1. Basic Communications Model Standards are needed at all Layers
User Layer
Application Layer
Computer (Transport) Layer
Transmission Layer

2. Subnet Layer Transmission of Messages 1. Within a Single Subnet, or
Station A
Station B 2 2 1 1 4 3
Transmission of Messages
1. Within a Single Subnet, or
2. in Point-to-Point Links Between Subnets

3. Across multiple subnets in an internet
Internet Layer
Station A
Station B 2 1 4 3
Routing of Messages
Across multiple subnets in an internet

4. Internetting
Station A
Station B 2 1 4 3
internet: collection of subnets such that any station on any subnet can communicate with any other station on any other subnet simply by giving the internet address of the other station.

5. Layering in Major Architectures
Basic Model
TCP/IP
IPX/SPX
OSI
Application
Application
Application
Application (7)
Presentation (6)
Computer
(Transport)
Transport:
TCP, etc.
Complex:
SPX, etc.
Session (5)
Transport (4)
Internet
Internet
Internet
Network (3):
Internet &
Subnet
Subnet
(OSI)
Subnet
(OSI)
Subnet
(OSI)
Data Link (2)
Physical (1)

6. OSI Architecture
Reference Model for Open Systems Interconnection (OSI)
Standards Agencies
ISO (computers)
Don’t confuse OSI and ISO!
ITU-T (telecommunications)
De jure standards (official/open)

7. OSI Architecture Standards are sophisticated
Sophistication brings complexity
Slow standards development
Products are late to market and expensive
The result: low acceptance of OSI standards in general
But OSI dominates at the single network (subnet) transmission layer

8. Physical Layer (OSI Layer 1)
Physical transmission standards
Physical
Connector
Transmission media
Electrical
Voltage levels
Meanings of various voltage levels

9. The Data Link Layer (OSI Layer 2)

10. Data Link Layer (OSI Layer 2)
Organize data for transmission over a data link
Data packages at various layers are called protocol data units (PDUs)
The Data Link Layer PDU is called a frame
Organization allows addressing on shared data links
Organization allows error checking and other meta delivery processes
Media Access Control
Controls when stations may transmit in shared media LANs and other shared data links

11. TCP/IP Architecture Internet Engineering Task Force (IETF)
Of the Internet Society
De jure (official/open)

12. TCP/IP Architecture Standards are simple Widely Used
Often have “Simple” in the name
Standards and products are fast to market
Products are inexpensive and fast to market
Widely Used
On the Internet
In many corporate networks
Dominates at internet and transport layers