54-80-50 Implementing a Complex Ethernet Previous screen David Levin Payoff The company referred to in this article as Servco is an international accounting firm with approximately 100 offices throughout the United States providing tax, audit, and management consulting services. Each practice group within Servco had been using a different computer and networking technology. Servco's management wanted to reorganize the firm from practices into industry focus groups and streamline its information technology environment by maximizing the effectiveness of support personnel and equipment expenditures. Problems Addressed Servco's tax department had IBM personal computers and Token Ring networks. The audit department used Apple microcomputers and Apple's LocalTalk network. The management consulting department used different brands of microcomputers and minicomputers with many different types of LANs. The administration department used Wang minicomputers with Wangnet, Apple micros with LocalTalk, and IBM microcomputers with both Token- Ring Networks and Ethernets. Each of Servco's offices had several LANs when only a single LAN, interconnecting all practice and functional areas, was needed. LAN applications included: access to practice information on CD-ROM, access to local data bases, electronic mail, printer sharing, building-to-building communication, and network management. Servco also wanted to build a corporate WAN to connect all its office LANs. Applying Ethernet Technology Servco decided to standardize on a single networking technology. The technologies that were evaluated included Ethernet, Token-Ring, Arcnet, FDDI, and FDDI-over-copper. As Ethernet was the LAN technology that was most widely implemented, Servco decided that Ethernet was the most cost-effective networking alternative for the short term. In the long term, Servco expects to migrate to a 100M bps shielded cable LAN when this technology matures and is truly needed. This design process began after the decision was made to standardize on Ethernet. Ethernet comes in many forms (i.e., thicknet 10BASE5, thinnet 10BASE2, broadband Ethernet 10BROAD36, and twisted-pair Ethernet 10BASE-T). Broadband Ethernet was attractive because some of the larger Servco offices already had Wangnet cable plants installed. Twisted-pair Ethernet was attractive if the network would run on existing Twisted-pair cable. Thicknet and thinnet were the least attractive alternatives owing to doubts about the reliability of a bus topology network. Hub concentrators were chosen as the primary LAN platform and supplemented by fiber-optic backbone cabling. Servco's requests for proposals (RFPs) were based on detailed technical designs for small, medium-sized and large offices. RFPs went to selected vendors including Bytex, Cabletron, Chipcom, IBM, Synoptics, and Timeplex. After initial evaluation of the vendor bid responses, Servco further evaluated products from Cabletron, Chipcom, and Synoptics. The most important result of the structured bidding process was that the leading vendors provided bids based on discounts averaging between 40% and 50%. The management features built into the hubs also enable substantial cost reduction in the Previous screen network support function. This chapter summarizes Servco's requirements analysis, conceptual design, and detailed planning phases for the new networking platform. The details of the planning process are presented with emphasis on the largest Servco office, which is located in New York City. User Population Exhibit 1 is a summary of the network user population in the New York office. The user population per floor varies from 90 to 150 people with an average of approximately 130 people. Additional ports have to be provided for servers, routers, and printers. The total number of network ports needed in the New York office was projected to be approximately 1,500. Each floor is made up of several groups of people whose work primarily requires information exchange and network connectivity within each group. Each group must also be connected to a backbone network to exchange information outside the group. Intelligent network hub concentrators permit and facilitate this type of connectivity. User Population Summary, Servco, New York Office Stations by Department ----------------------------------------------------------------- Previous screen Administration- Management Word Floor Audit Tax Consulting Processing Additional ----- ----- --- ---------- ---------- ---------- 40th 47 15 45 23 12 39th 28 95 8 17 38th 92 32 11 37th 31 83 7 14 36th 141 14 35th 20 83 24 5 29th 53 30 10 28th 54 61 21 6 27th 49 24 20 4 7 Lower Level 7 26 33 17 12 14 B level 7 Lexington Avenue 33 117 18 Totals: 414 651 147 146 112 (For additional columns, see below) Floor Total Floor Additional Stations Are in ----- ----------- -------------------------- 40th 142 Administrations 39th 148 Communications 38th 135 37th 135 36th 155 35th 155 29th 132 28th 93 27th 142 Lower 104 Financial reporting Level 95 Administration Telecommunications Central files Facilities 14 Personnel 7 168 1470 (Total) The New York office consists of people located in two office buildings that are across the street from one another. Servco needed a network design that supported a close link between staff members located in the two buildings. The best way to link both buildings was a bridge or router in each location connected by a T-carrier transmission line. The Hub Concentrator Previous screen Exhibit 2 shows a typical hub concentrator. It includes a chassis, one or more power supplies, and different types of modules. Port or host modules connect a workstation to the network segment. A network segment may consist of a single port module or several port modules connected through the backplane in the chassis. Backplanes may be segregated into separate Ethernet, Token-Ring, and FDDI backplanes. Cabletron combines an older backplane for older modules with a newer backplane for newer modules; they call this their Flexible Network Bus (FNB). Typical Hub Configuration Cabletron MMAC-M8FNB Hub Concentrator Slots ------------------------------------------- 8 7 6 5 4 3 2 1 E TPRMIM36 TPRMIM36 TPRMIM36 TPRMIM36 TPRMIM36 TPRMIM36 M M EPIM E Channel C Channel C Isolated Channel B Channel B Channel B Stations Segment No. Slot Use: -------- ----------- ---- ---- 2. Tax 68 1 3. Tax 1 4. Tax 1 5. Administration-Word Processing 8 2 6. Audit 27 3 7. Audit 3 8. Empty Bill of Materials ----------------- Item Description Part No. Quantity ---- ----------- -------- -------- 1. 8-slot media access center MMAC-M8FNB 1 2. Power supply PSM-M8 2 3. Ethernet management module EMME 1 4. Multi-Channel 26-port 10BASE-T module TPRMIM36 6 5. Ethernet port interface module-fiber EPIM-F2 1 6. 1-port standalone 10BASE-T transceiver TPT-4 0 Hub concentrators support Ethernets, Token-Rings, and FDDI LANs. Most vendors offer different modules for shielded and unshielded cabling. The leading hub modules support three or more network segments per box. All hubs restrict to some extent the mix of network segments and the types of connectivity. Network management modules manage one or more segments depending on the vendor. Router modules connect segments together and pass only traffic for other segments. Bridge modules connect segments but do less intelligent filtering among segments. Retiming modules perform signal regeneration for host modules and may be required when connecting hubs together. Exhibit 2 shows a Cabletron hub fitted with an Ethernet management module and six port modules. Three slots have Cabletron TPRMIM36 26-port 10 BASE-T modules, which form Segment 1 on Channel B, which is used by tax personnel. Slot 5 has an isolated 26-port module used by administrative personnel. Slots 6 and 7 have port modules Previous screen for a third segment on channel C. Exhibit 2 includes a bill of materials for this hub. The hub is a Cabletron module MMAC-M8FNB eight-slot hub with the FNB and redundant power supplies. Cabletron's Ethernet management module provides retiming, management, and bridging if required. Servco chose to turn off the bridging function within the module. A fiber-port interface module is installed in the port module in the fifth slot to connect administrative users from different floors to a Netframe server in the computer room. A Cabletron FOT-F2 one-port standalone fiber-optic transceiver connects the segment 1 users to the buildingwide tax backbone. This hub serves 103 nodes or one-half of all network connections on one floor. Alternative LAN Architectures Four alternative LAN architectures were developed by Servco and are shown in Exhibits 3 to 5. These generic designs differed in the type of router (internal versus standalone) and the choice of backbone (fiber-optic versus coaxial cable). Exhibit 3 illustrates how the existing coaxial backbone network, which can support five 10M-bps Ethernets, can support the new LAN. Standalone routers connect the multiple LAN segments in each hub. A standalone router in the lower level computer room supports connection to the Lexington Avenue offices and WAN transmission facilities. At the right-hand side of Exhibit 4 is a backbone network design that uses fiber- optic cable and additional hubs to provide what is called a collapsed backbone network. Standalone routers connect each segment to the backbone hubs through fault-tolerant fiber- optic transceivers. Redundant backbone hubs may be needed because the backbone hub is a single point of potential failure. Router modules within the hub may