What the OSI Protocol Layers Do 1-3 What the OSI Protocol Layers Do Layer In a Technical Sense ... In a Practical Sense ... Application End User Services E-Mail, File Transfer, Presentation General Services Code Conversion, Compression, Encryption Session Ease of Use Establishes Connections Mostly Software Transport End-to-End Integrity Acknowledgement Network Routing in the Network Logical Channel Control Data Link Point-to-Point Integrity Framing, Error Control Mostly Hardware Physical Transports Bits Signal Propagation

OSI Layer 1: Physical Application Application Presentation 1-4 OSI Layer 1: Physical Application Presentation Session Transport Network Data Link Physical Application Presentation Session Transport Network Data Link Physical Mechanical Electrical Functional Procedural

OSI Layer 2: Data Link Application Application Presentation 1-5 OSI Layer 2: Data Link Application Presentation Session Transport Network Data Link Physical Application Presentation Session Transport Network Data Link Physical Frame structure Error control Synchronization Sequencing Flow control

OSI Layer 3: Network Application Application Presentation Presentation 1-6 OSI Layer 3: Network Application Presentation Session Transport Network Data Link Physical Application Presentation Session Transport Network Data Link Physical Network routing Establishing Maintaining Terminating connections Flow control

OSI Layer 4: Transport Application Application Presentation 1-7 OSI Layer 4: Transport Application Presentation Session Transport Network Data Link Physical Application Presentation Session Transport Network Data Link Physical End-to-end data integrity Flow control

OSI Layer 5: Session Application Application Presentation Presentation 1-8 OSI Layer 5: Session End-to-end session integrity Flow control Recovery/ restart Application Presentation Session Transport Network Data Link Physical Application Presentation Session Transport Network Data Link Physical

OSI Layer 6: Presentation 1-9 OSI Layer 6: Presentation Application Presentation Session Transport Network Data Link Physical Application Presentation Session Transport Network Data Link Physical Platform independence Form/syntax translation

OSI Layer 7: Application 1-10 OSI Layer 7: Application Application Presentation Session Transport Network Data Link Physical Application interface standardization TFTP, SMTP, Telnet directory services, and message handling Application Presentation Session Transport Network Data Link Physical

Comparing the OSI Model to Other Protocols IP IPX X.25 Frame Relay Application R I P B G P A p l i c a t o n s R I P S A P A p l i c a t o n s 7 6 5 4 3 2 1 Presentation Session Transport TCP/UDP IPX/SPX Network IP IPX X.25 Data Link Network Interface Network Interface LAPB Frame Relay Physical Physical Physical

The Networked OSI Model 1-12 The Networked OSI Model 1 2 Application Protocols 7 Application 7 Application Presentation Protocols 6 Presentation 6 Presentation Session Protocols 5 Session 5 Session Transport Protocols 4 Transport 4 Transport 3 Network Network Protocols 3 Network Data Link Protocols 2 Data Link 2 Data Link 1 Physical Physical Protocols 1 Physical

OSI Data Structures Peer Protocols Host A Host B 7 7 6 6 5 5 4 4 3 3 2 1-13 Peer Protocols Host A Host B D = Data H = Header T = Trailer 7 Application Protocol 7 H7 D H7 D 6 Presentation Protocol 6 H6 H7 D H6 H7 D 5 Session Protocol 5 H5 H6 H7 D H5 H6 H7 D 4 Transport Protocol 4 H4 H5 H6 H7 D H4 H5 H6 H7 D 3 Network Protocol 3 H3 H4 H5 H6 H7 D H3 H4 H5 H6 H7 D Packet or Datagram Packet or Datagram 2 Data Link Protocol 2 H2 H3 H4 H5 H6 H7 D T H2 H3 H4 H5 H6 H7 D T Frame Frame 1 Physical Protocol 1 H2 H3 H4 H5 H6 H7 D T H2 H3 H4 H5 H6 H7 D T Frame Frame H2 H3 H4 H5 H6 H7 D T Frames as bits 10110110

Layer Functions H6 H7 H5 H3 H4 Data 1-14 Frame Header Frame Trailer 6 Presentation Presentation Data Link Frame Header 2 Data Link H7 7 Application Application H5 5 Session Session H3 3 Network Network H4 4 Transport Transport Frame Trailer Data Link Data FTP, TFTP, Telnet, DHCP TCP, UDP, SPX, IPX IP, IPX, X.25 HDLC, SDLC, Frame Relay, Ethernet, Token Ring No Header 1 Physical

Physical Addressing E t h e r n 8 2 . 3 5 F D I 802.2 LLC LAN WAN 1-15 Physical Addressing E t h e r n 8 2 . 3 5 F D I 802.2 LLC LAN Dial on Demand ISDN PPP WAN S D L C H X.25 Link V.24 EIA/TIA-232 G.703 V.35 EIA/TIA-449 EIA-530 HSSI Frame Relay Data Link Physical

MAC (Media Access Control) LLC (Logical Link Control) 1-16 Layer 2 — Data Link Layer Presentation Frame Header Data Link Application Network Transport Session Frame Trailer Data Link H3 H4 H5 H6 H7 Data Layer 2 Data Link Layer MAC (Media Access Control) LLC (Logical Link Control)

MAC Address 0 0 0 0 . 0 C A 4 . 6 3 2 B 1-17 Reserved for Manufacturer Start Delimiter Source Address Dest. Address Control Data End Frame End Delimiter 0 0 0 0 . 0 C A 4 . 6 3 2 B Reserved for Manufacturer Serial Number of Card Hex 1 hex value = 4 bits 12 hex values = 48 bits

Layer 3 — Network Layer H3 H4 H5 H6 H7 Data 1-18 Frame Header Frame Presentation Frame Header Data Link Application Network Transport Session Frame Trailer Data Link H3 H4 H5 H6 H7 Data Layer 3 Header Network Layer DSAP Node Network IP Address 32 Bits IPX Address 80 Bits

Directions to My House 1-19 1 Get to Main Street 2 Look for 1234 Main Street

1-20 Network Addressing

Routing — How the Router Thinks 1-21 Routing — How the Router Thinks 1.2.34.0 H2 H3 H4 H5 H6 H7 D T Port 1 Port 2 Packet 6.7.89.0 Port 3 11.12.1.0

Router Communication B 1 2 A C E D 1-22 Here is my current routing table. E D Routing protocols convey information about networks. Routed protocols are responsible for moving the data from host to host.

Static vs. Dynamic Routing 1-23 Static vs. Dynamic Routing Static Route A route that the network administrator types T1 T1 56Kbps T1 Dynamic Route A learned route that can be automatically adjusted due to topology or traffic changes

Transport Layer H3 H4 H5 H6 H7 Data TCP Header 1-25 Frame Header Frame Presentation Frame Header Data Link Application Network Transport Session Frame Trailer Data Link H3 H4 H5 H6 H7 Data Source Port Destination Sequence Number Ack HLEN Reserved Code Bits TCP Header

Connection-Oriented vs. Connectionless Data Acknowledgement Connectionless Data No Acknowledgement

Packet Flow — Step One: The Proxy — ARP Network 2.0 Client A Who is device 4.1? WAN Proxy ARP To get to device 4.1 send data to me, Router A. 4.1 Network 3.0 B Network 4.0

Packet Flow — Step Two: The Source Encapsulation Client Dest. A 1.2 4.1 Link Network 1234 23 Data Trailer Transport WAN A Client 1.2

Packet Flow — Step Three: Across the Ethernet Source 1.2 Dest. A 4.1 Data Trailer Source 1.2 Dest. A 4.1 Data Trailer WAN A 1.2

Packet Flow — Step Four: Across the WAN HDLC Data Network 2.0 C To B WAN A 4.1 1.2 B Network 4.0

Packet Flow — Step Four: Across the WAN (cont.) HDLC Data Network 2.0 C WAN A 4.1 1.2 HDLC Data B Network 4.0

Packet Flow — Step Four: Across the WAN (cont.) Network 2.0 C WAN A 4.1 1.2 Source 1.2 Dest. 4.1 Data HDLC Data B B Network 4.0

Packet Flow — Step Five: The ARP 1-32 Packet Flow — Step Five: The ARP Network 2.0 C WAN 1234.5678.9abc A ARP Query 4.1 1.2 MAC Address B Network 4.0

Packet Flow — Step Five: The ARP (cont.) Network 2.0 C LAN 1234.5678.9abc A 4.1 1.2 B LAN Frame Network 4.0 Data

Packet Flow — Step Five: The ARP (cont.) Network 2.0 C LAN Frame Data LAN A 4.1 1.2 LAN Frame Data B Network 4.0

Packet Flow — Step Six: The Server 1-34 Packet Flow — Step Six: The Server 7 Application Network 2.0 6 Presentation LAN Frame Data 5 Session 4 Transport 3 Network 4.1 1.2 2 Data Link Network 4.0 1 Physical