Week 9- Transport layer Flashcards
What does the transport layer provide?
It provides the logical communication between application processes running on different hosts.
It may also provide transport services such as congestion/flow control
What does transport layer not provide?
Any speed,delay or bandwidth guarantees
What’s the difference between transport layer and network layer?
Transport Layer: logical communication between processes
Network Layer: Logical communications between hosts
Which systems run transport protocols?
It run on network edge devices (hosts/end-systems)
What does the sender
- Gets message from the Application Layer
- Breaks it into logical segments
- Passes it on to the network layer
What does the receiver
- Gets segments from the Network Layer
- Reassembles them into a message
- Passes it on to the Application Layer (via socket)
What are the 2 key Transport Protocols
- TCP
- UDP
Define TCP
Gives us reliable, in order delivery as a connection-oriented protocol
Define UDP
Gives us unreliable, unordered delivery
Define Multiplexing
It is when data is handled from multiple sockets and split into segments
Define Demultiplexing
When the header information is used to deliver received segments to the correct socket, which are then reassembled into data
Define Transport headers
This include source and destination port numbers are added at this stage
Define UDP
It is the ‘best effort’ transport service
Which applications use UDP?
- Streaming multi-media apps ( less tolerant)
- DNS (Domain Name System)
- SNMP (Simple network Management Protocol)
Why is there a UDP in transport protocol, what are the benefits?
- No connection establishment ( which can add delay)
- Simplicity: no connection state at sender or receiver
- Smaller header size than TCP (only 8 bytes)
- No congestion control so UDP can send data as fast as possible
What does the UDP checksum do?
It offers some basic error checking
- Error: A bit is erroneously flipped during transmission
What are the steps includes whilst the UDP checksum do?
- Sender breaks the whole segment into 16-bit chunks
- Each section is treated like a binary integer and is added together - any carry bits are added to the LSB
- Each digits of the 16- bit result is flipped at each digit - checksum now
- Checksum is added to the datagram before it is sent
What are the steps after the UDP checksum segment is received?
- Once the segment is received, the receiver recalculates the checksum in the same way the sender did
- The receiver calculated checksum is compared to the checksum in the UDP header
Why is packet- Switched network unreliable?
-Delay causes packet loss
- Errors can occur
- UDP cannot guarantee packets arrive is the same order in which they are sent
How can we achieve Reliable Data Transfer (RDT)?
What is shown in RDT 1.0 design?
In the RDT 1.0 design it is assumed that the underlying channel is 100% reliable - no bit errors or packet loss.
