Network Protocols and Data Encapsulation

Network Protocols

• Protocols allow network operations

Module Objectives

• Network Communications Process explains data networked communications
• Communications Protocols explains how these protocols enable network operations
• Data Encapsulation explains how data encapsulation allows data to be transported across networks

Network Communications Process

Networks of Many Sizes

• Networks range in size
• Some networks consist of 2 computers
• Others connect millions of devices
• Networks provide consolidation, storage, and access to information on network servers
• Networks also provide email, instant messaging, and collaboration among employees
• Many organizations use their network’s connection to the internet to provide products and services to customers
• In smaller settings, peer-to-peer networks mean computers function as both the servers and clients

Network Types (contd.)

• Small home networks connect a few computers to each other and the internet
• Small Office and Home Office (SOHO) networks allow a home or remote office to connect to a corporate network, or access centralized, shared resources
• Medium to Large networks are used by corporations and schools
• These large networks have many locations with hundreds or thousands of interconnected hosts
• World Wide networks, such as the internet, connect hundreds of millions of computers

Client-Server Communications

• Hosts are all computers directly connected to a network and participate in network communication
• Hosts are also called end devices, endpoints, or nodes
• Servers have specialized software and enable other end devices to get information across the network
• Servers can be single-purpose, such as web pages, or it can be multipurpose such as email, and file transfers
• Client computers have software that enables them to request and see the info from the server
• A single computer can run multiple types of client software

Client-Server Examples

• File Servers store corporate and user files in a central location
• Client devices access these files via client software, such as Windows Explorer
• Web Servers run web server software
• Clients use their browser software, such as Windows Internet Explorer, to access web pages
• Email Servers run email server software, such as Microsoft Outlook, so clients can access email

Typical Sessions for Network Use

• A typical network user uses a computing device to establish many connections with network servers that can be located anywhere

Network Use at School Example

• Students can use devices such as laptops and tablets to access learning resources
• Terry connects to the school’s wi-fi network and searches for the required resources with a search engine
• The search is submitted wirelessly from Terry's device to the school’s network
• All search data is addressed so that it can find its way back to Terry
• The binary data search string is encoded into radio waves and converted into electrical signals
• These signals go through the school’s wired network to reach the school’s Internet Service Provider’s (ISP) network
• Technologies take Terry’s search to the website, where it is processed by the Search Engine’s servers
• The website results are encoded and addressed to her school and eventually to Terry’s device

Network Use While Gaming Example

• Michelle uses a gaming console to play games against other players
• Michelle's network connects to an ISP using a router and a cable modem
• The router and cable modem allows her home network to connect to a cable TV network belonging to her ISP
• Cable wires connect Michelle’s neighborhood to a central point on a telephone pole and then to a fiber-optic network
• The fiber-optic network connects many neighborhoods served by Michelle’s ISP
• When Michelle connects her gaming console to a company that hosts a popular online game, her in-game actions become data that is sent to the gamer network
• Other data identifies Michelle, including the game, and her network location
• This collective data is sent at high speed to the game provider’s network
• The results are returned to Michelle in the form of graphics and sounds

Network Use in Medical Consultations Example

• Dr. Ismael Awad frequently needs to consult with other specialists on patient cases
• His hospital subscribes to a Cloud service that allows medical data, including patient x-rays, to be stored in a central location that accessible via the internet
• When a patient has an X-ray taken, the image is digitized as data
• A hospital uses network services which encrypts the image data and patient information
• This encrypted data cannot be intercepted and read as it travels across the internet to the cloud service provider's data centers
• The data is addressed so that it can be routed to the cloud provider’s data center to reach the correct services that provide storage and retrieval of high-resolution digital images
• All of this interaction is digital via networked services provided by the medical cloud service

Tracing the Path of a Network

• Cybersecurity analysts deeply understand how networks operate
• They determine the origin of traffic and its destination
• Traffic from a computer to an internet server takes many paths

Network Connections

• Copper and fiber-optic cables carry data traffic over land and under the ocean
• These connections link telecommunications facilities and ISPs throughout the world
• Global Tier 1 and Tier 2 ISPs connect portions of the internet together, usually through an Internet Exchange Point (IXP)
• Larger networks connect to Tier 2 networks through a Point of Presence (PoP)
• PoPs are usually located in a building where physical connections to the ISP are made
• Tier 3 ISPs connect homes and businesses to the internet

Route Tracing Utilities

• Route tracing utilities examine the internet pathway to destination networks
• The objectives are to verify connectivity to a website, use the traceroute utility on the Linux command line and use a web-based traceroute tool

Communications Protocols

What are Protocols?

• Protocols are the rules of how a device communicates
• Protocols must be specific to the communication method being used
• Network protocols specify many features of network communication

Network Protocols

• Network protocols give computers the means for network communication
• These protocols dictate the message encoding, formatting, encapsulation, size, timing, and delivery options
• Networking protocols define a format and rules for exchanging messages between devices
• Some common networking protocols are Hypertext Transfer Protocol (HTTP), Transmission Control Protocol (TCP), and Internet Protocol (IP)
• IP refers to both the IPv4 and IPv6 protocols
• IPv6 is the most recent version of IP and will eventually replace the more common IPv4

Network Protocol Structure

• Message Structure specifies how the message is formatted or structured
• Path Sharing specifies the process by which networking devices share information about pathways with other networks
• Information Sharing specifies how and when error and system messages are passed between devices
• Session Management manages the setup and termination of data transfer sessions

TCP/IP Protocol Suite

• TCP/IP is the protocol suite used by the internet and today’s networks
• This open standard protocol suite is freely available to the public
• Any vendor can use the TCP/IP protocol suite in their hardware or software
• It is a standards-based protocol suite endorsed by the networking industry and approved by standards organizations

Application Layer

• The Domain Name System (DNS) translates domain names into IP addresses
• DHCPv4 dynamically assigns IPv4 addressing information to DHCPv4 clients at start-up
• DHCPv4 allows the addresses to be re-used when no longer needed
• DHCPv6 dynamically assigns IPv6 addressing information to DHCPv6 clients at start-up
• SLAAC lets a device obtain its IPv6 addressing information without using a DHCPv6 server

TCP/IP Email Protocols

• Simple Mail Transfer Protocol (SMTP) enables clients to send email to a mail server so the server can send email to other servers
• Post Office Protocol version 3 (POP3) enables clients to retrieve email from a mail server and download the email to the client's local mail application
• Internet Message Access Protocol (IMAP) enables clients to access email stored on a mail server and also to maintain email on the server

TCP/IP File Transfer Protocols

• File Transfer Protocol (FTP) sets the rules that enable a user on one host to access and transfer files to and from another host over a network
• SSH File Transfer Protocol (SFTP) establishes a secure file transfer session with file transfer encryption
• Trivial File Transfer Protocol (TFTP) has a simple, connectionless protocol with best-effort, unrecognized file delivery

TCP/IP Web and Web Services Protocols

• Hypertext Transfer Protocol (HTTP) defines rules for exchanging text, graphic images, sound, video, and other multimedia files on the World Wide Web
• Hypertext Transfer Protocol Secure (HTTPS) is a secure form of HTTP that encrypts the data exchanged over the World Wide Web
• REST (Representational State Transfer) offers web services that use application programming interfaces (APIs) and HTTP requests to create web applications

Transport Layer Protocols

• Transmission Control Protocol (TCP) enables reliable communication between processes running on separate hosts and provides reliable transmissions confirming successful delivery
• User Datagram Protocol (UDP) enables a process running on one host to send packets to a process running on another host

Internet Layer Protocols

• Internet Protocol version 4 (IPv4) receives message segments from the transport layer, packages messages into packets, and addresses packets for end-to-end delivery via a 32-bit address
• Internet Protocol version 6 (IPv6) functions like IPv4 but uses a 128-bit address
• Network Address Translation (NAT) translates IPv4 addresses from a private network into globally unique public IPv4 addresses

Protocol Messaging Info

• Internet Control Message Protocol for IPv4 (ICMPv4) gives feedback from a destination host to a source host about errors in packet delivery
• Internet Control Message Protocol for IPv6 (ICMPv6) is similar, but used for IPv6 packets
• ICMPv6 Neighbor Discovery (ICMPv6 ND) includes four protocol messages to resolve addresses and detect duplicate addresses

Protocol Routing Info

• Open Shortest Path First (OSPF) is a link-state routing protocol which uses a hierarchical design based on areas, and it is an open standard interior routing protocol
• Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary routing protocol which uses a composite metric based on bandwidth, delay, load, and reliability
• Border Gateway Protocol (BGP) describes a standard exterior gateway routing protocol used between Internet Service Providers (ISPs)

Network Access Layer Protocols

• Address Resolution Protocol (ARP) provides dynamic address mapping between an IPv4 address and a hardware address
• Ethernet defines standards for wiring/signaling within a network access layer
• Wireless Local Area Network (WLAN) defines rules for wireless signaling across the 2.4 GHz and 5 GHz radio frequencies

Message Formatting and Encapsulation

• A message sent from source to destination must use a specific format or structure, based on the message type and channel used

Message Analogy

• Sending a letter requires correct formatting
• An envelope contains the sender and receiver addresses at the proper location
• Encapsulation puts one message format (the letter) inside another message format (the envelope)
• De-encapsulation occurs when the recipient reverses the process and removes the letter from the envelope

Network Message Formatting

• Instead of a letter, a message going over a computer network needs to follow specific format rules to be delivered and processed
• The Internet Protocol (IP) has a similar function to the envelope where it sends a message from source to destination

Message Size

• Another communication rule is message size

Message Size Analogy

• People usually break the messages into parts or sentences
• The limited sentences allow the receiving person to process at one time
• It makes it easier for the receiver to read and comprehend

Network Message Size

• Encoding between hosts require an appropriate medium format
• Messages are converted into bits by the sending host
• Each bit is encoded into a pattern of sounds, light waves, or electrical impulses depending on the network media
• The destination host receives and decodes the signals to interpret the message

Message Timing

• Message timing includes flow control, response timeout, and access method

Flow Control, Response Timeout and Access Method

• Flow Control defines how much information can be sent and the speed at which it can be delivered
• Response Timeout describes how network hosts wait for responses and what action to take if the response times out
• Access Method occurs when a device sends a message
• For a wireless LAN, the WLAN NIC has to determine whether the wireless medium is available

Communication Delivery Options

• Messages have delivery options on a network, these include unicast, multicast, and broadcast

Unicast, Multicast and Broadcast

• A Unicast is a one-to-one delivery option
• A Multicast is required when a host sends messages using a one-to-many delivery option
• Broadcasting happens when all hosts need to receive the message
• Broadcasting represents a one-to-all message delivery option

Using a Layered Model

• A layered model modularizes a network into manageable layers
• In protocol design, it assists protocol design, fosters competition, prevents technology/capability changes, and provides a common language
• The network uses Open Systems Interconnection (OSI) Reference and TCP/IP Reference models

The OSI Reference Model

• The OSI reference model provides a list of functions and services that can occur at each layer
• This model provides consistency in network protocols and services by describing the work at a layer, but not how it should be accomplished
• OSI also describes the interaction of each layer
• Also, the 7 OSI layers are referred to more often by number rather than by name

OSI Model Layers

• Layer 7, Application, contains protocols for process-to-process communications
• Layer 6, Presentation, provides representation of data transferred between application layer services
• Layer 5, Session, provides services to the presentation layer to organize communication and manage data exchange
• Layer 4, Transport, defines services to segment, transfer, and reassemble individual data communications between devices
• Layer 3, Network, provides transmission of individual pieces of data over the network
• Layer 2, Data Link, describes transfer methods for exchanging data frames between devices over a common medium
• Layer 1, Physical, describes the mechanical, electrical, functional, and procedural means to activate, maintain, and de-activate physical connections for bit transmission between devices

The TCP/IP Protocol Model

• The TCP/IP protocol model is also referred to as the internet model
• It describes the functions that occur at each layer of protocols in the TCP/IP suite and also acts as a reference model

TCP/IP Layers

• 4 - Application represents data to the user, plus encoding and dialog control
• 3 - Transport supports communication between devices across diverse networks
• 2 - Internet determines the best path through the network
• 1 - Network Access controls the hardware devices and media that make up the network

Data Encapsulation

• Data encapsulation is covered

Segmenting Messages

• If large streams of data are sent across a network, delays would occur
• If any link in the network failed during transmission, the complete message may be lost
• Segmentation divides a stream of data into smaller units for network transmissions
• Segmentation is necessary for networks using TCP/IP protocol to send data in individual IP packets
• Segments for the same destination are sent in separate packets over different paths

Segmenting Messages (cont.)

• Multiplexing increases speed through allowing a greater amount of data being sent over the network while not tying up a communications link
• Increased efficiency happens when segments that fail to reach its destination, instead only that segment is transmitted again

Sequencing

• When transmitting messages using segmentation and multiplexing, the data may reach the destination in an incorrect order
• Segments of messages have a sequencing process to ensure it gets to the correct destination and can be reassembled like the original message
• TCP helps to sequence the individual segments

Protocol Data Units

• The encapsulation process adds protocol information for sending application data passed down the protocol stack on the network
• Protocol Data Units (PDUs) are the form that a piece of data takes at any layer
• During encapsulation, each layer encapsulates the PDU it receives from the layer above
• Each stage of the process has different PDU names that reflect its new functions
• UDP PDU is called a datagram
• IP packets are sometimes also considered IP datagrams

Types of PDUs

• Data refers to the term for the PDU used at the application layer
• Segment refers to the transport layer PDU
• Packet refers to network layer PDU
• Frame refers to the Data Link layer PDU
• Bits refers to the physical layer PDU used when transmitting data over the medium

TCP, UDP and Segments

• If the transport header is TCP, then it is a segment
• If the transport header is UDP, then it is a datagram

Network Addresses

• Network protocols require addresses
• The OSI transport, network and data link layers use addressing
• The transport layer uses protocol addresses that use port numbers to identify network applications
• The network layer uses addresses that identify the networks for clients and servers
• The data link layer specifies devices on the local LAN that should handle data frames
• All three addresses are required for client-server communication

Encapsulation Example

• Messages being sent on a network will have the encapsulation process working from top to bottom
• Info from each upper layer is considered data within the encapsulated protocol
• A TCP segment will be considered data within the IP packet

De-encapsulation

• The reverse of the encapsulation happens at the receiving host
• This is called de-encapsulation
• In it, a receiving host removes protocol headers
• Then the data is de-encapsulated as it moves through the stack toward the end-user

Introduction to Wireshark

• Wireshark is a software protocol analyzer used for network troubleshooting, analysis, and protocol development/education
• You can use Wireshark to capture and analyze network traffic

Network Protocols Summary

• What was learned in this module

Module 5 Learning Outcomes

• Networks come in all sizes for homes, businesses, and other organizations, such as the internet
• Servers are hosts which use specialized software that handle data requests from clients
• Clients are hosts that use web browsers, email, or file transfers to request data from servers
• Larger businesses may connect to Tier 2 ISPs through a Point of Presence (POP)
• Tier 3 ISPs connect homes and businesses to the internet
• Network protocols specify network communication features such as message encoding, message formatting/encapsulation, and delivery options

More Module 5 Learning Outcomes

• Protocols describe messages that are structured, and the way networking devices share information about pathways to other networks
• Common protocols at the application layer of the suite are DNS, DHCP, POP3, and HTTPS
• OSI includes seven layers, while TCP/IP includes four layers
• Segmentation describes data being broken up into smaller pieces
• Multiplexing describes how increased speed is gained thanks to the many data conversations happen at the same time on the network
• Encapsulation occurs because data is passed down the protocol stack
• Protocol Data Unit (PDU) is the form that data takes at each layer
• De-encapsulation the is process where a receiving device removes one or more of the protocol headers