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The Dilemma


Your firm has just acquired another company and you need to interconnect key Information Systems (IS) applications that will truly integrate the new firm with yours.

Yet you have one small challenge. The Local Area Networks they use do not use the same protocols you do, and worse yet, it appears that they will not be relocating to your facility from their existing one anytime soon. You need to integrate them onto your network.

Such is the dilemma many of us face in today's ever changing global market, and one of recent mergers and acquisitions.

As the market needs expand globally, so do the needs of our user community. 

  • The Local Area Network, of course, provides network connectivity within a single department, workgroup, or building, 

  • The Campus network interconnects LANs in different buildings of a campus or industrial park area 

  • The Metropolitan Area Network (MAN) typically encompasses a geographical metropolitan area, many times also making specific services available to the public, 

  • The Wide Area Network (WAN) expands the network further to potentially global proportions. 

  • The Enterprise-wide network brings the WAN within an organization's IS resources over local and wide areas, regardless of operating systems, communication protocols, or platforms.


Connecting The Internetwork


It has been just a few short years since LANs have become a common vehicle to network, whose function is to connect users within one department. As LANs have evolved and the need to interconnect, so have various hardware components and markets, each more increasing in complexity.

  • Repeaters simply extend the signal from one like LAN to another, but typically increases congestion of data traffic quickly, 

  • Bridges have been a typical means of building an "internetwork" at a basic level, i.e., building small networks of the same type, or bridging several all-Ethernet networks. Bridges are appropriate with networks of fewer than 15 - 20 segments, and bridges offer the flexibility to allow multiple protocols, i.e., TCP/IP and IPX. Bridges operate at the second layer of the OSI (Open Systems Interconnection) model, the data link layer. 

  • Routers have now become today's access method to interconnect various networks over local and wide areas. For example, routers can be used to interconnect an Ethernet with a Token Ring network. Routers are packet switches that operate at the network layer, or third layer of the OSI model.

Routers are essential in large, multi-protocol networks. They offer excellent control of traffic loads and routing paths. They can adjust to link failures and congested paths, automatically routing traffic to another path. If one router is bottlenecked, it can let other routers know.

Because networks are becoming ever-increasingly complex, a mix of bridges (handling interconnection of like network systems) and routers (handling multiple network systems) is a real-world scenario. Bridges should be used to connect departmental networks, or used to subdivide loaded departmental networks. Routers should be used when a network is made up of multiple LAN types running different network protocols, i.e., a network consisting of Token Ring and Ethernet running TCP/IP, IPX, and Appletalk. Routers give you the ability to have tight path control and security over where data packets can travel. Routers commonly require a higher level of internal administrative management to configure, operate, and manage than bridges.

Gateways (or protocol converters) connect two dissimilar computer systems and translations between them. For example, an X.25 gateway can connect a LAN to an X.25 packet switched network, or an SNA mainframe gateway can connect a LAN to an IBM SNA network. Gateways operate at layers four through seven of the OSI model, or the transport, session, presentation, and application layers.

In an SNA mainframe gateway, a dedicated PC is typically used as the gateway and emulates an IBM cluster controller. The individual workstations must run gateway and terminal emulation software so that they can communicate to the host computer through the gateway.


Defining The Protocols


Communications protocols are commonly defined within the context of "layered" network architectures, commonly based on the OSI model (although the recent surge in the Internet now supports TCP/IP over OSI models). Protocols specify how an interchange takes place, including format, timing, sequencing, and error checking.

Communication protocols are commonly grouped into three categories, as follows:

  • Application Protocols - which include the application, session, and session layers and provide application-to application data exchange. Common application protocols include IBM Advanced Program-to-Program Communication (APPC), File Transfer Protocol (FTP), and Single Network Management Protocol (SNMP). 

  • Transport Protocols - provide connection of data services across networks and typically handle error handling, prioritizing, and security while regulating traffic flow. Common transport protocols include IBM's Advance Peer-toPeer Networking (APPN), Transmission Control Protocol (TCP) of the TCP/IP "suite", and the SPX portion of the SPX/IPX Novell protocol suite. 

  • Network Protocols - provide "linking" of services for connecting systems. They handle the address, routing information, and error checking as well as methodology for accessing the network. They include the Internet Protocol (IP) portion of the Internet TCP/IP protocol suite and the IPX portion of Novell's SPX/IPX protocol suite. 

  • Another protocol type, routing protocols, provide routers with the information they need to create the best paths through complex networks based on routing information that routers share. Routing protocols are typically categorized in two areas - distance-vector and link-state. 

    • Distance-Vector - route the packets based on decisions about the number of "hops" from one destination to the other; this information is provided by neighboring routers. Common routing protocols here include RIP (Routing Information Protocol - Novell), IGRP (Interior Gateway Routing Protocol - developed by Cisco), and RTMP (Routing Table Maintenance Protocol - Apple). 

    • Link-State - provides better control over the routing process and responds faster to changes, and subsequently requires more processing power. The most common protocol here is OSPF (Open Shortest Path First).



Building Your Network


As you build your own internetwork, ask yourself several key questions, including:

  • What IS services do you want to offer to your user community (or are users requesting) locally (within a department) and to various departments? 

  • What services are needed by various user departments within the department as well as outside - database, E-mail, spreadsheets, word processing? 

  • What particular protocols must be supported to interconnect various systems, and what network systems are used within your company? 

  • What is the geography of the users to be served - department, campus, metropolitan, national, international?

  • What are the anticipated traffic loads for each group, and each internetwork? 

  • What is the anticipated short term (1 year) and longer term (3) anticipated user and application growth? 

  • What security issues need to be addressed to maintain the proprietary nature of many user applications and data files? 

  • What network administrative issues need to be addressed to maintain control and deployment of the internetwork? 

  • What kind of back up methodologies will be used to back up the various networks in the event of data loss on the network? 

  • What standards will you develop for congruity among users? What manufacturers (PCs, bridges, routers, hubs, etc.) will you support? 

  • What kind of documentation will be developed to support the network, and how often will this documentation be updated? What areas will be documented - network "hub" locations, user addresses, circuit numbers, model and serial numbers, diagrams of various network components and geographies, trouble logs, etc.?

These are just a few of the questions to be considered when designing and building your network.


An Application Example


One of our client's networks involves the interconnection of over 30 different networks, most using Token Ring. Some of the interconnections involve multiple protocols, where routers and gateways become a means of interconnection. Some of the networks are MAC Appletalk while others are Novell-based SPX/IPX networks.

Recently we added a new facility via a dedicated T-1 link. Ethernet was used over Token Ring for cost and lower traffic load requirements. Routers were used to interconnect the facilities. Applications included access to mainframe billing systems, E-mail, imaging applications, electronic textbooks, scheduling, records management, and terminal emulation traffic among others. A category 5 twisted pair and fiber backbone cable network were implemented to support the interconnections.


Building For Tomorrow


The success of the design of the network, i.e., access methods and internetworking devices, determines the longevity of your enterprise-wide network. A network designed for today's technology only may show bottlenecks and degradation in performance within just one year, yet a network designed for tomorrow's technology is riskier and more difficult to design, build and troubleshoot, yet it will have a longer life cycle. You must decide on your own investment strategy.

We are right on-the-edge of seeing a myriad of new products and networks to be deployed that will give us interconnection of data, voice, and video services to the desktop. Videoconferencing to the desktop is a real-world application today and is in its infancy, but currently presents challenges over LANs and LAN/WAN interconnections, i.e., slow response and inevitable network collisions. Asynchronous Transfer Mode (ATM) and SONET (Synchronous Optical NETwork), however, are two such technologies that will open the doors to such interconnection. Many new product announcements revolve around the ATM platform.


In Summary


Routers, bridges, and gateways are currently a means to interconnect various subnetworks in an Enterprise-wide network environment. New products are about to be "unleashed" by various vendors that will truly lend themselves toward higher speeds and even greater multi -protocol integration and applications. In your business and technical strategies, be sure to address your short term as well as long term needs to serve your users as their needs grow. 

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