will be disappointed.
One final point is that by building smarter and bandwidth-aware applications, you will not only provide your customers with a better user experience, you will help reduce the overall data usage within a given cell sector or hotspot location and this will result in more customers being able to access information when they want and need it while mobile.
Andrew M. Seybold is an authority on technology and trends shaping the world of wireless mobility. A respected analyst, consultant, commentator, author and active participant in industry trade organizations, his views have influenced strategies and shaped initiatives for telecom, mobile computing and wireless industry leaders worldwide. On Oct. 5, 2010 at the CTIA Enterprise & Applications conference, Seybold will lead the Andrew Seybold Wireless University seminar examining the elements of wireless now and into the future: technologies, devices, applications and content. For more information click here.
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