As the amount of digital computer data flowing through MANs and WANs has increased and as those networks have become increasingly digital, the networking and telecommunications vice president role has significantly changed over the past five to ten years.
Traditionally this vice president has been responsible for computer communications; today in most companies, this individual is also responsible for telephone and voice services.
T carrier, SONET, and ATM have traditionally dominated the MAN and WAN market. However, with the growing use of VPNs and Ethernet services, we are beginning to see a major change. In the early 1990s, the costs of MANs and WANs were quite high. As these networks have changed to increasingly digital technologies, and as competition has increased with the introduction of new companies and new technologies (e.g., VPNs, Ethernet services), costs have begun to drop. More firms are now moving to implement software applications that depend upon low-cost MANs and WANs.
The same factors that caused the LAN and BN to standardize on a few technologies (Ethernet, wireless Ethernet) are now acting to shape the future of the MAN and WAN. We believe that within five years, X.25 and ATM, will disappear, replaced by Ethernet and IP services. Within ten years, ISDN, T-carrier, and SONET may also disappear.
These changes have also had significant impacts on the manufacturers of networking equipment designed for MANs and WANs. Market shares and stock prices have shifted dramatically over the last five years in favor of companies with deep experience in backbone technologies (e.g., Ethernet) and Internet technologies (e.g., IP) as those technologies spread into the MAN and WAN market.
summary
Circuit-Switched Networks Circuit-switched services enable you to define the end points of the WAN without specifying all the interconnecting circuits through carrier’s cloud. The user dials the number of the destination computer to establish a temporary circuit, which is disconnected when the data transfer is complete. POTS is traditional dial-up service. BRI ISDN provides a communication circuit with two 64-Kbps digital transmission channels and one 16-Kbps control channel. PRI ISDN consists of 23 64-Kbps data channels and one 64-Kbps control channel. Broadband ISDN, not yet widely available, offers much faster data speeds up to 622 Mbps. Dedicated-Circuit Networks A dedicated circuit is leased from the common carrier for exclusive use 24 hours per day, 7 days per week. Faster and more noise-free transmissions are possible, but you must carefully plan the circuits you need because changes can be expensive. The three common architectures are ring, star, and mesh. T carrier circuits have a set of digital services ranging from FT1 (64 Kbps) to T1 (1.544 Mbps) to T4 (274 Mbps). A SONET uses fiber optics to provide services ranging from OC-1 (51 Mbps) to OC-12 (622 Mbps).
Packet-Switched Networks Packet switching is a technique in which messages are split into small segments. The user buys a connection into the common carrier cloud and pays a fixed fee for the connection into the network and for the number of packets transmitted. X.25 is an older, traditional service that provides slower service (up to 2 Mbps) but guarantees error-free delivery. ATM does not perform error control, and it offers data rates up to 622 Mbps. Frame relay is a newer packet-switching service with higher data rates (up to 45 Mbps), but it does not perform error control. Ethernet services use Ethernet and IP to transmit packets at speeds between 1 Mbps and 1 Gbps.
VPN Networks A VPN provides a packet service network over the Internet. The sender and receiver have VPN devices that enable them to send data over the Internet in encrypted form through a VPN tunnel. Although VPNs are inexpensive, traffic delays on the Internet can be unpredictable.
The Best Practice MAN/WAN Design For small MANs and WANs with low data transmission needs, POTS dial-up services are a reasonable alternative. For networks with moderate data transmission needs (64 Kbps-2 Mbps), a VPN is a good choice if cost is more important than reliability; otherwise, frame relay or T carrier services are good choices. For high-traffic networks (2 Mbps-45Mbps), the new Ethernet services are a dominant choice, but some organizations may prefer the more mature—and therefore proven—T3 or frame relay services. For very high-traffic networks (45Mbps-10 Gbps), Ethernet services are a dominant choice but again some organizations may prefer the more mature ATM or SONET services. Unless their data needs are stable, network managers often start with more flexible packet-switched services and move to the usually cheaper dedicated-circuit services once their needs have become clear and an investment in dedicated services is safer.
Improving MAN/WAN Performance One can improve network performance by improving the speed of the devices themselves and by using a better routing protocol. Analysis of network usage can show what circuits need to be increased or decreased in capacity, what new circuits need to be leased, and when additional switched circuits may be needed to meet peak demand. Reducing network demand may also improve performance. Including a network usage analysis for all new application software, using data compression, shifting usage to off-peak times, establishing priorities for some applications, or redesigning the network to move data closer to those who use it are all ways to reduce network demand.
