Download Lecture # 2 CH. 2 Network Models

Islamic University of Gaza
Faculty of Engineering
Computer Engineering Department
Data com. Discussion ECOM 4014
Lecture # 2
CH. 2
Network Models
By
Eng. Wafaa Audah
Sep. 2013
‫‪OSI Model‬‬
‫)‪Open Systems Interconnection (7-Layers‬‬
‫الشكل المقابل يمثل توزيع‬
‫ال ‪ layers‬وترتيبها باآللية‬
‫التي يمثلها ال ‪OSI‬‬
‫‪Every layer serve its upper layer.‬‬
‫‪-‬‬
‫‪- Peer-peer process:‬‬
‫كم ‪ layer‬ترعُف عهً انذاذا ‪ -‬انههٍ واصهح نها يٍ ال ‪ layer‬انهٍ فىقها – ‪ header‬هادا‬
‫انهُذر تُكىٌ تُذرىٌ عذج شغالخ يهًح دسة ال ‪ layer‬انهٍ ظافرى‪ .‬آنُح االظافح تركىٌ‬
‫تانذزكح يٍ االعهً نألسفم عُذ انًزسم ويٍ االسفم انً االعهً عُذ انًسرقثم ونكٍ‬
‫تاخرالف اَى عُذ انًسرقثم تُرى انذذف او االسانح نهادا ال ‪ header‬فثانرانٍ يذرىي‬
‫انثاكُد او انهٍ واصم كم غثقح عُذ انًزسم رح َكىٌ َفسى عُذ انًسرقثم تهُك تُكىٌ‬
‫انرىاصم وكأَى صار تٍُ كم غثقح ويثُهرها يٍ انُادُرٍُ تغط انُظز شى صارتانطزَق تُُهى‪.‬‬
‫* بيكىن في الشبكة بيه المرسل والمستقبل ‪intermediate nodes‬‬
‫عهً سثُم انًثال ‪ – router‬تُكىٌ ذعايم هادا انزاوذز وانرىاصم يعى يٍ خالل انثالز غثقاخ‬‫االونً يٍ االسفم وانهٍ تُسًُهى انطثقاخ انذاعًح نهشثكح‪.‬‬
‫ايا تانُسثح ل ‪ switch‬فثُعًم تس عاول غثقرٍُ يٍ االسفم‪.‬‬
‫‪2‬‬
‫اضافة الهيدرز مه الطبقات السفلية بيكىن كالتالي‬
‫‪3‬‬
The Physical Layer
- The physical layer is responsible for ensuring that a stream of bits is
transmitted between two nodes sharing a single link.
- The physical layer coordinates all the functions required to transmit
a bit stream over the physical medium.
- Data rate: Transmission rate – number of bits sent per second
- Synchronization of bits.
‫ كًا أَعا َجة اٌ َرى‬data rate ‫هذا َعٍُ اٌ انًزسم وانًسرقثم َجة اٌ َسرعًهى َفس ال‬
‫ ترشايٍ تٍُ انًزسم وانًسرقثم نعًاٌ َقم انثراخ تانرزذُة وانىقد‬clock ‫َقم انثراخ دسة ال‬
.‫انصذُخ‬
The Data Link Layer
- The data link layer is responsible for ensuring that a packet of data
is successfully transmitted between two adjacent nodes in the
network.
- Flow control: Prevent overwhelming the receiver.
- Error control: Detect and retransmit damaged or lost frames;
Prevent duplication of frames; using trailer.
Hop-to-hop (node-to-node) delivery: add physical address as a header,
also add a tailor for error control.
Network Layer
The network layer is responsible for the delivery of packets from the
original source to the final destination.
The responsibilities of the network layer:
- Logical addressing.
- Routing:
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Transport Layer
The transport layer is responsible for delivery of a message from one
process to another.
Responsibilities of the transport layer
- Port addressing
- Flow control
- Error control
Session, presentation layers (according to the Dr’s recommendations)
are not important 
Application Layer
The application layer is the interface between the user and the network
(session, presentation and application layers are user support layers)
Some of services
- Network virtual terminal: Logon to a remote host.
- File transfer, access, and management.
- Mail services
TCP/IP Protocol Suite
(Internet Model)
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Packet or
Stream of bits
The most important protocols according to the layers
ADDRESSING
There are four levels of addresses are used in an internet employing the
TCP/IP protocols.
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Physical Address
Link address (ٍ‫)يرغُز وًَثم عُىاٌ انهُُك انرانٍ ونُس انًسرقثم انُهائ‬
Logical Address
Universal addressing (ٍُُ‫)ثاتد وًَثم انًزسم وانًسرقثم انُهائ‬
Port Address
Processes addresses
Specific Address
www.iugaza.edu
Text-Book Questions
Review Questions
2. Which layers in the Internet model are the network support layers?
The network support layers are the physical, data link, and network layers.
3. Which layer in the Internet model is the user support layer?
The application layer supports the user.
7. What are headers and trailers, and how do they get added and removed?
Headers and trailers are control data added at the beginning and the end of each data
unit at each layer of the sender and removed at the corresponding layers of the
receiver. They provide source and destination addresses, synchronization points,
information for error detection, etc.
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Exercises
16. Match the following to one or more layers of the OSI model:
a. Route determination: Network Layer
b. Flow control: Data link, Transport Layers
c. Interface to transmission media: Physical Layer
d. Provides access for the end user: Application Layer
20. In Figure 2.22, computer A sends a message to computer D via LANl, router Rl,
and LAN2. Show the contents of the packets and frames at the network and data
link layer for each hop interface.
:‫حسب الشرح السابق واضافة كل طبقة للهيدرز الخاصة بها الحل هى كالتالي‬
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21. In Figure 2.22, assume that the communication is between a process running
at computer A with port address i and a process running at computer D with port
address j. Show the contents of packets and frames at the network, data link, and
transport layer for each hop.
22. Suppose a computer sends a frame to another computer on a bus topology
LAN. The physical destination address of the frame is corrupted during the
transmission. What happens to the frame? How can the sender be informed about
the situation?
If the corrupted destination address does not match any station address in the
network, the packet is lost. If the corrupted destination address matches one of the
stations, the frame is delivered to the wrong station. In this case, however, the error
detection mechanism, available in most data link protocols, will find the error and
discard the frame. In both cases, the source will somehow be informed using one of
the data link control mechanisms discussed in Chapter 11.
‫َعٍُ عُا ادرًانٍُ هُا ايا اٌ َكىٌ انعُىاٌ انجذَذ تعذ ياصار انخهم َىافق ادذ انعُاوٍَ انًىجىدج‬
!! ‫تانرانٍ رح ذىصم انذاذا تس نهعُىاٌ انغهػ‬
‫ايا االدرًال انراٍَ فهى اَى ياَىافق انعُىاٌ اَا عُىاٌ نسرُشٍ يىجىدج تانرانٍ انثاكُد انًزسهح‬
 ‫ذعُع‬
‫ السو ذعزف اَى صار اَزور وذعًم انغاء‬detection error ‫تانذانرٍُ يفزوض َكىٌ فٍ يُثىد خاصح ب‬
 ‫نهذاذا وذعُذ ارسانها تشكم صذُخ‬
See You at Next lecture
Best Wishes
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