Networking Protocols and Standards

Rules and Protocols

• Communication relies on protocols, which are predetermined rules.
• Protocols define the format/structure of messages.
• Protocols also manage information sharing between networking devices about pathways, error/system message handling, and session setup/termination.

Standards

• A standard is a protocol endorsed by the networking industry, ratified by a standards body like IEEE or IETF.
• Standards ensure interoperability of equipment from different vendors.

Reference Models

• Designed to aid in understanding communication functions and processes.
• Used for network design, operation specifications and troubleshooting.
• Primary models are OSI and TCP/IP.

OSI Model

• The Open Systems Interconnection (OSI) model was created by the International Organization for Standardization (ISO).
• Intended to provide a framework for Open Systems Protocols.
• Contains 7 layers: Application, Presentation, Session, Transport, Network, Data Link, Physical.
• Each layer is responsible for specific functions governed by protocols.

TCP/IP Model

• Consists of four layers: Application, Transport, Internet, and Network Access.

OSI vs. TCP/IP Model

• OSI Application, Presentation and Session Layers map to the TCP/IP Application layer.
• OSI Transport layer also the TCP/IP transport layer.
• OSI Network layer also the TCP/IP Internet layer.
• OSI Data Link and Physical Layers map to the TCP/IP Network Access layer.

Encapsulation and Decapsulation

• Data is passed down the stack during encapsulation, where each layer adds headers.

Protocol Data Units (PDU)

• A Protocol Data Unit (PDU) is the form data takes at each layer.
• Each layer encapsulates the PDU from the layer above it.
• Application Layer PDU = Data.
• Transport Layer PDU = Segment (T-PDU).
• Internetwork Layer PDU = Packet (N-PDU) or datagram.
• Data Link or Network Access Layer PDU = Frame.
• Physical Layer PDU = Bits.

Addressing

• A data stream is divided into pieces which are interleaved with messages traveling to different destination hosts.
• Addresses are necessary to ensure correct delivery.
• Layer 2 address: MAC or physical address.
• Layer 3 address: logical address.
• Layer 4 address: port number.
• MAC addresses are unique and found in the Layer 2 PDU header (frame).
• Layer 3 addresses enable network devices to locate hosts on different networks.
• Layer 4 addresses (port numbers) represent individual applications, and specify where to send data upon receipt.

Intermediary Devices

• Three types are classified by the OSI model layer they operate on.

Repeaters and Hubs

• A repeater has two ports and extends the reach of Ethernet cables.
• Hubs are multi-port repeaters that operate at Layer 1 (Physical).
• Devices connected through hubs or series of hubs form a collision domain.
• Collision domains are also called network segments.
• Hubs/repeaters increase the collision domain size.

Bridges and Switches

• Hubs do not filter traffic.
• Bridges are an alternative to contention-based Ethernet.
• Bridges can filter traffic based on MAC addresses.
• Switches are multi-port bridges with a switching (MAC) address table that matches MAC addresses to ports and operate at layer 2.
• Switches populate MAC tables statically or dynamically.
• Switches segment a LAN into separate collision domains.
• Each switch port represents a separate collision domain, providing dedicated bandwidth.
• Switch advantages = dedicated bandwidth, collision-free environment, full-duplex operation.
• Physical star topologies using switches are generally point-to-point links.
• Switches buffer incoming frames and forward them to the correct port after checking for errors, an operation called store and forward.
• Switch operations = learning, aging, flooding, selective forwarding, filtering.

Routers

• Routers operate at Layer 3, making decisions based on IP addresses.
• Routers use a routing table to match destination networks to the correct interfaces for packet forwarding.
• Routing tables can be statically configured or dynamically populated using routing protocols.