Chapter 4 - OSI Transport Layer CCNA Exploration version 4.0

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Explain the role of Transport Layer protocols and services in supporting communications across data networks Analyze the application and operation of TCP mechanisms that support reliability Analyze the application and operation of TCP mechanisms that support reassembly and manage data loss. Analyze the operation of UDP to support communicate between two processes on end devices

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Nội dung Text: Chapter 4 - OSI Transport Layer CCNA Exploration version 4.0

Chapter 4 - OSI Transport Layer CCNA Exploration version 4.0
Overview • Explain the role of Transport Layer protocols and services in supporting communications across data networks • Analyze the application and operation of TCP mechanisms that support reliability • Analyze the application and operation of TCP mechanisms that support reassembly and manage data loss. • Analyze the operation of UDP to support communicate between two processes on end devices H c vi n m ng Bách khoa - Website: www.bkacad.com 2
Transport Layer Role and Services • Explain the purpose of the Transport layer • 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. H c vi n m ng Bách khoa - Website: www.bkacad.com 3
Transport Layer Role and Services • Major functions of the transport layer and the role it plays in data networks – Tracking the individual communication between applications on the source and destination hosts. – Segmenting data and managing each piece. – Reassembling the segments into streams of application data. – Identifying the different applications. H c vi n m ng Bách khoa - Website: www.bkacad.com 4
Separating Multiple Communications • Computer connected to a network that is simultaneously receiving and sending e-mail and instant messages, viewing websites, and conducting a VoIP phone call. Each of these applications is sending and receiving data over the network at the same time. However, data from the phone call is not directed to the web browser, and text from an instant message does not appear in an e-mail. H c vi n m ng Bách khoa - Website: www.bkacad.com 5
Segmentation • Without segmentation, only one application, the streaming video for example, would be able to receive data. You could not receive e-mails, chat on instant messenger, or view web pages while also viewing the video. H c vi n m ng Bách khoa - Website: www.bkacad.com 6
Controlling the Conversation • Segmentation • Conversation and Reassembly - Multiplexing - Most networks There may be have a limitation on many applications the amount of data or services running that can be on each host in the included in a single network. Each of PDU. The these applications Transport layer or services is divides application assigned an data into blocks of address known as data that are an a port so that the appropriate size. At Transport layer can the destination, the determine with Transport layer which application reassembles the or service the data data before is identified. sending it to the destination application or service. H c vi n m ng Bách khoa - Website: www.bkacad.com 7
Controlling the Conversation H c vi n m ng Bách khoa - Website: www.bkacad.com 8
Transport Layer Role and Services • At the Transport layer the three basic operations of reliability are: – Tracking transmitted data – Acknowledging received data – Retransmitting any unacknowledged data H c vi n m ng Bách khoa - Website: www.bkacad.com 9
Transport Layer Role and Services • Transmission Control Protocol (TCP) – TCP is a connection-oriented protocol, described in RFC 793. TCP incurs additional overhead to gain functions. Additional functions specified by TCP are the same order delivery, reliable delivery, and Web, email, file transfer flow control. Each TCP segment has 20 bytes of overhead in the header encapsulating the Application layer data, whereas each UDP segment only has 8 bytes of DNS, Video streaming, VoIP overhead • UDP is a simple, connectionless protocol, described in RFC 768. It has the advantage of providing for low overhead data delivery, datagrams are sent as "best effort" by this Transport layer protocol. H c vi n m ng Bách khoa - Website: www.bkacad.com 10
TCP Header format: H c vi n m ng Bách khoa - Website: www.bkacad.com 11
TCP Header format: Port number • Source Port 16 bits. • Destination Port 16 bits. H c vi n m ng Bách khoa - Website: www.bkacad.com 12
TCP Header format: Sequence • Sequence Number: 32 bits – The sequence number of the first data octet in this segment (except when SYN is present). H c vi n m ng Bách khoa - Website: www.bkacad.com 13
TCP Header format: Acknowledgment • Acknowledgment Number: 32 bits – This field contains the value of the next sequence number the sender of the segment is expecting to receive. H c vi n m ng Bách khoa - Website: www.bkacad.com 14
TCP Header format: Code bits • Control Bits: 8 bits – ACK: Acknowledgment field significant – RST: Reset the connection – SYN: Synchronize sequence numbers – FIN: No more data from sender H c vi n m ng Bách khoa - Website: www.bkacad.com 15
TCP Header format: Window • Window: 16 bits – The number of data octets beginning with the one indicated in the acknowledgment field which the sender of this segment is willing to accept. H c vi n m ng Bách khoa - Website: www.bkacad.com 16
User Datagram Protocol (UDP) • UDP is a simple protocol that exchanges datagrams, without acknowledgments or guaranteed delivery. Error processing and retransmission must be handled by higher layer protocols • UDP is designed for applications that do not need to put sequences of segments together H c vi n m ng Bách khoa - Website: www.bkacad.com 17
UDP header fields • Source port – Number of the calling port • Destination port – Number of the called port • Length – Number of bytes including header and data • Checksum – Calculated checksum of the header and data fields • Data – Upper-layer protocol data • The protocols that use UDP include: - TFTP (Trivial File Transfer Protocol). - SNMP (Simple Network Management Protocol). - DHCP (Dynamic Host Control Protocol). - DNS (Domain Name System). H c vi n m ng Bách khoa - Website: www.bkacad.com 18
Transport Layer Role and Services • Identify how a port number is represented and describe the role port numbers play in the TCP and UDP protocols. H c vi n m ng Bách khoa - Website: www.bkacad.com 19
Port and TCP port • Reserved for services and applications. They are commonly used for applications such as HTTP (web server) POP3/SMTP (e-mail server) and Telnet • These port numbers are assigned to user processes or applications. When not used for a server resource, these ports may also be used dynamically selected by a client as its source port. • These are usually assigned dynamically to client applications when initiating a connection. It is not very common for a client to connect to a service using a Dynamic or Private Port H c vi n m ng Bách khoa - Website: www.bkacad.com 20