- 2071 Chaitra · 1+2 marks
Port numbers and transport services
Short answer
Port numbers (16-bit) identify specific processes on a host, enabling process-to-process delivery since IP addresses only identify hosts. Transport layer services include process-to-process delivery, segmentation/reassembly, multiplexing/demultiplexing, connection management (TCP), reliable delivery with error control and sequencing (TCP), flow control, and congestion control.
Why is port number used in networking? What are the services of the transport layer?
Why port numbers are used
An IP address only identifies the host, but many processes run on one host at the same time. A port number (16 bits, 0 to 65,535) identifies the particular application process, so the transport layer can deliver data to the correct process (process-to-process delivery). The pair IP address + port is a socket.
| Range | Name | Examples |
|---|---|---|
| 0 to 1023 | Well-known | HTTP 80, HTTPS 443, FTP 21, SMTP 25, DNS 53 |
| 1024 to 49151 | Registered | MySQL 3306 |
| 49152 to 65535 | Dynamic / ephemeral | Client-side ports |
Services of the transport layer
- Process-to-process delivery using ports.
- Segmentation and reassembly of application data.
- Multiplexing and demultiplexing of many applications over the single network-layer (IP) service.
- Connection management (set-up and release; TCP).
- Reliable delivery: error control, sequencing and retransmission (TCP).
- Flow control to protect the receiver and congestion control to protect the network.
✓ Answer checked by Claude Opus 5.5 (high effort)
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