What Does Layer 4+ Refer To?

Layer 4+ refers to the Internet layers 4 and above (transport and application layers)

The term Layer 4+ refers to the Internet layers 4 and above, which are more closely related to customers/subscribers’ applications and the way they use Ethernet, the Internet, and perceive performance or quality.

Here is a summary of the seven layers defined by the Open Systems Interconnection (OSI) Model for communication systems, applied to Ethernet and Internet links

  • Layer 7 – Application Layer (e.g., Telnet, FTP, HTTP, HTTPS, POP, SMTP, DNS, etc.)
  • Layer 6 – Presentation Layer or Encoding/Encryption (e.g., MIME, SSL/TLS, etc.)
  • Layer 4 – Transport Layer or TCP/UDP Layer (manages and terminates connections between local and remote applications)
  • Layer 3 – Network Layer or IP Layer (uses IP addresses for data routing and forwarding between different networks)
  • Layer 2 – Data Link Layer or MAC and LLC Layer (node to node data transfer)
  • Layer 1 – Physical Layer (Electrical/Copper, Laser/Fiber, etc.)

The modern Internet is not directly based on the OSI model, but on a simpler TCP/IP model:

OSI Model

TCP/IP Model

7 - Application Layer

Application Layer

6 - Presentation Later

5 - Session Layer

4 - Transport Layer

Transport Layer

3 - Network Layer 3

Internet Layer

2 - Data Link Layer

Network Access Layer

1 - Physical Layer

Related Test Applications

With regards to VeEX test and measurement solutions, the following stateful test features are considered part of the Layer 4+ test suite:

  • V-TEST Internet Access Speed Test (compatible with Ookla Speedtest™)
  • V-PERF RFC6349-based Test (compatible with iPerf3)
  • V-FTP FTP Upload and Download Performance Test