IP Layering and Protocols: Understanding IP, TCP, UDP, and Other Protocols, Slides of Fundamentals of E-Commerce

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Layering in the IP Protocols

Internet Protocol

Transmission Control

Protocol

User Datagram

Protocol

Telnet

HTTP

(Web)

SONET

ATM

Ethernet

Real-Time

Protocol

Domain Name

Service

Internet Architecture

ISP 1

ISP 2

ISP 3

NAP

commercial

customer

access router

gateway router

dial-in access

destination destination

interdomain

protocols

intradomain

protocols

private peering

IP Packet Structure

4-bit

Version

4-bit

LengthHeader

8-bit

Type of Service

(TOS)

16-bit Total Length (Bytes)

16-bit Identification

3-bit

Flags

13-bit Fragment Offset

8-bit Time to

Live (TTL)

8-bit Protocol

16-bit Header Checksum

32-bit Source IP Address

32-bit Destination IP Address

Options (if any)

Payload

HeaderHeader20-byte20-byte

Main IP Header Fields

• IP options (security, routing, timestamping, etc.)• Length in bytes (up to 65,535 bytes)• Upper-level protocol (e.g., TCP, UDP)• Source and destination IP addresses• Header checksum (error check on header)• Header length (number of 4-byte words)• Version number (e.g., version 4, version 6)

Type-of-Service Bits

• Initially, envisioned for type-of-service routing

– So, the ToS bits are ignored in most routers today– And, most routers have first-in-first-out queuing– However, current IP routing protocols are static– Low-delay, high-throughput, high-reliability, etc.

• Now, heated debate for differentiated services

– Arguments about consistent meaning across networks– Affect router packet scheduling and buffering polices– ToS bits used to define a small number of classes

Transmission Control Protocol

(TCP)

• Multiplexing of multiple logical connections• Simultaneous transmission in both directions• Flow-control to respond to network congestion• Retransmission of lost or corrupted packets• Byte-stream socket abstraction for applications

source

network

destination

TCP connection

Establishing a TCP Connection

• Three-way handshake to establish connection

– Host A sends an ACK to acknowledge the SYN ACK– Host B returns a SYN acknowledgement (ACK)– Host A sends a SYN (open) to the host B

• Closing the connection

– Finish (FIN) to close and receive remaining bytes (and other

host sends a FIN ACK to acknowledge)

– Reset (RST) to close and not receive remaining bytes

SYN

SYN ACK

ACK

Data

FIN

FIN ACK

ACK

time

A

B