Communication Subsystems
Typical layers in a communication subsystem
System 1
System 2
Application
Application
Presentation
Presentation
Session
Session
Transport
Network
Data Link
Physical Link
Transport
Network
Data Link
Physical Link
The layers communicate via protocols
Communication Subsystems
Typical layers in a communication subsystem
System 1
System 2
Application
Application
Presentation
Presentation
Session
Session
Transport
Network
Data Link
Physical Link
Virtual
communication
Transport
Network
Data Link
Physical Link
The layers communicate via protocols
Communication Subsystems
Typical layers in a communication subsystem
System 1
System 2
Application
Application
WSFTP,Netscape
Presentation
Session
Transport
Network
Data Link
Physical Link
FTP, HTTP
Sockets
TCP,SPX
IP,IPX
Ethernet
Wire
Presentation
Session
Transport
Network
Data Link
Physical Link
The layers communicate via protocols
Fitting it together
Application Program Data
Socket Definition
Data
TCP Header
Data
IP Header
Data
Ethernet Header
Data
Check
Application
• The program that the user interfaces with to
gain access to the network
• Internet Explorer, Outlook, WSFTP, SSH all
provide the keystroke reception and display
presentation to the user in a human readable
format.
Presentation
• Takes data to/from the Application and provides a
protocol for formatting the data in a method
unique to the application.
• HTTP (HyperText Transfer Protocol), handles
commands for interfacing with the servers of the
World Wide Web.
• FTP (File Transfer Protocol), handles commands
for listing, sending, and receiving files.
Session
• The session layer decodes socket
information from the packet and dispatches
the program that will process the protocol
that the socket defines.
Transport
• The transport layer determines which
transport protocol is being sent to the upper
layers. TCP (Transmission Control
Protocol), ICMP (Internet Control
Messaging Protocol), SPX (Service Packet
Exchange), or UDP (User Datagram
Protocol).
Network
• The network layer handles the internet
protocols, decodes the proper address
(internet or IPX), decodes the transport
type, and the time to live values.
Data Link
• This layer is the protocol used on the wire
such as, ethernet, token ring, Point to Point
Protocol (PPP, dialup), DSL, broadband and
so on.
• This layer has low level addressing and
frame checking.
Directing Packets
• At this the lower levels of the OSI model, drivers can
either packet forward or packet filter the frames being
processed.
• If the packet is of the proper type and address it will be
forwarded up the stack.
• If the packet is not of the proper type, identification, or
address it will be ignored by the upper layers of the model.
• Packet forwarding and filtering allow lower levels of the
model to take the load off of the higher levels by ignoring
packets not needed. The filtering process also adds to
system security by ignoring services we don’t want to
handle on a particular system.
OSI layer mnemonics
•
•
•
•
•
•
•
All
People
Seem
To
Need
Data
Processing
Away
Pizza
Sausage
Throw
Not
Do
Please
Application
Presentation
Session
Transport
Network
Data Link
Physical
OSI Layers and Operating
Systems
• Windows NT
– File System Drivers (application, presentation,
and session layers)
– Transport Protocols (transport and network)
– Network interface card drivers (datalink and
physical)
NT Interfaces
• Application Programming Interfaces ort
APIs, allow programmers to access network
services.
• Transport Driver Interfaces or TDIs are
between the transport and the API levels.
• Network Driver Interface Specifications or
NDISs communicate from the NIC to the
TDI.
IEEE Ethernet Frame Categories
• 802.3
– Novell’s Ethernet (handled IPX, limited use)
• 802.3 (Ethernet II)
– Based on 802.3
– Most commonly used today
– Type byte instead of Total Packet length
• 802.5
– Token ring definition
• Ethernet 802.11
– Wireless definition
– 900mhz, 2.4 ghz, 5.7 ghz
OSI Model Enhancements
(Data Link Layer)
• Logical Link Control (LLC)
– Control links, frame traffic, sequencing, and
frame acknowledgment
– Uses logical service access points (SAP) to
transfer information up the OSI layers
• Media Access Control (MAC)
– Handles media (wire) access, frame start/end,
frame error check, and frame addresses.
Drivers and the OSI Model
Network Software
Driver
Network Interface Card
Network Driver Interface
Specification (NDIS)
• Sets rules for driver interfaces from the MAC
(media access control) sublayer and the protocol
drivers.
• Protocol Stack
– Frame assembler and disassembler
• Adapter Driver
– To/from NIC and protocol stack
• Protocol Manager
– Controls traffic from protocol stack to the MAC
Open Data-Link Interface (ODI)
•
•
•
•
Novell and Apple specification
Supports multiple protocols
Incompatible with NDIS
Driver compatibility can be handled through
translator programs.
Review
Transmission Lines Full Duplex Half Duplex
Resistance (Loss)
Capacitance/Inductance (waveform modification)
Timing problems
Star and Bus topologies
Broadband vs. Baseband netorks
Security: Party Line, Physical access
Network Operating systems, Microsoft, Novell, Apple
Client/Server vs. Peer to Peer systems
More Review
Ethernet addresses, uniqueness
Physical Layer (Network Model), ethernet
Ethernet, coax, twisted pair, fiber
Transmit and receive on different pairs of wire
Crosstalk
Cable Lengths, rules
Token ring
Hubs, Repeaters, Bridges, and Switches
3-4-5 rule for 10mb
Network diameter rule for 100mb
10baseT jacks, cables, connectors
100baseT rules
Network layers, IEEE 802 categories, drivers