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1、附录A：英文原文The Future of Wireless NetworkingWireless networking is becoming increasingly ubiquitous, on both the large and small scales. David Chisnall attempts to better Arthur C. Clarke at predicting where these technologies are heading.January 1, 2000a historic day. Telecom companies around the worl
2、d would simultaneously abolish long-distance calling charges, making every call a local call. At least, according to Arthur C. Clarke, writing around a decade earlier.In the real world, this didnt happen. Telephone companies still charge different amounts based on your distance from the other endpoi
3、nt of a call. It wasnt exactly unlike Sir Arthurs prediction, however. International calls Ive made in the past few years have cost me absolutely nothing beyond the fixed network connection rate I pay for a broadband connection. But their endpoints have been other devices connected to the Internet,
4、rather than the old telephone network. In practice, most of the cable between the two endpoints will be the same, irrespective of which logical network places the call. 1.The All-IP NetworkThe wired infrastructure in the UK (operated by BT) and the next-generation wireless telephone networks all hav
5、e one thing in common: They use IP internally and run telephone calls as Voice over IP (VoIP). My current phone supports UMTS, and is assigned a 10/8 IP address whenever I use it. This means that its behind a Network Address Translation (NAT) and therefore cannot receive inbound connections.The 10/8
6、 subnet is the largest private allocation. As a /8, it has 224a little under 17 millionunique addresses. This isnt a very large number in comparison to the number of devices connected to the mobile phone network, which is why mobile operators are likely to be among the first major deployments of IPv
7、6. With v6, a company (or even an individual) can easily get a /64, meaning that the first 64 bits identify the network and the last 64 bits identify the device. To put this into perspective, the company has enough address space for every valid IPv4 address to be a network the size of the Internet,
8、or for every person to have three billion devices on his or her network. More to the point, it allows every device to have its own IP address, and the routing tables to be sufficiently sparse that routing is cheap.One other advantage that IPv6 adds, of particular relevance in this arena, is Mobile I
9、Pv6, in which a device can change its location in the network and still be routable, without dropping existing connections. Moving between towers is generally handled lower down the protocol stack, but this new arrangement allows a phone to move between currently-separate networks while still mainta
10、ining connections, as long as both endpoints have IPv6 connectivity.An all-IP network emphasizes the distinction between selling access and selling servicesa distinction that mobile phone companies currently try to blur. When you make a telephone call, youre using their network, and youre also makin
11、g use of the peer agreements they have with other phone networks, while enjoying the use of their routing system.Mapping from telephone numbers is much less important than it used to be. I used to make telephone calls by a complicated process. First, I would look up a number in a paper directory or
12、a local cacheeither a personal address book or my brainand then enter this number on a dial (later, on a keypad). By contrast, now I just select the persons name from my address book and press call. A recent study claimed that peoples memories are getting worse because they cant remember their frien
13、ds phone numbers. For me, its not just that I dont remember my friends numbers anymoreI never knew them. In many cases, a friend sent me a vCard via email or Bluetooth, and I never looked at the number field in the first place. Already, the idea of calling a phone (rather than a person) seems faintl
14、y archaic.2.Connection MobilityOne of the less well-known of the 802.11 family of standards is 802.11r. The point of this standard is to make switching between wireless access points fast. The range of an 802.11 access point is typically only a few rooms if inside, or about a hundred meters when out
15、side. A person walking around may want to jump between a half-dozen access points in a few minutes. The 802.11r standard provides a mechanism for doing just that. If youve ever sat roughly an equal distance between two access points, you may have noticed that your connections periodically pause brie
16、fly as your networking stack decides to switch between the access points. The 802.11r standard improves this pause time, dropping the switching time down to well under a second. This change makes 802.11 feasible for mobile telephone use. In an area with a load of .11r-supporting access points, you can walk around while talking on the telephone, and not notice when your call jumps between those pointsjust as you dont notice now when your mobi
