Chapter 1: The Internet - Complete PDF Content (Full Version)

📑 page 1 & 2 🔖 1. The Internet: Basic Components

1. Millions of Connected Computing Devices

Hosts (End Systems) – devices running network applications at the edge

🖥️ What are Hosts?

Run network applications
Sit at the edge of the network

Examples: PCs, Laptops, Smartphones, Servers, IP phones, Access points, Fingerprint terminals, Card readers, Printers

Important: Hosts run applications; network only transports data

🔗 Communication Links

Fiber optic, Copper cables, Radio (wireless), Satellite
Transmission rate (Bandwidth) – bits per second (bps)
Bandwidth = max transmission rate

📦 Packet Switches

Data divided into packets
Routers & Switches forward packets
Job: receive packet → determine next hop → forward
Do NOT understand application data

الصفحة 1-2: الإنترنت يتكون من ملايين الأجهزة الطرفية (hosts) التي تشغل التطبيقات: حواسيب، هواتف، خوادم، نقاط وصول، قارئات بصمة، طابعات. الشبكة فقط تنقل البيانات. خطوط الاتصال: ألياف بصرية، نحاس، لاسلكي، قمر صناعي. سرعة الإرسال (bandwidth) تقاس بـ bps. المبدلات (routers & switches) تقسم البيانات إلى حزم (packets) وتوجهها، لكنها لا تفهم بيانات التطبيق.

📑 pages 2-3 🌐 network of networks · protocols

2. The Internet as a "Network of Networks"

Internet = interconnected ISPs
ISPs connect: home networks, company networks, university networks, data centers

📋 3. Protocols

What is a Protocol?

Set of rules defining: format of messages, order, actions when sent/received

Without protocols → devices cannot understand each other, communication fails

Human vs Network Protocols

Human: "What's the time?" – expected reply: a time

Network: strict technical rules for machines

📡 Examples of Internet Protocols

TCP – reliable UDP – fast, unreliable IP – addressing/routing HTTP – web HTTPS – secure web FTP – file transfer SMTP – sending email IMAP – manage email on server POP3 – download email SNMP – manage devices 802.11 – Wi-Fi

Internet Standards: RFC (Request for Comments) documents describe standards. IETF (Internet Engineering Task Force) develops, promotes, maintains Internet standards.

الصفحات 2-3: الإنترنت هو شبكة من مزودي الخدمة (ISPs). البروتوكول: مجموعة قواعد تحدد تنسيق الرسائل وترتيبها والإجراءات. بدون بروتوكولات يفشل الاتصال. أمثلة: TCP (موثوق)، UDP (سريع غير موثوق)، IP (عنونة وتوجيه)، HTTP (ويب)، HTTPS (آمن)، FTP (نقل ملفات)، SMTP/IMAP/POP3 (بريد إلكتروني)، 802.11 (واي فاي). معايير الإنترنت: RFC و IETF.

📑 pages 4–6 ⚙️ protocol details · infrastructure · API

5. Internet Infrastructure and Services

Services: Web, Email, VoIP, Online games, E-commerce, Social networks
Programming interface (API) – allows apps to send/receive data, choose service options
Analogy: like postal service – apps send messages without delivery details

📌 6. What's a Protocol? (Detailed)

A protocol specifies: 1. Format – structure, 2. Order – sequence, 3. Actions – upon send/receive. Example: TCP defines connection start, acknowledgment, loss behavior. If protocols not followed → data corrupted or communication fails.

📑 pages 6–7 🧬 OSI 7 layers

7. OSI Reference Model (7 Layers)

1. Physical
2. Data Link
3. Network
4. Transport

5. Session
6. Presentation
7. Application

Layer explanations quick: Physical: bits as signals; Data Link: frames between neighbors, MAC, error detection; Network: routing, IP; Transport: end-to-end, TCP/UDP; Session: manages dialogue; Presentation: translation/encryption; Application: HTTP, SMTP, FTP.

نموذج OSI (7 طبقات): 1 مادية (بتات)، 2 ربط بيانات (إطارات، MAC)، 3 شبكة (توجيه، IP)، 4 نقل (اتصال end-to-end، TCP)، 5 جلسة، 6 عرض (ترجمة، تشفير)، 7 تطبيق (HTTP, SMTP...).

📑 page 8 📦 TCP/IP & 5-layer model

8. TCP/IP Model (4 layers)

1. Application
2. Transport
3. Internet
4. Link

Comparison: OSI = theoretical, TCP/IP = practical used in real Internet. Network layer (OSI) corresponds to Internet layer (TCP/IP).

📶 9. Internet Protocol Stack (5 Layers)

Application – message format
Transport – process-to-process
Network – routing
Link – communication between neighboring devices
Physical – bits to signals

📑 pages 9–11 🌿 network edge · access networks

10. Network Structure

🌐 Network Edge

Contains hosts (clients and servers). Servers often located in data centers.

🚪 Access Networks

Connect end systems to edge router. Types: Residential, Institutional (school/company), Mobile. Considerations: bandwidth, shared/dedicated.

📡 11. Access Network Types

DSL (Digital Subscriber Line)

Telephone copper lines, FDM
Speeds: < 2.5 Mbps upstream, < 24 Mbps downstream
Dedicated access

Cable (HFC)

Fiber backbone + coax to homes
Shared access, up to 30 Mbps down, 2 Mbps up

NAT (Network Address Translation)

Share one public IP, translate private to public

Enterprise Ethernet

10 Mbps – 10 Gbps, end systems connect to switch

Wireless Access

WLAN (Wi-Fi) short range ~100 ft, standards 802.11b (11M) → 802.11be (46G)
WWAN (cellular) 1G (2.4Kbps) → 2G→3G→4G/LTE (10-100M) →5G (several Gbps) →6G (up to 100G expected)

شبكات الوصول: DSL (خط هاتف، سرعة تحميل حتى 24 ميجابت)، كابل (مشارك، 30 ميجابت)، NAT (مشاركة عنوان IP عام)، إيثرنت مؤسسات (10M-10G)، لاسلكي WLAN (واي فاي 802.11b/g/n/ac/ax/be بسرعات تصل 46 جيجابت)، خلوي WWAN (1G حتى 6G، 5G عدة جيجابت).

📑 pages 11–12 🧪 Physical Media

12. Physical Media

Guided media

Twisted pair (Cat5: 100M/1G, Cat6: 10G)
Coaxial (broadband, bidirectional, used in HFC)
Fiber optic: glass fiber, light pulses, high speed (10-100+ Gbps), low error, immune to noise

Unguided media

Radio waves (affected by reflection, obstruction, interference)

📑 pages 13–15 ⏱️ Delay · Loss · Throughput · Traceroute

Transmission and Delays

T = L / R (transmission time)

Packet L bits, rate R bps

⏲️ Four sources of delay

d_nodal = d_proc + d_queue + d_trans + d_prop

Processing Delay (dproc)

Check errors
Determine output link
Usually < 1 ms

Queueing Delay (dqueue)

Waiting in buffer
Depends on congestion

Transmission Delay (dtrans)

                  dtrans = L / R
                

Depends on Packet size
Depends on Bandwidth

Propagation Delay (dprop)

                  dprop = d / s
                

Depends on Distance

📊 Traffic Intensity

(L * a) / R

If <1 → small delay; ≈1 → large delay; >1 → infinite delay (congestion).

💔 Packet Loss

Occurs when buffer full → packet dropped (may be retransmitted or permanently lost).

📈 Throughput

Throughput = rate of successful data transfer (instantaneous or average)
End-to-end throughput = minimum link rate (bottleneck)
If 10 connections share backbone: each gets R/10

🧭 Traceroute

Measures delay from source to each router
Sends 3 packets per router, measures RTT
*** means no response (timeout or firewall)
Trans-oceanic links show high latency

التأخير الكلي: dproc (معالجة) + dqueue (طابور) + dtrans (إرسال) = L/R + dprop (انتشار). كثافة الحركة (L*a)/R. إذا >1 ازدحام لا نهائي. الفقد عندما يمتلئ المخزن المؤقت. الإنتاجية = أقل معدل (bottleneck). Traceroute يقيس التأخير لكل راوتر.

🌍 CHAPTER 1: THE INTERNET