In this article, we learn about what a leased line is, Leased Line Definition, Leased Line Benefits, Infrastructure, Components, Types of Leased Lines, and Disadvantages
Leased lines
As a dedicated connection option for connecting endpoint devices across several Local Area Networks (LANs), leased lines are a fundamental technology in Wide Area Networks (WANs). They are acknowledged as a private, dedicated telecommunications circuit that a company rents from a service provider.
Leased Line Definition
A dedicated point-to-point link with a fixed-bandwidth data connection is called a leased line. It’s a circuit for serial communications between two sites.
The term “leased line” describes a situation in which a client does not construct or permanently own the connection, but instead pays a set monthly cost to use an Internet service provider’s (ISP) infrastructure.
Additionally, there are a number of synonyms for leased lines, such as:
- Dedicated connections.
- Dedicated Internet Access (DIA).
- Dedicated lines.
- Point-to-point links/lines.
- Private lines or private circuits.
- Serial links/lines or leased circuits.
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Leased Line Benefits
Leased lines are generally chosen by businesses and large organizations due to their superior performance guarantees.
| Feature | Description |
|---|---|
| Dedicated & Private | The bandwidth is uncontended, meaning it is 100% reserved exclusively for the organization’s traffic, enhancing security and privacy. |
| Guaranteed Bandwidth | The connection provides a fixed, guaranteed amount of bandwidth that does not fluctuate due to congestion from other users. Higher bandwidth can be achieved and controlled. |
| Symmetrical Speeds | Many leased lines offer equal upload and download speeds, which is ideal for real-time applications like Voice over IP (VoIP) and video conferencing. |
| High Reliability | They offer a stable, always-on connection with minimal downtime, often backed by a Service Level Agreement (SLA) guaranteeing specific performance and uptime. |
| Low Latency | The direct, dedicated path minimizes delays (latency and jitter) in data transmission. |
Operation and Infrastructure
The Circuit
Contrary to popular belief, a leased line is not a lengthy physical wire that connects two sites. It creates a permanent, direct connection between two fixed places via a reserved, dedicated circuit, which may be copper or fiber optic cable.
Two wire pairs are needed for unidirectional data network transmission on each wire since the line uses full-duplex transmission, which transfers data in both directions at the same time. Due to their extensive regional network infrastructure, ISPs are typically the best option for obtaining a leased line.
Speed and Capacity
Leased lines traditionally use synchronous serial lines. Common types and speeds include:
- T1 (DS1): 1.544 Mbps.
- E1: 2.048 Mbps.
- T3 (DS3): 44.736 Mbps.
Leased lines’ dedicated capacity eliminates worries about fluctuating network conditions like jitter and latency. But by today’s standards, the speeds provided
Physical Routing and Components
The service provider uses a sophisticated network to establish the point-to-point link, even though the line seems straightforward to the client:
- Leased Line Service (Layer 1): The telco network, which is made up of cables and switches at central offices (COs), provides the service while concealing from the client the physical intricacy. Bit delivery between the connected devices is ensured via the leased line, which is a Layer 1 service.
- Local Loop: From the customer’s demarcation point (Demarc) to the closest Central Office (CO) of the provider, the cabling typically runs copper wiring.
- Demarcation Point (Demarc): Where the customer’s accountability starts and the provider’s responsibility ends is known as the Demarcation Point (Demarc).
- CPE and CSU/DSU: A router at the customer site (Customer Premises Equipment, or CPE) is connected to the provider’s line by a Channel Service Unit/Data Service Unit (CSU/DSU), which is necessary to give the router clocking.
- ISP Network: To preserve the point-to-point connection, specialized switching devices operate as signal boosters inside the ISP’s premises. In order to connect to the Optical Line Termination (OLT) at the ISP, traffic may pass via complex equipment, such as the Optical Network Terminal (ONT) at the customer’s branch. The OLT processes and multiplexes optical signals. The data may then travel through core routers (using BGP and OSPF) and edge routers (perhaps utilizing Virtual Routing and Forwarding (VRF) and Multiprotocol Label Switching (MPLS) labels).
- Technology: A leased line may make use of satellite, fiber optic, DSL, or MPLS, among other technologies. Dense Wavelength Division Multiplexing (DWDM) or Synchronous Digital Hierarchy (SDH) are two possible physical transmission technologies that are employed between ISP routers and OLTs.
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Data Link Protocols
The customer’s routers must wrap the network layer packet using a Layer 2 (data link) protocol because the leased line is a Layer 1 (physical) service. These are the two most widely used protocols:
- High-Level Data Link Control (HDLC): Cisco routers’ standard encapsulation on a serial connection.
- Point-to-Point Protocol (PPP): When connecting Cisco routers to non-Cisco devices or when capabilities like authentication are required, the Point-to-Point Protocol (PPP) is utilized.
Types of Leased Lines
Typical uses for leased lines include:
- Linking the headquarters and branch offices.
- Internet connectivity for companies that need consistent, assured bandwidth.
- Excellent video conferencing and voice over IP (VoIP).
- Connectivity to data centers and cloud service access.
Types of leased lines include:
- Internet Leased Line (ILL): A direct internet connection with guaranteed bandwidth is known as an Internet Leased Line (ILL).
- Point-to-Point Leased Line: Establishes a connection between two private sites, such as an office.
- MPLS Leased Line: Provides secure multi-site communication using MPLS.
- Ethernet Leased Line: Provides fast communications via Ethernet technology.
Disadvantages and Modern Context
Although they provide better service, leased lines do have disadvantages:
- Cost: Because the consumer pays for dedicated, always-on capacity even while the line is idle, they are substantially more expensive than traditional broadband and switched services.
- Scalability: Since they signify a long-term physical link, they are typically not scalable.
- Speed (Historical): In the past, speeds were restricted (e.g., T1 at 1.544 Mbps or T3 at 44.736 Mbps).
- Availability: They may take longer to set up and require adequate infrastructure availability.
Decline in Use
Although leased-line WANs have been around for more than 50 years (since the 1960s), they are becoming significantly less frequent and are rarely used nowadays. They have been mostly superseded by newer, faster, and more affordable WAN technology.
The functionality traditionally provided by leased lines has been superseded by technologies such as:
- A leased-line connection may occasionally use ISDN as a backup service.
- Ethernet wide area networks (WANs), such as E-Line service, use Ethernet standards to deliver a point-to-point service that is comparable to a long crossover connection.
- For private WAN services, MPLS (Multiprotocol Label Switching) has completely supplanted older technologies like Frame Relay, but it still allows access via serial leased lines.
A private, dedicated motorway connecting two fixed corporate locations is comparable to a leased line. No matter how clogged the public roadways (the ISP’s overall network) get, your private motorway guarantees that your traffic will always flow without interruptions or delays brought on by other customers.
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