TCP, UDP, OSI Model, and NAT

• Lecture 4 focuses on TCP, UDP, and the OSI model within the context of Network Architecture.

IP Protocol

• The IP protocol facilitates device communication on private networks or the internet.
• It operates in a single-way communication manner.
• The IP protocol relies on IP addressing and IP datagrams.

NAT and NAT-PAT

• Network Address Translation enables communication between networks.
• NAT achieves this by converting IP addresses across those networks.
• There are three types of NAT: Static, Dynamic, and PAT-NAT.
• Static NAT assigns a unique public IP to a private device on the internet.
• Dynamic NAT involves a router using a pool of public IPs for private devices.
• PAT-NAT (Port Address Translation) allows multiple private devices to share a single public IP.

Today's Problematic: Application Identification

• A key challenge is determining which application an IP packet is intended for.

TCP Protocol

• The IP protocol only provides an address and does not identify the intended application for a packet.
• Combining the IP protocol with other protocols becomes necessary to solve the problem of application identification for IP Packets.
• The diagram shows packets with MAC, IP, and TCP addresses

Encapsulation Overview

• Frame Header encapsulates IP Header, TCP or UDP Header, HTTP/HTTPS Header, HTML Header.

TCP (Transmission Control Protocol)

• TCP is an extension of the IP protocol, often discussed as TCP/IP.
• It establishes connections between two applications running on different devices.
• TCP uses virtual ports for application identification.
• TCP packets are incorporated into IP packets.
• TCP necessitates multiple routings to create a connection, with each routing processed by IP.

TCP Packet Datagram

• Header size: 20 bytes, encompassing source and destination ports (16 bits each).
• Sequence and acknowledgment numbers are 32 bits each.
• Furthermore, there are settings for header length (4 bits), reserved bits (3 bits), and flags (9 bits).

TCP/IP Packet Datagram

• Contains IP Header (96 bits), Source IP and Destination IP (32 bits each.)
• It also includes IP Options (32 bits), Source Port and Destination Port (16 bits each).
• TCP Header (128 bits).

TCP/IP Protocol: Connection Establishment

• TCP enables connection between devices.
• Both devices must follow a "three-way handshake" pattern.
• The handshake serves the purposes of confirming readiness to transfer data and prevents hijacking.
• The process involves agreeing on an initial sequence number and incrementing it with each data transfer.

TCP/IP Protocol: Three-Way Handshake

• Client sends SYN to the Server for Synchronization
• Server responds with SYN + ACK for Synchronization with Acknowledgement
• Client responds with ACK for Acknowledgement

TCP/IP Protocol: Data Transfer

• During Transfer: TCP uses sequence and acknowledgement numbers to confirm the reliability of its connection.
• Sequence numbers guarantee the arrival order of packets.
• Checksums detect errors.
• Acknowledgement numbers identify lost or late data segments.
• With TCP, assurance that its packets have been well received is guaranteed through acknowledgement.

TCP/IP Protocol: Data Transfer Diagram

• Client sends Data to Server; Server then sends Acknowledgement to Client.

TCP/IP Protocol: End of Connection

• Termination of a TCP connection uses a "four-way handshake".
• Both ends of the connection can independently manage the termination process.
• The end of connection involves a Four-way handshake of FIN and ACK signals.

UDP (User Datagram Protocol)

• UDP provides an alternative to TCP and UDP allows for data transfers without high reliability.

UDPs Problematic

• TCP is great for connection's reliability, but it imposes a heavy protocol for it and packet's order arrival.
• Sometime, speed over reliability and packet's order is wanted, mostly for real time services.
• For example, a direct visio conference (Skype, Teams...) or online video games, prefers a small data packet lost instead of blocking the flux while waiting for the packet to reach destination.

UDP Protocol Defined

• Alternative to TCP.
• UDP uses ports, but it doesn't control connection.
• Mostly used to send small amounts of data quickly, where the arrival order is not mandatory.
• Examples for usage: video streaming, video-games, music streaming, realtime information, DNS...etc.

UDP Datagram

• Header: 8 bytes includes 16 bits for source and destination ports.
• Total length and checksum also take 16 bits each.
• The datagram accommodates a max of 65,508 bytes including the header.

UDP/IP Datagram

• Contains IP Header (96 bits), Source IP and Destination IP (32 bits each.)
• IP Options (32 bits), Source Port and Destination Port (16 bits each).
• UDP Header (32 bits), and Data (Max. 65 505 bytes).

OSI Model

• The Open Systems Interconnection model is a conceptual model that is used to standardize the layers
• The OSI layers are required for enabling communication between devices over a network.
• Layers from top to bottom: Upper Layers, Transport Layer, Network Layer, Data Link Layer, Physical Layer

Encapsulation in OSI Model

• Encapsulation includes data from a protocol into another one

OSI Model Layers

• Application: Data from the application. no specific network service, example: applicative data
• Presentation: Encoding of applicative data, example: HTML, XML, JSON
• Session: Communication and sessions control, example: HTTP/HTTPS, MQTT
• Transport: Connection and data control, example: TCP/UDP
• Network: Network addressing, determines the path in a network, example: IP, LoraWAN
• Data-Link: Physical addressing (using MAC address) device to device, example: Ethernet/xDSL, LoRa
• Physical Layer: Binary transmission, digital or analog, example: RJ45 cables, optical fiber, WiFi waves, LoRa waves...etc.