Transport Layer Layer #4 (OSI-RM)

Transport Layer Main function of OSI Transport layer: Accept data from the Application layer and prepare it for addressing at the Network layer. The Transport layer is responsible for the overall end- to-end transfer of application data.

Transport Layer Functions of OSI Transport layer:  Segmentation of application data and reassemble these pieces into the various communication streams.  Enables multiple applications to communicate over the network at the same time on a single device.  Ensures that, if required, all the data is received reliably and in order by the correct application.  Employs error handling mechanisms.

Transport Layer services Two types of transport layer services:  Connection oriented  Connection Establishment  Reliable Data Transfer  Connection Termination Protocol example: TCP  Connectionless (datagram)  Unreliable Data Transfer Protocol example: UDP

Transmission Control Protocol (TCP) TCP is a connection-oriented protocol, described in RFC 793. Functions of TCP: 1.Connection establishment 2.Segmentation and reassembly of application data 3.Multiplexing of more than one applications 4.Error control 5.Flow Control 6.Connection termination

TCP Header

Connection establishment (Three way handshaking)

Connection establishment The 3 way handshake role: Establishes that the destination device is present on the network. Verifies that the destination device has an active service and is accepting requests on the destination port number. Informs the destination device that the source client intends to establish a communication session on that port number

Connection termination (Four way handshaking)

Segmentation and reassembly of application data

Error Recovery (Reliability)

TCP Congestion and Flow Control

Port addressing Port numbers – unique application identifiers Well known ports (Numbers 0 to 1023) : Assigned by The Internet Assigned Numbers Authority (IANA) Registered Ports (Numbers 1024 to 49151) Dynamic or Private Ports: Also known as Ephemeral Ports (Numbers to 65535)

TCP Ports

UDP Ports

TCP and UDP Protocols

Socket A socket is an IP address, a colon, and a port number. Example: :80 For servers, specifies a specific application on a specific server. For clients, specifies a specific connection on a specific client.

Multiplexing of more than one applications

User Datagram Protocol (UDP) UDP is a simple, connectionless protocol, described in RFC 768. It has the advantage of providing for low overhead data delivery. The pieces of communication in UDP are called datagrams. These datagrams are sent as "best effort" by this Transport layer protocol Functions of UDP: 1.Segmentation and reassembly of application data 2.Multiplexing of more than one applications

UDP Header Applications that use UDP include: Domain Name System (DNS) Video Streaming Voice over IP (VoIP)

TCP/UDP Comparison TCPUDP Connection-oriented deliveryConnectionless delivery, faster Uses windows and ACKsNo windows or ACKs Full headerSmaller header, less overhead SequencingNo sequencing Provides reliabilityRelies on app layer protocols for reliability FTP, HTTP, SMTP, and DNSDNS, TFTP, SNMP, and DHCP