[Day 10] 8. Wide Area Network (WAN)

Lines used for WAN are:

1. Dedicated Line (Point-to-Point or Leased Line)

• Explanation: As you correctly noted, a dedicated line, or leased line, is a point-to-point connection. This means it connects two specific locations directly, without any intermediate switching. The connection is always active, and bandwidth is fully reserved for the customer.
• Cost: This type of line is indeed expensive, especially as the distance between the two points increases. The cost is based on the distance and bandwidth, as you're paying for the exclusive use of the connection.
• Use case: It is often used by businesses requiring constant and reliable communication, like between data centers or headquarters and branch offices.

2. Circuit-Switched Line (e.g., Telephone Networks, ISDN)

• Explanation: In a circuit-switched network, a dedicated path is set up between the two points for the duration of the communication session (e.g., a phone call or an ISDN connection). Once the communication is complete, the circuit is disconnected, and the resources are released.
• Billing: You are only charged for the duration of the connection, unlike a leased line where the cost is fixed.
• Example:
  • PSTN (Public Switched Telephone Network): The traditional telephone network, where a circuit is set up for the duration of the call.
  • ISDN (Integrated Services Digital Network): A more advanced version of circuit-switched technology that can carry voice, video, and data simultaneously over the traditional telephone lines.

3. Packet-Switched Line

• Explanation: Packet-switched networks break data into smaller packets, which are sent independently through the network. Each packet might take different paths to reach its destination, and the packets are reassembled in the correct order when they arrive. This is different from circuit-switched networks, where a dedicated path is established for the entire session.
• Examples:
  • Frame Relay: One of the original packet-switched technologies, popular in the 1990s. It allowed for "virtual circuits" between locations, meaning the network was shared, and customers were billed based on their data usage.
  • MPLS (Multiprotocol Label Switching): A more advanced form of packet-switched technology that offers higher performance and QoS (Quality of Service).
  • Internet-based services: ISPs now largely use packet-switched networks (like MPLS and the internet) because they allow for better bandwidth utilization.
• Over-subscription: This is an advantage for ISPs, where the bandwidth sold to customers can exceed the actual physical bandwidth, since not all users need full bandwidth all the time. This reduces costs for the ISP but requires careful management to avoid congestion.

Clarification on Outdated Technologies

• Dedicated Lines: While dedicated leased lines are less common for general internet access due to cost, they are still used by enterprises for critical connections, such as between data centers or to connect large corporate offices.

• Circuit-Switched Networks: These are largely outdated for WANs and have been replaced by packet-switched technologies. ISDN, for example, has been almost entirely phased out in favor of more modern alternatives like fiber and broadband.

• Packet-Switched Networks: These have largely replaced the older technologies due to better scalability, efficiency, and cost-effectiveness. Most modern WANs, including the internet itself, are packet-switched networks. Even older protocols like Frame Relay have mostly been replaced by newer technologies like MPLS.

Revised Summary:

Traditional WAN technologies include:

1. Dedicated Line (Leased Line): Expensive point-to-point connections offering constant, reliable bandwidth.
2. Circuit-Switched Networks: Used in older telephone systems and ISDN, where a dedicated path is established for each communication session.
3. Packet-Switched Networks: Modern WANs that break data into packets and dynamically route them across shared networks, with technologies like MPLS now dominating.

While both dedicated and circuit-switched lines are largely outdated, packet-switched WAN technologies continue to evolve, enabling modern services like broadband internet and VPNs.