Lecture # 2

CH. 2

Network Models

Islamic University of Gaza

Faculty of Engineering

Computer Engineering Department

Data com. Discussion ECOM 4014

By

Eng. Wafaa Audah

Sep. 2013

2

OSI Model

Open Systems Interconnection (7-Layers)

- Every layer serve its upper layer.

- Peer-peer process:

هادا header –انه فىقها layerانهه واصهح نها ي ال -ترعف عه انذاذا layerكم

انه ظافرى. آنح االظافح تركى layerانهذر تكى تذرى عذج شغالخ يهح دسة ال

تانذزكح ي االعه نألسفم عذ انزسم وي االسفم ان االعه عذ انسرقثم ونك

فثانران يذرىي headerنسرقثم ترى انذذف او االسانح نهادا ال تاخرالف اى عذ ا

انثاكد او انه واصم كم غثقح عذ انزسم رح كى فسى عذ انسرقثم تهك تكى

انرىاصم وكأى صار ت كم غثقح ويثهرها ي انادر تغط انظز شى صارتانطزق تهى.

intermediate nodesمستقبل * بيكىن في الشبكة بيه المرسل وال

تكى ذعايم هادا انزاوذز وانرىاصم يعى ي خالل انثالز غثقاخ – routerعه سثم انثال -

.وانه تسهى انطثقاخ انذاعح نهشثكحاالون ي االسفم

فثعم تس عاول غثقر ي االسفم. switchايا تانسثح ل

الشكل المقابل يمثل توزيع

وترتيبها باآللية layersال

OSIالتي يمثلها ال

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بيكىن كالتالي مه الطبقات السفليةاضافة الهيدرز

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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.

كا أعا جة ا رى data rateهذا ع ا انزسم وانسرقثم جة ا سرعهى فس ال

انرزذة وانىقد زسم وانسرقثم نعا قم انثراخ تنشاي ت اتر clockقم انثراخ دسة ال

انصذخ.

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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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.

Stream of bits

Packet or

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Physical Address

Link address ( ثم عىا انهك انران ونس انسرقثم انهائويرغز )

Logical Address

Universal addressing (ثاتد وثم انزسم وانسرقثم انهائ)

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.

:يلاتلاك ىه لحلا اهب ةصاخلا زرديهلل ةقبط لك ةفاضاو قباسلا حرشلا بسح

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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.

جدىجىنا واعنا ذدا قفاى مهخنا راصاي ذعت ذذجنا اىعنا ىك ا ايا اه ناردا اع ع

!! ػهغنا اىعهن ست اذاذنا مصىذ حر نارنات

حهسزنا دكاثنا نارنات جدىجىي شرسن اىع اا اىعنا قفاىاي ىا ىهف ارنا لاردالا ايا

ععذ

ءاغنا معذو روزا راص ىا فزعذ وسال error detection ب حصاخ دىثي ف ىك ضوزفي رناذنات

خذص مكشت اهناسرا ذعذو اذاذهن

See You at Next lecture

Best Wishes