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					Software Protocol Layers




                           Slide 1
Outline:
Software Protocol Layers
     • Concepts:
     • Open Systems
       Interconnection model
     • TCP/IP model
     • Network Access Layer
     • Internet Layer
     • Transport Layer
     • Application Layer



                               Slide 2
Concepts:
• Complex data communication systems require a
  set of cooperative protocols (called a protocol
  family or protocol suite) which solve the
  following communication problems:
   – Hardware failure.
   – Congestion.
   – Packet delay or loss.
   – Error detection and/or correction.
   – Flow control.
   – Redundant packet arrival.
                                                Slide 3
Protocol Type by Layer:
• Hardware/Firmware protocols usually reside at the
  Physical and Link Layers.
• Software protocols conceptually reside above
  hardware protocols and can be located within:
   – Device drivers - lowest software layers, hardware
     dependent.
   – The operating system - middle software layers,
     hardware independent.
   – Application programs - applications and highest
     software layers.

                                                         Slide 4
  ISO - Open Systems Interconnection
  (OSI) model:
 #        Layer                    Function
 7    Application    application programs that use the network
 6    Presentation   standardized data representation
 5    Session        manages sessions between applications
 4    Transport      error detection and correction
 3    Network        manages network connections
 2    Data Link      data delivery across the physical connection
1.5   MAC sublayer   access method for the transmission medium
 1    Physical       defines the physical network media


                                                            Slide 5
ISO - Open Systems Interconnection
(OSI) model:
  #        Layer                    Example
  7    Application    X.400 (Message Handling Systems)
  6    Presentation   Abstract Syntax Notation 1
  5    Session        Synchronization
  4    Transport      End-to-end reliability
  3    Network        Communication subnet, routing
  2    Data Link      Point-to-point control
 1.5   MAC sublayer   Specific medium access, IEEE 802.3
  1    Physical       Voltage level determines 0 or 1, X.21


                                                        Slide 6
TCP/IP model:
#         Layer                 Example
4   Application      Application-to-application data delivery
3   Transport        Process-to-process data delivery
2   Internet         Host-to-host data delivery
1   Network Access   Hides the details of the physical network
    Hardware




                                                       Slide 7
TCP/IP model:

  #         Layer                Example
  4   Application      FTP, TELNET, E-mail, SNMP
  3   Transport        UDP, TCP
  2   Internet         IP, ICMP
  1   Network Access   ARP, RARP, Device Drivers
      Hardware         Ethernet NIC




                                               Slide 8
OSI Model and TCP/IP Model mapping:

      OSI            TCP/IP
  Application
  Presentation     Application
  Session
  Transport        Transport
  Network          Internet
  Data Link
  MAC sublayer   Network Access
  Physical


                                  Slide 9
TCP/IP model encapsulation:




                              Slide 10
   Host A                          Host B
Application                      Application
                    identical
                    message
 Transport                       Transport
                    identical
                     packet
  Internet                        Internet
                   identical
                   datagram
Net. Interface                  Net. Interface
                    identical
                      frame


                 Physical Net
                                                 Slide 11
Network Access Layer:

• The purpose of the layer:
   – to get data out of or to put data into the physical
     network.
   – to determine how hardware address can be
     mapped to the IP address.
• The Protocols that are used:
   – ARP (Address Resolution Protocol)
   – RARP (Reversed ARP)
   – different hardware protocols

                                                    Slide 12
Internet Layer:

• The purpose of the layer:
   – routing decision.
   – moving data from host A to host B.
• Different IP addresses can be used:
   – IPv4: 32-bit number
   – IPv6: 128-bit number
• The Protocols that are used:
   – IP (Internet Protocol)
   – ICMP (Internet Control Message Protocol)

                                                Slide 13
Internet Layer:

• Internet Protocol (IP):
   – best effort IP datagram delivery.
   – no guarantee at all: loss, duplicate, etc.
   – improvements: QoS-aware IP delivery.
• Internet Control Message Protocol (ICMP):
   – communicate error messages.
   – Types: destination unreachable, fragmentation needed,
     time exceeded, echo request, etc.



                                                       Slide 14
Internet Layer:

• IP fragmentation and re-assembly (data size vs. MTU size)
• IP routing:
   – static routing.
   – dynamic routing.
       • RIP (Routing Information Protocol)
       • OSPF (Open Shortest Path First)
       • BGP (Border Gateway Protocol)
• QoS in IP:
   – RSVP/IntServ – priority based on individual flows
   – DiffServ – priority based on service classes

                                                         Slide 15
Transport Layer:

• The purpose of the layer:
   – process-to-process data delivery.
• Port numbers are used:
   – processes attach themselves to ports
   – port number range: 0 ~ 65535 (RFC 1700)
• The Protocols that are used:
   – UDP (User Datagram Protocol)
   – TCP (Transmission Control Protocol)


                                               Slide 16
Transport Layer:

• User Datagram Protocol (UDP) – no additional features on
  top of IP:
   – connectionless protocol
   – datagram delivery
   – best effort delivery
• Example applications:
   – reliability is not needed
   – simplicity
   – real time
   – multicast

                                                      Slide 17
Transport Layer:

• Transmission Control Protocol (TCP):
   – connection oriented protocol
   – segment delivery
       • tries to avoid fragmentation along the path
   – reliable delivery
       • acknowledgements
       • retransmission
• Example applications:
   – reliability is needed


                                                       Slide 18
Application Layer:

• Different communication models can be used:
   – peer-to-peer
      • hosts offer/take services from other peers
      • e.g. CORBA, DCOM, etc.
   – client/server
      • client sends a request to a server, server sends reply
      • e.g. RPC (remote procedure call), LDAP (directory access),
        web access, etc.




                                                                Slide 19
Application Layer:

• The Protocols that are used:
   – standard protocols
       • most of them defined in RFCs
       • e.g. FTP, HTTP, SMTP,LDAP, etc.
   – self-defined protocols
       • design your own protocol for your application
       • advantage: flexible, light-weight, efficient
       • disadvantage: may not be interoperable with other
         applications

                                                        Slide 20

				
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