41902 Lecture Notes - Lecture 4: Transport Layer, Network Layer, Network Congestion
Network Fundamentals – Lecture 4:
Chapter 3: Transport Layer
Chapter 3.1: Transport-layer services
Transport services and protocols provide logical communication between application processes
running on different hosts. Transport protocols run in end systems (from transport layer):
- Sender side: breaks app messages into segments and passes to network layer
- Receiver side: reassembles segments into messages and passes to app layer
Transport layer: services and protocols provide logical communication between app processes
Network layer: logical communication between hosts
Transport layer: logical communication between processes
relies on and enhances network layer services
Internet transport-layer protocols:
• TCP (reliable, ordered delivery): congestion control, flow control, connection setup
• UDP (unreliable, unordered delivery): no-frills etesio of est-effort IP
• Services not available: delay guarantees, bandwidth guarantees
Chapter 3.2: Multiplexing and demultiplexing
Multiplexing at sender:
Handles data from multiple sockets, adds transport header used later for demultiplexing
Demultiplexing at receiver:
Uses header information from multiplexing to deliver the received segments to the correct socket
How demultiplexing works (possibly examined)
The host receives IP datagrams:
- Each datagram has a source IP address and destination IP address
- Each datagram carries one transport-layer segment
- Each segment has a source and destination port number
Hosts use IP addresses & port numbers to direct segments to the appropriate sockets
Connectionless demultiplexing:
• A created socket has a host-local port number. When creating a datagram to send into UDP
pocket, the destination IP address and destination post number must be specified.
• When a host receives a UDP segment: it checks the destination port number in the segment
and directs the UDP segment to the socket with that same port number.
• IP datagrams with the same destination port number but different source IP
addresses/source port numbers will be directed to the same socket at destination
Connection-oriented demultiplexing:
TCP socket is identified by the 4-tuple:
- source IP address, source port number, destination IP address, destination port number
Demultiplexing: receiver uses all four values to direct segments to the appropriate socket
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Document Summary
Transport services and protocols provide logical communication between application processes running on different hosts. Transport protocols run in end systems (from transport layer): Sender side: breaks app messages into segments and passes to network layer. Receiver side: reassembles segments into messages and passes to app layer. Transport layer: services and protocols provide logical communication between app processes. Transport layer: logical communication between processes relies on and enhances network layer services. Internet transport-layer protocols: tcp (reliable, ordered delivery): congestion control, flow control, connection setup, udp (unreliable, unordered delivery): no-frills e(cid:454)te(cid:374)sio(cid:374) of (cid:862)(cid:271)est-effort(cid:863) ip, services not available: delay guarantees, bandwidth guarantees. Handles data from multiple sockets, adds transport header used later for demultiplexing. Uses header information from multiplexing to deliver the received segments to the correct socket. Each datagram has a source ip address and destination ip address. Each segment has a source and destination port number. Hosts use ip addresses & port numbers to direct segments to the appropriate sockets.
