14.5 Systems Design

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Network design can get quite detailed, including the specific configuration of devices like switches and routers that are linked together with various lines and services. A relatively recent trend in systems design is the ability to do it on-line with vendor-provided tools that provide an easy way to design, configure, and quote a customized network solution without the involvement of salespeople or committing to a purchase. Cisco does this with routers, Extreme Networks with switches, and computer manufacturers like IBM do it with PCs and servers. By filling in various fields in an on-line form, different products can be customized according to specific performance and budgetary requirements. If a configuration is invalid, the on-line configuration tool identifies the mistake, giving the user a chance to make other feature selections until the system meets valid criteria.

There are two ways to design systems on-line. One is to select a basic configuration and then customize it by choosing various features, capabilities, and options from a series of pick lists. Along the way, or upon completion of the custom build, the price is recalculated. When the user is satisfied with the results, the information can be stored for reference or the user may go ahead and order the product on-line.

The other way to design a system on-line is to use a needs-analysis tool to arrive at an appropriate solution. This method is used when the buyer needs help deciding what product would best meet organizational needs but is not familiar enough with a vendor’s product line to select a particular model. Cisco, for example, has so many different kinds of routers that it takes some technical expertise to navigate its entire line of offerings and zero in on exactly the right one. For small and medium-size businesses, the needs analysis approach might be best.

For selecting a branch office router, for example, Cisco’s needs-analysis tool starts by asking the user about voice requirements, assuming that a branch location might be interested in saving money and simplifying network administration. The user is asked, “Do you require voice capability now or in the future?” The user clicks on one of the following answers:

• I require voice capability now;

• I require voice capability in the future;

• No, I require only data capability.

The needs-analysis tool then asks if the user has any VPN requirements, which provides a secure way to connect to the corporate network over the Internet. This is cheaper than using dedicated leased lines for that purpose, plus the VPN offers traffic prioritization, management, and new capabilities such as secure extranet communication among business partners. The user is asked, “Do you require VPN capability now or in the future?” The user clicks yes or no.

Following up on the VPN requirements, the needs analyzer asks the user about security; specifically, whether the user intends to use the DES for protecting VPN traffic, or 3DES, which iterates three times with three separate keys, effectively doubling the strength of DES. The user answers by clicking DES or 3DES.

Next, the analyzer inquires about the level of performance that will be required from the VPN connection, which determines whether or not the router will need to be equipped with a VPN module. The VPN module encrypts data using the DES and 3DES algorithms at speeds suitable for a full-duplex T1/E1 serial connection. The user must specify the type of connection that the VPN will run over. The choices are: T1/E1, ADSL, ISDN BRI at 128 Kbps or 56/64 Kbps.

The needs analyzer asks the user to specify the type of LAN interfaces the router should have. This is determined by the type of LAN installed at the branch office, which most likely would be a 10BaseT Ethernet. Then the user must decide how many ports the router will provide for 10BaseT Ethernet, either one or two.

Assuming the user wants the router to support voice as well as data, the needs analyzer asks the user to select the voice interface type. (The number of ports is fixed at two.) For a branch office router, the following choices are available:

• Two-port FXS voice/fax interface card;

• Two-port FXO voice/fax interface card;

• Two-port FXO voice/fax interface card (for Europe);

• Two-port FXO voice/fax interface card with battery-reversal detection and caller ID support (for the United States, Canada, and others);

• Two-port FXO voice/fax interface card with battery-reversal detection and caller ID support (for Europe);

• Two-port FXO voice/fax interface card (for Australia);

• Two-port E&M voice/fax interface card;

• Two-port ISDN BRI voice/fax interface card (network and terminal side);

• Two-port DID voice/fax interface card.

The needs analyzer asks the user to provide requirements for WAN interfaces, specifying the type of port(s) and the number of ports. At this point, however, the user’s previous choices may not have left room to add any more modules, since the router has a limited number of slots. If this is the case, an error message pops up telling the user to go back and remove a module. If two 10BaseT Ethernet ports were specified previously, when only one would actually suffice, the configuration can be revised for one port, leaving room for a WAN interface. The choices for WAN interface include the following:

• ISDN BRI S/T;

• ISDN BRI U;

• Sync/async serial (T1/E1);

• Low-speed Sync/async serial (up to 128 Kbps);

• 56/64 Kbps, four-wire DSU/CSU;

• T1/Fractional T1 DSU/CSU ADSL.

The last step in the needs analysis asks the user to specify the software features of the Cisco operating system. To do this, the user must know what kind of operating systems, protocols, and applications are running on the LAN that the router will be connected to. Among the choices are the following:

• AppleTalk, which is used to interconnect Macintosh computers;

• BGP for load-balancing traffic between two Internet service providers;

• DHCP, which assigns IP addresses to clients when they require access to the Internet, thus conserving IP addresses;

• IP, which is required for sending and receiving information through the Internet;

• IPX, which is used on Novell networks;

• Layer 2 Tunneling Protocol (L2TP), a type of protocol for implementing secure private connections through the Internet;

• NAT, which is used to conserve IP addresses and provide rudimentary security by presenting one IP address to the Internet from a pool of IP addresses;

• Network Time Protocol (NTP), which provides a common frame of reference between all devices on the network for facilitating accounting, fault analysis, network management, and time-based authentication and authorization;

• Port address translation (PAT), which is similar to NAT, but only uses one registered IP address instead of a pool of addresses. PAT is a true many-to-one solution in that it manipulates a field in the public-data packet, which is then related back to the private-address packet.

When the user reaches the end of the on-line needs analyzer, the final configuration is depicted in graphical form, along with the router model number and a complete list of modules and interfaces.

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