Module 3: Protocols and Models

People exchange ideas using many different communication methods. However, all communication methods have the following three elements in common:

Message source (sender)

Message Destination (receiver)

Channel

Message source (sender)

People, or electronic devices, that need to send a message to other individuals or devices.

Message Destination (receiver)

The destination receives the message and interprets it.

Channel

This consists of the media that provides the pathway over which the message travels from source to destination.

Protocols must account for the following requirements to successfully deliver a message that is understood by the receiver:

An identified sender and receiver

Common language and grammar

Speed and timing of delivery

Confirmation or acknowledgment requirements

Common computer protocols include the following requirements:

Message encoding

Message formatting and encapsulation

Message size

Message timing

Message delivery options

Message timing is also very important in network communications. Message timing includes the following:

Flow Control, Response Timeout, Access Method

Flow Control

This is the process of managing the rate of data transmission. It defines how much information can be sent and the speed at which it can be delivered. For example, if one person speaks too quickly, it may be difficult for the receiver to hear and understand the message. In network communication, there are network protocols used by the source and destination devices to negotiate and manage the flow of information.

Response Timeout

If a person asks a question and does not hear a response within an acceptable amount of time, the person assumes that no answer is coming and reacts accordingly. The person may repeat the question or instead, may go on with the conversation. Hosts on the network use network protocols that specify how long to wait for responses and what action to take if it occurs.

Access Method

This determines when someone can send a message. Click Play in the figure to see an animation of two people talking at the same time, then a "collision of information" occurs, and it is necessary for the two to back off and start again. Likewise, when a device wants to transmit on a wireless LAN, it is necessary for the WLAN network interface card (NIC) to determine whether the wireless medium is available.

A message can be delivered in different ways.

Analogy and Network

Analogy

Sometimes, a person wants to communicate information to a single individual. At other times, the person may need to send information to a group of people at the same time, or even to all people in the same area.

The three types of data communications include:

Unicast, Multicast, Broadcast

Unicast

Information is being transmitted to a single end device.

Multicast

Information is being transmitted to a one or more end devices.

Broadcast

Information is being transmitted to all end devices.

Network Communications Protocols

Protocols enable two or more devices to communicate over one or more networks. The Ethernet family of technologies involves a variety of protocols such as IP, Transmission Control Protocol (TCP), HyperText Transfer Protocol (HTTP), and many more.

Network Security Protocols

Protocols secure data to provide authentication, data integrity, and data encryption. Examples of secure protocols include Secure Shell (SSH), Secure Sockets Layer (SSL), and Transport Layer Security (TLS).

Routing Protocols

Protocols enable routers to exchange route information, compare path information, and then to select the best path to the destination network. Examples of these include Open Shortest Path First (OSPF) and Border Gateway Protocol (BGP).

Service Discovery Protocols

Protocols are used for the automatic detection of devices or services. Examples of these include Dynamic Host Configuration Protocol (DHCP) which discovers services for IP address allocation, and Domain Name System (DNS) which is used to perform name-to-IP address translation.

Addressing

This identifies the sender and the intended receiver of the message using a defined addressing scheme. Examples of protocols that provide this include Ethernet, IPv4, and IPv6.

Reliability

This function provides guaranteed delivery mechanisms in case messages are lost or corrupted in transit.

Flow control

This function ensures that data flows at an efficient rate between two communicating devices. TCP provides flow control services.

Sequencing

This function uniquely labels each transmitted segment of data. The receiving device uses the sequencing information to reassemble the information correctly. This is useful if the data segments are lost, delayed or received out-of-order. TCP provides sequencing services.

Error Detection

This function is used to determine if data became corrupted during transmission. Various protocols that provide error detection include Ethernet, IPv4, IPv6, and TCP.

Application Interface

This function contains information used for process-to-process communications between network applications. For example, when accessing a web page, HTTP or HTTPS protocols are used to communicate between the client and server web processes.

Hypertext Transfer Protocol (HTTP)

This protocol governs the way a web server and a web client interact. It defines the content and formatting of the requests and responses that are exchanged between the client and server. Both the client and the web server software implement it as part of the application. It relies on other protocols to govern how the messages are transported between the client and server.

Transmission Control Protocol (TCP)

This protocol manages the individual conversations. It is responsible for guaranteeing the reliable delivery of the information and managing flow control between the end devices.

Internet Protocol (IP)

This protocol is responsible for delivering messages from the sender to the receiver. It is used by routers to forward the messages across multiple networks.

Ethernet

This protocol is responsible for the delivery of messages from one NIC to another NIC on the same Ethernet local area network (LAN).

Protocol suites

Sets of rules that work together to help solve a problem.

Internet Protocol Suite or TCP/IP

This is the most common and relevant protocol suite used today. It is a protocol suite is an open standard protocol suite maintained by the Internet Engineering Task Force (IETF).

Open Systems Interconnection (OSI) protocols

This is a family of protocols developed jointly in 1977 by the International Organization for Standardization (ISO) and the International Telecommunications Union (ITU). It also includes a seven-layer model called the OSI reference model. The OSI reference model categorizes the functions of its protocols. Today it is mainly known for its layered model. These protocols have largely been replaced by TCP/IP.

AppleTalk

A short-lived proprietary protocol suite released by Apple Inc. in 1985 for Apple devices. In 1995, Apple adopted TCP/IP to replace it.

Novell NetWare

A short-lived proprietary protocol suite and network operating system developed by Novell Inc. in 1983 using the IPX network protocol. In 1995, Novell adopted TCP/IP to replace IPX.

TCP/IP has two important aspects for vendors and manufacturers:

Open standard protocol suite and Standards-based protocol suite

Open standard protocol suite

This means it is freely available to the public and can be used by any vendor on their hardware or in their software.

Standards-based protocol suite

This means it has been endorsed by the networking industry and approved by a standards organization. This ensures that products from different manufacturers can interoperate successfully.

Internet Society (ISOC)

Responsible for promoting the open development and evolution of internet use throughout the world.

Internet Architecture Board (IAB)

Responsible for the overall management and development of internet standards.

Internet Engineering Task Force (IETF)

Develops, updates, and maintains internet and TCP/IP technologies. This includes the process and documents for developing new protocols and updating existing protocols, which are known as Request for Comments (RFC) documents.

Internet Research Task Force (IRTF)

Focused on long-term research related to internet and TCP/IP protocols such as Anti-Spam Research Group (ASRG), Crypto Forum Research Group (CFRG), and Peer-to-Peer Research Group (P2PRG).

Internet Corporation for Assigned Names and Numbers (ICANN)

Based in the United States, it coordinates IP address allocation, the management of domain names, and assignment of other information used in TCP/IP protocols.

Internet Assigned Numbers Authority (IANA)

Responsible for overseeing and managing IP address allocation, domain name management, and protocol identifiers for ICANN.

Institute of Electrical and Electronics Engineers(IEEE, pronounced "I-triple-E")

Organization of electrical engineering and electronics dedicated to advancing technological innovation and creating standards in a wide area of industries including power and energy, healthcare, telecommunications, and networking. Important networking standards include 802.3 Ethernet and 802.11 WLAN standard.

Electronic Industries Alliance (EIA)

Organization is best known for its standards relating to electrical wiring, connectors, and the 19-inch racks used to mount networking equipment.

Telecommunications Industry Association (TIA)

Organization responsible for developing communication standards in a variety of areas including radio equipment, cellular towers, Voice over IP (VoIP) devices, satellite communications, and more.

International Telecommunications Union-Telecommunication Standardization Sector (ITU-T)

One of the largest and oldest communication standards organizations. The ITU-T defines standards for video compression, Internet Protocol Television (IPTV), and broadband communications, such as a digital subscriber line (DSL).

These are the benefits of using a layered model to describe network protocols and operations:

Assisting in protocol design because protocols that operate at a specific layer have defined information that they act upon and a defined interface to the layers above and below

Fostering competition because products from different vendors can work together

Preventing technology or capability changes in one layer from affecting other layers above and below

Providing a common language to describe networking functions and capabilities

As shown in the figure, there are two layered models that are used to describe network operations:

Open System Interconnection (OSI) Reference Model

TCP/IP Reference Model

This leads to segmenting messages having two primary benefits:

Increases speed and Increases efficiency

Increases speed

Because a large data stream is segmented into packets, large amounts of data can be sent over the network without tying up a communications link. This allows many different conversations to be interleaved on the network called multiplexing.

Increases efficiency

If a single segment is fails to reach its destination due to a failure in the network or network congestion, only that segment needs to be retransmitted instead of resending the entire data stream.

Network layer source and destination addresses

Responsible for delivering the IP packet from the original source to the final destination, which may be on the same network or a remote network.

Data link layer source and destination addresses

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:

Source IP address and Destination IP address

Source IP address

The IP address of the sending device, which is the original source of the packet.

Destination IP address

The IP address of the receiving device, which is the final destination of the packet.

An IP address contains two parts:

Network portion (IPv4) or Prefix (IPv6) and Host portion (IPv4) or Interface ID (IPv6)

Network portion (IPv4) or Prefix (IPv6)

The left-most part of the address that indicates the network in which the IP address is a member. All devices on the same network will have the same network portion of the address.

Host portion (IPv4) or Interface ID (IPv6)

The remaining part of the address that identifies a specific device on the network. This portion is unique for each device or interface on the network.

Source MAC address

This is the data link address, or the Ethernet MAC address, of the device that sends the data link frame with the encapsulated IP packet. The MAC address of the Ethernet NIC of PC1 is AA-AA-AA-AA-AA-AA, written in hexadecimal notation.

Destination MAC address

When the receiving device is on the same network as the sending device, this is the data link address of the receiving device. In this example, it is the MAC address of the FTP server: CC-CC-CC-CC-CC-CC, written in hexadecimal notation.

The IP packet is encapsulated in a data link frame that contains the following data link information:

Source data link address and Destination data link address

Source data link address

The physical address of the NIC that is sending the data link frame.

Destination data link address

The physical address of the NIC that is receiving the data link frame. This address is either the next hop router or the address of the final destination device.