UDP/TCP/IP Protocol Architecture

Ø Overall Picture of the TCP/UDP/IP protocols

Ø Protocol Headers

Ø Overview of TCP

Ø State Transition Diagram

Ø Connection end-points

Ø Buffering

Ø Overview of UPD

Ø Standard Services and Protocol Usage

Ø Overall Picture of the TCP/UDP/IP protocols:

Ø Protocol Headers:

IP ,  UDP ,  TCP and  Encapsulation

Encapsulation

Ø Overview of TCP:

à Reliability: Requires ACK & Retransmission.

It dynamically computes RTT for estimating how long to wait for ACKs: 

millisecs for LANs, seconds WANs.

à Sequence Numbers: To detect packet loss, reordering and duplicate removal.

à Flow Control: Tell peer exactly how many bytes it is willing to accept

(receiver buffer called window).

à Full Duplex: send and recv data in both directions.

à Connection Establishment: 3-way handshake

à Options: Each synch segment contains:

• MSS Option: maximum segment size (the maximum amount of data it is willing to accept in each TCP segment).
• Window Scale Option: maximum window is 65,535 bytes,

it can be scaled (left-shifted) by 0-14 bits providing a maximum of 65,535x2**14 byte (one gigabyte).

à Connection Termination: Requires 4 segments

Ø State Transition Diagram:

• Watching the Packets: Packet exchange for TCP Connection

• Time-Wait state: (around 2 minutes)

To allow old duplicate segments to expire in the Network.

The end that performs the active close is the one that goes through TIME-WAIT state in order to ACK the final FIN.

Ø Connection end-points:

• Port numbers: 16 bit integers (65,535).
• Servers use well know ports, 0-1023 are privileged.
• Clients use ephemeral (short-lived) ports.

• Socket Pair: 4 tuple < localIP, localPort, foriegnIP, foriegnPort >

• Concurrent servers: listen, connect and accept ,

2nd Client:

Ø Buffering:

Buffer Sizes and Limitations:

• MTU: Maximum Transmission Unit (Ethernet 1500 bytes).
• Path MTU: smallest MTU in a path.
• If IP datagram exceeds MTU it is fragmented & reassembled at the final destination.
• If DF (Do't fragment) bit is set, ICMP is returned

(this is the basis for the path MTU discovery).

• IP with 576 bytes will not be fragmented.
• TCP MSS is = (interface MTU - header lengths).

TCP Output:

Return from write means: reuse application buffer,

but data may still be in  the socket buffer of sender and it does not mean the peer got it.

Ø Overview of UPD:

à Simple.

à Connectionless.

à Unreliable.

UDP Output:

No buffering, packets are copied directly into the datalink output queue.

Ø Standard Services and Protocol Usage:

Standard Internet Services:

Sample (More details at: /etc/services)

Protocol Usage by Common Internet Applications:

Examples