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
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)
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.