Understanding Serial Links in Networking | Generated by AI
Question: What are serial links in networking?
Answer:
In computer networking, serial links refer to point-to-point connections that transmit data one bit at a time sequentially over a single channel, as opposed to parallel links that send multiple bits simultaneously.
Key Characteristics
- Point-to-Point Nature: Serial links are typically dedicated connections between two devices (e.g., routers), with no need for link-layer addressing like MAC addresses. They are often “unnumbered” at the IP level since there’s only one possible destination.
- Common Use in WANs: Historically, serial interfaces on routers were used for Wide Area Network (WAN) connections, such as leased lines (T1/E1, DS3), Frame Relay, or PPP links. These provided reliable long-distance connectivity through telecom providers, where the carrier supplied clocking and the link operated at speeds from 56 kbps up to around 52 Mbps (e.g., via HSSI).
- DTE/DCE Roles: One end is Data Terminal Equipment (DTE, e.g., router), and the other is Data Circuit-terminating Equipment (DCE, e.g., CSU/DSU or modem), which provides clocking for synchronous transmission.
- Encapsulation Protocols: Common Layer 2 protocols include HDLC (default on Cisco serial interfaces), PPP, or Frame Relay.
Comparison to Ethernet Links
- Ethernet is designed for Local Area Networks (LANs), supports multi-device connectivity (via switches), uses MAC addressing, and operates at much higher speeds (100 Mbps+).
- Serial links prioritize distance and simplicity for dedicated point-to-point WANs, while Ethernet excels in shared, high-bandwidth local environments.
Modern Relevance
While serial links were standard for WANs in the past (common in CCNA/CCNP studies and older deployments), they are largely replaced today by Ethernet handoffs, Metro Ethernet, MPLS, or fiber-based services for higher speeds and easier management. They still appear in legacy systems, industrial controls, console access (RS-232), or niche low-speed applications.
References:
- Serial communication - Wikipedia
- What’s the difference between Ethernet link and Serial link? - Network Engineering Stack Exchange
-
[Serial Connections and HDLC CCNA Blog](https://www.ccnablog.com/serial-connections-and-hdlc/) - Serial Point-to-Point Overview - Cisco Press