View
4
Download
0
Category
Preview:
Citation preview
24/05/1439 AH
Computer Network Fundamentals (IT 221) أساسيات شبكات الحاسبLecture 1:• Computer network: collection of autonomous computers
interconnected by a single technology.
• Uses of computer networks: 1. Data communication: - communication: sharing info, can be local(face to face) or remote(over distance).- data communication: exchange of data between two devices via transmission
medium(wire cable).- communicating devices: made up of HW (physical equipments) and SW.The effectiveness depends on:A. Delivery: system must deliver data to correct destination.B. Accuracy: the system must deliver data accurately.C. Timeliness: system must deliver data in a timely manner.D. Jitter: Variation in the packet arrival time. it’s the uneven delay in the delivery of audio
or video packets.- Components: 1. Message: information to be communicated.2. Sender: the device that sends the data message.3. Receiver: the device that receives the message.4. Transmission medium: the physical path by which a message
travels.5. Protocol: set of rules that govern data communications.• Direction of data flow:
�1
Business Applications:
Goals: sharing physical resources such as printers or sharing information. example: one or more database with company information.- a computer network can provide powerful communication
medium among employees: Email.- telephone calls between employees can be carried by
computer network (IP telephony or voice over IP -VoIP-)- doing business electronically: E-commerce.
Home Applications: - users can access info and communicate with other using e-commerce.
- much of this info is accessed using client-server model.- different model for accessing information is peer-to-peer
communication.
Mobile Users: - combinations of wireless networks and mobile computing.
example in PDA >
Simplex: Half-Duplex Full-Duplex
communication is unidirectional (only one transmit; the other receives), example: keyboard(input) and monitors(output).
each station can both transmit and receive but one at a time. (walkie talkies)
both stations can transmit and receive at the same time. (telephone)
24/05/1439 AH2. Networks: set of devices(often referred to as nodes) connected by
communication links. (node = printer/computer…) Network criteria: - performance: depends on; a. number of usersb. type of transmission mediac. capabilities of connected HW and the efficiency os SW- reliability: measured by frequency of failure, the time it takes to recover from
failure, a network’s robustness in catastrophe.- security: protecting data from unauthorized access.• Physical Structures: A. Types of connections:
B. topology: the way in which network is laid out physically.
�2
Point-to-point Multipoint
between two devices(cable connected between two ends or microwave satellite are possible).
AKA: multi-drop. connection is one in which more that two specific devices share a single link.- capacity of a the channel is shared as:a. spatially: if several devices can use link simultaneouslyb. temporally: time shared connection
�
�
Mesh Star Tree Bus Ring
- every device has a dedicated point-to-point link to every other devices
- connections = n(n-1)/2 - every device must have
n-1 (I/O) ports.- Advantages: 1. privacy/security2. Eliminating traffic
problems3. it’s robust4. fault identification and
isolation- Disadvantages: 1. installation and
reconnection difficulty2. sheer bulk can be
greater that the available space
3. HW required to connect each link(ports and cables); expensive.
- each device has link only to a central controller (hub)
- doesn’t allow direct traffic between devices.
- sending data between devices:
device > hub > device - Advantages: 1. easy to install,
cheaper2. robustness3. Identification and
fault isolation- Disadvantages: 1. dependency of whole
topology on hub; if it goes down the whole system is dead.
- not every plugs directly into the central hub.
- Advantages and disadvantages the exact same as “star topology”
- nodes are connected to the bus cable by drop lines and taps.
- a drop line is a connection running between the device and the main cable.
- Advantages: 1. ease of installation, use
less calming than mesh or star.
- Disadvantages: 1. a fault in bus
cable(break) stops all transmission even between devices on the same side of the problem.
2. Reconnection, it can be difficult to add new devices.
- each device has a medicated point-to-point connection only with the two devices on either side of it.
- a signal is passed along the ring in one direction from device until it reaches its destination.
- each device in the ring incorporate as repeater.
- Repeater: regenerates the signal. it receives a weakened signal, creates a copy, bit for bit, at the original strength.
- Advantages: 1. easy to install and
reconfigure.2. fault isolation is simplified.- Disadvantages: 1. unidirectional traffic- another kind: Dual-ring
topology
24/05/1439 AHHybrid topology:
Network categories -two primary categories-: - local-area networks- wide-area networkscategories: 1. PAN(Personal Area Network): bluetooth is used to connect wirelessly,
it can be built with other technologies that communicate over short ranges, such as RFID.
2. LAN(Local Area Network): privately owned network in buildings like home or office.
- every computer has a radio modem and an antenna that to uses to communicate with other computers.
- each computer talks to a device in the ceiling called AP(Access Point), wireless router/ base station.
- IEEE 802.11 = WiFi, runs at speeds 11-100s Mbps.- most wired LANs uses copper wires but some uses optical fiber.- wired LANs = speeds of 100 Mbps - 1 Gbps, have low delay and make very few
errors.- signals easier to send over wires/optical fibers than air.- built from point-to-point links.- IEEE 802.3 = Ethernet << most common wired LAN.3. MAN 4. WAN(Wide Area Network): - large geographical area(country/continent).- consists of hosts and subnets owned and operated by different
people.- subnets components: transmission lines and switching elements.- when data arrive on an incoming line, the switching element must
choose an outgoing line on which to forward them.- routers connect different kinds of networking technology.Heterogeneous Networks The internet:
- people connected to one network often want to communicate with people attached to different one.- collection of interconnected networks is called an internetwork/internet.
- ISP(Internet Service Providers).- NAP(Network Access Points): complex switching stations(normally run by a third
party) which connects different national ISPs.- Peering Points: private switching stations which connects ISPs one to another.
Lecture 2: Network models: 1. OSI model: International Standards Organization(ISO) is a
multinational body dedicated to worldwide agreement on international standards and it covers all aspects of network communications is the Open System Interconnection(OSI).
�3
24/05/1439 AH- purpose of OSI model is to show how to facilitate communication between
two different systems without requiring change to the logic of the underling HW and SW.
- it’s flexible, robust and interoperable. - layer calls upon the services of the layer below it. eg:(3 uses 2).- between machines, layer x in machine 1 communicates with
layer x in machine 2, governed by an agreed-upon series of rules(protocols).
- each interface defines the information and services a layer must provide for the layer above it.
• Encapsulation: - at the sender device, in each layer, a header or a trailer can be
added to the data unit(payload). the trailer is added only at layer 2.- the data portion of a packet at level N-1 carries the whole packet(data and
header and maybe trailer) from level N. << this called encapsulation.- at the receiver device, each lower layer removes the header added by the
corresponding layer and sends the payload to the upper layer in a process called decapsulation.
• Layers in OSI mode: - 1,2,3 >> network support layers. - 5,6,7 >> user support layers. - 4 >> links two groups and ensure that what the lower layers have
transmitted is in a form that the upper layer can use. - the upper layers almost implemented in SW, lower layers are SW + HW,
except for the physical layer almost HW.
�4
1. Physical layer responsible for movement of individual bits from hop(node) to hop.
2. Data link layer
- responsible for moving frames from hop(node) to hop.- transforms physical layer to reliable link & makes it appear
error-free- other responsibilities: framing, physical addressing, flow
control, error control, access control.
3. Network layer
responsible for the delivery of individual packets from the source host to destination host(node with all layers). - if two systems are connected to the same link then no
need for network layer.- other responsibilities: logical addressing(IP address) and
Routing.
4. Transport layer
responsible for delivery of end users(source & destination).- other responsibilities: Service-point addressing,
segmentation and reassembly, connection control, flow control and error control.
5. Session layerresponsible for dialog control and synchronization.- it establishes, maintains and synchronizes the interaction
among communication.
6. Presentation layer responsible for translation, compression and encryption.
7. Application layerresponsible for providing services to the user. - specific responsibilities: Network virtual terminal, file
transfer, mail services, and directory services.
24/05/1439 AH
2. TCP / IP protocol suite: - layers in the TCP/IP don’t exactly match those in the OSI model.- 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 made of five layers: physical, data link, network, transport and application.
- it’s a Hierarchical protocol(it means each upper-level protocol is supported by one or more lower-level protocols.
- contains relatively independent protocols that can be mixed and matched depending on the needs of the system.
�5
1. Physical layerresponsible for carrying individual bits in a frame across the link in the form of either electrical or optical signals.- logical unit between two physical layers in two devices is a bit. - there are several protocols that transforms a bit to a signal.
2. Data link layer- the main functions are almost the same as of that for OSI model.- the logical unit between two data link layers in two devices is a frame.
3. Network layer
- the same main function of that in OSI model.- the logical unit between two network layers in two devices is a packet.- at the network layer supports the Inter-networking protocol(IP): • the transmission mechanism used by the TCP/IP protocols.• it’s an unreliable and connectionless protocol -a best- effort delivery service.• the term best effort means that IP provides no error checking or tracking.- IP uses four supporting protocols:• ARP(Address Resolution Protocol): is used to associate a logical address with a physical address.• RARP(Reverse Address Resolution Protocol): allows a host to discover its internet address when it knows only its
address.• ICMP(Internet Control Message Protocol): mechanism used by hosts and gateways to send notification of
datagram problems back to the sender + sends query and error reporting messages.• IGMP(Internet Group Message Protocol): is used to facilitate the simultaneous transmission of a message to a
group of recipients.
4. Transport layer
- represented int TCP/IP by: TCP and UDP.- IP is a host-to-host protocol, meaning that it can deliver a packet from one physical device to another.- the logical unit between two transport layers in two devices is a segment/datagram. - UDP/TCP are transport level protocols responsible for delivery of a datagram or segment from end-to-end(from the
source node to the destination node).1. Transmission Control Protocol(TCP): Advantages: - connection oriented; that first establishes a logical connection between transport layers at two hosts before
transferring data.- provides flow control, error, control, and congestion control.Disadvantages: - connection overhead- connection delay2. User Datagram Protocol(UDP): Advantages: - less overhead in the connection established.- lower delay in the connection established.Disadvantages: - it’s a connectionless protocol that transmits user datagrams without first creating a logical connection.3. Stream Control Transmission Protocol(SCTP): newly designed for applications emerging in the multimedia.
5. Application layer
- the logical unit between two application layers in two devices is a message.- Process(running program)-to-process communication is the duty of application layer.- many protocols are defined at this layer such as: HTTP, FTP, SMTP, DNS, TELNET.
Recommended