Lecture 04

Lecture:04

Prepared by ~ Bikramjit Chakrabarty EEE,L-4,T-2,BUET Sem-2,Cisco Networking Academy.

1

Contents of today’s Adventure:      

2

Review of Lecture-3 Ethernet CSMA/CD (Carrier Sense Multiple Access Collision Detection) Repeater (Layer-1 device ) Hub (Layer-1 device) Detail Analysis of Encapsulation and decapsulation process at different layers by different devices. (~optional)

Key Terms: (review…)       

Dispersion. Physical medium. NIC. MAC Address. Driver Connector. System bus.

      

3

Logical Addressing Flat Addressing (BIA) Encapsulation. Dencapsulation. Packet switching (Connection less). Circuit Switching (Connection oriented). Acknowledgement

Networking Technology     

4

IEEE 802.3: Carrier Sense Multiple Access/Collision Detect (CSMA/CD) Access Method. IEEE 802.3u: Fast Ethernet. IEEE 802.3z: Gigabit Ethernet. IEEE 802.5: IBM Token Ring. FDDI: The ANSI X3T9.5 standards committee produced the Fiber Distributed Data Interface (FDDI) standard & submitted FDDI to the International Organization for Standardization (ISO), who, then created an international version of the FDDI that is completely compatible with the ANSI standard version.

Layers associated with different LAN protocols

5

Ethernet : it’s Origin.. 







6

In the late 1960s, the University of Hawaii developed a WAN called ALOHA. In 1972, Robert Metcalfe and David Boggs invented a cabling and signaling scheme at the Xerox Palo Alto Research Center (PARC) and in 1975 introduced the first Ethernet product s a system of 2.94 megabits per second (Mbps) to connect over 100 computers on a 1-kilometer (.62 miles) cable. In the 1980s the IEEE published Project 802. This project generated standards for design and compatibility for hardware components that operated within the OSI physical and data-link layers. The standard that pertains to Ethernet is the IEEE 802.3 specification.

Ethernet Features  

  



7

Best effort delivery-analogy with postal system. Comparison with Token-Ring~ Broadcasting-Token, Collision, analogy with autocracy & democracy. Ethernet is ‘democratic’ !! Baseband architecture. Bus topology, usually transmits at 10 Mbps. Relies on CSMA/CD to regulate traffic on the main cable segment. This will not fail unless the media is physically cut or improperly terminated.

Ethernet Summary        

8

Traditional topology: Linear bus Other topologies: Star bus Logical topology: Broadcast Type of architecture: Baseband Access method: CSMA/CD Specification: IEEE 802.3 Transfer speed: 10 Mbps or 100 Mbps Cable type: Thicknet, thinnet, UTP

Ethernet Specifications (IEEE 802.3) 10BaseT Topology:

Star bus Cable type: Category 3, 4, or 5 unshielded twisted-pair cable Connection to NIC: RJ-45 Maximum cable segment length:100 meters (328 feet) Maximum connected segments: 100 meters (328 feet)

9

Comparison of Frame Format:

10

Frame fields  

 

11

preamble - The alternating pattern of 1's and 0's tells receiving stations that a frame is Ethernet or IEEE 802.3. destination and source addresses -The source address is always a unicast (single-node) address. The destination address can be unicast, multicast (group), or broadcast (all nodes). type (Ethernet) - The type specifies the upper-layer protocol to receive the data after Ethernet processing is completed. length (IEEE 802.3) - The length indicates the number of bytes of data that follows this field.

Frame fields…. 





12

data (Ethernet) - After physical-layer and link-layer processing is complete, the data contained in the frame is sent to an upperlayer protocol, which is identified in the type field. Although Ethernet version 2 does not specify any padding, in contrast to IEEE 802.3, Ethernet expects at least 46 bytes of data. data (IEEE 802.3) - After physical-layer and link-layer processing is complete, the data is sent to an upper-layer protocol, which must be defined within the data portion of the frame. If data in the frame is insufficient to fill the frame to its minimum 64-byte size, padding bytes are inserted to ensure at least a 64-byte frame. frame check sequence (FCS) - This sequence contains a 4 byte CRC value that is created by the sending device and is recalculated by the receiving device to check for damaged frames.

13

Layer-1(Physical) Devices:

14

HUB

15

…HUB



 

16

The purpose of a hub is to regenerate and retime network signals. Multiport repeater. This is done at the bit level to a large number of hosts (e.g. 4, 8, or even 24) using a process known as concentration

…HUB  The

17

reasons for using hubs is to create a central connection point for the wiring media, and an increase in the reliability of the network.  The reliability of the network is increased by allowing any single cable to fail without disrupting the entire network.  This differs from the bus topology where having one cable fail will disrupt the entire network.

HUB- Layer 1 Device 

18

Hubs are considered Layer 1 devices because they only regenerate the signal and broadcast it out all of their ports (network connections).

Classification of Hub  



19

Active or Passive hubs Most modern hubs are active; they take energy from a power supply to regenerate network signals. Passive hubs do not regenerate bits, so they do not extend a cables length, they only allow two or more hosts to connect to the same cable segment.

… Classification of Hub  



20

Intelligent and Dumb hubs Intelligent hubs have console ports, which means they can be programmed to manage network traffic. Dumb hubs simply take an incoming networking signal and repeat it to every port without the ability to do any management.

Repeater 



21

The maximum length for UTP(CAT-5) cable in a network, is 100 meters (approximately 333 feet). If we need to extend our network beyond that limit, we must add a device called a repeater As signals travel along a cable, they degrade and become distorted in a process called “attenuation” .If a cable is long enough, attenuation will finally make a signal unrecognizable. Installing a repeater enables signals to travel farther.

How Repeaters Work A

repeater works at the physical layer of the OSI Reference Model to regenerate the network's signals and resend them out on other segments.

22

…Repeater  The

23

repeater takes a weak signal from one segment, regenerates it, and passes it to the next segment.  To pass data through the repeater from one segment to the next, the packets and the Logical Link Control (LLC) protocols must be identical on each segment.  A repeater will not enable communication, for example, between an 802.3 LAN (Ethernet) and an 802.5 LAN (Token Ring).

…Repeater  



24

Repeaters do not translate or filter signals. For a repeater to work, both segments that the repeater joins must use the same access method. The two most common access methods are carrier-sense multipleaccess with collision detection (CSMA/CD) and token passing. Repeaters can move packets from one kind of physical media to another, Ethernet packet coming from a thinnet coaxial-cable segment and pass it on to a fiber-optic segment.

Repeater Considerations  Repeaters

afford the least expensive way to expand a network.  No Isolation or Filtering  Repeaters will also pass a broadcast storm along from one segment to the next  network performance will be degraded.

25

Repeater~~ 

Use repeater – –

–

– –

26

use!! or not use!!

To extend broadcast domain. Connect two segments of similar or dissimilar media. Regenerate the signal to increase the distance transmitted. Pass all traffic in both directions. Connect two segments in the most cost-effective manner.



Don’t use - There is heavy network traffic. - Segments are using different access methods. - Data filtering is needed. - Collision domain consideration.

Packet Flowing: (To understand this should be reviewed)



27

Device: Hub (Layer-1) Repeater (Layer-1) Bridge (Layer-2) Switch (Layer-2) Router(Layer-3)







Hub transmits signal to all of its ports. Switch,Bridge take decision depending on Layer-2 address(MAC). Router takes decision depending on Layer-3 address(IP).