OPENING THE DOOR TO ISDN

With service areas expanding and equipment costs diminishing, ISDN is finally becoming a viable choice for high-speed data communications. We set out to see how PC interface products stacked up against one another. We looked at products from 3Com Corp. (acquired with its purchase of AccessWorks Communications), Digi International Inc. (formerly Digiboard), IBM and ISDNtek, Inc.

Our tests focused on using ISDN to access the Internet, an increasingly popular practice. For the most part, we found the performance of our test products comparable. Where the products differ is in their choices of ISDN, hardware and software interfaces.

The 3Com Impact was the only external product used in this test. It employs an RS-232 interface and supports the conversion of asynchronous Point-to-Point Protocol on the serial port to synchronous PPP on the ISDN line.

The other three products are all Industry Standard Architecture (ISA) bus internal cards. IBM's WaveRunner is a full-size card that emulates a serial port and has software that converts Serial Line Internet Protocol (SLIP) from the PC to synchronous PPP on the ISDN line. Digi International's DataFire uses a Network Driver Interface Specification (NDIS) emulator that makes DataFire look like an Ethernet interface card. ISDNtek's CyberSpace Internet card supports NetManage, Inc.'s Win-ISDN application program interface (API). DataFire and CyberSpace Internet are both half-size cards.

Three of the products tested for this review cost less than $600, including all the accessories you need for a workable configuration. IBMs WaveRunner costs close to $700 as a complete package, but it also acts as a V.32bis modem over an ISDN line. While these products are not inexpensive, they do make ISDN affordable for those who need its enhanced speed.

ISDN BRI is delivered over a typical twisted-pair local loop. It is connected to a network termination device called NT1. NT1 has a two-wire interface to the network and a four-wire interface for the inside wiring.

The two-wire interface be-tween NT1 and the network is called the U interface. The four-wire interface to the inside wiring is called the S/T interface.

The street price of NT1 starts at $150, which must be added to the price of an S/T interface product for a complete configuration.

ISDN is being widely deployed just as interest in the Internet is exploding. Two of these products - ISDNtek's CyberSpace Internet and the 3Com's Impact - were introduced specifically for the Internet market. The other two manufacturers in the test - IBM and Digi International - are well aware of the potential for ISDN access to the Internet and have targeted it for their products, as well.

Impact

The 3Com Impact ISDN External Digital Modem (originally known as the AccessWorks QuickAccess Remote) connects to a computer's serial port and includes an RJ-11 port for voice communications using an ordinary analog telephone.

It has a U interface, so an NT1 is not required; consequently, Impact is the only one of these products that can be used with a variety of computers, including a PC, Macintosh or any other with a serial interface. To support ISDN speeds, users need a serial port with a 16550 UART on their desktop box.

Impact is quick and easy to set up and install. It comes with a DOS utility that configures the ISDN parameters. All of its configuration parameters, including those set by the DOS utility, can be viewed and modified using AT commands through a terminal emulator.

We used NetManage's Internet Chameleon configured for PPP on a serial port to access the Internet in our tests. It required a phone call to 3Com's technical support staff to find out how to change NetManage's SLIP.INI to get Internet Chameleon and Impact to work together.

The Windows 3.1 communications port drivers cannot support ISDN speeds, so Impact requires Pacific CommWare's TurboCom/2 communications drivers, which are shipped with the 3Com product. Impact uses NetManage connection profiles, which contain all of the required parameters.

While Impact was easy to install and set up, we had a lot of trouble getting it to work. At first, we could not get it to work at 57.6K bit/sec. We then switched from COM2 to COM1 so we could use the cable that came with Impact. At that point, things started working, but we were still unable to get Impact to work at 115.2K bit/sec. 3Com's engineers say thet were mystified by this be cause Impact worked fine in their labs.

After checking with Toptek, which provided the computer we were using for the tests, we found that the I/O board had an ISA bus interface and was being used to support the diskette and the disk drives in this system. The specifications for this board stated that it is limited to 57.6K bit/sec, even though it has a 16550 UART.

After installing a new I/O board that supported two serial and two parallel interfaces, we were able to get Impact to work fine at 115.2K bit/sec. The lesson here is that all 16550 boards are not created equal; it is important to ensure that the serial port is able to support these high speeds.

DataFire

Digi International's DataFire is a solid performer, but it requires a lot of manual configuration. It has a U interface, so it does not require an NT1.

The DataFire uses an NDIS or Open Datalink Interface (ODI) driver that makes it appear as an Ethernet network interface card (NIC) to application software. The driver is loaded as terminate and stay resident (TSR) and leaves only about 570K bytes of DOS memory available after it is loaded. This could be a problem, especially on multimedia machines that require CD-ROM and sound card drivers.

We used NetManage's Chameleon TCP/IP software package configured to support an Ethernet connection for our DataFire tests.

Installing DataFire required a lot of manual effort. We had to manually modify the CONFIG.SYS and the AUTOEXEC.BAT to load the required drivers, and manually create a PROTOCOL.INI file to bind Digi International's drivers to the NDIS driver.

DataFire comes with a DOS installation utility that sets up both the ISDN and the IP parameters, plus another DOS utility to use in setup and to make connections. This second utility is command-oriented and is not particularly user-friendly. It took several calls to Digi International's support line before we got the firm's product to connect to the Internet. We solved the problem when we talked to another DataFire user who helped us find the right combination of host and gateway IP addresses.

Users can automate making or breaking connections by creating a Windows program information file and creating an icon for it. Again, this is something the user has to set up manually.

The card includes switches that are used to set up DataFire's I/O port address. This was a little confusing because the diagram in the manual did not match the board we received.

Digi International has recognized these problems and plans to reduce the amount of memory its drivers use.

Employing DataFire for Internet access with PPP really does not show off its full power. But when DataFire is used with other Digi International products in a communications server for remote network access, then users really see fireworks. First of all, you can use Digi International's drivers that support their proprietary protocols, rather than PPP, and save 40K bytes of DOS memory. You can also use both B channels and on-demand connection management, which should significantly improve performance and automate connections.

Digi International says that Microsoft Corp. was planning to start shipping DataFire drivers along with Windows NT by the time this article hits the streets. This should make DataFire an attractive product under Windows NT.

WaveRunner

IBM's WaveRunner Digital Modem is a solid performer in a full-size ISA bus card. It has an S/T interface and includes V.32bis and fax modem emulation. WaveRunner also comes in a MicroChannel Architecture version. You need to connect via an NT1, which adds at least $150 for a complete configuration.

WaveRunner supports a variety of connection options that include V.32bis modem emulation and the V.120 rate adaptation protocol.

WaveRunner emulates a serial port on the PC and, like 3Com's Impact, requires loading Pacific CommWare's TurboCom/2 serial port drivers. We used the Internet Chameleon configured for a SLIP connection on a serial port. IBM's converter handles the PPP nego- tiation and takes the SLIP packets from NetManage and converts them to synchronous PPP. The board has three switch blocks that are used to change the communications port and direct memory access parameters.

The modem emulation makes it easy to place a call to an ordinary telephone to test the ISDN line during installation.

Using WaveRunner was a little complex because it was necessary to start the ISDN Port Manager program and the ISDN TCP/IP SLIP-to-PPP converter before using NetManage's Internet Chameleon.

We used IBM's Version 1.0 software, instead of 2.0, along with a beta SLIP-to-PPP converter that we downloaded from IBM's bulletin board for our tests. IBM's Version 2.0 software adds V.42 compression and Class 2 Group III fax support to its modem emulation, but it also adds an NDIS driver interface, rather than the serial interface emulation used by the software that we tested. This new NDIS driver software supports two B channels for 128K bit/sec communication using Combinet, Inc.'s proprietary protocols.

These new NDIS drivers allow WaveRunner to interoperate with Combinet products as well as others' products that interoperate with Combinet. However, the SLIP-to-PPP converter that we used in our testing requires the serial port emulation in IBM's Version 1.0 software. It is not compatible with Version 2.0. By the time this article appears, IBM should have released a new version of its software that supports NetManage's WinISDN API. This new WinISDN API support will handle PPP using NetManage's Internet Chameleon in the same manner as described for the ISDNtek board below.

IBM also has recently introduced WaveRunner PCMCIA ISDN Or Analog Modem with a list price of $595. It includes all of the ISDN capabilities of the WaveRunner Digital Modem ISA card, including its ability to support V.32bis and fax modem emulation over an ISDN line. In addition, an ordinary analog telephone line can be plugged into the PCMCIA card, enabling it to act as a V.32bis modem, with an upgrade to V.34 scheduled for July.

CyberSpace Internet

ISDNteks CyberSpace Internet was our slowest performer. It has an S/T interface, so it requires an NT1, which adds $150 to its base price.

CyberSpace Internet comes with a setup utility that records the hardware configuration, enters the ISDN parameters and verifies the operation of the ISDN interface by making a voice or data test call. A successful voice call goes a long way to verifying that the board and the ISDN line are working well together.

This product requires a copy of NetManages Internet Chameleon as its TCP/IP stack. Internet Chameleon uses the WinISDN API as its interface to CyberSpace Internet.

The WinISDN API was developed by NetManage of Cupertino, Calif. It is supported in the firm's Internet Chameleon TCP/IP software package that supports both modem and ISDN dial-up Internet access.

We had to copy the ISDNtek software into the same directory as Internet Chameleon because the ISDNtek setup program uses an ISDN.INI file to communicate configuration information to Internet Chameleon. It was also necessary to manually modify the SYSTEM.INI and the CONFIG.SYS in order to reserve 16K bytes needed by the ISDNtek card.

Internet Chameleon is configured to an ISDN interface that uses the WinISDN API to pass data through the ISDNtek card. The card itself has switches that we had to set to specify the address of the memory area used by the board. It also has a jumper that we had to set to assign an interrupt request to the board.

ISDNtek's board had much lower throughput when uploading to the Internet than the other products. NetManage ac-knowledged that this was a problem in its initial release of Internet Chameleon with the WinISDN API support.

According to the company, it has recognized this problem and plans to fix it in its next release during the second quarter. Since IBM also supports the Win-ISDN API, this improvement in Internet Chameleon will affect the performance of the new WaveRunner release as well as the ISDNtek board.

Performance

We measured the time it took to establish an ISDN connection to the Internet. An Internet connection comprises two phases: The first is the ISDN connection itself; the second is the PPP negotiation required to set up IP communications.

The Internet Engineering Task Force, which defines the TCP/IP standards, has defined techniques for sending TCP/IP and other networking protocols over an ISDN line based on PPP. We used PPP in these tests to connect to the Internet over a single ISDN B channel.

PPP, as commonly implemented today, does not support the aggregation of B channels for speeds higher than 64K bit/sec. The IETF issued The PPP-Multilink Protocol (MP) (RFC 1717) last November. The PPP-MP supports PPP over two or more B channels to take advantage of the full 128K bit/sec capability available from a BRI. PPP-MP implementations are just starting to appear, and interoperability issues are being worked out.

Digi Internationals DataFire in this test includes an implementation of PPP-MP. We were unable to test the PPP-MP implementation in DataFire because of interoperability problems with our Ascend Communications, Inc. Pipeline 50 ISDN router and the ISDN router at InterNex that we used in our tests.

Both the Digi International and the ISDNtek cards had ISDN connection times of less than 6 seconds (see Figure 1). 3Coms Impact had an ISDN connection time of nearly 9 seconds. The difference is probably due to the AT command processing required by Impact.

DataFire had a PPP negotiation time of 3 seconds, giving it a total Internet connection time of just under 9 seconds. The ISDNtek PPP negotiation took just over 7 seconds, which gave a total connection time of 13 seconds. The PPP negotiation is handled by Internet Chameleon software for both CyberSpace Internet and Impact. The Impact PPP negotiation took a little over 5 seconds, bringing its total negotiation to 14 seconds.

It was impossible to separate the ISDN connection time and the PPP negotiation time on the IBM WaveRunner; it had a total connection time of 12 seconds. WaveRunner rather anachronistically pulses out the ISDN number using dual-tone multifre- quency through the speaker on the board. It appeared that this extended the connection time by a couple of seconds.

On file transfers of a compressed and uncompressed Excel worksheet, 3Com's Impact and Digi International's DataFire had nearly identical performance, achieving an average throughput of 52K and 50K bit/sec, respectively (see Figure 2). IBM's WaveRunner was about 90% as fast, with average throughput of 46K bit/sec. ISDNtek's CyberSpace Internet was fourth in performance with an average throughput of 40K bit/sec.

We also tested what happens when the ISDN parameters are not entered correctly into each of these products. Most ISDN configurations and all National ISDN configurations require the entry of a Service Profile ID (SPID). SPID usually consists of the ISDN line's 10-digit phone number plus a suffix of at least one additional digit. Entering the SPID incorrectly is one of the most common errors made when installing an ISDN product.

IBM's WaveRunner did the best job of reporting on connection status and came back with a diagnostic stating that the SPID is incorrect.

Digi International's DataFire shows codes in the upper right-hand corner of a DOS screen that gives the ISDN line's status. This code is very useful but cryptic for those unfamiliar with ISDN protocols. If it sits in the "Q.921 established" state for a long time and does not proceed to the "Q.931 active" state, then it is almost certain that the SPIDs have not been entered correctly.

Impact uses a single light to show connection status. If it continues flashing and does not go out, then the SPID probably has not been entered correctly.

Even though ISDNtek's ISDN setup utility is generally very helpful, it does not detect a bad SPID. When you make a test call that fails, you get a "Bearer service not subscribed" message, but you have to be very familiar with ISDN protocols to understand that message. It would be much better if ISDNtek gave users a message when the initialization fails, as the WaveRunner does.

Which is the best?

There is no clear best product in this group; each has strong advantages. 3Com's Impact gives excellent performance and V.120 support for times when users want to call an ISDN bulletin board.

Its serial interface makes it the only product in this group appropriate for a Macintosh or other non-IBM PC or workstation. It's also the only product in this group to support voice calls directly.

Of the three ISA bus boards, Digi International's DataFire also had excellent performance, but it was the most difficult to set up. It also has large TSR-based drivers that use a lot of DOS memory.

IBM's WaveRunner has very good performance and supports both V.120 and V.34bis modem. Also, you can use WaveRunner to send and receive faxes, as well as to call modem-based data communications systems, which is valuable to many users.

ISDNtek's CyberSpace Internet had good performance, even though it had major degradation when uploading files to the Internet. It is less expensive than the other boards and was easy to install and use.

In buying a product to connect to the Internet, our advice is to choose an ISDN Internet service provider and then choose a product that it supports. All of these products require users to install NIC drivers along with an appropriate TCP/IP stack. Having a provider help you get everything up and working can be of real value.

The final question is whether to look at other kinds of products.

The products we looked at here represent the lowest priced ISDN products available. None support compression, and only Digi International's DataFire supports two B channels.

The next step up are the single-user ISDN bridges and routers.

They cost about $1,200 for U interface units that include NT1.

With on-demand support, two B channels and compression, they are more automated and have at least four times the throughput of the tested products.

We'll look at these in a future review.