Computer Networks / Vize Study Sheet

Bilgisayar Aglari Vize Calisma Sayfasi

Bu sayfa 4 haftalik networking notunu tek yerde toplar: tanimlar, kritik farklar, timeline, OSI, TCP/IP, portlar, socket mantigi, MAC, IPv4, IPv6, topolojiler, Internet, protocol ve son dakika tekrar kiti. Amaç sadece guzel gorunmek degil; hizli tekrar, derin calisma ve karsilastirma yapabilmek.

TR ana anlatim korunur; kritik basliklar, ozetler ve puf noktalar ise EN karsiliklarla birlikte verilir.

Slayt 1'den basla Son dakika tekrar kitine git
4 Ana modül
7 OSI layer
4 TCP/IP layer
1 Tek dosyalik study page
Slide 1

Computer Network TemelleriComputer Network Fundamentals

Computer network, birbirine bagli bagimsiz cihazlarin ve bilgisayarlarin standart protokoller kullanarak veri, kaynak ve servis paylasmasi icin olusturdugu sistemdir.

Bu tanimda sinavlik 4 kelime var: interconnected, autonomous devices, standardized protocols, share data/resources/services. Yani olay "iki bilgisayar birbirini buldu" degil; kurallarla ve amacla isleyen bir yapidan bahsediyoruz.

ENA computer network is a system of interconnected autonomous devices that share data, resources, and services using standardized protocols.

Sender Veriyi baslatan kaynak cihaz veya process.
Receiver Veriyi alan hedef cihaz veya process.
Medium Kablo ya da wireless channel uzerinden tasima.
Protocol Kurallar, format, sira ve davranis seti.
Operating System Iletisimi isletecek yazilim tabani.

Software part

Network'unde yalnizca fiziksel cihaz yoktur. Protocol stack cihazlarin neyi, ne zaman, nasil yollayacagini belirler.

Hardware part

Kablo, switch, hub, router, repeater, NIC gibi aygitlar veriyi fiziksel veya mantiksal olarak tasir ve yonlendirir.

Protocol

En kisa tanim: set of rules. Iletisim rastgele degil, standart davranislarla olur.

Sinavda gelir

"What is a computer network?" sorusunda tanimi sadece "connected computers" diye kisaltma. Bagimsiz cihazlar, standart protokoller ve paylasim amaci birlikte yazilmali.

Networking tarihcesi timeline

1961-1972 | Packet Switching

Kleinrock, bursty traffic icin packet switching'in verimli oldugunu gosterdi. Paul Baran askeri iletisim baglaminda guvenli iletim tarafini guclendirdi.

1967-1972 | ARPAnet

Roberts ilk paket anahtarlamali bilgisayar agi planini yayimladi. 1972'de ARPAnet yaklasik 15 node'a ulasti, NCP tamamlandi ve Robert Kahn halka acik gosterim yapti.

1972-1980 | Internetworking

Vinton Cerf ve Robert Kahn aglarin birbirine baglanmasi fikrini calisti. TCP, UDP ve IP dusuncesi bu donemde kavramsal olarak oturdu.

1980-1990 | TCP/IP standardization

1 Ocak 1983'te TCP/IP, ARPAnet'in resmi protokolu oldu. Host sayisi 100.000 seviyesine dayandi.

1990'lar | Internet explosion

NSFNET ticari kullanima acildi, ticari ISP'ler backbone trafigi tasimaya basladi. World Wide Web ile search engine, e-commerce ve social network uygulamalari patladi.

Yeni milenyum | Broadband ve wireless era

Broadband yayginlasti. 2011'de wireless device sayisi wired'i gecti, smartphone cagi sabitlendi.

Packet switching neden onemli?

Veri tek parca gitmez; kucuk paketlere bolunur. Bu, agi daha verimli kullanir, farkli yollardan iletimi kolaylastirir ve bugunku Internet'in temel tasima mantigini olusturur.

WWW neden donum noktasi?

Internet zaten vardi; ama World Wide Web onu kitlesel kullanim aracina cevirdi. Web, Internet'in kendisi degil; Internet uzerinde calisan bir application katmanidir.

Network components

End devices

Computer Server Smartphone IoT

Hardware devices

Router Switch Hub Repeater NIC

Physical media

Twisted Pair Coaxial Fiber Optic Wireless
Server mantigi

Server, agdaki kullanicilara paylasilan kaynaklari saglayan merkez makinedir. File server, print server, mail server, database server, web server gibi farkli roller ayni fiziksel makinede de toplanabilir.

Hub, Switch, Router, Repeater, NIC

Hub

Broadcast device

  • Tum cihazlarin baglandigi merkez aygittir.
  • Gelen veriyi tum ag'a yayinlar.
  • Akilli degildir; hedefi bilmez.
  • Collision riski daha yuksektir.
Switch

Specific receiver

  • Hub gibi gorunur ama built-in intelligence vardir.
  • Physical device address bilgisiyle dogru portu bulur.
  • Yalnizca hedef cihaza gonderir.
  • Modern LAN'larda hub'a gore acik ara ustundur.
Router

Best path finder

  • Mesaji bir agdan digerine tasir.
  • Routing algorithm ve routing table kullanir.
  • LAN, MAN, WAN baglaminda aglar arasi yonlendirme yapar.
  • Switch'ten farki: ayni ag icinde degil, aglar arasinda calisur.
Repeater

Signal booster

  • Mesafe nedeniyle zayiflayan sinyali guclendirir.
  • Ozellikle uzun iletimlerde sinyal kaybini azaltir.
  • Routing yapmaz; yalnizca sinyal seviyesine etki eder.
NIC

Ag kapisi

  • Bilgisayar ile ag arasinda arayuzdur.
  • Kablo NIC'e takilir; frame hazirlama ve alma/gonderme burada olur.
  • Flow control ve veri aktarimi tarafinda rol oynar.
Device Ne yapar? Ana ipucu Sinavlik fark
Hub Veriyi herkese gonderir. Broadcast Akilsiz; collision riski yuksek.
Switch Veriyi dogru cihaza yollar. Physical address kullanir LAN icinde hedefe ozel iletim.
Router Aglar arasinda en iyi yolu bulur. Routing table + algorithm Farkli networkler arasi iletim.
Repeater Zayiflayan sinyali guclendirir. Signal regeneration Adresleme yapmaz.
NIC Cihazi aga baglar. Interface card Bilgisayarin aga acilan kapisi.

Physical media ve wireless mantigi

Wired media

Twisted PairIki izole telin bukulmesiyle olusur. UTP daha yaygin, STP daha korumalidir.
CoaxialIcte copper wire, ortada insulator, dista conducting shield. TV sistemlerinde yaygindir.
Fiber OpticLight pulses ile veri tasir. Cok hizli, uzun mesafe, ama pahali.

Wireless media

Wireless transmission, tel yerine electromagnetic waves kullanir. En yaygin ortam air'dir ama vacuum ve water icin de teorik tanim sunulur.

Radio waves Microwaves Infrared

Wireless, mobility ve flexibility verdigi icin tercih edilir; ama hiz, guvenlik ve stabilite acisindan wired bazen daha iyidir.

Medium Bandwidth Distance Price Not
Twisted Pair Up to 1 Gbps Up to 100 m Least expensive Ucuz ve yaygin.
Coaxial 10-100 Mbps Up to 500 m Inexpensive Shield yapisi sayesinde parazite dayanikli.
Fiber Optic Up to 10 Gbps or higher Up to 60 km Most expensive En hizli ve en uzun mesafe.
Wireless LAN Up to 54 Mbps Up to 100 m Moderate Mobilite saglar.
Yorum sorusu

Wireless neden tercih edilir? Artan mobility, hizli kurulum, wider reach, flexibility, uzun vadeli sahip olma maliyeti ve scalability. Ama "wired her zaman kotu" sonucu cikmaz; kararlilik ve guvenlik tarafinda wired cozumler one cikabilir.

PAN, LAN, MAN, WAN

PAN

Personal Area Network. Bluetooth, NFC, kulaklik, mouse, smartwatch gibi kisa menzilli kisisel ag.

LAN

Local Area Network. Ofis, bina, kampus gibi yerel alanlarda printer, scanner, data ve tools paylasimi icin tasarlanir.

MAN

Metropolitan Area Network. Sehir veya kasaba duzeyinde; LAN'den buyuk, WAN'dan kucuk.

WAN

Wide Area Network. Ulke, kita, dunya olcegi. Internet bunun en buyuk ornegidir.

Topology board

Mesh

  • Her node digerlerine bagli olabilir.
  • Full mesh baglanti sayisi: n(n-1)/2
  • Yuksek reliability, ama maliyet ve karmaşıklık yuksek.

Star

  • Her node merkezi cihaza baglanir.
  • Yonetimi kolay, LAN'larda cok yaygin.
  • Merkez bozulursa tum ag etkilenir.

Bus

  • Tek backbone cable uzerine baglanir.
  • Ucuz ve basit, ama fault isolation zordur.
  • Backbone bozulursa ag coker veya bolunur.

Ring

  • Dairesel veri yolu.
  • Tek yonlu akista collision azalir.
  • Bir kirilma tum yapiyi etkileyebilir.

Hybrid

  • Iki veya daha fazla topolojinin karisimi.
  • Esnek ve scalable, ama tasarimi daha zordur.
Topology Advantage Disadvantage Ana fikir
Bus Low cost Difficult fault isolation Ucuz ama backbone hassas.
Star Easy management Central device failure Yonetimi kolay, merkez tek hata noktasi.
Ring Equal access Single break affects network Duzenli akis, ama kirilma etkili.
Mesh High reliability High cost Cok guvenilir ama pahali.

Network diagram mantigi

Ornek store tasariminda her shop icinde CAT5 cable secmek dusuk maliyet ve kolay kurulum nedeniyle mantiklidir. Wireless secilmeyebilir; bunun nedeni daha yuksek maliyet, stabilite veya saha kosullari olabilir.

Cashier printer'lar receipt icin, management alanindaki laser printer ise ofis kullanimi icin ayrilabilir. Bu, network design sorularinda teoriyi uygulamaya baglayan klasik senaryodur.

Why switch instead of hub?

Switch hedefe ozel iletim yaptigi icin collision riskini azaltir. Hub tum ağa broadcast yaptigindan collision olasiligi daha yuksektir. Bu nedenle modern tasarimlarda switch hub'in yerini alir.

Hub = broadcast Switch = targeted forwarding Less collision with switch
VPN note

Branch'lerin merkez shop'a VPN ile baglanmasi, remote network'leri Internet uzerinden secure ve cost-effective bicimde birlestirir. Bu modelde protected inside network ile less trustworthy outside network ayrimi sinavda yorum sorusuna donusebilir.

Computing models

Client-Server

Merkezi guclu server vardir; client'lar servis alir. Yonetim kolaydir ama server bozulursa sistem etkilenir.

Peer-to-Peer

Cihazlar es duzeydedir. Kalici veya ad hoc olabilir; merkez olmadan kaynak paylasimi yapabilir.

Centralized

Tum kaynaklar ve islemler tek makinede toplanir. Talep ve kontrol merkezden gider.

Distributed

Kaynaklar ve islem gucu birden fazla makineye dagilir; farkli konumlarda da olabilir.

Puf Noktalar / Key Takeaways

Bu bolumde hocanin en rahat soru uretecegi yerler tanimlar, device farklari ve topology karsilastirmalaridir.

Network tanimi eksik yazilmaz EN: Include autonomous devices, standardized protocols, and sharing purpose together.
Hub, switch, router uclusu EN: Hub broadcasts, switch forwards to a specific device, router routes between networks.
Fiber ezber noktasi EN: Fastest, longest distance, and most expensive medium in the slide table.
Topoloji mantigi EN: Mesh = reliability, Star = easy management, Bus = low cost, Ring = equal access but fragile.
Slide 2

Data Communication, Internet ve ProtocolData Communication, Internet, and Protocol Essentials

Data communication, iki veya daha fazla cihaz arasinda bir iletim ortami uzerinden ve uzerinde anlasilmis protokoller kullanilarak dijital verinin degistokus edilmesidir.

Veri, sender'dan receiver'a signal formunda aktarilir. Text, image, audio, video fark etmez; medium icinde seyahat eden sey sinyaldir.

ENData communication is the exchange of digital data between two or more devices through a transmission medium by following agreed protocols.

Information Text, image, audio, video gibi ham bilgi.
Binary Sender tarafinda bit akisina cevrilir.
Signal Transmission medium'e uygun fiziksel temsil.
Medium Kablo veya wireless uzerinden iletim.
Reconstruction Receiver: signal -> binary -> original information.
Kilit akiş

Sinavda cok guzel yazar: Information -> Binary -> Signal -> Medium -> Signal -> Binary -> Information.

Example: photograph transfer

Bir fotograf pixel'lerden olusur. Pixel'ler binary'ye cevrilir, binary stream signal haline gelir, medium uzerinden gider. Alici tarafta ters islem uygulanir ve fotograf yeniden olusturulur.

Bit rate

Bit rate, birim zamanda iletilebilen bit sayisidir. Birimleri bps, kbps, Mbps, Gbps.

Analog vs Digital

Analog signal

  • Continuous signal
  • Sin wave ile gosterilir
  • Amplitude, frequency, phase, period ozellikleri vardir
  • Noise'a daha aciktir
  • Audio transmission icin uygundur

Digital signal

  • Discrete value formunda bilgi tasir
  • Square wave ile gosterilir
  • 0 ve 1 bitleriyle temsil edilir
  • Bit rate / bit interval ile karakterize edilir
  • Noise'dan daha az etkilenir

Periodic

  • Pattern belirli araliklarla tekrar eder
  • AM ve FM sinyalleri klasik ornektir

Aperiodic

  • Pattern duzenli araliklarla tekrar etmez
  • Konusma sesi gibi daha degisken sinyaller buraya oturur
Topic Analog Digital
Nature Continuous Discrete
Wave shape Sin wave Square wave
Representation Amplitude/frequency/phase Bits, bit rate
Noise resistance Lower Higher

Transmission disruption

Distortion

Sinyalin seklinin degismesidir. Medium boyunca ilerlerken form bozulabilir.

Attenuation

Mesafe ve direncten dolayi sinyal enerjisinin zayiflamasidir.

Noise

Orijinal sinyale karisan istenmeyen rastgele sinyallerin genel adidir.

Thermal noise

  • Elektronlarin rastgele hareketinden dogar.
  • Ekstra istenmeyen sinyal uretir.

Induced noise

  • Motor, kablo gibi dis kaynaklardan gelir.
  • Twisted pair bunu azaltmak icin tasarlanmistir.

Crosstalk

  • Bir hattaki iletimin diger hatta karismasidir.
  • Kablo ciftleri arasinda gorulebilir.

Impulse noise

  • Kisa sureli ani spike'lar.
  • Lightning, power line ve benzeri etkiler tetikleyebilir.
Ezber uclusu

Transmission disruption nedenleri: distortion + attenuation + noise. Noise turleri: thermal + induced + crosstalk + impulse.

Internet nedir?

Definition

Internet, standardized protocols ozellikle de TCP/IP suite kullanan, global system of interconnected computer networks yapisidir. Milyarlarca cihazin veri degisimi, resource sharing ve service access ihtiyacini tasir.

Technical view

Network of networksBirden cok bagimsiz ag, router ve acik protokollerle birbirine baglidir.
DecentralizedTek merkezli kontrol yoktur.
Layered architectureKarmasik islevler katmanlara ayrilir.
Best-effort deliveryPaketleri ulastirmaya calisir ama mutlak garanti vermez.
1969 | ARPANET

U.S. Department of Defense tarafindan gelistirilen ilk operasyonel packet-switching network.

1983 | TCP/IP standardization

Modern Internet'in resmi dogum tarihi olarak kabul edilir.

1980'ler | NSFNET

Universiteleri baglayan akademik ag; askeri alan disina yayilim sagladi.

1990'lar | Commercialization

Public access, ISP'ler ve Web buyumesi ile Internet kitlesellesti.

Hosts / End systems

Desktop, workstation, server, smartphone, tablet gibi cihazlar Internet jargonunda host veya end system diye gecer. Agin kenarindadirlar; network core'da degil.

Packets, route, path

Veri paketlere ayrilir, header eklenir, switch/router ve communication link zincirinden gecer. Bu gecilen diziye route veya path denir.

User device Browser veya app istegi baslatir.
Local LAN Cihaz ilk yerel aga baglidir.
ISP network Subscriber'i Internet'e tasiyan servis saglayici kati.
Backbone / destination network Bolgeler arasi ve hedef ağa gecis.
Server Yaniti paketler halinde geri yollar.

Bir kullanici website ziyaret edince

  1. Browser request yollar.
  2. DNS domain name'i IP address'e cozer.
  3. Data packet'lere bolunur.
  4. Packet'ler router'lardan gecer.
  5. Destination server cevap verir.
  6. Client tarafinda packet'ler tekrar birlestirilir.

Data centers

Arama sonuclari, e-mail, web pages, videos ve mobile app content gibi hizmetlerin cogu buyuk data center'larda duran server'lar tarafindan sunulur. End systems kullanici tarafini anlatirken, data centers servislerin arka taraftaki dev olcegini gosterir.

Internet vs Web

Internet altyapi ve aglar arasi iletim sistemidir. World Wide Web, Internet uzerinde calisan bir application'dir ve HTTP kullanir. E-mail, VoIP, file transfer ve cloud services de Internet servisidir ama Web ile ayni sey degildir.

Protocol nedir ve neden gerekli?

Official definition

A protocol defines the format and the order of messages exchanged between communicating entities, as well as the actions taken on transmission, receipt, or another event.

Format Timing Sequencing Error handling

Why needed?

Farkli vendor'lardan cihazlar ayni shared media uzerinde konusacaksa data structure, timing, error handling ve beklenecek davranis standard olmalidir. Interoperability protokolsuz kurulmaz.

Service interface

  • Ayni makinedeki ust veya yan objelere sundugu servis arayuzu.
  • "Local object bu protokole ne yaptirabilir?" sorusunun cevabi.
  • Ornek: send / receive message.

Peer interface

  • Baska makinedeki es protokolle nasil konusacagini tanimlar.
  • Mesaj formu, anlami ve kurallar burada belirlenir.

Encapsulation

  • Her katman usttekinden aldigi data'ya kendi header'ini ekler.
  • Asagi katmana verir; receiver'da ters sira ile acilir.

Protocol design

  • Message format, rules, error handling, state transitions, performance gereksinimlerini tanimlar.
  • Iyi protocol: simple, scalable, reliable, efficient, secure.

Encapsulation flow

Application data
Data
Transport
TCP/UDP Header Data
Network
IP Header TCP/UDP Header Data
Data Link
Frame Header IP Header TCP/UDP Header Data
Receiver
Decapsulation Original data

Encapsulation vs Protocol Design

Topic Encapsulation Protocol Design
Focus Data wrapping process Rule creation
Purpose Modular transmission Communication behavior'i tanimlamak
Example TCP header inside IP packet TCP reliability mechanism

Access network, DSL, Cable, Mobile, AS

Access network

Bir end system'i, uzak bir end system'e giden yol uzerindeki ilk router'a fiziksel olarak baglayan kisimdir. Access network kullaniciyi ilk ISP katmanina tasir; core network router ve ISP'leri birbirine baglar.

Residential Institutional Mobile

Autonomous System (AS)

Her bagimsiz network genelde bir organization tarafindan yonetilen ve kendi routing policy'si olan Autonomous System yapisinda duzenlenir. Iceride OSPF gibi, dis baglantida BGP gibi protokoller kullanilir.

DSL

Telefon altyapisini kullanir. Tek hat uzerinde telefon, upstream data ve downstream data farkli frequency band'lere ayrilir.

0-4 kHz voice 4-50 kHz upstream 50 kHz-1 MHz downstream

Cable Internet

Kablo TV altyapisini kullanir. Cable modem gerekir, genelde PC veya router'a Ethernet ile baglanir.

Wide-area wireless

3G, LTE/4G, 5G gibi teknolojiler cellular infrastructure ve base station uzerinden mobil access saglar.

Puf Noktalar / Key Takeaways

Slide 2'nin omurgasi su zincirdir: signal mantigi, Internet'in network-of-networks yapisi ve protocol kurallari.

Success uclusu EN: Correctness, timeliness, and correct destination are the three classic conditions.
Analog vs digital EN: Analog is continuous and noise-prone; digital is discrete and more noise-resistant.
Internet != Web EN: The Internet is infrastructure; the Web is one application running on it.
Encapsulation EN: Each lower layer adds its own control information and the receiver removes it in reverse order.
Slide 3

OSI Reference Model ve Katmanli DusunmeOSI Reference Model and Layered Thinking

Network architecture mantigi su: ag iletisimi cok karmasik oldugu icin, butun isi tek parca halde dusunmek yerine katmanlara boleriz. Her katman belli bir gorev alir, ust ve alt katmanla iliski kurar, boylece sistem moduler ve troubleshoot edilebilir hale gelir.

Bu mantigin klasik referansi OSI Reference Model'dir. OSI'nin protokolleri birebir her yerde kullanilmiyor olabilir ama modelin kendisi hala egitim acisindan cok gucludur.

ENThe OSI model divides communication into layers so that complex networking tasks become modular, understandable, and easier to troubleshoot.

Open system

Alttaki hardware veya software mimarisi ne olursa olsun farkli sistemler birbiriyle haberlesebilsin diye dusunulur.

Reference model

Bu model birebir urun degildir; network designer'a hangi servislerin ve protokollerin gerekebilecegini gosteren rehberdir.

Layers

Her katman belirli gorevlere sahiptir. Zincirin her halkasi kendi sorumlulugunu yerine getirir.

OSI 7 layers

L7Application - network services to applications
L6Presentation - translation, compression, encryption
L5Session - session establishment and management
L4Transport - end-to-end, ports, reliability, flow control
L3Network - packets, logical addressing, IP, routing
L2Data Link - frames, MAC, local delivery, error detection
L1Physical - bits, signaling, cabling

PDU ve sender/receiver akisi

Sender
Application Presentation Session Transport Network Data Link Physical
Receiver
Physical Data Link Network Transport Session Presentation Application
PDU list
APDU PPDU SPDU TPDU Packet Frame Bit
En kritik PDU uclusu

Vizede en cok sorulan hatirlatma: Network layer -> packet, Data Link layer -> frame, Physical layer -> bit.

Layer Main duty Keywords Examples
Application Kullaniciya yakin network service verir. Web, e-mail, file transfer, remote login HTTP, HTTPS, FTP, SMTP, DNS, SNMP, SSH
Presentation Data representation, translation, encryption, compression Format compatibility TLS/SSL, JPEG, MP3, ASCII, Unicode
Session Session kurar, yonetir, bitirir. Dialog control, token management, synchronization RPC, NetBIOS session
Transport Process-to-process delivery Segmentation, ports, reliability, flow control TCP, UDP, SCTP
Network Host-to-host, logical addressing, routing Packet, IP, forwarding IPv4, IPv6, ICMP, IPsec
Data Link Node-to-node delivery on same local network Frame, MAC, error detection, access control Ethernet, Wi-Fi, ARP, PPP
Physical Raw bit transmission Signal, cabling, timing, duplex Fiber, twisted pair, radio, voltage signaling

Layer detaylari

Physical layer

Raw bit'leri physical medium uzerinden tasir. Electrical, optical ve radio signaling ile ilgilenir; IP, frame veya port bilmez.

Bits Signaling Cabling Simplex / Half / Full duplex

Data Link layer

Ayni local network icinde node-to-node delivery saglar. Bits'i frame haline getirir, MAC kullanir, error detection ve access control yapar.

Frame MAC LLC MAC sublayer

Network layer

Farkli networkler arasinda logical addressing ve routing yapar. Source'tan destination'a packet'lerin hangi yoldan gidecegini belirler.

Packet IP Routing Host-to-host

Transport layer

Farkli host'lardaki process'ler arasinda end-to-end, daha dogrusu process-to-process delivery kurar. Port kullanir, segmentation ve reassembly yapar.

Segment Port Reliability Flow control

Session layer

Session establishment, maintenance ve termination. Dialog control, token management ve synchronization tarafini tutar.

Presentation layer

Translation, encryption ve compression. Farkli sistemlerin data formatlari arasinda ceviri yapar.

Application layer

En ust katmandir. User applications'a dogrudan network service saglar. Dikkat: Chrome'un kendisi Application layer degildir; Chrome'un kullandigi HTTP/HTTPS gibi communication protocols bu katmanda degerlendirilir.

HTTP / HTTPS FTP SMTP DNS Telnet SSH

Data Link vs Network

Data Link ayni local network icinde calisir. Network layer ise farkli networkler arasinda routing yapar.

Network vs Transport

Network = host-to-host. Transport = process-to-process. Bu fark soru gelmeye cok aciktir.

Session vs Presentation

Session oturumun kontroludur; Presentation verinin nasil gosterilecegi, sifrelenecegi ve sikistirilacagidir.

Advantages

  • Clear structure
  • Vendor neutrality
  • Easy troubleshooting
  • Modular design
  • Educational clarity

Limitations

  • Mostly theoretical
  • Some layers overlap
  • Real Internet uses TCP/IP model
Layer-by-layer troubleshooting

Sorun varsa asagidan yukari bak: Physical -> Cable?, Data Link -> MAC / local link?, Network -> IP / routing?, Transport -> port / process?.

Puf Noktalar / Key Takeaways

OSI sorularinda hocanin bekledigi sey katman adlarini ezberlemen degil; her katmanin neyi tasidigini ve digerinden nasil ayrildigini net soylemen.

PDU ayrimi EN: Packet belongs to Network, frame to Data Link, bit to Physical.
Addressing farki EN: MAC appears at Layer 2, IP at Layer 3, port numbers at Layer 4.
Delivery farki EN: Network layer is host-to-host, Transport layer is process-to-process.
Troubleshooting akisi EN: Start from Physical and move upward instead of guessing randomly.
Slide 4

TCP/IP Model, Ports, Sockets, MAC, IPv4, IPv6TCP/IP Model, Addressing, and Endpoints

TCP/IP protocol suite, adini iki kritik protokolden alir: TCP ve IP. Asil gucu, farkli fiziksel sistemlerdeki aglari bir internetwork halinde birlestirmesidir.

OSI daha ogretici ve teorik bir referansken, TCP/IP gercek Internet'in pratikte calisan modelidir.

ENTCP/IP is the practical protocol suite behind the Internet. It connects heterogeneous networks and enables real-world end-to-end communication.

OSI

Application Network services to applications
Presentation Translation / encryption / compression
Session Session control
Transport Ports and end-to-end delivery
Network IP and routing
Data Link Frames and MAC
Physical Bits and media
TCP/IP Application ~= OSI 5 + 6 + 7 TCP/IP Transport ~= OSI 4 TCP/IP Internet ~= OSI 3 TCP/IP Link ~= OSI 1 + 2

TCP/IP

Application HTTP, DNS, SMTP, FTP, RTP, Telnet
Transport TCP, UDP
Internet IP, ICMP
Link Ethernet, 802.11, DSL, SONET ve benzeri altsistemler

Link layer

TCP/IP'nin en alt katmani. OSI'deki Physical ve Data Link gorevlerini daha gevsek bir bicimde birlestirir. Framing, local delivery ve physical transmission burada duser.

Internet layer

Logical addressing, routing ve packet forwarding yapar. Connectionless ve best-effort mantigindadir; reliability garanti etmez.

Transport layer

End-to-end ve process-to-process iletisim. Segmentation, reassembly, multiplexing, gerektiğinde reliability ve congestion control burada.

Application layer

Session ve Presentation ayri katmanlar olarak yoktur; gerektigi kadar uygulama seviyesinde emilir. HTTP, DNS, SMTP, FTP gibi protokoller buradadir.

Baglanti mantigi

TCP/IP Internet layer sadece connectionless delivery verir. Connection-oriented / reliable davranis gerekiyorsa bu yukaridaki Transport layer, ozellikle de TCP tarafinda saglanir.

TCP/IP advantages

  • Scalable
  • Practical and Internet-proven
  • Client-server architecture support
  • Cok sayida routing protocol ile uyumlu

TCP/IP disadvantages

  • Services, protocols ve interface ayrimi OSI kadar sert degildir.
  • Transport layer her durumda delivery guarantee vermez; UDP bunun klasik ornegidir.
  • Less strict layering nedeniyle function overlap gorulebilir.

TCP vs UDP

Feature TCP UDP
Connection Connection-oriented Connectionless
Reliability Reliable No delivery guarantee
Ordering Ordered delivery Ordering garanti etmez
Typical use Web apps, e-mail, databases Online games, streaming, DNS

TCP congestion control

Slow start Congestion avoidance Fast retransmit Fast recovery

Hafiza kancasi

TCP = guvenilir ama agir. UDP = hizli ama rahattir. Bu cizgi acik uclu cevaplarda cok ise yarar.

Ports and sockets

Port nedir?

Port, Transport layer'da kullanilan 16-bit logical identifier'dir. IP adres cihazı bulur; port numarasi o cihazdaki belirli uygulamayi veya servisi bulur.

Aralik: 0-65535

Socket nedir?

Socket = IP address + Port number. Uygulamalarin veri gonderip aldigi logical communication endpoint budur.

Client socket: 192.168.1.5:53021 Server socket: 142.250.190.78:443
Well-known ports 1-1023

80 HTTP, 443 HTTPS, 21 FTP, 25 SMTP, 53 DNS

Registered ports 1024-49151

3306 MySQL, 5432 PostgreSQL gibi application-specific alan

Ephemeral ports Gecici client portlari, 1023 ustu

Tarayici web server'a baglanirken rastgele gecici port alir; server sabit taninan portta bekler.

Socket types

TCP socket stream socket'tir; connection-oriented, reliable ve ordered delivery sunar.

UDP socket

Datagram socket connectionless'tir; hizlidir ama teslim garantisi yoktur.

Kullanim alanlari

Backend servers, microservices, REST APIs, database drivers, WebSockets, Docker, Kubernetes ve cloud services.

MAC address

Definition

MAC address, NIC'e atanan 48-bit hardware identifier'dir. Data Link layer'da kullanilir ve local network icinde cihazi tanimlar.

Physical Address Hardware Address Ethernet Address

Core facts

  • MAC bilgisayara degil NIC'e aittir.
  • NIC baska bilgisayara tasinirse MAC de onunla gider.
  • 6 byte = 48 bit, hexadecimal formatta yazilir.
  • Ornek: 00:1A:2B:3C:4D:5E
MAC structure

IEEE address space'i yonetir. Ilk 24 bit OUI, son 24 bit Device Identifier'dir.

00:1A:2B 3C:4D:5E
MAC address types
Unicast Broadcast Multicast

Broadcast tum station'lara gider. Multicast belirli gruba. Unicast tek NIC'e yoneliktir.

Property MAC address IP address
Layer Data Link (L2) Network (L3)
Type Hardware / physical Logical / configurable
Length 48-bit 32-bit / 128-bit
Scope Local network Inter-network / global routing
Assigned by Manufacturer / IEEE block Admin / ISP / configuration
Benzetme

Slayttaki guclu benzetme: MAC = social security number, IP = postal address. MAC donanima yakin yerel kimliktir; IP ise agda nerede oldugunu gosterir.

IPv4 structure

Definition

IPv4, 32-bit logical numerical identifier'dir. Dotted decimal formatta yazilir: 91.67.15.28. Bir host birden fazla interface'e sahipse her interface icin ayri IP olabilir.

Core logic

IPv4 adresi iki parca dusunulur: network portion + host portion. Bu bolum subnet mask veya CIDR prefix length'e gore belirlenir.

Subnet mask

255.255.255.0 = ilk 24 bit network, son 8 bit host. Binary mantigi: network bits 1, host bits 0.

11111111 11111111 11111111 00000000
CIDR notation

192.168.1.10/24 demek: ilk 24 bit network bits, kalan 8 bit host bits.

Efficient allocation Route aggregation Smaller routing tables

IPv4 summary

32-bit logical address 4 octet dotted decimal Subnetting / broadcasting / routing Longest prefix match

IPv6

Neden cikti?

  • IPv4 address exhaustion
  • Routing efficiency
  • Simpler header processing
  • Auto-configuration support
  • Security and mobility improvements

Structure

IPv6, 128-bit hierarchical address'tir. 8 grup hexadecimal bloktan olusur ve : ile ayrilir.

2001 0db8 85a3 0000 0000 8a2e 0370 7334

Hierarchical parts

Global Routing Prefix + Subnet ID + Interface Identifier mantigiyla okunur.

Key facts

3.4 x 10^38 adres alanina yaklasir. Standart subnetting cogu yerde /64 olarak dusunulur.

Address types

Unicast, multicast ve anycast vardir. Broadcast kaldirilmistir.

Feature IPv4 IPv6
Length 32-bit 128-bit
Notation Dotted decimal Hexadecimal blocks
Broadcast Var Yok
NAT Sik gerekir Tipik olarak gerekmez
Auto-configuration Sinirli Built-in SLAAC
Scalability Daha kisitli Adres alani ve hiyerarsi daha guclu

Puf Noktalar / Key Takeaways

TCP/IP ve addressing tarafi genelde karistirilir; burada hedef kavramlari bir cift olarak ayirmaktir: TCP vs UDP, MAC vs IP, IPv4 vs IPv6, port vs socket.

TCP vs UDP EN: TCP is reliable and ordered; UDP is faster but provides no delivery guarantee.
Port vs socket EN: A port identifies an application; a socket is the full endpoint made of IP plus port.
MAC vs IP EN: MAC is local hardware identity; IP is logical routable identity across networks.
IPv6 motive EN: IPv6 exists mainly to solve IPv4 exhaustion and improve scalability, hierarchy, and autoconfiguration.
Question Pool

Muhtemel Acik Uclu SorularLikely Open-Ended Exam Questions

Slide 1 odakli

  1. What is a computer network? Explain its objectives.
  2. Explain the difference between hub, switch and router.
  3. What are the main hardware components of a computer network?
  4. Compare twisted pair, coaxial and fiber optic cables.
  5. What are PAN, LAN, MAN and WAN? Give examples.
  6. What is network topology? Explain mesh, star, bus and ring topologies.
  7. Explain client-server and peer-to-peer models.
  8. Why are switches preferred over hubs in modern networks?

Slide 2 odakli

  1. What is data communication?
  2. What are the characteristics of successful data communication?
  3. Explain analog and digital signals.
  4. What is bit rate?
  5. What are the causes of transmission disruption?
  6. Explain types of noise.
  7. What is the Internet?
  8. What is the difference between Internet and World Wide Web?
  9. What is a protocol and why is it necessary?
  10. Explain protocol encapsulation.

Slide 3 odakli

  1. What is the OSI model?
  2. Why was the OSI model created?
  3. Write the seven layers of the OSI model in order.
  4. Explain the function of each OSI layer.
  5. What is the difference between Layer 2 and Layer 3?
  6. What is the difference between host-to-host and process-to-process delivery?
  7. How is troubleshooting performed using the OSI model?
  8. Which layer uses MAC addresses, IP addresses and port numbers?

Slide 4 odakli

  1. Explain the TCP/IP model and its layers.
  2. Compare OSI and TCP/IP models.
  3. What is the difference between TCP and UDP?
  4. What is a port? Why is it needed?
  5. What is a socket?
  6. What is the difference between MAC and IP address?
  7. Explain the structure of an IPv4 address.
  8. What is CIDR notation?
  9. Why was IPv6 introduced? Compare IPv4 and IPv6.
Final Kit

Son Dakika Ezber KitiFinal Rapid Review Kit

Sinavdan once son 2-3 dakikada donulecek yer burasi. Ama buz gibi kisa yazmak yerine mantigi koruyacak kadar yogun tutuldu; bu sayede son tekrar gercekten ise yarar.

Network basics

  • Network = interconnected autonomous devices + protocols + sharing
  • Objectives = sharing, communication, scalability, cost reduction, distributed processing
  • Need = sender + receiver + medium + protocol + operating system
  • Hub = broadcast
  • Switch = specific device
  • Router = best path between networks
  • Repeater = signal booster
  • NIC = interface to network

Media and topology

  • Twisted pair = cheap, up to 100 m
  • Coaxial = shielded, TV use, longer than twisted pair
  • Fiber = fastest, longest distance, most expensive
  • PAN = personal short range
  • LAN = office/building/campus
  • MAN = city
  • WAN = country/world/Internet
  • Mesh = reliable but expensive
  • Star = easy management but central failure
  • Bus = cheap but backbone failure kills network
  • Ring = circular path, break affects network

Data communication + Internet

  • Success = correctness + timeliness + correct destination
  • Flow = information -> binary -> signal -> medium -> signal -> binary -> information
  • Analog = continuous, sin wave
  • Digital = discrete, square wave, bits
  • Disruption = distortion + attenuation + noise
  • Noise = thermal + induced + crosstalk + impulse
  • Internet = global network of networks using TCP/IP
  • Web = application on the Internet using HTTP
  • Host = end system
  • Protocol = communication rules

OSI + TCP/IP + Addressing

  • OSI 7 layers: Application, Presentation, Session, Transport, Network, Data Link, Physical
  • Physical = bits
  • Data Link = frame + MAC
  • Network = packet + IP + routing
  • Transport = segment + port + process-to-process
  • TCP/IP 4 layers: Application, Transport, Internet, Link
  • TCP = reliable, ordered, connection-oriented
  • UDP = fast, connectionless, unreliable
  • Port = application identifier
  • Socket = IP + port
  • MAC = 48-bit local hardware address
  • IPv4 = 32-bit dotted decimal
  • IPv6 = 128-bit hex, no broadcast
Final warning

Sinavda en cok karisan farklar: Internet != Web, MAC != IP, Network layer != Transport layer, Hub != Switch, TCP != UDP, Encapsulation != Protocol design.