Four steps to more effective network services - Page 4

By Paul Strauss | Posted Sep 1, 1999
Page 4 of 4   |  Back to Page 1
Print ArticleEmail Article
  • Share on Facebook
  • Share on Twitter
  • Share on LinkedIn


There are plenty of misleading calculations showing that secure Internet data networks, known as virtual private networks (VPNs), are cheaper than ATM or frame relay networks. (VPNs are considered secure because they use a form of encryption known as "tunneling," but this only prevents outsiders from reading the communications; it doesn't tunnel packets through the network in the sense of giving them priority or additional robustness.) The rationale for asserting that VPNs are cheaper than frame relay or ATM is that with frame relay and ATM services, you pay for access and then you pay for the long-distance service, usually several hundreds of dollars a month per permanent virtual circuit (PVC). With a VPN, you pay only for access; the Internet backbone is said to be free.

This is not true, of course. Nothing is really free. If you pay for Internet access, you pay for the wide area backbone services used. If they are congested and must be upgraded, the carrier will pass the charge on to you. In fact, Internet backbones are badly congested and often suffer from extensive packet loss.

Also, VPNs are slower, less robust, and more vulnerable than other data services (see text box, "The downside of virtual private networks"). So, although Internet VPNs are cheaper than other data services, in terms of their ability to deliver data, they are often less cost-effective.

There are many interesting technologies proposed to improve the Internet's congestion and increase bandwidth. One of the most promising is Multiprotocol Label Switching (MPLS), which allows carriers to toggle between their current networks--based only on the Internet Protocol--and ATM backbones, and it allows large IP backbones to have better flow control. However, MPLS is not likely to appear for a year at least.

In short, VPNs appear attractive, but in most cases they're not as cost-effective as frame relay or other network services. There are a number of important exceptions, however. An Internet VPN is an attractive option for a corporation that must put together a truly global network but doesn't require high-speed communications to all points. Leased lines and packet services often are highly expensive in developing countries.

A second attractive use for a VPN is to replace modem banks and other dial-in equipment, such as remote-access servers. In this case, users dial in to the Internet and access the corporate VPN by giving passwords. This approach is usually much cheaper than having to maintain multiple telephone lines for dial-in modems, and it eliminates the often heavy expense of maintaining staff who are specialists in modem access. //

Paul Strauss is an independent networking writer and consultant who formerly worked as a senior editor with Datamation and held various editorial positions at Network World and Data Communications.


A brief history of networking services

First, there was Samuel Morse. Actually, first there were smoke signals. Then there was Samuel Morse.

Electronic networking services date to Morse's telegraph in the 1840s. The cost was horrendous. The first messages sent by trans-Atlantic cable in 1866 cost $150 in greenbacks (or $100 in gold) for 20 words!

Not many organizations use telegraph any more, but some financial-services companies still use its successor, telex, for certain legal purposes, according to Unitel (http://www.unitel.nl), supplier of telex hardware and software. Users number 1 million and are concentrated in the banking and shipping industries, Unitel says.

(The telegraph's great-great grandchild, e-mail, emerged as a popular technology in the 1980s, initially as a paid service offered by carriers and later as a mere capability of an Internet service or a feature of network software.)

The first of the networking services to affect today's data networks emerged during World War II. A digital circuit was used to make encrypted trans-Atlantic telephone calls between Winston Churchill and Franklin D. Roosevelt. But the earliest computer data circuits, in the 1960s, didn't use digital circuits; they used analog circuits that transmitted data at such breakneck speeds as 1.2 kilobits a second (some of today's Internet backbones are running at 2.4 gigabits a second, about two million times faster).

Switching over to digital

Throughout the 1960s and 1970s, telephone carriers transformed their own networks to digital circuits, but carriers only began selling digital circuits to corporate users in the late 1970s. The first such digital circuits, under the AT&T brand name Digital Dataphone Service (DDS), were sold at the rated speeds of 4.8Kbps and 9.6Kbps.

Although telecommunications competition did not emerge until the Modified Final Judgment that broke up AT&T in 1985, data-network professionals by the late 1970s were already conducting cost/benefit comparisons among leased-line options. Leased voice lines, known as "tie lines," had none of the frequency-limiting factors of data services, and so at times they could carry more information at a lower cost than data services. Tie lines had broader bandwidth than data circuits, but they also had relatively poor sound quality. Rated analog data circuits were provided on "groomed circuits," in most cases giving higher quality transmissions. They allowed more data to be carried because of fewer retransmissions.

Soon there were other quality considerations. For a time, there were both analog 4.8Kbps circuits and digital 4.8Kbps circuits. The latter were considerably more expensive, but the quality was higher. Many corporations didn't have the opportunity to choose, however, because digital leased-line services were unable to emulate the "multidrop" analog (hierarchical) configurations that most mainframe networks had installed.

By the mid-1980s, AT&T was carrying its analog leased-line circuits on digital circuits, improving the quality of "analog" so much that in many cases it appeared a better buy than digital. That perception faded quickly when some network specialists realized that AT&T had placed no bandwidth restrictions on its 4.8Kbps digital circuits--meaning that they were really 9.6Kbps digital circuits!

Analog leased lines were multidropped, meaning they were capable of handling many points. But today's digital leased lines run only from Point A to Point B. Connecting more points requires multiplexing technology and additional leased lines. Also, leased lines are expensive, especially if they're not in constant use.

The Internet: the first packet service

Packet services addressed these problems. The first packet service was the Internet, but in the beginning the Internet was limited to government agencies and universities. Innovative carriers created Telenet and Tymnet, now known as X.25 services. There are plenty of X.25 services left in the world. Sprint, for example, continues to run Tymnet under the name SprintNet.

Packet services are merely more efficient ways of using circuits. They often are cheaper to the end user because a carrier can aggregate packets from various users on the same circuits. For a carrier to send packets from Atlanta to Chicago requires an underlying circuit. Companies that access packet services still must do so over circuits, usually leased lines, although X.25 and some frame relay services allow dial-in connections.

Because X.25 services are charged on the basis of packets received accurately, the carriers went to great lengths to do error checking on each packet at each relay point. This turned out to reduce the total bandwidth of the network and impose high latency.

In some ways X.25 remains more mature and flexible than later technologies. Here are a few examples: X.25 networks interface between carriers, much as Internet carriers interface; users can easily dial in to X.25 services, where dial-in is just emerging with frame relay; and X.25 networks are often value-added services, meaning that the carriers will do other things besides transport packets--such as translate between protocols.

However, by the mid-1980s X.25 was considered a slow network transport protocol, so the telecommunications standards bodies created frame relay, a packet format that allows for faster transmissions because it doesn't require error checking at each switch. X.25 is no longer a popular service in the United States, while frame relay and ATM are soaring.

ATM is one of the more misleading names in networking. Many people are surprised to hear that it's not asynchronous. The name comes from its ability to carry packet data, which is asynchronous because packets vary in length. All ATM transmissions are in the form of 53-byte cells, meaning that switches can determine network timing from the cells and the specified intervals between them. This is the definition of synchronous communications.

To carry both voice and data, and potentially such exotic applications as two-way television, ATM had to be synchronous. Unfortunately, like ISDN--a complex circuit-switching capability--ATM offers too many capabilities to be used in all the ways planned.

The Internet turns 30

Everyone tends to think of the Internet as new. Actually, it will be 30 years old in 1999. For some reason, telecommunications carriers regard the Internet as a very simple network. The Internet was designed to be so smart that it could continue to function even without any humans left alive.

Like the digital circuit, the Internet--originally called ARPANET--was born out of war, in this case the Cold War. It was, in a sense, the original doomsday machine, since it was designed to ensure that nothing could prevent the command "shoot the missile" from getting through. Over the years, the Internet has been much changed from its original technology (the original idea was that no packets could be dropped; now packet drop rates of 10% are normal). But it's still the same self-routing network as ARPANET.

The big change came in 1995, when the Internet was thrown open to commercial users. Since then the aggregate bandwidth of all Internet carriers is thought to have increased by about 10 times. The Internet is largely a Web-surfing phenomenon these days, with some 58 million North American adults regularly on line, according to a CommerceNet/Nielsen Media Research study in late 1998. This indicates a growth rate of about 2.5% a month, or 30% annually. Outside North America, there are thought to be around 100 million regular Internet users, a number that is increasing at a rate of nearly 100% per year.
--Paul Strauss

The downside of virtual private networks

Virtual private networks (VPNs)--data networks that use the Internet and encryption--can be less expensive than other data services. But there's a downside. VPNs are also:

 ...slower in terms of throughput and latency (until a new standard is commonly used, encrypted LANs cannot use the data-compression features of modems);

 ...less robust in general (although AT&T's frame relay collapse shows that disasters can happen to any data service); and

 ...vulnerable to hackers and other security problems, hence requiring expenditure for security equipment and security staff.

Comment and Contribute
(Maximum characters: 1200). You have
characters left.
Get the Latest Scoop with Enterprise Networking Planet Newsletter