Network Protocols

Transmission Control Protocol (TCP)

TCP Principles and Mechanisms

Key features:

1. Connection Establishment: Three-way handshake (SYN, SYN-ACK, ACK)
2. Reliable Delivery: Acknowledgment and retransmission
3. Flow Control: Sliding window mechanism
4. Congestion Control: Slow start, congestion avoidance, fast retransmit, and fast recovery
5. Ordered Data Transfer: Sequence numbers
6. Error Detection: Checksum

Example of TCP header:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|          Source Port          |       Destination Port        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Sequence Number                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Acknowledgment Number                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Data |           |U|A|P|R|S|F|                               |
| Offset| Reserved  |R|C|S|S|Y|I|            Window             |
|       |           |G|K|H|T|N|N|                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Checksum            |         Urgent Pointer        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                    Options                    |    Padding    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             data                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

TCP Performance Characteristics

1. Throughput:

   • Affected by Round-Trip Time (RTT) and packet loss
   • Theoretical max: Window Size / RTT

2. Latency:

   • Connection setup time: 1.5 RTT (three-way handshake)
   • Data transfer: At least 1 RTT per request-response cycle

3. Reliability:

   • Guaranteed delivery through acknowledgments and retransmissions
   • Ordered delivery ensures data integrity

4. Scalability:

   • Limited by connection state maintenance on servers
   • C10K problem: difficulty in handling 10,000+ concurrent connections

TCP Use Cases and Limitations

Use Cases:

• Web browsing (HTTP)
• Email (SMTP, IMAP, POP3)
• File transfers (FTP, SFTP)
• Remote administration (SSH)

Limitations:

• Head-of-line blocking in multiplexed scenarios
• Performance degradation in high-latency networks
• Overhead for small, frequent transmissions

User Datagram Protocol (UDP)

UDP Core Concepts

Key features:

1. Connectionless: No handshake required
2. Unreliable: No guarantee of delivery, ordering, or duplicate protection
3. Lightweight: Minimal protocol overhead
4. Stateless: No connection state tracking

UDP header structure:

 0      7 8     15 16    23 24    31
+--------+--------+--------+--------+
|     Source      |   Destination   |
|      Port       |      Port       |
+--------+--------+--------+--------+
|                 |                 |
|     Length      |    Checksum     |
+--------+--------+--------+--------+
|
|          data octets ...
+---------------- ...

UDP Performance Analysis

1. Throughput:

   • Higher potential throughput than TCP due to less overhead
   • Not limited by congestion control mechanisms

2. Latency:

   • Lower latency than TCP for initial data transfer (no handshake)
   • Consistent latency due to lack of retransmission delays

3. Packet Loss:

   • No built-in recovery from packet loss
   • Application must implement its own reliability if needed

4. Scalability:

   • Excellent for broadcast and multicast scenarios
   • Efficient for large numbers of small transactions

UDP Applications and Constraints

Applications:

• Real-time gaming
• Voice over IP (VoIP)
• Streaming media
• DNS lookups

Constraints:

• Lack of built-in reliability mechanisms
• No congestion control (potential for network flooding)
• Limited message size (65,507 bytes maximum)

Hypertext Transfer Protocol (HTTP)

http1_http2_http3

WebSocket Protocol

WebSocket Full-Duplex Communication

WebSocket provides a persistent, full-duplex communication channel over a single TCP connection.

Key features:

1. Bi-directional: Both client and server can send messages
2. Low-latency: Reduced overhead after initial handshake
3. Real-time: Immediate message delivery

WebSocket Performance Metrics

1. Connection Overhead:

   • Initial handshake: Similar to HTTP
   • Subsequent messages: Minimal frame overhead (2-14 bytes)

2. Latency:

   • Low latency for real-time updates
   • No need for polling or long-polling

3. Scalability:

   • Efficient for large numbers of concurrent connections
   • Challenges with very high connection counts (C10K problem)

4. Bandwidth Usage:

   • Reduced compared to polling techniques
   • Efficient for small, frequent updates

WebSocket Use Cases and Limitations

Use Cases:

• Real-time collaborative applications
• Live sports updates
• Financial trading platforms
• Multiplayer games

Limitations:

• Not supported in older browsers
• Potential for abuse (e.g., bypassing same-origin policy)
• Challenges with load balancing and scaling

Comparative Analysis