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OSI Model
Pyramid
Interface between user & computer; API’s are used in
this layer; allows apps to use network; handles network
access; messages sent between layers
data compression and encryption; Determines
data structure; redirections works at this layer;
communicates through gateways and API’s;
services: TELNET, FTP; use TCP, TFTP, NFS,
SNMP, SMTP use TCP
Sends messages between layers; places
checkpoints on data flow; handles remote
procedure calls; communicates through
gateway
Corrects faulty transmission;
acknowledges successful data
receipt; sliding window –
segments of msg frags sent to
this layer TCP/SPX oriented
Protocols: SNMP, FTP, TELNET, WWW, HTTP, SMB, NCP –
TCP; TFTP, NFS; SMTP
Layer 7
Application
Gateways
Layer 6 Presentation
Gateways
Translates data into
understandable format for
transmission
Protocols: JPEG, MIDI, MPEG, VISUAL,
MUSICAND NCP
Layer 5 Session
Opening/closing session; provides synchronization
between communicating computers (nodes);
Services: TELNET, FTP use TCP, TFTP,
NFT, SMMP, SMTP use TCP
Protocols: NFS, SLQ , RPC
Layer 4 Transport
Packet Handling; ensures error-free delivery; repackages messages; divides
messages into smaller packets; ensures proper sequencing; Data Flow Ctrl
Services: routers and brouters.
Protocols: TCP, UDP, SPX,
NETBEUI (non routable)
Layer 3 Network
Logical addressing; ( s/w -> h/w resolved); message(packets) routing between hosts & networks;
determines best routing; moves info to correct address; sends msgs and reports errors per packet
delivery; Rpts HOST mbrship to local multicast routers (IGMP); COMMS thru gateway svcs,
Routers & brouters.
Srvcs: routers/brouters
Protocols: IP, IPX
ICMP,ARP, RARP, OSPF;
EGP, EIMP, NETBEUI,
DCC, DECNET
Layer 2 Datalink
Flow of data over single link btwn devices; controls communication channel access; organizes data in logical frames; ID’s
specific computers on the network; error detection added at this layer; MAC addresses are resolved at this layer; sends data
from network to physical layer; manages physical layer – comms btwn connections systems; data forms sent betwn layers;
ethernet, token ring; FDDI occurs here; devices: brouters, routers. Switches; protocols: HDLC, LLS Flow Control, SLSP & PPP
Layer 1 Physical
Data sent across physical media; responsible for coding schemes; defines cables, cards & physical aspects; provides electrical/physical interfaces for a network;
specifies how signals are xmitted; comms through repeaters/hubs/switches/cables/connectors/xmitters/receivers/multiplexers; no protocols