Networking Fundamentals

• A network combines hardware and software to transmit data between locations
• Hardware consists of physical equipment for carrying signals
• Software consists of instruction sets enabling network services

Comparison to Solving Math Problems

• Networking is comparable to solving math problems using computers
• Computer hardware does the fundamental job
• Software simplifies tasks by directing problem-solving, leaving hardware details to lower software layers

E-mail Example

• Sending an e-mail involves breaking the task into sub-tasks handled by different software packages
• Software packages use each other's services
• Signals are sent from source to destination computer at the lowest layer

Layered Tasks

• Layering is a concept used in daily life
• Sending a letter becomes complex without postal services

Postal Mail Analogy: Sender's Site

• Higher layer: writing and mailing the letter
• Middle layer: letter picked up and delivered to post office
• Lower layer: sorting and transporting the letter

Postal Mail Analogy: En Route

• The letter goes to a central office then to the recipient's local post office
• The letter is transported by truck, train, airplane, or boat

Postal Mail Analogy: Receiver's Site

• Lower layer: carrier transports letter to post office
• Middle layer: sorting and delivery to mailbox
• Higher layer: recipient retrieves and reads letter

Postal Mail Analogy: Hierarchy

• Three activities each occur at the sender and receiver sites: letter writing, mailing, and reading
• Carrier transports the letter, and tasks follow a specific order in the hierarchy

Postal Mail Analogy: Services

• Each layer uses services from the layer below it
• Sender uses middle layer's services, middle layer relies on lower layer, and lower layer relies on carrier

Evolution

• Before 1990, the OSI model was the dominant layered model for data communications
• The TCP/IP protocol suite became the dominant architecture due to its extensive use and testing

ISO and OSI Model

• The International Standards Organization (ISO) promotes worldwide agreements on standards
• The Open Systems Interconnection (OSI) model, introduced in the late 1970s, is an ISO standard for network communications
• An open system is a protocol set facilitating architecture-independent communication between systems
• The OSI model isn't a protocol itself, but a blueprint for designing flexible, robust, interoperable network architectures

OSI Model Basics

• The OSI model provides a basis for exploring data communications
• It's a layered framework with seven distinct layers that enable communication between computer systems

OSI Model Layers

• Physical (layer 1), data link (layer 2), network (layer 3), transport (layer 4), session (layer 5), presentation (layer 6), and application (layer 7) are the seven layers
• Message from device A to B may pass through intermediate nodes
• Intermediate nodes typically involve the first three layers

OSI Model Design

• Designers distilled data transmission into fundamental elements and grouped related networking functions into layers
• Layers have distinct functions to ensure comprehensive and flexible architecture
• The OSI model ensures interoperability between incompatible systems

Layer Interactions

• Layers use services from the layer below
• Communication between machines at layer 'x' follows agreed-upon protocols
• Peer-to-peer processes: Communication occurs using appropriate protocols for a given layer

Peer-to-Peer

• Direct communication at the physical layer via bit streams
• Higher layers on device A communicate down the stack, over to device B, and up the stack

Data Handling

• Each layer adds information as it sends, and strips info as its receives
• The physical layer transmits the entire package to the destination
• The receiving machine unwraps the message layer by layer, and removes data meant for it

Interfaces

• Interfaces enable data and network information to pass through the layers
• Each interface defines information and services for the layer above
• Well-defined interfaces and functions provide modularity
• Specific functions are modified or replaced without affecting surrounding layers

Layer Organization

• The seven layers are in three subgroups: network support, user support and transport
• Network support layers(physical, data link, and network) deals with moving data
• User support(session, presentation, and application) allows interoperability
• The transport links the subgroups

Data Units

• D7 is data at layer 7, D6 at layer 6, etc
• A header and/or trailer is added at each layer
• A trailer is usually added at layer 2 only
• Formatted data unit becomes an electromagnetic signal and is transmitted

OSI Model Communications Details

• Encapsulation: A packet at level 7 is encapsulated into a packet at level 6 and 5 etc
• At level N - 1, packet carriers the data, header and trailer from level N
• Level N - 1 is not aware of what the packet is
• Level N - 1 is treated as one integral unit

Physical Layers Functions

• Coordinates carrying a bit stream over a physical medium
• Deals with mechanical and electrical specifications of interface, includes definitions and functions physical devices must do

Physical Later Concerns

• Defines the interface attributes to a transmission, and the transmission medium
• Data consist of bits with no interpretation, and must be turned into signals, which can be electrical or data
• Defines number of bits and the length
• Sender and receiver must use rates and be synchronized by clock
• Concerned with devices to media. point-to-point has dedicated link, multipoint shares link
• Defines how devices connect via: mesh, star, ring, bus, and hybrid topologies topologies
• Defines direction of transmission between devices; includes: Simplex, Half-duplex and Full-duplex

Data Link Layer Functions

• Transforms the physical layer to a reliable link
• Makes the physical appear error-free to the network layer
• Moving frames from one hop to the next

Data Link Later Responsibilities

• Divides bits into manageable frames
• Adds a header defining the sender and/or receiver of the frame
• If a frame is intend outside the network, the receiver is the address of the device connecting to the next one
• Flow control avoids the receiver being overwhelmed
• Error control uses mechanisms to detect lost or damaged frames and to recognize duplicate frames
• Error Control uses a trailer, and Access Control determines device control, as illustrated by hop-to-hop delivery

Hop-to-Hop Node Delivery

• Communication occurs between adjacent nodes
• Data from node A to F goes through three partial deliveries, from node A to B, from B to E, then from E to F
• Exchanges between the three nodes have different values in headers
• From A to B, the source address is A, and the destination is B
• Error checking includes the header of the frame

Network Layer Functions

• Responsible for source-to-destination delivery of a packet, across many networks
• While the data link layer oversees packet of two system, network layers ensures that each packet gets from its origin and to its destination
• No needs for the data layer if its on the same link

Delivery Responsibilities

• Logical addressing enables source or destination system distinction
• Adds a header, which includes the logical address of the sende and receiver
• Routing entails routers to make decisions along intemetworks, using mechanisms

Transport Responsibilities

• Delivery ensures message arrives entirely, overseeing error and flow
• Service-point addressing (or port address). The network layer gets each packet and the transport layer gets the messsage
• Segmentation and reassembly enables the transport layer to reassemble the meassge, and to detect packets that are lost

Transport Connections & Controls

• Connection Control can be connectionless or oriented for independent packets
• Flow and Error Control ensures flow is performed end to end not across a link
• To perform error process to process guarantees no damage, retransmission corrects

Session Functions

• Control dialogues, it is the network dialog controller
• Establishes, maintains, and synchronizes interact

Session Responsibilities

• Enables communication in half or full duplex mode.
• Synchronization adds checkpoints to confirm data

Presentation Functions

• Concerned with correct syntax and semantics between systems
• Responsible for translation, compression and encryption

Presentation Responsibilities

• Translation changes data to to bit streams, interoperability encodes methods
• Encryption protects to ensure sentive and and privacy

Application Characteristics

• Enables user access via interface to connect to electronic mail, file access, database management, etc
• Shows relationship, where the figure employs XAOO to send an e-mail

Layer Function

• Provides network, transfer, and data sources
• Network is software

TCIP/IP PROTOCOL Suite

• Layers do not match OSI model.
• Original layers are: host, network, transport, and application for physical and data
• Session, presentation, application function with TCP/IP for session duties
• Levels for transport

TCP/IP Protocols

• Transmission Control Protocol (TCP)
• User Datagram Protocol (UDP)
• Stream Control Transmission Protocol (SCTP)
• Internetworking Protocol (IP), provides data

Physical and Data Link Layers

• TCP/IP supports all standard and proprietary protocols
• Can network on local-area or wide-area network

TCIP Supporting Protocols

• Supports (or internetworking) protocol and four supporting protocols:
  • ARP, RARP, ICMP, and IGMP

Communication Types

• Internetworking Protocol (IP) is the transmission TCP/IP mechanism.
• Protocol connects best-effort unreliable deliver

Operation Types

• Best-effort means checks no error and tracking with guarantees, it is transport in datagrams
• Datagrams move separated and can duplicate, so IP does not track with no reorder, discussed in chapter 20

Protocol Components

• Address Resolution Protocol (ARP), is used for physical address with physical network ID
• ARP finds physical address for when computer knows its
• Reverse Address Resolution Protocol (RARP) allows host to physical address for when computer knows
• RARP is used when a computer first connects to the network when booting

Message Protocol

• Internet Control Message Protocol (ICMP) sends sender datagram problems with query and error reports
• Internet Group Message Protocol (IGMP) facilitates simultaneous transmission, and is discussed in chapter 22
• IP can deliver, and UDP/TCP delivers from process/program, used TCP chapter, UDP chapter and SCTP chapter

Addressing Types

• Physical address, logical address, port addresses, specific addresses

Physical Addressing

• Also known as the link address, is the address of node from WAN to LAN, used by the data link layer
• The size may differ depending on the network
• Note localTalk has 1 byte changes station that comes up

Numerical Examples Example 1

In Figure 2.19 physical address 10, computer from bus LAN connected layer provides rest bits for detection. Layer detects 10 source before its address

Numerical Examples Example 2

Most local-area networks use a 48-bit (6-byte) physical address in hexadecimal digits, colon separated like: 07:01:02:01:2C:4B

Logical Addresses

Necessary from independent, physical networks, adequate with universal identifies. Logical address is currently a IP. Two publicly visible IDs can have same IP

Numerical Examples Example 3

Figure 2.20 has two routers connecting them to LANs. Computer may three devices need connections. Router connected two, has all connections addresses

Hop Addresses

Frame received by device, destination and the reads matches to the knows the next-hop is needed with ARP