Summary
Highlights
This section introduces WANs (Wide Area Networks) as communication networks spanning large geographical areas, essential for connecting beyond LAN boundaries. It contrasts LANs and WANs based on geographic scope, interconnection purpose, ownership/management, cost, and bandwidth capabilities. The discussion highlights that WANs are typically managed by ISPs and involve service fees, unlike LANs which are owner-managed with no usage fees beyond infrastructure costs.
The lecture differentiates between private WANs, which offer guaranteed service levels, consistent bandwidth, and security for single customers, and public WANs, which use the internet through ISPs and may have varying service levels and security. Various WAN topologies are then discussed: Point-to-Point, Hub and Spoke (prone to single point of failure), Dual Home (enhanced redundancy and load balancing), Fully Mesh (most fault-tolerant but expensive), and Partially Mesh (cost-effective compromise). Large networks often combine these topologies.
This part covers carrier connections, emphasizing Service Level Agreements (SLAs) with providers for reliability and availability. It explains single versus dual carrier connections, with dual carriers offering redundancy. The evolution of network requirements is illustrated through a hypothetical company, 'Span Engineering,' showing its growth from a small local network using DSL to a global enterprise utilizing campus, metropolitan, and distributed networks with VPNs.
WAN standards are governed by organizations like TIA/EIA, ISO, and IEEE. Most WAN standards focus on the physical (Layer 1) and data link (Layer 2) layers of the OSI model. Layer 1 protocols include SDH, SONET, and DWDM, while Layer 2 protocols cover broadband, Ethernet WAN, MPLS, PPP, HDLC, Frame Relay, and ATM. Common WAN terminology such as DTE, DCE, CPE, PoP, Demarcation Point, Local Loop, Central Office (CO), and Tall/Backbone Networks are defined.
Various WAN devices are outlined, including voice modems, DSL/cable modems, CSUs/DSUs, optical converters, wireless routers/access points, and WAN core devices like high-speed routers and Layer 3 switches. The lecture then distinguishes between serial communication (bits transmitted sequentially over a single channel, suitable for long distances) and parallel communication (simultaneous transmission over multiple wires, limited to short distances due to synchronization issues).
Circuit switch communication establishes a dedicated circuit before data transmission, exemplified by PSTN and ISDN. In contrast, packet switch communication segments data into packets routed over a shared network, offering more flexibility and cost-effectiveness. Examples include Ethernet WAN, MPLS, Frame Relay, and ATM, with the latter two being legacy technologies. The advantages of fiber optics over copper for long-distance transmission are highlighted, along with SDH, SONET, and DWDM technologies for optical fiber data transport.
This section delves into traditional WAN connectivity, including leased lines (T-carriers in North America, E-carriers in Europe), which offer simplicity, quality, and guaranteed availability but are expensive and lack flexibility. Circuit-switched options like PSTN (limited to 56 kbps) and ISDN (up to 2.048 Mbps) are also discussed. Packet-switched options like Frame Relay and ATM, while largely replaced by modern solutions, are explained as legacy technologies that segment data into packets for routing over shared networks.
Modern WANs offer faster and more flexible options, replacing traditional ones due to cost, availability, or bandwidth limitations. Key modern options include dedicated broadband (fiber, dark fiber), packet-switched Ethernet WAN (Metro E, EoMPLS, VPLS), and MPLS. Ethernet WAN offers reduced expenses, ease of integration, and enhanced productivity. MPLS is presented as a high-performance, versatile routing technology capable of supporting various client access methods and encapsulating IPv4/IPv6 traffic, offering QoS, traffic engineering, redundancy, and VPN support.
Internet-based broadband connectivity is explored as a cost-effective alternative to dedicated WANs, divided into wired and wireless options. Wired options include DSL (Digital Subscriber Line), cable, and optical fiber networks. DSL technologies (ADSL, SDSL) use existing telephone lines, with transfer rates dependent on local loop length and cable condition. DSLAMs (DSL Access Multiplexers) at central offices concentrate connections from multiple subscribers. PPP over Ethernet (PPPoE) is used by ISPs for authentication and IP address assignment with DSL connections.
Cable technology, using coaxial cables and DOCSIS standards, offers high-speed internet. Unlike DSL, cable bandwidth is shared among users, which can lead to reduced speeds during peak usage. Optical fiber provides the highest bandwidth, marketed as Fiber To The X (FTTX), including FTTH (Fiber To The Home), FTTB (Fiber To The Building), and FTTN (Fiber To The Node). FTTH and FTTB offer superior performance, especially when combined with fiber LAN connections, but can be more costly.
Wireless broadband utilizes unlicensed radio spectrum and includes municipal Wi-Fi, cellular systems (3G, 4G, 5G, LTE), satellite internet (common in rural or mobile settings but prone to weather issues and higher cost), and WiMAX (IEEE 802.16 standard, providing broad coverage). VPNs (Virtual Private Networks) are crucial for security over public networks, offering encrypted connections, cost savings by eliminating dedicated lines, scalability, and compatibility with broadband. VPNs are implemented as site-to-site or remote access VPNS.
The final section covers ISP connectivity options based on organizational needs and budget: single-homed (single link, no redundancy), dual-homed (two links to same ISP, redundancy but ISP outage remains a single point of failure), multi-homed (two different ISPs, increased redundancy and load balancing but expensive), and dual multi-homed (redundant links to multiple ISPs, most resilient but most expensive). A comparison of broadband solutions highlights factors like shared bandwidth for cable, distance sensitivity for DSL, cost for fiber, coverage for cellular, and reliability for satellite.
A comprehensive summary of the module's key concepts is provided. This includes the definitions and distinctions of WANs and LANs, private and public WANs, various WAN topologies, carrier connections, network evolution, WAN standards (OSI Layers 1 and 2), common terminology, WAN devices, serial vs. parallel communication, circuit-switched vs. packet-switched networks, traditional (leased lines, PSTN, ISDN, Frame Relay, ATM) and modern (Ethernet WAN, MPLS, broadband) WAN connectivity, and ISP connectivity options. The importance of VPNs for secure communication is also reiterated.