Download Presentation - The PPT/PDF document "OSI Transport Layer" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Presentation on theme: "OSI Transport Layer"— Presentation transcript:
Slide1
OSI Transport Layer
Network Fundamentals – Chapter 4
Slide2
Objectives
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.
Slide3
Transport Layer Role and Services
Transport layer is responsible for overall end-to-end transfer of application data
Slide4
Transport Layer Role and Services
Transport layer enables applications on devices to communicate
Fig 4.2
Slide5
Purpose of Transport Layer
Tracking the individual communications 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
Performing flow control between end users
Enabling error recovery
Initiating a session
Slide6
1. Tracking Individual Conversation
Any host can have multiple applications communicating across the network
TL maintain the multiple communication streams between these applications.
Ex. Email, IM, Websites and VoIP simultaneously
Fig 4-3
Slide7
Segmenting Data
AL passes large amounts of data to TL
TL has to break data into smaller pieces =segments – suited transmission
Without segmentations, only one application would be able to receive data
Fig 4.4
Slide8
Reassembling Segments
Networks prove multiple routes – diff trans times
Data can arrives in the wrong order
N
umbering and sequencing – TL ensure segments are reassembled into the proper order
Each segment of data reassembled and directed to appropriate application.
Slide9
Identifying the Applications
To pass data streams to the proper applications
TL must identify target application
TL assigns an identifier to an application
In TCP/IP, the identifier = port number
Port number used in TL header to indicate which application the data is associated
Each particular set of pieces flowing between a source application and destination application is known as conversation
Dividing data into small parts enables many diff
comm
to be interleaved/multiplexed on the same network
Slide10
Flow Control
Network hosts have limited resources – memory, bandwidth
When TL aware, some protocol can request the sending application to reduce the rate of data flow
This is done at TL by regulating the amount of data source transmits as a group.
=FLOW CONTROL
Prevent the loss of segments on net and avoid retransmission
Slide11
Error Recovery
PossiblePiece of data corrupted or lost while transmitted over the networkTL ensure all pieces reach destination – source device retransmit any data that is lost
Initiating a Session
TL can provide connection
orientation by creating a session between the app.
These
connections prepare the app to communicate with each other before any data transmitted
Data
can be closely managed
Slide12
Transport Layer Role and Services
Supporting Reliable
Communication
Diff apps have diff requirements for their data
Diff transport protocols have been developed to meet these requirements
TCP is a TL protocol – ensure reliable delivery
In networking, reliability means each piece of data the source sends arrives at the destination
Three basic operation at TL to support reliability
Tracking transmitted data
Acknowledging received data
Retransmitting any unacknowledged data
More control data (in Layer 4 header) is exchanged to support acknowledgement, tracking and retransmission
Slide13
Transport Layer Role and Services
Supporting Reliable Communication
Slide14
TCP and UDP
Two most common TL protocols of TCP/IP are
Transmission Control Protocol (TCP) and User Datagram Protocol (TCP)
Slide15
UDP
Simple and connectionless protocol
Low-overhead data delivery
8 bytes of overhead
UDP segments =
datagrams
UDP sends
datagrams
as ‘best effort’
Applications of UDP
DNS
Video Streaming
VoIP
Slide16
Transport Layer Role and Services
Identify the basic characteristics of the UDP and TCP protocols
Slide17
TCP
Connection-Oriented protocol
Additional overhead to gain functions
Additional functions
Same-order delivery
Reliable delivery
Flow-control
Each TCP segments has 20 bytes of overhead
Applications
Web browsers
E-mail
File transfer
Slide18
Transport Layer Role and Services
Identify the basic characteristics of the UDP and TCP protocols
Slide19
Transport Layer Role and Services
Slide20
Port Addressing
TCP and UDP based services keep track of various applications.
To differentiate segments and
datagrams
for each application – TCP and UDP have header fields that uniquely identify these apps.
Header contains source and
dest
port
Server processes have static port number assigned
Client dynamically choose a port number for each conversation.
Slide21
Port Addressing
Identifying Conversations
Slide22
Port Addressing
The combination of TL port number and NL IP address uniquely identifies a particular process running on specific host device.
This combination = socket
Ex : Web server on host 192.168.1.20, web browser (dynamically assigned port 49152) on host 192.168.100.48
Destined socket = 192.168.1.10:80
Socket for the web page = 192.168.100.48:49152
Slide23
Port Addressing
Slide24
Port Addressing
Different types of port numbers
Well-known ports (0-1023)
Reserved for services and apps
FTP 20, SMTP 25, HTTP 80
Registered Ports (1024-49151)
Assigned to user processes or application
Dynamic or private ports (49152-65535)
Netstat
command
Slide25
TCP Connection Establishment and Termination
TCP Three-Way Handshake
Three steps in TCP connection establishment:
1. Initiating client sends a segment containing an initial sequence value.
2. Server responds with segment containing an acknowledgement value of received sequence+1, plus its own synchronizing sequence value
3. Initiating client responds with an acknowledgement
received
sequence+1
Fig 4.11
Slide26
TCP Connection Establishment and Termination
Slide27
TCP Session Termination
Client has no more data to send, it sends a segment with FIN flag set
The server sends an ACK to acknowledge the receipt of the FIN to terminate the session from client to server
The server sends a FIN to the client to terminate server to client session
Client responds with ACK to acknowledge the FIN from server
Fig 4-12
Slide28
TCP Session Termination
Slide29
Managing TCP Sessions
Describe how TCP sequence numbers are used to reconstruct the data stream with segments placed in the correct order
Slide30
Managing TCP Sessions
TCP Acknowledgement with Windowing
The sequence number indicates the relative number of bytes that have been transmitted in this session, including the bytes in the current segment.
TCP use acknowledgement number in segment sent back to indicate the next byte expects to receive.
Fig 4-13
But if A had to wait for
ack
of the receipt of each 10 bytes – lot of overhead
Slide31
Managing TCP Sessions
TCP Acknowledgement with Windowing
Slide32
Managing TCP Sessions
TCP Acknowledgement with Windowing
Multiple segments of data can be sent and
ack
with a single TCP message in opposite direction.
Ex start with SEQ = 2000, if 10 segments of 1000bytes were received, an ACK = 12001 would be returned to the source.
Amount of data can be transmitted before ACK = window size
Window size is a field in TCP header used for management of lost data and flow control
Slide33
TCP Retransmission
Data loss
will occasionally occur
Dest
host using TCP only
ack
data for contiguous sequence bytes
If one or more segments are missing, only segments that complete the stream is
ack
Ex. Segments with SEQ=1500 to 3000 and SEQ=3400 to 3500 were received, the ACK will be =3001
Slide34
TCP Retransmission
Slide35
TCP Congestion Control
Flow Control & Dynamic Window Sizes
Slide36
TCP Congestion Control
Flow Control
Adjusting the effective rate of data flow.
Window size field in TCP header specifies amount of data can be transmitted before an ACK
Initial window size determined through 3-way handshake
TCP feedback mechanism adjusts the effective rate to the maximum flow network and destination can support without loss
Fig 4-14
During the delay in receiving the ACK, sender will not sent additional segments for the session
Slide37
TCP Congestion Control
Dynamic Window Size
When network resources are constrained, TCP can reduce the window size
After no data losses or constrained resources, receiver will begin to increase the window size field
This dynamic increasing and decreasing of window size is a continuous process in TCP
Slide38
TCP Congestion Control
Slide39
UDP Protocol
Communicating with low overhead
Slide40
UDP Protocol
Simple protocol
Basic TL functions
Not connection oriented
Does not provide sophisticated retransmission, sequencing and flow control mechanism
UDP does not provide reliability..so be careful..
but, are not always unreliable just the reliability is not provided
Slide41
UDP Datagram Reassembly
Session are not established
When app has data to send, it simply sends the data
When larger amounts of data – split into multiple segments =
datagrams
Multiple
datagrams
– may take different paths and arrives in the wrong order
UDP has no way to reorder the
datagrams
into their transmission order.
UDP
simply reassembles the data in order it was received and forward to app
If
seq
is important for app, the app will have to identify the proper sequence and how it should be processed
Slide42
UDP Datagram Reassembly
Slide43
UDP Protocol
Servers use port numbers to identify a specified application layer process and direct segments to the proper service or application
Slide44
UDP Protocol
UDP protocol and port numbers are utilized in client-server communication
