Layered architecture

• Shows how communication should take place
• Clarify the general functions of a communication process
• To break down complex networking processes into more manageable sub-layers
• Using industry standard interfaces enables interoperability
• To change the features of one layer without changing the code in every layer
• Easier troubleshooting

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Open Systems Interconnect (OSI) Model

Layer 7 – Application

• Responsible for all application-to-application communications
• User information maintained at this layer is user data
• Security: Confidentiality, Authentication, Data Integrity, Non-repudiation
• Technology: Gateways
• Protocols: FTP, SMB, Telnet, TFTP, SMTP, HTTP, NNTP, CDP, GOPHER, SNMP, NDS, AFP, SAP, NCP, SET

Layer 6 – Presentation

• Responsible for the formatting of the data so that it is suitable for presentation
• Responsible for character conversion (ASCII/EBCDIC)
• Encryption/Decryption, Compressions and Virtual Terminal Emulation
• User information maintained at this layer is called messages
• Security: Confidentiality, Authentication, Encryption
• Technology: Gateway
• Protocols: ASCII, EBCDIC, Postscript, JPEG, MPEG, GIF

Layer 5 – Session

• Responsible for the setup of the links, maintaining of the link and the link tear-down between applications
• Security: None
• Technology: Gateway
• Protocols: Remote Procedure Calls (RPC), SQL, RADIUS, DNS, ASP

Layer 4 – Transport

• Responsible for the guaranteed delivery of user information
• Also responsible for error detection, correction and flow control
• User information at this layer is called datagram
• Security: Confidentiality, Authentication, Integrity
• Technology: Gateway
• Protocols: TCP, UDP, SSL, SSH-2, SPX, NetBIOS, ATP

Layer 3 – Network

• Responsible for the routing of user data from one node to another through the network including the path selection
• Logical addresses are used at this layer
• User information maintained at this layer is called packets
• Security: Confidentiality, Authentication, Data Integrity
• Technology: Virtual Circuits (ATM), routers
• Protocols: IP, IPX, ICMP, OSPF, IGRP, EIGRP, RIP, BOOTP, DHCP, ISIS, ZIP, DDP, X.25

Layer 2 – Data Link

• Responsible for the physical addressing of the network via MAC addresses
• There are two sublevels: MAC & LLC
• Has error detection, frame ordering and flow control
• User information maintained at this layer is called frames
• Security: Confidentiality
• Technology: Bridges, switches
• Protocols: L2F, PPTP, L2TP, PPP, SLIP, ARP, RARP, SLARP, IARP, SNAP, BAP, CHAP, LCP, LZS, MLP, Frame Relay, Annex A, Annex D, HDLC, BPDU, LAPD, ISL, ,MAC, Ethernet, Token Ring, FDDI

Layer 1 – Physical

• Responsible for the physical transmission of the binary digits through the physical medium
• Includes things such as the physical cables, interfaces and data rate specifications
• User information maintained at this layer is called bits
• Security: Confidentiality
• Technology: ISDN, Hubs, Repeaters, Cables