Physical versus software-based WANs

• WAN router
  • physical device
  • a.k.a. border routers or edge routers
  • facilitate an organization’s access to a carrier network
  • has a digital modem interface for the WAN, which works at OSI link layer and ethernet interface for the LAN
• Software-Defined WAN (SD-WAN)
  • developed for cloud-based WAN environment
  • used alone or in conjunction with a traditional WAN
  • less costly

WAN optimization

• Compression
  • reducing file size
• Deduplication
  • one copy saved in central location
• Protocol Optimization
• Local Caching
  • storing local copies of network and internet files on a user’s computer
  • Traffic Shaping: Optimizing network performance by controlling the flow of network traffic. Three techniques are commonly used in traffic shaping
    • bandwidth throttling
    • rate limiting
    • use of complex algorithms

WAN Protocols

• Packet switching
  • packets are triplicated.
  • 3 packets are compared with each other to check for data corruption
  • at least 2 of the copies should match
• Frame relay
  • older technology designed for use on integrated services digital network but now used in other network interfaces
  • transmit data between endpoints of a WAN through a packet switching method that works at the OSI data link and physical layers
  • A fast data communication network, called a Frame Relay Network, is used to transport data packets in frames
  • includes routing address information for the destination
    • Permanent Virtual Circuits (PVCs) - Used for long-term data connections. Stays open even when data is not being transmitted
    • Switched Virtual Circuits (SVCs) - Used in temporary session connections for sporadic communications
• Asynchronous Transfer Mode (ATM)
  • older technology that encodes data using asynchronous time-division multiplexing
  • encoded data is packed into small, fixed-sized cells.
  • can send the cells over a long distance
  • uses routers as end-points between ATM networks and other networks
  • replaced for the most part by IP technologies
• High Level Data Control (HLDC)
  • Encapsulation or data link protocol that delivers data frames through a network
  • frames include multiple fields that can hold information about start and end flags, controls, Frame Chek Sequence (CS), and protocol used.
  • developed to use multiple protocols to replace Synchronous Data Link Control, which used only one protocol
  • HLDC includes error correction, flow control, and data transmission through polling
  • has three modes to define relationship between devices
    • Normal Response Mode (NRM) - Primary node must give permission to the secondary node to transmit
    • Asynchronous response mode (ARM) - Primary node allows the secondary node to initiate communication
    • Asynchronous Balanced Mode (ABM) - Both nodes can act as either the primary or secondary nodes. They can each initiate communications without permission
• Packet over Synchronous Optical Network (SONET) or Synchronous Digital Hierarchy (SDH)
  • used in WAN transport
  • define how point-to-point links communicate over fiber optics cables
• Multiprotocol Label Switching (MPLS)
  • technique for optimizing network routing
  • replaces inefficient table lookups for long network addresses with short path labels