Communication Subsystems

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Communication Subsystems
Typical layers in a communication subsystem
System 1
System 2
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Network
Network
Data Link
Data Link
Physical Link
Physical Link
The layers communicate via protocols
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Communication Subsystems
Typical layers in a communication subsystem
System 1
System 2
Application
Application
Presentation
Presentation
Session
Session
Virtual communication
Transport
Transport
Network
Network
Data Link
Data Link
Physical Link
Physical Link
The layers communicate via protocols
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Communication Subsystems
Typical layers in a communication subsystem
System 1
System 2
Application
Application
WSFTP,Netscape
Presentation
Presentation
FTP, HTTP
Session
Session
Sockets
Transport
Transport
TCP,SPX
Network
Network
IP,IPX
Data Link
Data Link
Ethernet
Physical Link
Physical Link
Wire
The layers communicate via protocols
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Fitting it together
Application Program Data
Data
Socket Definition
Data
TCP Header
IP Header
Data
Ethernet Header
Data
Check
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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.

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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.

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Session

• The session layer decodes socket information from
  the packet and dispatches the program that will
  process the protocol that the socket defines.

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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).

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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.

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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.

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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 dont want to handle on a
  particular system.

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OSI layer mnemonics

• All Away Application
• People Pizza Presentation
• Seem Sausage Session
• To Throw Transport
• Need Not Network
• Data Do Data Link
• Processing Please Physical

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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)

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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.

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IEEE Ethernet Frame Categories

• 802.3
• Novells 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

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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.

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Drivers and the OSI Model
Network Software
Driver
Network Interface Card
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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

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Open Data-Link Interface (ODI)

• Novell and Apple specification
• Supports multiple protocols
• Incompatible with NDIS
• Driver compatibility can be handled through
  translator programs.

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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
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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