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Network Layers August 1, 2005

Posted by Coolguy in Networks.
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Application Layer 7 Provides misc protocols for common activities (ftp, telnet, http, etc)
Presentation Layer 6 Structures information and attaches semantics
Session Layer 5 Provides dialog control and synchronization facilities
Transport Layer 4 Breaks messages into packets and guarantee delivery
Network Layer 3 Select a route from sender to receiver
Data Link Layer 2 Detects and corrects errors in bit sequences
Physical Layer 1 Transmits bits: velocity, bit-code, connection, etc

Physical Layer

Data Link Layer

  • Puts data in frames and ensures error free transmission.
  • A header with a hardware (MAC) destination and source address are added
  • Data Link Layer WAN protocols:
    HDLC – High Level Data Link Control – Implemented by the INternational Standards Organization (ISO). SDLC – Synchronous Data Link Control uses a master slave relationship between primary and secondary devices. The master always initiates communication. This protocol was started by IBM to communicate between offices with mainframe computers.
    LAPD – Link Access Procedure Balanced – Can detect missing or out of sequence frames and is used with X.25.
    X.25 – Defines specification between a DTE and a DCE and is a packet switching network.
    SLIP – Used to support TCP/IP communications over a slow serial interface.
    PPP – Used to support several protocols over a slow serial interface with several enhancements over SLIP.
    ISDN – Integrated Services Digital Network – Digital phone lines for voice and data transmission.
    Frame Relay – Higher speed than X.25 packet switching network.
  • e.g. Ethernet, Token ring, PPP, HDLC, Frame relay, ISDN, ATM, 802.11 WiFi, FDDI

Network Layer

  • IP network protocol. Routes messages using the best path available.
  • The network layer addresses messages and translates logical addresses and names into physical addresses. It also determines the route from the source to the destination computer and manages traffic problems, such as switching, routing, and controlling the congestion of data packets.
  • Examples:
  • IP
    ICMP
    IPX
    NWLink
    NetBEUI
    Appletalk/DDP.
    IPSec
    ISO protocol suite
    DECnet
    Router
  • e.g. IP, ICMP, IGMP, X.25, CLNP, ARP, RARP, BGP, OSPF, RIP, IPX, DDP

Transport Layer

  • Maintains flow control which prevents buffer overflow and data loss.
  • Reliable data transmission provides for:
    Acknowledgement of received segments.
    Retransmission of segments not acknowledged.
    Proper re-sequencing of segments.
    Flow control to manage the data so no data is lost.
  • Two main protocols:
    TCP – Reliable with establishment of virtual circuit and numbering and and acknowledgement of packets. Also establishes the connection before sending data.
    UDP – Unreliable with no virtual circuit and numbering without acknowledgement of packets.
  • e.g. TCP, UDP, RTP, SCTP, SPX, ATP

Session Layer

  • Establishes, manages and terminates connections (sessions) among cooperating applications
  • Offers three communications modes
    Simplex – Only one device transmits.
    Half-duplex – Each side takes turns transmitting from one side at a time.
    Full-duplex – Devices on both sides of the communications channel can talk at the same time.
  • Connection split into the following three phases:
    Connection establishment
    Data transfer
    Connection termination
    Session Layer Protocols
  • Session Layer Protocols
  • NCP Network Control Protocol
    SMB Server Message Block
    NFS Network File System
    AppleTalk Data Stream Protocol (ADSP)
    Data Link Control (DLC)
    Named Pipes
    NBT
    NetBIOS
    NWLink
    Printer Access Protocol (PAP)
    Zone Information Protocol (ZIP)
    SQL – Structured Query Language
    RPC – Remote Procedure Call
    X Window
    ASP – AppleTalk Session Protocol used for Apple client to server communications.
    DNA SCP – Digital Network Architecture Session control Protocol. A Digital DECnet protocol.
  • e.g. TLS, SSH, ISO 8327 / CCITT X.225, RPC, NetBIOS, ASP

Presentation layer

  • The presentation layer is responsible for the delivery and formatting of information to the application layer for further processing or display.
  • Encryption is typically done at this level
  • Makes the type of data transparent to the layers around it. Used to translate date to computer specific format such as byte ordering
  • In many widely used applications and protocols, no distinction is made between the presentation and application layers. For example, HTTP, generally regarded as an application layer protocol, has presentation layer aspects such as the ability to identify character encodings for proper conversion, which is then done in the application layer.
  • Examples:
  • HTTP/HTML
    ASN.1
    XML
    TDI
    XDR
    SNMP
    FTP
    Telnet
    SMTP
    Netware Core Protocol
    Apple Filing Protocol (AFP)

Application Layer

  • Provides services software applications need.
  • Provides the ability for user applications to interact with the network.
  • Examples
    AIM (AOL Instant Messenger Protocol)
    APPC
    AFP (Appletalk Filing Protocol)
    BitTorrent
    CFDP (Coherent File Distribution Protocol)
    FTAM
    FTP (File transfer protocol)
    gopher
    HTTP
    IMAP
    ITMS (iTunes Music Store Protocol)
    IRC (Internet Relay Chat)
    LDAP (Lightweight Directory Access Protocol)
    Modbus
    NNTP
    POP3
    SSH
    SIP (Session Initiation Protocol)
    SMTP (Simple Mail Transfer Protocol)
    SNMP (Simple network management protocol)
    TFTP (Trivial File Transfer Protocol)
    TSP (Time Stamp Protocol)
    Telnet
    X.400
    X.500
    XMPP

More:

http://www.comptechdoc.org/independent/networking/protocol/protlayers.html

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