Fundamental concepts of computer networks (chapter 1)

Chapter 1
Fundamental concepts of computer networks.
Lecture 1
1.

1-1 DATA COMMUNICATIONS
The term telecommunication means communication at a distance. The word data refers to information presented in whatever form is agreed upon by the parties creating and using the data.
Data communications are the exchange of data between two devices via some form of transmission medium such as a wire cable or wireless.
Delivery → Correct destination
Accuracy → Accurate data
Timelines → Real-time transmission
Jitter → Uneven delay
1.

Figure 1.1 Five components of data communication
Components
Data Representation
Data Flow
Topics discussed in this section:
Components
2
1
3
4
5
1.

Data Representation
Text
Numbers
Images
Audio
Video
Data flow
Simplex
Half-duplex
Full-duplex
1.

1-2 NETWORKS
A network is a set of devices (nodes) connected by communication links. A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network.
Distributed Processing
Network Criteria (performance, reliability, and security)
Physical Structures ( type of connections and topologies)
Network Models
Categories of Networks ( LAN, MAN and WAN)
Interconnection of Networks: Internet
Topics discussed in this section:
1.

Types of connections
Point to point
A dedicated link is provided between two devices
Multipoint
More than two specific devices share a single link
1.

Physical Topology
Tree
1.

MESH Topology
Every device has a dedicated point-to-point link to every other devices
Dedicated
Link carries traffic only between the two devices it connects
A fully connected mesh network has n(n-1)/2 physical channels to link n devices
Every device on the network must have n-1 input/output (I/O) ports
Advantage
Less traffic, robust, secure, easy to maintain
Disadvantage
Need more resource (cable and ports), expensive
n(n-1)/2 physical duplex links
1.

STAR Topology
Each device has a dedicated point-to-point link only to a central controller, usually called a hub.
No direct traffic and link between devices
Advantages
Less expensive
Easy to install and reconfigure
Robustness
Disadvantage
Single point of failure
1.

BUS Topology
A multipoint topology
All devices are linked through a backbone cable
Nodes are connected to the bus cable by drop lines and taps.
Drop line
A connection running between the device and the main cable
Tap
A connector that either splices into the main cable or punctures the sheathing of a cable to create a contact with the metallic core
Advantage:
Ease of installation
Disadvantages:
Difficult reconnection and fault isolation
Broken or fault of the bus cable stops all transmission
1.

RING Topology
Each device is dedicated point-to-point connection only with the two devices on either side of it
A signal is passed along the ring in the direction, from device to device, until it reaches its destination
Each device in the ring incorporates a repeater
Advantages
Relatively easy to install and reconfigure
Fault isolation is simplified
Disadvantage
Unidirectional traffic
1.

Tree Topology
Advantages:
Point-to-point wiring for individual segments.
Supported by several hardware and software venders.
Disadvantages:
Overall length of each segment is limited by the type of cabling used.
If the backbone line breaks, the entire segment goes down.
More difficult to configure and wire than other topologies.
Tree topologies integrate multiple topologies together
Example: Tree topology integrates multiple star topologies together onto a bus
1.

A hybrid topology: a star backbone with three bus networks
1.

An isolated LAN connecting 12 computers to a hub in a closet
Categories of Networks
Local Area Network (LAN)
Wireless Local Area Network (WLAN)
Metropolitan Area Network (MAN)
Wide Area Network (WAN)
1.

WANs: a switched WAN and a point-to-point WAN
1.

A heterogeneous network made of four WANs and two LANs
Interconnection of Networks: internet
1.

1-3 THE INTERNET
The Internet has changed many aspects of our daily lives. It has affected the way we do business as well as the way we spend our leisure time. The Internet is a communication system that has brought a wealth of information to our fingertips and organized it for our use.
A Brief History → ARPANET
1967 ACM
1969 UCLA, UCSB, SRI, UoU
1972 TCP
The Internet Today (ISPs)
Topics discussed in this section:
1.

Hierarchical organization of the Internet
1.

1-4 PROTOCOLS AND STANDARDS
protocols and standards.
Protocol is synonymous with rule.
Standards are agreed-upon rules.
Protocols
Standards
Standards Organizations
Internet Standards
Topics discussed in this section:
1.

PROTOCOLS AND STANDARDS
Protocols
Syntax → format of the data
Semantics → meaning of each section
Timing → when data should be sent and how fast.
Standards
De facto → by fact (not approved as a standard)
De jure → by Law (approved)
1.

PROTOCOLS AND STANDARDS
Standards Organizations
International Organization for Standardization (ISO)
International Telecommunication Union - Telecommunication Standards (ITU-T)
American National Standards Institute (ANSI)
Institute of Electrical and Electronics Engineers (IEEE)
Electronic Industries Association (EIA)
1.

Lecture 2
OSI Model
Network Models
1.

1-5 LAYERED TASKS
A network model is a layered architecture
Task broken into subtasks
Implemented separately in layers in stack
Functions need in both systems
Peer layers communicate
Protocol:
A set of rules that governs data communication
It represents an agreement between the communicating devices
1.

Tasks involved in sending a letter
Sender, Receiver, and Carrier
Hierarchy (services)
Topics discussed in this section:
1.

1-5.1 THE OSI MODEL
Established in 1947, the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards.
An ISO is the Open Systems Interconnection (OSI) model is the standard that covers all aspects of network communications from ISO. It was first introduced in the late 1970s.
1.

ISO is the organization.
OSI is the model.
Layered Architecture
Peer-to-Peer Processes
Encapsulation
Topics discussed in this section:
1.

Seven layers of the OSI model
Layered Architecture
Sender
Receiver
1.

Layered Architecture
A layered model
Each layer performs a subset of the required communication functions
Each layer relies on the next lower layer to perform more primitive functions
Each layer provides services to the next higher layer
Changes in one layer should not require changes in other layers
The processes on each machine at a given layer are called peer-to-peer process
1.

Communication must move downward through the layers on the sending device, over the communication channel, and upward to the receiving device
Each layer in the sending device adds its own information to the message it receives from the layer just above it and passes the whole package to the layer just below it
At the receiving device, the message is unwrapped layer by layer, with each process receiving and removing the data meant for it
PEER – TO – PEER PROCESS
1.

PEER – TO – PEER PROCESS
The passing of the data and network information down through the layers of the sending device and backup through the layers of the receiving device is made possible by interface between each pair of adjacent layers
Interface defines what information and services a layer must provide for the layer above it.
1.

The interaction between layers in the OSI model
1.

An exchange using the OSI model
1.

LAYERS IN THE OSI MODEL
Physical Layer
Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer
Topics discussed in this section:
1.

The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
Function
Physical characteristics of interfaces and media
Representation of bits
Data rate
Synchronization of bits
Line configuration (point-to-point or multipoint)
Physical topology (mesh, star, ring or bus)
Transmission mode ( simplex, half-duplex or duplex)
Physical Layer
1.

Physical layer
1.

The data link layer is responsible for moving
frames from one hop (node) to the next.
Function
Framing
Physical addressing
Flow control
Error control
Access control
Data Link Layer
1.

Data link layer
1.

Hop-to-hop delivery
1.

Example 1
In following Figure a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link. At the data link level this frame contains physical addresses in the header. These are the only addresses needed. The rest of the header contains other information needed at this level. The trailer usually contains extra bits needed for error detection
1.

The network layer is responsible for the
delivery of individual packets from
the source host to the destination host.
Source-to-destination delivery
Responsible from the delivery of packets from the original source to the final destination
Functions
Logical addressing
routing
Network Layer
1.

Network layer
1.

Source-to-destination delivery
1.

Example 2
We want to send data from a node with network address A and physical address 10, located on one LAN, to a node with a network address P and physical address 95, located on another LAN. Because the two devices are located on different networks, we cannot use physical addresses only; the physical addresses only have local influence. What we need here are universal addresses that can pass through the LAN boundaries. The network (logical) addresses have this characteristic.
1.

The transport layer is responsible for the delivery
of a message from one process to another.
Process-to- process delivery
Functions
Port addressing
Segmentation and reassembly
Connection control ( Connection-oriented or connection-less)
Flow control
Error control
Transport Layer
1.

Transport layer
Segmentation and reassembly
1.

Reliable process-to-process delivery of a message
1.

Example 3
Data coming from the upper layers have port addresses j and k (j is the address of the sending process, and k is the address of the receiving process). Since the data size is larger than the network layer can handle, the data are split into two packets, each packet retaining the port addresses (j and k). Then in the network layer, network addresses (A and P) are added to each packet.
1.

The session layer is responsible for dialog
control and synchronization.
Session Layer
It establishes, maintains and synchronize the interaction between communicating system
Function
Dialog control
Synchronization (checkpoints)
1.

Session layer
Synchronization
1.

The presentation layer is responsible for translation, compression, and encryption.
Presentation Layer
Concerned with the syntax and semantics of the information exchanged between two system
Functions
Translation ( EBCDIC-coded text file ? ASCII-coded file)
Encryption and Decryption
Compression
1.

Presentation layer
1.

The application layer is responsible for
providing services to the user.
Functions
Network virtual terminal (Remote log-in)
File transfer and access
Mail services
Directory services (Distributed Database)
Accessing the World Wide Web
Application Layer
1.

Application layer
1.

Summary of layers
1.

Summary of layers
Sender
Receiver
1.

Lecture 3
TCP/IP Model
Network Models
1.

1-5.2 TCP/IP PROTOCOL SUITE
The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application.
Physical and Data Link Layers
Network Layer
Transport Layer
Application Layer
Topics discussed in this section:
1.

TCP/IP and OSI model
OSI Model
TCP/IP Model
1.

Internet Layer
TCP/IP support the Internet Protocol IP ( unreliable).
IP is a host-to-host protocol.
Supporting protocols:
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)
Internet Control Massage Protocol (ICMP)
Internet Group Massage Protocol (IGMP)
1.

Transport Layer
Process-to-process protocol.
User Datagram Protocol (UDP)
Transmission Control Protocol (TCP)
Stream Control Transmission Protocol (SCTP)
1.

1-6 ADDRESSING
Four levels of addresses are used in an internet employing the TCP/IP protocols: physical, logical, port, and specific.
Physical Addresses
Logical Addresses
Port Addresses
Specific Addresses
Topics discussed in this section:
1.

Addresses in TCP/IP
1.

Relationship of layers and addresses in TCP/IP
1.

Physical addresses are imprinted on the NIC. Most local-area networks (Ethernet) use a 48-bit (6-byte) physical address written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon.
Physical Address
Example:
07:01:02:01:2C:4B
A 6-byte (12 hexadecimal digits) physical address.
1.

The physical addresses in the datagram may change from hop to hop.
known also as the MAC address
Is the address of a node as defined by its LAN or WAN
It is included in the frame used by data link layer
Physical Address
1.

The physical addresses will change from hop to hop,
but the logical addresses usually remain the same.
IP addresses are necessary for universal communications that are independent of physical network.
No two host address on the internet can have the same IP address
IP addresses in the Internet are 32-bit address that uniquely define a host.
Logical Address
1.

Port address is a 16-bit address represented by one decimal number ranged from (0-65535) to choose a process among multiple processes on the destination host.
Destination port number is needed for delivery.
Source port number is needed for receiving a reply as an acknowledgments.
In TCP/IP , a 16-bit port address represented
as one single number. Example: 753
The physical addresses change from hop to hop,
but the logical and port addresses usually remain the same.
Port addresses
1.

Port addresses
1.