==OSI Stack== Six layers work together and are collectively known as the ‘stack’ or more formally the OSI reference model. {| | align=”center” style=”background:#f0f0f0;”|’'’Layer’’’ | align=”center” style=”background:#f0f0f0;”|’'’Name’’’ | align=”center” style=”background:#f0f0f0;”|’'’Description’’’ | align=”center” style=”background:#f0f0f0;”|’'’Popular examples’’’ | align=”center” style=”background:#f0f0f0;”|’'’Other examples’’’ |- |1||Physical layer||The actual physical infrastructure connecting devices together: Cabling and interfaces.||Ethernet, 802.11g||Token ring, T-Bone connectors |- |2||Link layer||Conversion between physical hardware with other forms of addressing.||ARP, PPP||SLIP |- |3||Network layer||Delivers and routes packets of data||IP, ICMP, Ipsec||IGMP |- |4||Transport layer||Formats/encodes/decodes data for transportation over a network||TCP, UDP, PPTP||L2TP |- |5||Session layer||Not always used: Facilitates a temporary session between two nodes/hosts.||NetBIOS|| |- |6||Presentation layer||Not always used: Facilitates further formatting of data for the application layer of necessary.||MIME|| |- |7||Application layer||The protocol that the application itself uses - the reason why all the previous layers have performed the function!||HTTP, SMB, DNS, FTP, SSH, SMTP, RDP||NTP, SNMP, NNTP, Gopher |- | |}

==Data link frame== All data on a network is sent/received in packets, all packets are sent within data link frames:

{| | align=”center” style=”background:#b0f080;”|’'’Layer 1/Ethernet/MAC Destination Address’’‘
48 bits | align=”center” style=”background:#b0f080;”|’'’Layer 1/Ethernet/MAC Source Address’’‘
48 bits | align=”center” style=”background:#b0f080;”|’'’Layer 3/IP Source Address’’‘
32 bits | align=”center” style=”background:#b0f080;”|’'’Layer 3/IP Source Address’’‘
32 bits | align=”center” style=”background:#b0f080;”|’'’Data’’’ | align=”center” style=”background:#b0f080;”|’'’PCB’’‘
32 bits |- | ||<——————————–||IP datagram||—————||—>|| |- | <——————————–||———————————||Ethernet data link frame||——————–||—–||–> |- | |} *The layer 3 source/destination never change along the entire routing of the packet. *The layer 1 source/destination will change from each hop to the next.

==See Also== [http://www.soi.asia/pkg1/06/1.html Introduction to routing]