CPEG514 Advanced Computer Networkst University of Nizwa Faculty of Engineering and Architecture Electrical and Computer Engineering CPEG514 Advanced Computer Networkst Week 12 Atef Abu Salim Spring 2014/2015

Transport Layer Layer 4. The transport layer is responsible for: CPEG514 Advanced Computer Networks Transport Layer Layer 4. The transport layer is responsible for: the delivery of a message from one process to another ( Process-to-Process delivery ). Port addressing : get the message to the correct process on the computer via port address. provides virtual end-to-end links between peer processes. Segmentation and reassembly : a message is divided into transmittable segments each segment containing a sequence no. Connection Control: connection oriented or connectionless. Flow control : Error control:

Process-to-Process delivery CPEG514 Advanced Computer Networks Process-to-Process delivery

Process-to-Process delivery cont. CPEG514 Advanced Computer Networks Process-to-Process delivery cont. The transport layer is responsible for Process-to- Process delivery , the delivery of a packet, part of a message, from one process to another. The process communication in a client/ server relationship.

CPEG514 Advanced Computer Networks Port Address At the transport layer, we need a transport layer address called Port Number, to choose among multiple processes running on the destination. The destination port number is needed for delivery. The source port number is needed for reply. In the internet model , the port numbers are 16- bit integer between 0 and 65535.

CPEG514 Advanced Computer Networks IANA range The IANA(Internet Assigned Number Authority) has divided the port numbers into three ranges: Well known port: 0-1023 (assigned and controlled By IANA). Registered ports :1024 – 49151(registered with IANA). Dynamic ports: 49152 – 65535, they can be used by any process.

CPEG514 Advanced Computer Networks Socket address The socket address is the combination of IP address and UDP/TCP port number.

Connectionless Versus Connection-Oriented Service CPEG514 Advanced Computer Networks Connectionless Versus Connection-Oriented Service A transport layer protocol Can either be connectionless or connection-oriented. Connectionless service: *The packet are sent from one to another with no need for connection establishment or connection release. * The packet are not numbered ; they may be delayed or lost or may arrive out of sequence. * There is no acknowledgment either. UDP is connectionless

Connectionless Versus Connection-Oriented Service cont. CPEG514 Advanced Computer Networks Connectionless Versus Connection-Oriented Service cont. connection-oriented service: *In a connection-oriented service, a connection is first established between the sender and receiver. * Data are transferred. * At the end , the connection is released. TCP and SCTP are connection-oriented protocol.

User Datagram Protocol (UDP) CPEG514 Advanced Computer Networks User Datagram Protocol (UDP)

User Datagram Protocol (UDP) cont. CPEG514 Advanced Computer Networks User Datagram Protocol (UDP) cont. UDP (User Datagram Protocol) creates a transport layer connection between two processes. The UDP is called a connectionless, unreliable transport protocol. It does not add anything to the service of IP except to provide process-to-process communication, also it performs very limited error checking. UDP is a very simple protocol using a minimum of overhead and faster than TCP.

User Datagram Protocol (UDP) cont. CPEG514 Advanced Computer Networks User Datagram Protocol (UDP) cont. If a process wants to send a small message and does not care much about reliability , it can use UDP. Sending a small message by using UDP takes much less interaction between the sender and receiver than using TCP and SCTP. The port number identifies the process, or running application program. So using the port number, UDP directs the packet to the correct location. No flow control. No ack of received packets. Only error control is if a checksum error is detected, it quietly drops the packet.

User Datagram Protocol (UDP) cont CPEG514 Advanced Computer Networks User Datagram Protocol (UDP) cont UDP works well with apps that have their own error and flow control; works well with multicasting, SNMP, FTP,TFTP and RIP. No error control mechanism in UDP except the checksum. When the receiver detect the an error through the checksum, the user datagram is silently discarded.

CPEG514 Advanced Computer Networks Example Example: a user wants to know the day and time from a remote machine. Daytime client port # = 52000, but Daytime server port # = 13.

Well-known ports used with UDP CPEG514 Advanced Computer Networks Well-known ports used with UDP

CPEG514 Advanced Computer Networks User datagram format Checksum : This failed is used to detect errors over the entire user datagram (header and data).

User datagram format cont. CPEG514 Advanced Computer Networks User datagram format cont. Ethernet Frame IP Datagram UDP Datagram Ethernet Header IP Header UDP Header UDP Data UDP Length = IP length – IP header’s length

Multiplexing and De-multiplexing CPEG514 Advanced Computer Networks Multiplexing and De-multiplexing Port 1 Port 2 Port n UDP: Multiplexing IP

Multiplexing and De-multiplexing cont. CPEG514 Advanced Computer Networks Multiplexing and De-multiplexing cont. Port 1 Port 2 Port n UDP: De-multiplexing Based on port number IP

Transmission Control Protocol (TCP) CPEG514 Advanced Computer Networks Transmission Control Protocol (TCP)

Transmission Control Protocol (TCP) cont. CPEG514 Advanced Computer Networks Transmission Control Protocol (TCP) cont. TCP provides a process-to-process (program-to- program) communication service using port numbers. TCP is a connection oriented protocol; it creates a virtual connection between 2 TCPs to send data. TCP uses the flow, error control and congestion control mechanisms at the transport level. The TCP packet is called a segment

Transmission Control Protocol(TCP) cont. CPEG514 Advanced Computer Networks Transmission Control Protocol(TCP) cont. TCP is called reliable transport protocol , it adds connection-oriented and reliability to the services of IP. TCP can create a full-duplex service.

Well-known ports used by TCP CPEG514 Advanced Computer Networks Well-known ports used by TCP

TCP Services: Process-to-process communication: Reliable services: CPEG514 Advanced Computer Networks TCP Services: Process-to-process communication: Reliable services: Connection-Oriented service: Full-Duplex Communication: TCP can create a full-duplex service. Data can flow in both directions at the same time

TCP Services cont. Sending and Receiving Buffers: CPEG514 Advanced Computer Networks TCP Services cont. Sending and Receiving Buffers: Buffers on each side hold the data to be transmitted , sent and received. Stream Delivery service: TCP provides a stream delivery service. It breaks up the data stream into segments of variable size. Each segment receives a header and is handed off to the IP layer.

TCP Services cont. Segments: CPEG514 Advanced Computer Networks TCP Services cont. Segments: breaks up the data stream into segments of variable size. Each segment receives a header and is handed off to the IP layer.

CPEG514 Advanced Computer Networks TCP segments

CPEG514 Advanced Computer Networks TCP segment format