The University of Pennsylvania's Online Computing Magazine

PENN PRINTOUT April 1993 - Volume 9:6

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Consumer guide to PennNet access: Cost advantage shifts to Ethernet

By Randall Couch

Change. Competition. Advancing technology. Now that "it's the economy, stupid" for universities as well as presidential candidates, the academic world is coping with these pressures at a much faster pace than it was even a year ago.

PennNet is at the focus of these forces. The traditional choice between asynchronous and Ethernet access must be made in a completely new context. And off-campus access is in the midst of sweeping changes, led by SLIP technology. The common element is the standard provided by the Internet Protocol (IP), part of the TCP/IP protocol suite used throughout the worldwide Internet. It's becoming clear that Ethernet and IP are where you want to be.

Consider: Within months, DCCS will stop adding new asynchronous connections for work groups in campus offices and labs. Over the next few years, all existing asynchronous connections will be converted to Ethernet. PennNet is now expanding the pool of high-speed modems to support off-campus access via Serial Line IP (SLIP). And beginning this year, ResNet, a five-year project to wire the dorms for data and video, will add some 8,000 new Ethernet/IP connections to PennNet--a number equal to the entire current PennNet population (see front cover).

This article is designed to help you understand and plan for the changes ahead. It presents a brief review of asynchronous and IP data communications, followed by a comparison of the costs and benefits of the two methods to the PennNet consumer. It concludes with a discussion of the trends affecting PennNet and their implications.

The bottom line is a strong statement of direction: PennNet is moving to IP. Have we got your attention? Good. Read on.

Asynchronous: point to point

Originally PennNet, designed in partnership with AT&T, emphasized only asynchronous service, presenting most users with a DIAL prompt. The term "asynchronous" describes a method of data transmission that results in certain characteristics, including moderate data transfer speed (up to 9600 bits, or about 960 characters, per second for most campus traffic). In this method a connection, or open path, is established between the sender and receiver. A series of intervening devices directs the data stream to the correct destination, much like a telephone switching system. Each data stream can take only one path, and if one of the intermediate devices fails, the connection "goes dead" and the exchange cannot take place.

The asynchronous model was developed for linking character-based terminals to host computers. Today, most PennNet users with asynchronous connections are linking personal computers to PennNet devices called terminal servers (the annex prompt). But their communication is still limited to alphanumeric characters and symbols, and their view of the wider network is framed by the host computer they reach from the DIAL or annex prompt. Asynchronous connections to PennNet can be made through a wall outlet on campus, by dialing in to a pool of modems, or through the PennNet Residential service in West Philadelphia.

Ethernet/IP: peer to peer

As the cost of Ethernet devices came down in the late 1980s, more hosts and personal computers were connected directly to PennNet's IP network. While asynchronous access requires a single connection to be maintained as long as data is being exchanged, the IP network is "connection-less." Each device on it is a peer that can communicate with many other peers at the same time. This flexibility is possible because each unit of data ("packet") transmitted by the sender carries with it the address of its intended recipient. Data can take one of many paths from sender to receiver; network hardware forwards the packets by the most efficient route at the time. If one part of the network fails, or if traffic is heavy in an area, the exchange can still take place by a different route through the "web."

The IP network operates at up to 10 megabits, or about one million characters, per second. The vast majority of traffic between host computers on PennNet is now IP. IP access is provided on campus through individual Ethernet wall outlets or through gateway devices. Off-campus access (at somewhat lower speeds) requires Serial Line IP (SLIP) software and either a high-speed dial-up modem or PennNet Residential service (for West Philadelphia residents).

What's in it for me?

Those who need PennNet access from campus have long had a choice between asynchronous network connections and direct access to the IP network via the heretofore more expensive Ethernet connections. This year PennNet's pricing reverses that cost relationship, reflecting the changing market in these services (see chart opposite). Equally important, the greater potential of IP technology is at last being realized in useful services that don't require an engineering degree to understand. Let's look at some of the benefits of IP networking today.

The most obvious advantage of direct IP access is speed. "But," you may say, "I'm an occasional network user. Do I need something fast?" Well, the most important thing about speed is not so obvious. It's not just that more characters scroll across your screen in a minute. The high speed of the IP protocols behind the scenes makes a difference in the kinds of things you can do. Direct IP access transforms your view of the net-work, since you are no longer bound by the limitations of terminal-host interaction. Some examples:

Point and click. Windows fans in great numbers have now joined Macintosh users in the realization that many tasks are easier to learn and easier to do with a graphical interface. In the growing number of IP client/server applications, direct manipulation of objects on your screen gets results from a remote computer. And using your com-puter's graphical interface, you can cut and paste between several network sessions running con-currently.

FTP. High-speed file transfer means that large files--long texts, images, business data--which used to take prohibitively long to transmit, can be exchanged routinely. The proliferation of easy-to-use FTP client software like Fetch for the Macintosh, along with finding aids like Gopher, Archie, WAIS, and WWW, have spurred custodians of information to start filling public FTP archives at a rapid rate. And now it's not just abstracts and bibliographical citations that are available, but full texts--often with full-text searching tools--images, and sounds. Some of these resources are accessible through asynchronous connections, if you have an account on a suitably equipped host computer. But you won't be able to match the smooth integration into your personal tools--word processor, spreadsheet, or authoring program-- available via a direct IP connection.

Two samples: The Clinton administration has announced its intention to make the full text of all important speeches and policy announcements available by network as they are released. The Library of Congress's spectacular exhibition of treasures from the Vatican Library can be experienced in a "network version," consisting of high-quality digitized images of the objects with accompanying text descriptions, accessible via FTP. At Penn, some of these images are available on the Gopher server maintained by the Center for the Computer Analysis of Texts (CCAT).

Volume distribution. The fact that ordinary people can now find their way around the Internet presents repositories with new opportunities to economize by sharing resources. Libraries, for example, have tried to minimize expensive duplication of print holdings by agreeing to specialize and exchange material. As more information is disseminated in digital form, this trend is accelerating for both print and electronic formats. Increasingly, the information you need, whether administrative or scholarly, will be distributed among several sites. It may not be at Penn--or even in the U.S.--at all. The proposed National Research and Education Network will only speed the process.

Consistency in remote access. Until now, PennNet users who work often from home may have avoided software tools requiring office IP connections because equivalent access was not available from home. The advent of SLIP and more stable high-speed modems means that you can use most IP functions whether you're working on campus or dialing in from home. Notebook computers can likewise be equipped for IP access. As more and more data can be stored on, and retrieved from, servers, the Internet becomes an extension of your (overcrowded) hard drive. Computer users can travel lighter!

Ethernet for LANs

In addition to providing direct access to TCP/IP services, Ethernet connections to PennNet can be used to set up AppleTalk or Novell local area networks within buildings using PennNet wiring. To extend these LANs across campus, the proprietary protocols can be "encapsulated" in IP for transport across the PennNet backbone.

Looking ahead

The Office of Information Systems and Computing takes very seriously President Hackney's charge to reduce administrative costs

For technical reasons, asynchronous communication can be more expensive to support than IP once a threshold number of Ethernet/IP users has been reached. The connection-based nature of asynchronous communications means that for each user, dedicated pieces of network hardware must stay tied up for the duration of a session. Maintaining the equipment that provides the DIAL prompt (the ISN) and providing adequate terminal server capacity represent large fixed costs. The "connectionless" nature of IP, as we have seen, permits a much more efficient use of network hardware.

In addition, advances in transport media (such as the 10BaseT standard, which allows less expensive twisted-pair copper wires to be used instead of coaxial cable for Ethernet installations) are providing alternatives that can reduce wiring costs in appropriate circumstances. And organizations such as University Management Information Services anticipate significant cost savings from the eventual elimination of asynchronous interfaces to administrative applications.

The implications of such facts are straightforward: The fixed costs of supporting asynchronous communication are rising as the technology ages. As fewer people participate, the unit cost increases rapidly. Likewise, as more people adopt the maturing IP service, its unit cost drops. In the current economic climate, Penn cannot afford to subsidize a declining population of asynchronous users. This year's PennNet price structure reflects this, and the disparity in favor of IP will widen in the future.

More than that, the time will soon come when it no longer makes economic sense to continue to offer direct asynchronous connections at all. The service will have to be phased out, and the transition to IP negotiated. The question is not whether PennNet will have to go all-IP, but when. Bear this in mind as you make your computing plans and budgets for the future.

The reasons to embrace Ethernet and IP networking are not primarily defensive, though. Many of the finest new IP tools--Fetch, Gopher, WAIS, WWW--are public-domain products, creatures of the Internet. This of course saves Penn and its users money, but it also represents the best traditions of cooperation and open exchange in the research community. (Though corporate networks are rapidly moving to IP as well.)

As the volume and complexity of data increase, a new "basic platform" for individual computing is emerging: a robust workstation, possibly mobile, with a graphical interface and IP access. Such a platform can make use of standard tools like FTP, the library community's Z39.50 document retrieval protocol, and other emerging protocols for network navigation. Such a platform should also be ready for tomorrow's client/server-based administrative systems.

So if you thought Ethernet was too expensive and IP networking was too complicated, take another look. They're Penn's strategic direction, they're where education, government, and industry are going, and they're getting cheaper all the time.

[Ed. note: For additional information on some of the topics mentioned in this article, refer to previous issues of Penn Printout: Network navigation tools (Gopher, WAIS, etc.), February 1993, page 1; SLIP, November 1992, page 8; PennNet Residential, September 1992, page 15. All are posted to PennInfo under computing/penn printout.]


What hardware and software do you need to use Ethernet/IP services on PennNet?

On campus:


  • Transceiver (for a Mac with a built-in Ethernet interface) FriendlyNet TN: about $70.

  • Add-on interface card/EtherTalk software (Asante, model varies with Mac type)
    -internal: about $150 (not yet available for PowerBooks).
    -external (SCSI): under $300 (PowerBook model to be specified.
(NOTE: Users connecting to 10BaseT-wired outlets, such as those in the wired residence halls, may require different models.)


  • Gateway device (Cayman Gatorbox CS): about $1700; connects up to 32 users via LocalTalk cabling to one PennNet Ethernet outlet, provides LocalTalk routing and IP access (speed limited by LocalTalk media).


  • MacTCP software configured for your assigned IP address or for SLIP (Penn Mac networking distribution disk, available from your network administrator or CRC without charge).
  • Public-domain TCP/IP applications (available on Penn server
(NOTE: Users of MicroPhone Pro may wish to purchase its Telnet tool instead of using the public-domain Telnet application.)

IBM PC/compatibles:

  • Add-on interface card
    -internal: about $120-$210 (SMC, Standard Micro-systems, formerly Western Digital, model varies with PC type).
    -external: about $200-$400 (parallel port adapter).
    (NOTE: Users connecting to 10BaseT-wired outlets, such as those in the wired residence halls, may require different models.)

  • PC/TCP for DOS (FTP Software Inc.'s TCP/IP package; includes drivers and basic applications): Contact PennNet Services Center at 898-8171 or psc@dccs for pricing.
    Drivers must be configured with IP address; consult your network administrator or PennNet Services Center.

From LANs:

  • IBM PC/compatible computers, whether standalone or part of a Novell network, require Ethernet interface hardware as above. Each computer can have its own PennNet Ethernet outlet or several computers may be daisy chained from one outlet. LAN Workplace for DOS software provides TCP/IP drivers and the ability to encap- sulate Novell's protocol (IPX) in IP to extend LANs across the PennNet backbone: $75 + $10/user; contact PennNet Services Center at 898-8171 or psc@dccs for details.

  • Macintoshes in AppleTalk LANs linked by Apple's LocalTalk cabling can at the same time have Ethernet/IP access as standalone or daisychained workstations using the hardware and software described earlier; or, they can obtain Ethernet/IP access via a gateway device. A third configuration uses individual Ethernet outlets and interface cards to send both AppleTalk (within a building) and IP data over PennNet wiring. To extend an AppleTalk LAN of this type across buildings requires a gateway device.

From off campus:

Serial Line IP (SLIP):

  • High-speed modem (Practical Peripherals PM14400 FXSA): under $400; less expensive models will be qualified for PennNet access in the future.

  • PennNet Residential service: about $325 + $22.50/ month; contact PennNet Services Center at 898-8171 or psc@dccs for details.

  • SLIP software:
    For Macs: MacSLIP by Hyde Park Software and a version of the TCP/IP driver configured for SLIP is now included in the Penn Mac networking distribution available from the CRC without charge.
    For IBM PC/compatibles: A SLIP module is now included in FTP software's PC/TCP package described earlier; contact PennNet Services Center at 898-8171 or psc@dccs for pricing.

RANDALL COUCH is a Senior Technical Writer for the ISC Communications Group.