4. Transport Layer Flashcards
What is the transport layer responsible for?
- Logical communications between applications running on different hosts
What layers are responsible for network transmission?
- Link between the application layer and the lower layers
What information does Transport Layer adds? ( Responsibilities )
- Header Information
What does Transport Layer track? ( Responsibilities )
- Individual conversations
What does transport layer segment and reassembling ? ( 2 , Responsibilities )
- Data ( Segmenting )
- Segments ( Reassembling )
- Uses segmentation and multiplexing to enable different communication conversations to be interleaved on the same network
What will transport layer do on multiple conversations? ( 3 , Responsibilities )
- Identify
- Separate
- Manage
What does transport layer protocols specify? ( 2 )
- How to transfer between hosts
- Responsible for managing reliability requirements of a conversation
- IP does not specify how the delivery or transportation of the packets takes place
Transport Layer includes what protocols? ( 2 )
- TCP Protocols
- Provides reliability and flow control
- UDP Protocols
- Provides basic functions for delivering datagrams between the appropriate applications, with very little overhead and data checking
List out TCP basic operations ( 5 )
- Number and track data segments transmitted to a specific host from a specific application
- Acknowledge received data
- Retransmit any unacknowledged data after a certain amount of time
- Sequence data that might arrive in wrong order
- Send data at an efficient rate that is acceptable by the receiver
- Transmission Control Protocol ( TCP )
What is the required protocol properties for UDP and TCP?
TCP
1. Reliable
2. Acknowledges Data
3. Resends Lost Data
4. Delivers Data in Sequencial Order
UDP
1. Fast
2. Low Overhead
3. Does not Require Acknowledgements
4. Does not Resend Lost Data
5. Delievers Data as it Arrives
What is UDP is known for?
- Best-effort delivery protocol because there is no acknowledgement that that data is received at the destination
- It was an unreliable protocol because it has little overhead and data checking
- User Datagram Protocol ( UDP )
- It is also a connectionless protocol
What applications uses UDP?
- Request-and-Reply applications
- Where data is minimal, and retransmission can be done quickly
When will TCP used?
- If it is important that all the data arrives and that it can be processed in its proper sequence, TCP is used as the transport protocol
What are the features for TCP? ( 4 )
- Establishes a Session
- Ensures Reliable Delievery
- Provides Same-Order Delivery
- May provide multiple routes
- Supports Flow Control
- It is a stateful protocol which means it keeps track of the state of the communication session
What will TCP records? ( 2 )
- Which information it has sent
- Which information has been acknoledged
What is the 2 most important things in TCP and UDP header?
- Source Port
- Destination Port
What does TCP handles?
- All tasks associated with driving the data stream into segments, providing reliability, controlling data flow, and reording segments
What is the features for UDP? ( 4 )
- Data is reconstructed in the order that it is received
- Any segments that are lost are not resent
- There is no session establishment
- The sending is not informed about resource availability
What application uses UDP? ( 3 )
- Live video and multimedia applications
- Simple request and reply applications
- Applications that handle reliability themselves
What does TCP and UDP transport layer protocols uses to manage multiple, simultaneous conversations?
- Port Numbers
What are placed within the segment?
- Source Port Number
- Destination Port Number
- They are then encapsulated within an IP packet
What is the name for the source IP address and source port number, or the destination IP address and destination port number?
- Socket
What does sockets enable?
- Enable multiple process, running on a client, to distinguish themselves from each other, and multiple connections to a server process to be distinguished from each other
What is the number range for well-known ports?
- 0 - 1023
- Reserved for common or popular services ( web-browser, remote access clients )
What is the number range for registered ports?
- 1024 - 49151
- Assigned by IANA
- Are primarily individual applications that a user has chosen to instal, rather than common applications that would receive a well-known port number
What is the number range for private and / or dynamic ports?
- 49152 - 65535
- It only have value until 65535 due to the 2^16 ( 16 bit )
- It is also known as ephemeral ports
What port numbers are assigned by IANA?
- Registered ports
What port are also known as ephemeral ports?
- Private and / or Dynamic Ports
What is the Port Number for :
Protocol - TCP
Application - File Transfer Protocol ( FTP ) , Data
- 20
What is the Port Number for :
Protocol - TCP
Application - File Transfer Protocol ( FTP ) , Control
- 21
What is the Port Number for :
Protocol - TCP
Application - Secure Shell ( SSH )
- 22
What is the Port Number for :
Protocol - TCP
Application - Telnet
- 23
What is the Port Number for :
Protocol - TCP
Application - Simple Mail Transfer Protocol ( SMTP )?
- 25
What is the Port Number for :
Protocol - TCP, UDP
Application - Domain Name Service ( DNS )
- 53
What is the Port Number for :
Protocol - UDP
Application - Dynamic Host Configuration Protocol ( DHCP ) - Server
- 67
What is the Port Number for :
Protocol - UDP
Application - Dynamic Host Configuration Protocol ( DHCP ) , Client
- 68
What is the Port Number for :
Protocol - UDP
Application - Trivial File Transfer Protocol ( TFTP )
- 69
What is the Port Number for :
Protocol - TCP
Application - Hypertext Transfer Protocol
- 80
What is the Port Number for :
Protocol - TCP
Application - Post Office Protocol Version 3 ( POP3 )
- 110
What is the Port Number for :
Protocol - TCP
Application - Internet Message Access Protocol ( SNMP )
- 143
What is the Port Number for :
Protocol - UDP
Application - Simple Network Management Protocol ( SNMP )
1.161
What is the Port Number for :
Protocol - TCP
Application - Hypertext Transfer Protocol Secure ( HTTPS )
1.443
What is the code for verify connections to prevent major security threat in unexplained TCP connections
- netstat
What is configured when each application process running on a server?
- Port Number
An individual server cannot have what within the same transport layer services?
- 2 services assigned to the same port number
What does it means that an active server application assigned to a specific port is considered open?
- The transport layer accepts, and processes segments addressed to that port.
- Any incoming client request addressed to the correct socket is accepted, and the data is passed to the server application
What is the step for TCP connection establishment ? ( 3 )
- The initiating client requests a client-to-server communication session with the server
- The server acknowledges the client-to-server communication session and requests a server-to-client communication session
- The initiating client acknowledges the server-to-client communication session
List out the steps for TCP Session Termination
- When the client has no more data to send in the stream, it sends a segment with the 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 the server-to-client session
- The client responds with an ACK to acknowledge the FIN from the owner
What are the functions for TCP Three-Way-Handshake Analysis?
- It establishes the destination device is present on the network.
- It verifies that the destination device has an active service and is accepting requests on the port number that the initiating client intends to use.
- It informs the destination device that the source client intends to establish a communication that port number.
What will happen after the communication is completed ? ( 2 )
- Sessions are closed
- Connection is terminated
What enable TCP reliability function? ( 2 )
- Connection
- Session Mechanisms
List out the six control bit flags
- URG ( Urgent )
- Urgent pointer field significant
- ACK ( Acknowledgement )
- Acknowledgement flag used in connection establishment and session termination
- PSH ( Push )
- Push function
- RST ( Reset )
- Reset the connection when an error or timeout occurs
- SYN ( Synchronize )
- Synchronize sequence numbers used in connection establishment
- FIN ( Finish )
- No more data from sender and used in session termination
What can TCP help ( Reliability ) ?
- Maintain the flow of packets so that devices do not become overloaded
- There may be times when TCP segments do not arrive at their destination or arrive out of order
*All the data must be received and the data in these segments must be reassembled into the original order.
*Sequence numbers are assigned in the header of each packet to achieve this goal.
What will happen no matter how well designed a network is?
- Data loss occasionally occurs
- TCP provides methods of managing these segment losses. Among these is a mechanism to retransmit segments for unacknowledged data
What feature that host operating system today typically employed?
- Selective Acknowledgement ( SACK )
- Negotiated during the Three-Way Handshake
- If both hosts support SACK, the receiver can explicity acknowledge which segments ( bytes ) were received including any discontinuous segments
What is flow control?
- The amount of data that the destination can receive and process reliably
What does Flow Control maintain?
- The realiability of TCP transmission by adjusting the rate of data flow between source and destination for a given session
What does Maximum Segment Size ( MSS ) defined for?
- The maximum amount of data that the destination device can receive
- A common MSS is 1460 bytes when using IPv4
- A host determines the value of its MSS field by subtracting the IP and TCP headers from the Ethernet maximum transmission unit (MTU), which is 1500 bytes be default.
- 1500 minus 60 (20 bytes for the IPv4 header and 20 bytes for the TCP header) leaves 1460 bytes.
What will happen when congestion happen on a network?
- it results in packets being discarded by the overloaded router
- To avoid and control congestion, TCP employs several congestion handling mechanisms, timers, and algorithms.
How does UDP provides low overhead data transport?
1.It has a small datagram header and no network management traffic
What is the characteristics of UDP ? ( 3 )
- Does not track sequence numbers the way TCP does
- UDP has no way to reorder the datagrams into their transmission order
- UDP simply reassembles the data in the order that it was received and forwards it to the application
