Transport Layer Module 6

Transport Layer Module 6

• This module covers the transport layer in the IT & CS departments.
• The transport layer's primary function is to provide data transport from one process to another, independent of the physical network.

Topic Learning Outcomes

• Define the transport layer's main function.
• Define design issues of the transport layer.

Role of the Transport Layer

• The transport layer is central to the protocol hierarchy.
• The network layer facilitates packet delivery (datagrams or virtual circuits).
• The transport layer builds on this, delivering data between processes on different machines reliably.
• This reliability is independent of the physical network's current setup.

Key Topics/Outline of Discussion

• Introduction to the transport layer
• Sockets
• Transmission Control Protocol (TCP)
• User Datagram Protocol (UDP)

Introductory Concepts on the Transport Layer

• The transport layer functions only between end hosts (not intermediary nodes).
• Transport layer protocols handle data as packets (segments).

Transport Layer: Multiplexing Services

• The network layer handles communication between hosts.
• The transport layer facilitates communication between processes on different hosts.
• A process is a program instance running on a host.
• Multiple processes can communicate between two hosts (e.g., FTP and Telnet sessions).

Transport Layer: Multiplexing Services (continued)

• The transport layer enables multiplexing/demultiplexing between various processes by adding an address to each segment.
• These addresses only need to be unique within a given host, and are called port numbers in TCP/IP.
• The 5-tuple uniquely identifies a process-to-process connection.

Intro: TPDU

• Transport Protocol Data Units (TPDUs) nest within packets and frames.

Intro: Connection Establishment

• This section describes the process of setting up a connection across multiple hosts, employing Transmission Sequence Access Points (TSAPs).

Intro: Transport Service Primitives

• LISTEN: Blocks until a connection attempt is made.
• CONNECT: Initiates a connection attempt.
• SEND: Sends data.
• RECEIVE: Blocks until data arrives.
• DISCONNECT: Releases the connection.

Introduction: Protocol Stacks

• The application protocol (e.g., an application program interface), which facilitates communication between the application program and the TCP stack.
• Socket interface: the communication bridge between the application program and the transport layer (e.g., TCP or UDP)
• Transport Layer protocols: e.g., TCP and UDP protocols are used.
• Network Layer: handles data between hosts.
• Data Link Layer: Handles data frames between connected devices.
• Physical Layer: The physical medium through which data is transmitted.

Section B: Sockets

• Sockets are programs designed to interact between the user program and the TCP/IP protocol stack.
• They are implemented as sets of library function calls and operate as data structures within a program on an end-host system.
• Client-server communications rely on paired sockets for interaction.

Socket Framework

• Application programs utilize sockets in user space and socket libraries to handle the interaction.
• The TCP/UDP protocols are located in kernel space, responsible for the communication between the programs and the host’s physical network.
• The physical network (driver) handles communication at the hardware level.

Socket Families

• Different socket domains include Internet (AF_INET), Unix (AF_UNIX), Novell IPX (AF_IPX), and AppleTalk (AF_APPLETALK).
• Internet sockets use IP addresses and port numbers for communication, Unix domain sockets use filenames.

Type of Socket

• Stream sockets (SOCK_STREAM) use TCP.
• Datagram sockets (SOCK_DGRAM) use UDP.
• Raw sockets (SOCK_RAW) are used for testing.

Creating a Socket

• The socket() function creates a communication endpoint.
• The function arguments define the protocol family, socket type, and protocol.
• The type defines whether communication is connection-oriented (e.g., TCP) or connectionless (e.g., UDP).

TCP Client/Server

• This section outlines the steps involved in a TCP client-server communication.

TCP Server & System Calls

• sock_init(): Creates the socket.
• bind(): Registers a port with the system.
• listen(): Establishes a client connection.
• accept(): Accepts client connections.
• read/write(data): Exchanged data.
• close(): Shuts down.

TCP Client & System Calls

• sock_init(): Creates the socket.
• connect(): Sets up the connection.
• read/write(data): Exchanged data
• close(): Shuts down.

Server Side Socket Details

• Describes the system calls for server-side sockets, including socket(), bind(), listen(), accept(), read(), and write().

Client Side Socket Details

• Explains client-side socket procedures using socket(), connect(), read(), and write().

Section C: Transmission Control Protocol (TCP)

• A reliable, connection-oriented protocol.
• Full duplex communication (simultaneous transmission in two directions).
• TCP provides services such as reliable transport, flow control, and congestion control.
• UDP doesn't offer these features.

TCP Services

• TCP converts the unreliable IP service into a reliable service, ensuring correct delivery, sequenced data transfer, and only one occurrence of a segment.
• TCP uses ARQ (Automatic Repeat reQuest) protocols for recovering lost segments.
• Some TCP versions employ Go-Back-N and Selective Repeat.

TCP Services (continued)

• TCP segments have unique segment numbers to help manage them and recover lost data.
• Key differences between TCP and data link layer ARQ protocols involve the implementation, which operates between two hosts connected to a network rather than between nodes.

The TCP Header

• A TCP header contains fields for source port, destination port, sequence number, acknowledgment number, window size, urgent pointer, checksum, and data (optional).

Sample TCP Packet

• Sample example of a TCP packet structure.

TCP Connection Establishment

• Active and passive participants use a three-way handshake to establish a connection.
• Synchronization messages (SYN) specify the sequence numbers, followed by acknowledgment numbers.

Closing a TCP Connection

• A client initiates the closure by sending a FIN (Finish) signal.
• The server acknowledges the request and also sends its respective FIN, which is then acknowledged by the client, signaling the disconnection.

Closing a TCP Connection (continuation)

• After closing the connection, the client enters a timed wait state to avoid errors with simultaneous messages.
• This waiting period allows for all data to be processed before the final closure.

The two-army problem.

• Illustrates the challenges in symmetric release scenarios and identifies issues with the two-army problem.

Four protocol scenarios for releasing a connection

• This outlines scenarios involving normal three-way handshakes and situations where the final acknowledgment, or subsequent data signals (DR) to release the connection is lost.

Section D: User Datagram Protocol (UDP)

• An unreliable, connectionless protocol.
• TCP doesn't offer flow control and UDP has no flow control.
• Ideal for applications prioritizing speed over accuracy (e.g., video and voice).
• UDP uses a simple packet format using a metaphorical analogy to postal service delivery.

UDP Protocol

• UDP works by taking application data, packaging it, passing it to the IP layer, sending data, and allowing the transmission to end.
• No connection setup is required before sending data.

UDP Packet

• UDP segments primarily offer multiplexing capabilities over IP.
• The length field represents the entire packet, including the header.
• The checksum field helps verify data integrity.

This quiz delves into the transport layer of networking, focusing on its primary functions and design issues. You'll explore critical topics such as TCP, UDP, and the role of sockets in delivering data between processes reliably, regardless of the physical network setup.