Modern WAN Connectivity
Modern WANS have more connectivity options that traditional WANs. Enterprises now require faster and more flexible WAN connectivity options. Traditional WAN connectivity options have rapidly declined in use because they are either no longer available, too expensive, or have limited bandwidth.
The figure displays the local loop connections most likely encountered today.
Modern WAN Connectivity Options
New technologies are continually emerging. The figure summarizes the modern WAN connectivity options.
In the late 1990s, many telecommunication companies built optical fiber networks with enough fiber to satisfy projected next generation needs. However, optical technologies such as wavelength division multiplexing (WDM) were developed and dramatically increased the transmitting ability of a single strand of optical fiber. Consequently, many fiber-optic cable runs are not in use. Fiber-optic cable that is not in use, and therefore, “un-lit” (i.e. dark) is referred to as dark fiber.
Fiber can be installed independently by an organization to connect remote locations directly together. However, dark fiber could also be leased or purchased from a supplier. Leasing dark fiber is typically more expensive than any other WAN option available today. However, it provides the greatest flexibility, control, speed, and security.
Two packet-switched WAN network options are available.
Advances in Ethernet LAN technology have enabled it to expand into the MAN and WAN areas. Metro Ethernet provides fast bandwidth links and has been responsible for replacing many traditional WAN connectivity options.
Multi-protocol Label Switching (MPLS) enables the WAN provider network to carry any protocol (e.g., IPv4 packets, IPv6 packets, Ethernet, DSL) as payload data. This enables different sites to connect to the provider network regardless of its access technologies.
Organizations are now commonly using the global internet infrastructure for WAN connectivity. To address the security concerns, the connectivity options are often combined with VPN technologies.
Valid WAN network options include Digital Subscriber Line (DSL), cable, wireless, and fiber.
Note: There are several WAN access connection options that the enterprise edge can use to connect over the local loop to the provider. These WAN access options differ in technology, bandwidth, and cost. Each has distinct advantages and disadvantages. Familiarity with these technologies is an important part of network design.
Ethernet was originally developed as a LAN access technology and was not suitable as a WAN access technology due primarily to the limited distance provided by copper media.
However, newer Ethernet standards using fiber-optic cables have made Ethernet a reasonable WAN access option. For instance, the IEEE 1000BASE-LX standard supports fiber-optic cable lengths of 5 km, while the IEEE 1000BASE-ZX standard supports cable lengths up to 70 km.
Service providers now offer Ethernet WAN service using fiber-optic cabling. The Ethernet WAN service can go by many names, including the following:
- Metropolitan Ethernet (Metro E)
- Ethernet over MPLS (EoMPLS)
- Virtual Private LAN Service (VPLS)
The figure displays a simple Metro Ethernet topology example.
The following are several benefits to an Ethernet WAN:
- Reduced expenses and administration – Ethernet WAN provides a switched, high-bandwidth Layer 2 network capable of managing data, voice, and video all on the same infrastructure. This increases bandwidth and eliminates expensive conversions to other WAN technologies. The technology enables businesses to inexpensively connect numerous sites in a metropolitan area, to each other, and to the internet.
- Easy integration with existing networks – Ethernet WAN connects easily to existing Ethernet LANs, reducing installation costs and time.
- Enhanced business productivity – Ethernet WAN enables businesses to take advantage of productivity-enhancing IP applications that are difficult to implement on TDM or Frame Relay networks, such as hosted IP communications, VoIP, and streaming and broadcast video.
Note: Ethernet WANs have gained in popularity and are now commonly being used to replace the traditional serial point-to-point, Frame Relay and ATM WAN links.
Multiprotocol Label Switching (MPLS) is a high-performance service provider WAN routing technology to interconnect clients without regard to access method or payload. MPLS supports a variety of client access methods (e.g., Ethernet, DSL, Cable, Frame Relay). MPLS can encapsulate all types of protocols including IPv4 and IPv6 traffic.
Refer to the sample topology of a simple MPLS enabled network.
An MPLS router can be a customer edge (CE) router, a provider edge (PE) router, or an internal provider (P) router. Notice that MPLS supports a variety of client access connections.
MPLS routers are label switched routers (LSRs). This means that they attach labels to packets that are then used by other MPLS routers to forward traffic. When traffic is leaving the CE, the MPLS PE router adds a short fixed-length label in between the frame header and packet header. MPLS P routers use the label to determine the next hop of the packet. The label is removed by the egress PE router when the packet leaves the MPLS network.
MPLS also provides services for QoS support, traffic engineering, redundancy, and VPNs.