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CPEG512 Advanced Computer Networks

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Presentation on theme: "CPEG512 Advanced Computer Networks"— Presentation transcript:

1 CPEG512 Advanced Computer Networks
University of Nizwa College of Engineering and Architecture Electrical and computer Engineering CPEG512 Advanced Computer Networks Week7 Fall 2014/2015 Atef Abu Salim

2 Code Division Multiplexing
Also known as code division multiple access An advanced technique that allows multiple devices to transmit on the same frequencies at the same time.

3 CDM cont. Each mobile device is assigned a unique 64-bit code
To send a binary 1, mobile device transmits the unique code To send a binary 0, mobile device transmits the inverse of code

4 Transmission Mode The transmission of binary data across a link can be accomplished in either parallel or serial mode.

5 Transmission Modes cont.
Data Transmission Serial Asynchronous synchronous Isochronous Parallel

6 Transmission Modes cont.
Parallel Transmission: uses n wires to transmit n bits at one time. Ex. Computer to printer

7 Transmission Modes cont.
Serial Transmission: In serial Transmission one bit follows another, so we need one communication channel to transmit data between two communication devices. Serial transmission occurs in one of the three way: Asynchronous, Synchronous and Isynchronous. Ex. computer to modem

8 Serial Transmission In asynchronous Transmission, we send 1 start bit (0) at the beginning and 1 or more stop bits or gaps at the end of each byte. ….. Stop Bit Byte N Start Bit Stop Bit Byte2 Start Bit Stop Bit Byte1 Start Bit

9 Serial Transmission cont.
In synchronous Transmission, we send one bit after another without start or stop bits. It is the responsibility of the receiver to group the bits. Synchronous transfer (self-clocking), uses sync bytes in the frame. Frame has multiple bytes. (global or synchronized clocks). Byte 1…ByteN=Block Sync Byte Byte N Byte 2 Byte 1 Sync Byte

10 Serial Transmission cont.
The isochronous mode provide synchronized for the entire stream of bit must. It guarantees that data arrive at the fixed rate.

11 Ethernet Ethernet Technology (IEEE 802.3) : It is the most important technology of LAN. Definition Ethernet standards define Physical and MAC layers of the OSI model only. Physical layer Electrical characteristics of cable connectors, including maximum lengths Bit encoding (e.g., Manchester coding) and transmission rate (10/100/1000 Mbps) Medium Access Control (MAC) layer Ethernet frame format and addressing Access protocol = Carrier Sense Multiple Access with Collision Detection (CSMA/CD).

12 Ethernet cont Easy to understand, implement, manage, and maintain
Most popular industry use and acceptance. Easy to understand, implement, manage, and maintain Low-cost network implementations Extensive topological flexibility for network installation. Interoperability and operation of standards- compliant products, regardless of manufacturer.

13 Ethernet Standards IEEE 802.3 Committee standards 10Base5 (1985)
Compatible with DIX Ethernet Small difference in frame format (Frame Type vs. Length field) and signal naming. 10Base2 (1988) Uses less expensive, thinner coaxial cable. Eliminates external transceiver (MAU) and puts transceiver onto Network Interface Card. Also called ThinNet and CheaperNet. 1Base5 (1988) 1Mbps StarLAN star topology over unshielded twisted pair. 250m max distance from node to hub.

14 Ethernet Standards cont.
10BaseT (1990) 10Mbps star topology over unshielded twisted pair meters max. distance from node to hub 10BaseF (1993) 10Mbps star topology over optical fiber meters max. distance from NIC to hub. Replaces previous FOIRL (Fiber Optic Inter-Repeater Link) specification for inter-connecting repeaters or hubs. 100BaseT / 100BaseF (1995) 100Mbps Ethernet using CSMA/CD over twisted pair or fiber.

15 Ethernet Standards cont.
1000BaseX / 1000BaseT (1998/1999) Gigabit Ethernet over coaxial cable and fiber / over 4 - Category 5 twisted pair. 10GB Ethernet – 802.3ae (2002)

16 Multiple-access protocols

17 CSMA/CD Carrier Sense Multiple Access with Collision Detection:
Carrier sense: listing to physical medium if other station is transmitting. Collision detection: During transmission, station listens if no other station is corrupting its message.

18 CSMA/CD cont. Basic Idea
When a station has frame to transmit: Listen for Data Transmission (Carrier Sense) When no other station is transmitting Start to transmit frame, listening for collision. If collision is heard, stop transmitting, wait random time, and transmit again. If channel is in-use, then the station backs off.

19 Station is ready to send
CSMA/CD Procedure Station is ready to send try again Wait Sense Channel channel busy Send jam signal Transmit data and sense channel collision detected successful transmission

20 Collision in CSMA t1 – A sense medium idle and transmits. t2 – Z senses medium idle and transmits. t3 – signals collide.

21 Non-persistent CSMA When a station has a frame to transmit:
Listen for data transmission (Carrier) a) When medium is quiet(idle), transmit. When medium is busy, wait a random period of time and go back to step 1. The random wait gives a probability that stations will be sensing the channel at different periods when helps in avoiding collision.

22 p-persistent CSMA P stands for probability.
When a station has a frame to transmit: Listen for data transmission (Carrier) When medium is idle Choose random value,  , between 0 and 1. If  < p then Transmit frame Wait for Ack If no Ack received within time T, go to step 1. If  > p then Wait for 1 contention slot time. Go to step 1.

23 1-persistent CSMA A station transmits immediately upon sensing the channel is idle. Upon collision, station waits a random period before sensing the channel again. Called 1-persistent, because station transmits with probability of 1 when the channel is sensed idle.

24 Persistence strategies

25 CSMA/CD procedure

26 Token-passing network

27

28 Channelization Channelization is a multiple-access method in which the available bandwidth of a link is shared in time, frequency, or through code, between different stations. There are three basic forms of channelization: Frequency division multiple access (FDMA) Time division multiple access (TDMA) Code division multiple access (CDMA)

29 In FDMA, the bandwidth is divided into channels.
In TDMA, the bandwidth is just one channel that is timeshared. In CDMA, one channel carries all transmissions simultaneously.

30 IEEE Networking Specifications

31 Data Link - MAC Sub Layer
This is the first layer where data can be manipulated above the physical layer In OSI, Data Unit is exchanged between two ends. In LANs, this layer sends/receives IP packets. The information is transmitted in “Frame”. IP packets are encapsulated in Ethernet frames.

32 Data Link - MAC Sub Layer
Stations transmit when channel is idle. If a collision occurs, a back-off mechanism is applied. 10Mbps LAN give about 33% true throughput (user information successfully exchanged taking out contention, collision and other overhead)

33 MAC Address Medium Access Control.
Ethernet address/MAC address is 48bits. XX XX XX XX XX XX B-E1-50

34 Questions??????????????? Q1: does every workstation (PC) have a MAC address? How do I find the MAC address of my PC (Windows)? Q2: could one workstation have more than one MAC address? Q3: who assign the MAC address? Q4: Can I change the MAC address? Q5: is MAC address local (to LAN) or global (like Internet)?

35 Data Link - MAC Sub Layer
Physical Layer OSI Layers LLC LAN Sub Layers MAC IEEE 802.x IEEE 802.3 CSMA/CD LLC: Logical Link Control MAC: Medium Access Control

36 Data Link - MAC Sub Layer cont.
LLC Physical Layer Station B MAC Station A P-P

37 Data Link - MAC Sub Layer cont.
LLC hides the details of the different IEEE 802.x(4=token bus, 5=token ring, 3=Ethernet) from the network layer.

38 A network with and without a bridge

39 Switched Ethernet

40 Full-duplex switched Ethernet

41 802.3 MAC frame Preamble (PRE) (for synchronization): Consists of 7 bytes. The PRE is an alternating pattern of ones and zeros that tells receiving stations that a frame is coming, and that provides a means to synchronize the frame-reception portions of receiving physical layers with the incoming bit stream. The preamble is actually added at the physical layer and is not (Formally) part of the frame.

42 802.3 MAC frame cont. Start-of-frame delimiter (SFD): the second filed, (1 byte : ) signals the beginning of the frame . The SFD warns the station that this is the last chances for synchronization. The last 2 bits is 11 and alert the receiver that the next field is the destination address. Destination address (DA): Consists of 6 bytes(48-bits) , MAC Station HW address. Source addresses (SA): Consists of 6 bytes(48-bits) , MAC Station HW address.

43 802.3 MAC frame cont. Length or type : this field is defined as a type field or length field (used it as the length field to define the number of bytes in the data field). the original Ethernet used this filed as the type field to define the upper layer protocol using the byte. Data : this field carries data encapsulated from the upper layer protocol (min 64 byte , max 1518 bytes).

44 802.3 MAC frame cont. CRC(Cyclic Redundancy Check ): the last field contains error detection information.

45 802.3 MAC frame and Ethernet Frame
16 56 8 48* 48* Variable 32 Preamble SFD Dest Add Src Add TYPE Data CRC ETHERNET Frame 16 56 8 48* 48* Variable 32 Preamble SFD Dest Addr Src Addr DATALEN Data CRC IEEE Frame LLC Data PAD LLC: Link Logical Control Data: Encapsulated information , (User data, protocol-ARP…) PAD: Packet Assembly/De-assembly, to make the data field to a minimum of 38 bytes.

46 MAC Sub Layer 8 8 8 DSAP SSAP Control LLC Field
DSAP: Destination Service Access Point = 170 (0xaa) SSAP: Source Service Access Point = 170 (0xaa) 170=SNAP=Network Layer is not determined (since it is determined in the type field) IP was not defined to a have a code as part of the SAP definition. The Type defines the protocol. Control: 3, LLC frame type, Information Frame


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