As seen in the February/March 2002 issue of LAW OFFICE COMPUTING www.lawofficecomputing.com O rganizations with seve ral offices located in the same city usually want to link them into a single secure n e t work. Although, not applicable for all situations, if your organizations are with- in the same city, you might be able to set up a “campus” type system using sin- gle-line Digital Subscriber Line (SDSL ) modems connected by a single pair of phone wires. This pair of wires, re f e r red to by various names by different phone com- panies, is most often called a “dry pair.” This is an unconditioned telephone wire c i rcuit from one location to another without telephone equipment connect- ed to it. These circuits are often much less expensive than other alternative s offered by the phone company, and can a c h i e ve synchronous speeds of 2 Megabits per second (Mbps) in each direction within dis- tances not exceeding two miles. Connection speed begins to drop after distances exceeding two miles, but respectable speeds can be achieved at distances of four to five miles. SDSL modems are bridging devices used to connect to remote segments of your Local Area Network (LAN). These segments can be in different buildings or separated by many floors in a build- ing. The connecting pair of wires can be user-owned as in a campus LAN or p rovided by the phone company using its wiring circuits. Traffic is synchro n o u s , meaning the same speed in both dire c- tions, which is an important considera- tion if you are sharing databases or files or want to backup data over the link. C o n f i g u ration from point to point looks like the following: Office A Hub <——> SDSL modem <——> dry pair wiring <——> SDSL modem <——> Office B Hub To give an example of their use and how easy or hard it is to connect offices with this setup, we will take you thro u g h an actual installation we performed. The objective was to link five offices, each with its own LAN into a single network where various facilities a re located any w h e re from 4,000 to 13,000 feet line distance. (Line distance is the length of the wire between the t wo end points and will have to go t h rough a telephone wire center or switch office unless you are running your own direct wire.) The Wide Area Network (WA N ) was constructed to share netwo r k re s o u rces and to minimize the number of Internet Service Provider (ISP ) accounts and the need to secure each access point (including emergency ser- vice providers), which is best done using h a rd - w i red land line communications using a single broadband access point that is shared by all offices and secured with a firewall and antivirus system. We looked at seve ral options, including a virtual private network (VPN) and wire- less networking, before deciding to use SDSL modem bridging. Although 80 2 .11b wireless net- working was feasible and could provide 11 Mbps basic Ethernet performance, 80 2 .11b is expensive, with pre l i m i n a r y Create a WAN Using SDSL Modems These bridging devices can connect to remote segments of your LAN. By Joseph L. Kashi and Thomas Boedeker Bridging the Gap: The 300S modem was plugged in at each end point and connected phone cords to wall jacks on each end for this installation. As seen in the February/March 2002 issue of LAW OFFICE COMPUTING www.lawofficecomputing.com ments than using routers. Some ro u t e r s offer encryption and can be used ove r a dry pair link. It’s also possible to use encryption techniques in a bridging setup such as the one that we described h e re, but an extra level of hard wa re encryption complicates the installation and was not a significant concern. When the remote segments we re added, our network branches all came together as a single network. The SDSL modems are tra n s p a rent to various net- works and protocols. The ability to con- nect to servers and other re s o u rces is simply based on the network opera t i n g system softwa re clients and pro t o c o l s that need to be installed on your re s p e c- tive servers and workstations regardless of how the workstations physically con- nect to the network file servers. All of the links under 13,000 feet line length operate at near 2 Mbps. N e t work packet collisions cause some reduction when multiple computers are trying to use the link simultaneously, but with small remote networks of four We installed four dry pairs in the main office, one from each of the four remote locations, and then had the phone com- p a ny install four regular phone jacks in our central office, one for each end of e very dry pair link. Then, we simply plugged in a 300S modem at each end point and connected the phone cord s to the wall jacks on each end. Wi t h i n about 30 seconds, the modem indica- tor lights showed good circuits. We then connected the SDSL modem to our net- work using Ethernet cables. Initially, we had some internal net- work problems until we determined that we needed to use an uplink port on our hub or switch or use a cro s s over cable if connecting the modems to a standard Ethernet port. Once the modems we re p roperly connected to our main net- work, individual segments we re able to see each other. No other configura t i o n was re q u i red. Although you give up some flexibility, security and contro l , simple WAN bridges are an easier method of connecting network seg- estimates at about $25,000, and it’s also potentially less secure. VPN wa s also possible, but in our local market, a vailable VP N options we re not syn- c h ronous with an $8,000 estimated setup charge. VPN also had a re c u r r i n g monthly fee of more than $700 per month for a mere 328 Kbps (kilobits per second) bandwidth. VPN also left no option for connecting to another office location located at a line distance of 24,000 feet because our local provider planned to use an asymmetric Digital Subscriber Line (ADSL), which could not reach that far. Although our local telephone com- p a ny doesn’t actively market the dry pair SDS L service, we we re able to obtain dry pair connections for a monthly rate of only $53 for each end- point to endpoint link, for a total re c u r- ring cost of about $210 to $265 for all f i ve offices. This lower monthly cost caused us to look closely at the SDSL/dry pair option. Initially, our re s e a rch indicated we could achieve ave rage line speeds in excess of 1 Mbps over most of our net- work, with published data indicating that speed dropped dramatically as line distances increased. Based on our actu- al field results, though, we can only assume the published performance esti- mates are very cautious and intended to c over a wide variety of line quality and o p e rating conditions because we have consistently obtained better thro u g h p u t for a given line distance than the ve n- dors’ published estimates. We installed an ADC Megabit Modem 300S (www.adc.com) with switch selectable speed options of up to 2 Mbps, partly because we knew some- one who already had good experience with this product. The 300S has an RJ - 45 port to connect to the network and an RJ-11 port to connect to the dry pair using a standard phone to wall cord. It uses an external power supply and is priced at around $400. S e ve ral other SDSL modem models a re available, including the NetTo N e t SNE 2000-S, the MuLogic DSL - 2048 and the Netopia R7200. Howe ve r , some models are limited to 1.54 Mbps. Some other models also offer differe n t connector options, so we suggest yo u check carefully to be sure you have the correct parts and connections on hand. Our plan to connect five separa t e locations required us to choose our cen- t ral office, where the main servers are located, as the WAN’s common point. Benefits and Downsides of SDSL The benefits we achieved using dry pair SDSL WAN were: 1. Simple setup and maintenance. 2. Synchronous connections at 2 Mbps speeds, which is faster than most common VPN options. 3. Simplified data backup from remote segments to a central system. 4. Easy sharing of a single Internet access point. 5. Robust firewall at a single public access point with reduced network management costs. 6. Intranet entirely within the local network, with no need to access the public Internet. 7. Improved administration of remote computers. 8. All LAN segments can be accessed from anywhere in the system as if they were in the same segment, although it’s slower than Ethernet. Dry pair SDSL has some disadvantages compared to other approaches, although these disadvantages were not critical in our installation: 1. Reduced security between the various network segments because all segments are accessible from anywhere in the system. 2. Conflicts can arise from multiple DHCP servers if several are active on various LAN segments. 3. If the DHCP server is down (due to a power outage), it’s possible that remote computers can lose their current address assignment, which causes difficulties using single-point Internet access or some database programs that require a current IP address for the workstation. 4. Bridged SDSL is limited to 255 total computers or devices using an IP address unless we want to choose different firewall and antivirus securi- ty devices. This is really a limit of those devices because the SDSL bridge can recognize 8,192 network devices. Although if you need that many network addresses, you probably need a more robust solution anyway. 5. Traffic going out over the wiring is not encrypted by the SDSL modems. As seen in the February/March 2002 issue of LAW OFFICE COMPUTING www.lawofficecomputing.com to six computers we found no significant reduction in speed. As we extended to three and a half miles we saw throughput speed drop to about 1.5 Mbps, still T-1 speed at a small fraction of the cost. These re s u l t s e n c o u rage us to consider a longer link of five miles. Although that longer link has not been installed and tested, we h a ve read about similar SDSL bridges achieving T-1 speeds over distances of four to five miles, but these longer dis- tances work better if the copper wire is the heavier 24 AWG rather than the 26-gauge wire that is common in older areas. S e ve ral other points should be noted. If you have been using a Dynamic Host Configuration Pro t o c o l ( DHCP) server on each LAN segment to assign Internet Protocol (IP) addre s s- es, you need to shut off all but one in o rder to avoid potential conflicts in a d d ress assignment. And, with many security systems, you are limited to one range of IP addresses. This will limit yo u to 255 devices connected to the net- work on all segments combined. If you have a need to connect sev- e ral offices located within two to seve n miles of each other, then SDSL modems using dry pair wiring to bridge between offices is a viable solution. Our re s e a rch leads us to conclude that given the price of ISP and tele- phone company services, the cost of dry pair wiring offers some distinct cost sav- ing possibilities worth considering. The simplicity is such that the connection easily can be made without extensive technical consultant costs. In addition, in some areas, it might prove to be a faster, less expensive alternative than other types of broadband access. A B O U T T H E A U T H O R S THOMAS BOEDEKER is the city man- ager of Soldotna, Alaska. He is the for- mer borough attorney for the Kenai Peninsula. For a break from work and computers, Boedeker plays golf and reads mysteries and science fiction. Boedeker has been an active attorney and litigator for more than two decades. JOSEPH L. KASHI practices law in Soldotna, Alaska. He has held various posi- tions in the ABA’s Law Practice Management Section. He received his bach- elor’s and master’s degrees from the Massachusetts Institute of Technology in 1973 and his law degree from Georgetown University in 1976. He is admitted to prac- tice before the Alaska Supreme Court, the U.S. Supreme Court and the U.S. Court of Appeals for the 9th Circuit and speaks fre- quently on legal automation topics. . done using h a rd - w i red land line communications using a single broadband access point that is shared by all offices and secured with a firewall and antivirus. practices law in Soldotna, Alaska. He has held various posi- tions in the ABA’s Law Practice Management Section. He received his bach- elor’s and master’s