The OSI model defines a standard framework for how applications can communicate over a network through 7 layers of abstraction: Physical, Data Link, Network, Transport, Session, Presentation, and Application. Each layer has a specific purpose and set of protocols to convert data between layers, establish connections, route packets, ensure reliable and secure delivery of data, and interface with applications. The layers work together to take a message from an application, convert it to bits for transmission over a physical medium, and reconstruct it back to a message at the destination.
23. How do the layers talk? Sevice Access Points (SAP) – an address in memory that acts as a conduit between the two entities.
24. The Application Layer Acts as an interface between user apps and the network PDU of the layer is a message The first line of command for a process called flow control Making sure data moves at a rate acceptable to both parties involved in the transfer
25. Application Layer Protocols Network Terminal Protocol (Telnet) File Transfer Protocol (FTP) Simple Mail Transfer Protocol (SMTP) Post Office Protocol (POP) Domain Names Services (DNS) Hyper Text Transfer Protocol (HTTP) Routing Information Protocol (RIP) AppleShare
26. Presentation Layer Makes sure data is in the correct format Manages uniform character sets Handles data encryption Manages data compression
27. The Session Layer Sets up and breaks down virtual connections between communicating devices Maintains connection while it is active Juggles multiple open connections at the same time
28. Session Layer Protocols Network File System (NFS) Structured Query Language (SQL) Remote Procedure Call (RPC) X Window Network Basic Input/Output Services (NetBIOS) User Datagram Protocol (UDP) NetWare Core Protocol (NCP) AppleTalk Session Protocol (ASP) AppleTalk Data Stream Protocol (ADSP)
29. The Transport Layer Breaks data stream down into manageable chunks called segments Performs packet-level error detection/ correction Monitors time to live (TTL) to determine if packets have been lost Handles end-to-end flow control
30. Transport Layer Protocols Transmission Control Protocol (TCP) User Datagram Protocol (UDP) NWLink Sequenced Packet Exchange (SPX) Name Binding Protocol (NBP) AppleTalk Transaction Protocol (ATP) Zone Information Protocol (ZIP) Sequenced Packet Protocol (SPP) Packet Exchange Protocol (PEP)
31. The Network Layer Manages traffic between different networks Controls network addressing functions Responsible for routing PDU of the Network layer The packet
32. Network Layer Protocols Internetwork Packet Exchange (IPX) Routing Information Protocol (RIP) Datagram Delivery Protocol (DDP) Routing Table Maintenance Protocol (RTMP) Internet Protocol (IP) Address Resolution Protocol (ARP) Reverse Resolution Protocol (RARP) Internet Control Message Protocol (ICMP) Open Shortest Path First (OSPF)
33. The Data Link Layer Subdivided into to sub-layers Media Access Control (MAC) Logical Link Control (LLC) Determines methods by which data moves across the medium Defines network access methods
34. Data Link Protocols 802.3 Ethernet 802.3u Fast Ethernet 802.3.z Gigabit Ethernet 802.5 Token Ring 802.11 Wireless Signaling 802.12 Demand Priority Integrated Services Digital Network (ISDN) Fiber Distributed Data Interface (FDDI) X.25
35. The Physical Layer Defines the network media Defines the physiology of connectors and plugs Places the data onto the wire as bits
![The 7 Layers of OSI PURPOSE ,[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)