Networking Basics:

OSI Model:

• Layer 7 : Application  | HTTP, FTP |  Program that creates and open data | User applications
• Layer 6: Presentation  | JPEG, ASCII, GIF | Formats data, encrypt, decrypt/translates data 
• Layer 5: Session  | NFS, RPC, SQL, NetBIOS | synchronize and send to ports | Logical ports
• Layer 4: Transport | TCP, UDP, SPX | Host to host, flow control | Hosts, Firewalls
• Layer 3: Network  | IP, IPX, ICMP | L3 Addressing | Routers
• Layer 2: Data Link | ARP, Frame Relay, HDLC, PPP | L2 Addressing | NICs, L2 Switches
• Layer 1: Physical | Hubs, Repeaters, Connectors, Cables, Lights | Physical pathways

TCP/IP Mode:

• Application Layer (L7,6,5) (TFTP, FTP, Telnet)
• Transport Layer (L 4)  (TCP,UDP)
• Internet Layer (L3)  (IPv4, IPv6, ICMP)
• Data Link Layer (L2) (ARP, MAC, PPP)
• Physical Layer (L1) (Ethernet)

1. Physical layer – provides the mechanical, electrical and procedural means for transmitting bits over a communication medium.

2. Data link layer – provides services for the transmission of data between directly connected systems in a communication network.

3. Network layer – handles the routing of data through communication networks.

4. Transport layer – provides reliable end-to-end services without being concerned about the route through communication networks.

5. Session layer – provides facilities to organise and synchronise dialogues, i.e. communications that consist of several strands such as audio and video components.

6. Presentation layer – deals with issues about how data is represented and ensures that the systems agree on how the information is transferred.

7. Application layer – provides the means for application programs to access the communication system represented by the OSI reference model. For instance, the application layer can provide services for supporting file transfer and email.

TCP vs UDP:

Sequenced vs Unsequenced

Reliable vs Unreliable

Connection Oriented vs Connectionless

Virtual Circuit vs Low Overhead

Acknowledgements vs No Acknowledgements

Windowing Flow Control vs No Windows Flow Contol

Infrastructure components:

Switches:

Layer 2 - makes forwarding decision based on layer 2 addressing

Layer 3 - make routing decision based on layer 3 addressing

Network Topologies:

Star : Used for LANs

Mesh: Used for WANs

Hybrid: Provides redundancy for critical services and single connectivity for devices that are not critical but important

Networking Architecture:

Three Tier: Core, Distribution, Access

Collapsed Core: Core & Distribution, Access

Cabling:

Crossover: switch to switch, router to router, PC to PC

Straight through : switch to PC, router to switch

Rollover : connect to router interface