Network Protocols and Models

Module 3: Protocols and Models

• Module Objective: Explain how network protocols enable devices to access local and remote network resources.

3.1 The Rules

• Networks can vary in size and complexity, but all devices must agree on "how" to communicate.
• The three elements of all communication are a source (sender), a destination (receiver), and a channel (media).
• All communications are governed by protocols.
• Protocols are the rules that communications will follow, but these rules will vary depending on the protocol.
• Individuals must use established rules or agreements to govern conversation.
• Protocols must account for an identified sender and receiver, common language and grammar, speed and timing of delivery, and confirmation or acknowledgment requirements.
• Common computer protocols must be in agreement and include message encoding, message formatting and encapsulation, message size, message timing, and message delivery options.
• Encoding is the process of converting information into another acceptable form for transmission, while decoding reverses the process to interpret information.
• When a message is sent, it must use a specific format or structure.
• Message formats depend on the type of message and the channel that is used to deliver the message.
• Encoding between hosts must be in an appropriate format for the medium.
• Messages sent across the network are converted to bits, the bits are encoded into a pattern of light, sound, or electrical impulses, and the destination host must decode the signals to interpret the message.
• Message timing includes flow control, response timeout, and access method.
• Flow Control manages the rate of data transmission and the speed at which it can be delivered.
• Response Timeout manages how long a device waits when it does not hear a reply from the destination.
• Access Method determines when someone can send a message, and may involve rules governing issues like "collisions."
• Message delivery may employ one of the following methods: Unicast (one-to-one), Multicast (one-to-many, typically not all), and Broadcast (one-to-all).
• Broadcasts are used in IPv4 networks, but are not an option for IPv6, but Anycast can be used as an additional delivery option.
• Documents may use the node icon, typically a circle, to represent all devices.

3.2 Protocols

• Network protocols define a common set of rules, and can be implemented in software, hardware, or both.
• Protocols have their own function, format, and rules.
• Network Communications protocols enable two or more devices to communicate over one or more networks.
• Network Security protocols secure data to provide authentication, data integrity, and data encryption.
• Routing protocols enable routers to exchange route information, compare path information, and select best path.
• Service Discovery protocols are used for the automatic detection of devices or services.
• Devices use agreed-upon protocols to communicate.
• Protocols may have one or many functions.
• Addressing protocol identifies sender and receiver.
• Reliability protocol provides guaranteed delivery.
• Flow Control protocol ensures data flows at an efficient rate.
• Sequencing protocol uniquely labels each transmitted segment of data.
• Error Detection protocol determines if data became corrupted during transmission.
• Application Interface protocol allows process-to-process communications between network applications.
• Networks require the use of several protocols, and each protocol has its own function and format.
• Hypertext Transfer Protocol (HTTP) governs the way a web server and a web client interact, and defines content and format.
• Transmission Control Protocol (TCP) manages the individual conversations, provides guaranteed delivery, and manages flow control.
• Internet Protocol (IP) delivers messages globally from the sender to the receiver.
• Ethernet delivers messages from one NIC to another NIC on the same Ethernet Local Area Network (LAN).

3.3 Protocol Suites

• Protocols must be able to work with other protocols in protocol suites.
• Protocol suites are a group of inter-related protocols necessary to perform a communication function and solve a problem.
• Protocols can be viewed in terms of layers: higher and lower.
• Lower Layers are concerned with moving data and providing services to upper layers.
• Common protocol suites are: Internet Protocol Suite or TCP/IP, Open Systems Interconnection (OSI) protocols, AppleTalk, and Novell NetWare.
• The Internet Protocol Suite or TCP/IP is the most common protocol suite and is maintained by the Internet Engineering Task Force (IETF).
• Open Systems Interconnection (OSI) protocols are developed by the International Organization for Standardization (ISO) and the International Telecommunications Union (ITU)
• TCP/IP protocols operate at the application, transport, and Internet layers.
• The most common network access layer LAN protocols are Ethernet and WLAN (wireless LAN).
• TCP/IP is the protocol suite used by the Internet and includes many protocols.
• TCP/IP is an open standard protocol suite that is freely available to the public and can be used by any vendor.
• TCP/IP is a standards-based protocol suite that is endorsed by the networking industry and approved by a standards organization to ensure interoperability.
• In TCP/IP: a web server is encapsulating and sending a web page to a client, and that client is de-encapsulating the web page for the web browser.

3.4 Standards Organizations

• Open standards encourage interoperability, competition, and innovation.
• Standards organizations are vendor-neutral, non-profit organizations established to develop and promote the concept of open standards.
• Internet Society (ISOC) promotes the open development and evolution of the internet.
• Internet Architecture Board (IAB) is responsible for management and development of internet standards.
• Internet Engineering Task Force (IETF) develops, updates, and maintains internet and TCP/IP technologies.
• Internet Research Task Force (IRTF) is focused on long-term research related to internet and TCP/IP protocols.
• Internet Corporation for Assigned Names and Numbers (ICANN) coordinates IP address allocation, the management of domain names, and assignment of other information.
• Internet Assigned Numbers Authority (IANA) oversees and manages IP address allocation, domain name management, and protocol identifiers for ICANN.
• Institute of Electrical and Electronics Engineers (IEEE) dedicates to creating standards in power and energy, healthcare, telecommunications, and networking.
• Electronic Industries Alliance (EIA) develops standards relating to electrical wiring, connectors, and the 19-inch racks used to mount networking equipment.
• Telecommunications Industry Association (TIA) develops communication standards in radio equipment, cellular towers, Voice over IP (VoIP) devices, and satellite communications.
• International Telecommunications Union-Telecommunication Standardization Sector (ITU-T) defines standards for video compression, Internet Protocol Television (IPTV), and broadband communications.

3.5 Reference Models

• Complex concepts like how a network operates are difficult to explain and understand, so a layered model is used.
• Two layered models describe network operations: Open System Interconnection (OSI) Reference Model, and TCP/IP Reference Model
• The benefits of using a layered model are assisting in protocol design, fostering competition, preventing technology or capability changes in one layer from affecting other layers, and providing a common language to describe networking functions and capabilities
• The OSI Model Layer 7 - Application contains protocols used for process-to-process communications.
• The OSI Model Layer 6 - Presentation provides for common representation of the data transferred between application layer services.
• The OSI Model Layer 5 - Session provides services to the presentation layer and to manage data exchange.
• The OSI Model Layer 4 - Transport defines services to segment, transfer, and reassemble the data for individual communications.
• The OSI Model Layer 3 - Network provides services to exchange the individual pieces of data over the network.
• The OSI Model Layer 2 - Data Link describes methods for exchanging data frames over a common media.
• The OSI Model Layer 1 - Physical describes the means to activate, maintain, and de-activate physical connections.
• The TCP/IP Model Layer 4 - Application represents data to the user, plus encoding and dialog control.
• The TCP/IP Model Layer 3 - Transport supports communication between various devices across diverse networks.
• The TCP/IP Model Layer 2 - Internet determines the best path through the network.
• The TCP/IP Model Layer 1 - Network Access controls the hardware devices and media that make up the network.
• The OSI model divides the network access layer and the application layer of the TCP/IP model into multiple layers, while the TCP/IP protocol suite does not specify which protocols to use when transmitting over a physical medium.
• OSI Layers 1 and 2 discuss the necessary procedures to access the media and the physical means to send data over a network.

3.6 Data Encapsulation

• Segmenting is the process of breaking up messages into smaller units.
• Multiplexing interleaves multiple streams of segmented data.
• Segmenting messages increases speed and efficiency.
• Increases speed because it allows large amounts of data to be sent over a network without tying up a communications link.
• Increases efficiency because only segments which fail to reach the destination need to be retransmitted, not the entire data stream.
• Sequencing messages is the process of numbering the segments so that the message may be reassembled at the destination.
• TCP is responsible for sequencing the individual segments.
• Encapsulation is the process where protocols add their information to the data.
• Passing down the stack, at each stage of the encapsulation process, a PDU has a different name to reflect its new functions.
• There is no universal naming convention for PDUs.
• For TCP/IP the PDUs are: Data (Data Stream), Segment, Packet, Frame, and Bits (Bit Stream).
• Encapsulation is a top-down process, where each level does its process, passes it down to the next level of the model, and this process is repeated by each layer until it is sent out as a bit stream.
• Data is de-encapsulated as it moves up the stack.
• When a layer completes its process, it strips off its header and passes it up to the next level to be processed.
• This is repeated at each layer until it is a data stream that the application can process.

3.7 Data Access

• Both the data link and network layers use addressing to deliver data from source to destination.
• Network layer source and destination addresses are responsible for delivering the IP packet from original source to the final destination.
• Data link layer source and destination addresses are responsible for delivering the data link frame from one network interface card (NIC) to another NIC on the same network.
• The IP packet contains two IP addresses: a source IP address and a destination IP address, and these addresses may be on the same link or remote.
• The Source IP address is the IP address of the sending device, or the original source of the packet, while the Destination IP address is the IP address of the receiving device, or the final destination of the packet.
• An IP address contains two parts: a network portion (IPv4) or prefix (IPv6), and host portion (IPv4) or interface ID (IPv6).
• The left-most part of the address (network portion) indicates the network group to which the IP address belongs.
• Each LAN or WAN will have the same network portion.
• The remaining part of the address (host portion) identifies a specific device within the group, and is unique for each device on the network.
• When devices are on the same network, the source and destination will have the same number in network portion of the address.
• When devices are on the same Ethernet network, the data link frame will use the actual MAC address of the destination NIC.
• MAC addresses are physically embedded into the Ethernet NIC and are local addressing.
• The Source MAC address will be that of the originator on the link.
• The Destination MAC address will always be on the same link as the source, even if the ultimate destination is remote.
• When the actual destination is not on the same LAN and is remote: What happens when the destination is not on the same LAN and is remote? This impacts the network and data link layers?
• When the source and destination have a different network portion, this means they are on different networks.
• When the final destination is remote, Layer 3 will provide Layer 2 with the local default gateway IP address, which is also known as the router address.
• The default gateway (DGW) is the router interface IP address that is part of this LAN and will be the "door" or "gateway” to all other remote locations.
• All devices on the LAN must be told about this address or their traffic will be confined to the LAN only.
• Once Layer 2 on PC1 forwards to the default gateway (Router), the router then can start the routing process of getting the information to actual destination.
• The data link addressing is local addressing so it will have a source and destination for each link.
• MAC addressing for the first segment is: Source - AA-AA-AA-AA-AA-AA (PC1) Sends the frame and Destination – 11-11-11-11-11-11 (R1- Default Gateway MAC) Receives the frame.
• While the L2 local addressing will change from link to link or hop to hop, the L3 addressing remains the same.