Introduction to Data Communication and Networking

VI SEM EEE

EEE- 324T

Department of Electrical and Electronics Engineering, BVCOE, New Delhi

Subject: IDCN, Instructor: Dr.SUDHA.K

1

�COURSE OBJECTIVES

• 1. To build an understanding of the fundamental concepts of data communication.
• 2. To familiarize the student with the basic taxonomy of data link layer.
• 3. To understand and implement the network routing, IP addressing, subnetting.
• 4. To enumerate the functions of transport layer and application layer.

​

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

2

COURSE OUTCOMES(CO)

CO 1 Understand basic concepts of data communications.

CO 2 Understand and explain various functions of data link layer.

CO 3 Understand and implements the network routing, IP addressing, subnetting.

CO 4 Enumerate the functions of transport layer and application layer.

3

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

�UNIT-II

• Data Link Layer: Design issues, Data Link Control and Protocols.
• Flow and Error Control, Stop-and-wait ARQ.
• Sliding window protocol, Go-Back-N ARQ, Selective Repeat ARQ, HDLC.
• Medium Access Sub layer: Channel allocation problem, Controlled Access, Channelization, multiple access protocols.
• IEEE standard 802.3 & 802.11 for LANS and WLAN, high-speed LANs, Network Devices-repeaters, hubs, switches, bridges.

​

4

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

����������Data Link Layer-Design Issues�

The data link layer in the OSI (Open System Interconnections) Model, is in between the physical layer and the network layer. This layer converts the raw transmission facility provided by the physical layer to a reliable and error-free link.

The main functions and the design issues of this layer are

Providing services to the network layer

Framing

Error Control

Flow Control

5

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

6

Services to the Network Layer:

In the OSI Model, each layer uses the services of the layer below it and provides services to the layer above it. The data link layer uses the services offered by the physical layer. The primary function of this layer is to provide a well defined service interface to network layer above it.

• The types of services provided can be of three types −
• Unacknowledged connectionless service
• Acknowledged connectionless service
• Acknowledged connection - oriented service

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

7

Framing

• The data link layer encapsulates each data packet from the network layer into frames that are then transmitted.
• A frame has three parts, namely
• Frame Header
• Payload field that contains the data packet from network layer
• Trailer

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

8

• Error Control
• The data link layer ensures error free link for data transmission. The issues it caters to with respect to error control are:
• Dealing with transmission errors
• Sending acknowledgement frames in reliable connections
• Retransmitting lost frames
• Identifying duplicate frames and deleting them
• Controlling access to shared channels in case of broadcasting

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

9

• Flow Control
• The data link layer regulates flow control so that a fast sender does not drown a slow receiver. When the sender sends frames at very high speeds, a slow receiver may not be able to handle it. There will be frame losses even if the transmission is error-free. The two common approaches for flow control are:
• Feedback based flow control
• Rate based flow control

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

10

• When a data frame (Layer-2 data) is sent from one host to another over a single medium, it is required that the sender and receiver should work at the same speed.
• That is, sender sends at a speed on which the receiver can process and accept the data. What if the speed (hardware/software) of the sender or receiver differs? If sender is sending too fast the receiver may be overloaded, (swamped) and data may be lost.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

11

• Two types of mechanisms can be deployed to control the flow:
• Stop and Wait
• This flow control mechanism forces the sender after transmitting a data frame to stop and wait until the acknowledgement of the data-frame sent is received.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

12

• Sliding Window
• In this flow control mechanism, both sender and receiver agree on the number of data-frames after which the acknowledgement should be sent.
• Stop and wait flow control mechanism wastes resources, this protocol tries to make use of underlying resources as much as possible.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

13

• Error Control
• When data-frame is transmitted, there is a probability that data-frame may be lost in the transit or it is received corrupted.
• In both cases, the receiver does not receive the correct data-frame and sender does not know anything about any loss.
• In such case, both sender and receiver are equipped with some protocols which helps them to detect transit errors such as loss of data-frame.
• Hence, either the sender retransmits the data-frame or the receiver may request to resend the previous data-frame.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

14

• Requirements for error control mechanism:
• Error detection  - The sender and receiver, either both or any, must ascertain that there is some error in the transit.
• Positive ACK  - When the receiver receives a correct frame, it should acknowledge it.
• Negative ACK  - When the receiver receives a damaged frame or a duplicate frame, it sends a NACK back to the sender and the sender must retransmit the correct frame.
• Retransmission:  The sender maintains a clock and sets a timeout period. If an acknowledgement of a data-frame previously transmitted does not arrive before the timeout the sender retransmits the frame, thinking that the frame or it’s acknowledgement is lost in transit.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

15

• There are three types of techniques available which Data-link layer may deploy to control the errors by Automatic Repeat Requests (ARQ):

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

16

• The following transition may occur in Stop-and-Wait ARQ:
• The sender maintains a timeout counter.
• When a frame is sent, the sender starts the timeout counter.
• If acknowledgement of frame comes in time, the sender transmits the next frame in queue.
• If acknowledgement does not come in time, the sender assumes that either the frame or its acknowledgement is lost in transit. Sender retransmits the frame and starts the timeout counter.
• If a negative acknowledgement is received, the sender retransmits the frame.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

17

• Go-Back-N ARQ
• Stop and wait ARQ mechanism does not utilize the resources at their best.
• When the acknowledgement is received, the sender sits idle and does nothing. In Go-Back-N ARQ method, both sender and receiver maintain a window.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

18

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

19

• The sending-window size enables the sender to send multiple frames without receiving the acknowledgement of the previous ones. The receiving-window enables the receiver to receive multiple frames and acknowledge them. The receiver keeps track of incoming frame’s sequence number.
• When the sender sends all the frames in window, it checks up to what sequence number it has received positive acknowledgement. If all frames are positively acknowledged, the sender sends next set of frames. If sender finds that it has received NACK or has not receive any ACK for a particular frame, it retransmits all the frames after which it does not receive any positive ACK.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

20

• Selective Repeat ARQ
• In Go-back-N ARQ, it is assumed that the receiver does not have any buffer space for its window size and has to process each frame as it comes.
• This enforces the sender to retransmit all the frames which are not acknowledged.
• In Selective-Repeat ARQ, the receiver while keeping track of sequence numbers, buffers the frames in memory and sends NACK for only frame which is missing or damaged.
• The sender in this case, sends only packet for which NACK is received.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

21

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

22

HDLC Protocol�

• HDLC (High-Level Data Link Control) is a bit-oriented protocol that is used for communication over the point-to-point and multipoint links.
• This protocol implements the mechanism of ARQ(Automatic Repeat Request). With the help of the HDLC protocol, full-duplex communication is possible.
• HDLC is the most widely used protocol and offers reliability, efficiency, and a high level of Flexibility.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

23

• In order to make the HDLC protocol applicable for various network configurations, there are three types of stations and these are as follows:
• Primary Station�This station mainly looks after data like management. In the case of the communication between the primary and secondary station; it is the responsibility of the primary station to connect and disconnect the data link. The frames issued by the primary station are commonly known as commands.
• Secondary Station�The secondary station operates under the control of the primary station. The Frames issued by the secondary stations are commonly known as responses.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

24

• Combined Station�The combined station acts as both Primary stations as well as Secondary stations. The combined station issues both commands as well as responses.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

25

• Transfer Modes in HDLC
• The HDLC protocol offers two modes of transfer that mainly can be used in different configurations. These are as follows:
• Normal Response Mode(NRM)
• Asynchronous Balance Mode(ABM)

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

26

• 1. Normal Response Mode(NRM)
• In this mode, the configuration of the station is unbalanced. There are one primary station and multiple secondary stations. Where the primary station can send the commands and the secondary station can only respond.
• This mode is used for both point-to-point as well as multiple-point links.

​

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

27

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

28

• 2. Asynchronous Balance Mode(ABM)
• In this mode, the configuration of the station is balanced. In this mode, the link is point-to-point, and each station can function as a primary and as secondary.
• Asynchronous Balance mode(ABM) is a commonly used mode today.

​

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

29

• HDLC Frames
• In order to provide the flexibility that is necessary to support all the options possible in the modes and Configurations that are just described above. There are three types of frames defined in the HDLC:
• Information Frames(I-frames)�These frames are used to transport the user data and the control information that is related to the user data. If the first bit of the control field is 0 then it is identified as I-frame.
• Supervisory Frames(S-frames)�These frames are only used to transport the control information. If the first two bits of the control field are 1 and 0 then the frame is identified as S-frame
• Unnumbered Frames(U-Frames)�These frames are mainly reserved for system management. These frames are used for exchanging control information between the communicating devices.
• Each type of frame mainly serves as an envelope for the transmission of a different type of message.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

30

Frame Format�

• There are up to six fields in each HDLC frame. There is a beginning flag field, the address field then, a control field, an information field, a frame check sequence field(FCS), and an ending field.
• In the case of the multiple-frame transmission, the ending flag of the one frame acts as the beginning flag of the next frame.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

31

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

32

• 1. Flag Field
• This field of the HDLC frame is mainly a sequence of 8-bit having the bit pattern 01111110 and it is used to identify the beginning and end of the frame. The flag field mainly serves as a synchronization pattern for the receiver.
• 2. Address Field
• It is the second field of the HDLC frame and it mainly contains the address of the secondary station. This field can be 1 byte or several bytes long which mainly depends upon the need of the network. In case if the frame is sent by the primary station, then this field contains the address(es) of the secondary stations. If the frame is sent by the secondary station, then this field contains the address of the primary station.

​

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

33

• 3. Control Field
• This is the third field of the HDLC frame and it is a 1 or 2-byte segment of the frame and is mainly used for flow control and error control. Bits interpretation in this field mainly depends upon the type of the frame.
• 4. Information Field
• This field of the HDLC frame contains the user's data from the network layer or the management information. The length of this field varies from one network to another.
• 5. FCS Field
• FCS means Frame check sequence and it is the error detection field in the HDLC protocol. There is a 16 bit CRC code for error detection.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

34

Features of HDLC Protocol�

• 1.This protocol uses bits to stuff flags occurring in the data.
• 2.This protocol is used for point-to-point as well as multipoint link access.
• 3.HDLC is one of the most common protocols of the data link layer.
• 4.HDLC is a bit-oriented protocol.
• 5.This protocol implements error control as well as flow control.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

35

Medium Access Sub layer

• To coordinate the access to the channel, multiple access protocols are requiring. All these protocols belong to the MAC sub layer.
• Data Link layer is divided into two sub layers:
• 1. Logical Link Control (LLC)- is responsible for error control & flow control.
• 2. Medium Access Control (MAC)- MAC is responsible for multiple access resolutions.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

36

THE CHANNEL ALLOCATION PROBLEM

• In broadcast networks, single channel is shared by several stations. This channel can be allocated to only one transmitting user at a time.
• There are two different methods of channel allocations:
• 1. Static Channel Allocation- a single channel is divided among various users either on the basis of frequency (FDM) or on the basis of time (TDM). In FDM, fixed frequency is assigned to each user, whereas, in TDM, fixed time slot is assigned to each user.
• 2. Dynamic Channel Allocation- no user is assigned fixed frequency or fixed time slot. All users are dynamically assigned frequency or time slot, depending upon the requirements of the user.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

37

• MULTIPLE ACCESS PROTOCOLS
• Many protocols have been defined to handle the access to shared link.
• These protocols are organized in three different groups:
• Random Access Protocols
• Controlled Access Protocols
• Channelization Protocols

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

38

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

39

Random Access Protocols

• There is no rule that decides which station should send next. If two stations transmit at the same time, there is collision and the frames are lost.
• The various random access methods are:
• 1. ALOHA
• 2. CSMA (Carrier Sense Multiple Access)
• 3. CSMA/CD (Carrier Sense Multiple Access with Collision Detection)
• 4. CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

40

• ALOHA
• ALOHA was developed at University of Hawaii in early 1970s by Norman Abramson.
• It was used for ground based radio broadcasting. In this method, stations share a common channel. When two stations transmit simultaneously, collision occurs and frames are lost.
• There are two different versions of ALOHA:
• Pure ALOHA
• Slotted ALOHA

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

41

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

42

• Pure ALOHA

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

43

• In pure ALOHA, stations transmit frames whenever they have data to send.
• When two stations transmit simultaneously, there is collision and frames are lost. In pure ALOHA, whenever any station transmits a frame, it expects an acknowledgement from the receiver.
• If acknowledgement is not received within specified time, the station assumes that the frame has been lost.
• If the frame is lost, station waits for a random amount of time and sends it again. This waiting time must be random; otherwise, same frames will collide again and again.
• Whenever two frames try to occupy the channel at the same time, there will be collision and both the frames will be lost. If first bit of a new frame overlaps with the last bit of a frame almost finished, both frames will be lost and both will have to be retransmitted.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

44

• Slotted ALOHA
• Slotted ALOHA was invented to improve the efficiency of pure ALOHA. In slotted
• ALOHA, time of the channel is divided into intervals called slots. The station can send a frame only at the beginning of the slot and only one frame is sent in each slot.
• If any station is not able to place the frame onto the channel at the beginning of the slot, it has to wait until the next time slot. There is still a possibility of collision if two stations try to send at the beginning of the same time slot.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

45

Overview of IEEE Standard 802 for LANS and MANS

• IEEE 802 is an Institute of Electrical and Electronics Engineers (IEEE) standard set that covers the physical and data link layers of the Open Systems Interconnection (OSI) model.
• It defines standards and protocols for wired local area networks (WLAN), metropolitan area networks (MAN) and wireless networks; defines characteristics, operating procedures, protocols and services for networks that carry variable sized packets and specifies the development and handling of compatible devices and equipment.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

46

• IEEE 802 is comprised of standards with separate working groups that regulate different communication networks, including IEEE 802.1 for bridging (bottom sublayer), 802.2 for Logical link (upper sublayer), 802.3 for Ethernet, 802.5 for token ring, 802.11 for Wi-Fi, 802.15 for Wireless Personal area networks, 802.15.1 for Bluetooth, 802.16 for Wireless Metropolitan Area Networks etc.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

47

• Ethernet: The original Ethernet was created in 1976 and since then, it has gone through four generations.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

48

• Ethernet is a family of computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN).
• Systems using Ethernet communication divide data streams into packets, which are known as frames.
• Frames include source and destination address information, as well as mechanisms used to detect errors in transmitted data and retransmission requests.
• An Ethernet cable is the physical, encased wiring over which the data travels. Compared to wireless LAN technology, Ethernet is typically less vulnerable to disruptions.
• It can also offer a greater degree of network security and control than wireless technology, as devices must connect using physical cabling, making it difficult for outsiders to access network data or hijack bandwidth for unsanctioned devices.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

49

• Token Ring:
• Token ring is the IEEE 802.5 standard for a token-passing ring in Communication networks.
• A ring consists of a collection of ring interfaces connected by point-to-point lines i.e. ring interface of one station is connected to the ring interfaces of its left station as well as right station.
• Internally, signals travel around the Communication network from one station to the next in a ring. These point-to-point links can be created with twisted pair, coaxial cable or fiber optics.
• Each bit arriving at an interface is copied into a 1-bit buffer. In this buffer the bit is checked and may be modified and is then copied out to the ring again. This copying of bit in the buffer introduces a 1-bit delay at each interface.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

50

• Token Ring is a LAN protocol defined in the IEEE 802.5 where all stations are connected in a ring and each station can directly hear transmissions only from its immediate neighbor.
• Permission to transmit is granted by a message (token) that circulates around the ring.
• A token is a special bit pattern (3 bytes long). There is only one token in the network. Token-passing networks move a small frame, called a token, around the network. Possession of the token grants the right to transmit.
• If a node receiving the token in order to transmit data, it seizes the token, alters 1 bit of the token (which turns the token into a start-of-frame sequence), appends the information that it wants to transmit, and sends this information to the next station on the ring.
• Since only one station can possess the token and transmit data at any given time, there are no collisions.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

51

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

52

Two examples of Token Ring networks

1. Using a single MAU
2. b) Using several MAUs connected to each other

Introduction to Wireless Network:

• A wireless network is a computer network that uses wireless data connections between network nodes i.e. not connected by cables of any kind.
• The use of a wireless network enables enterprises to avoid the costly process of introducing cables into buildings or as a connection between different equipment locations.
• The basis of wireless systems are radio waves, an implementation that takes place at the physical level of network structure.
• Examples of wireless networks include cell phone networks, Bluetooth, wireless local area networks (WLANs), wireless sensor networks, satellite communication networks etc.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

53

• There are four main types of wireless networks:
• • Wireless Local Area Network (LAN): Links two or more devices using a wireless distribution method, providing a connection through access points to the wider Internet.
• • Wireless Metropolitan Area Networks (MAN): Connects several wireless LANs.
• • Wireless Wide Area Network (WAN): Covers large areas such as neighboring towns and cities.
• • Wireless Personal Area Network (WPAN): Interconnects devices in a short span, generally within a person’s reach.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

54

• Wireless networks offer the following productivity, convenience, and cost advantages over traditional wired networks:

​

• Mobility: provide mobile users with access to real-time information so that they can roam around in the network without getting disconnected from the network. This mobility supports productivity and service opportunities not possible with wired networks.
• • Installation speed and simplicity: installing a wireless system can be fast and easy and can eliminate the need to pull cable through walls and ceilings.
• • Reach of the network: the network can be extended to places which cannot be wired.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

55

• More Flexibility: wireless networks offer more flexibility and adapt easily to changes in the configuration of the network.
• • Reduced cost of ownership: while the initial investment required for wireless network hardware can be higher than the cost of wired network hardware, overall installation expenses and life-cycle costs can be significantly lower in dynamic environments.
• • Scalability: wireless systems can be configured in a variety of topologies to meet the needs of specific applications and installations. Configurations can be easily changed and range from peer-to-peer networks suitable for a small number of users to large infrastructure networks that enable roaming over a broad area.

​

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

56

Introduction to Bridge, Switch and Router:

• Bridge – A bridge operates at data link layer. A bridge is a repeater, with add on functionality of filtering content by reading the MAC addresses of source and destination. It is also used for interconnecting two LANs working on the same protocol. It has a single input and single output port, thus making it a 2-port device.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

57

• Types of Bridges:
• Transparent Bridges: - These are the bridge in which the stations are completely unaware of the bridge’s existence i.e. whether or not a bridge is added or deleted from the network, reconfiguration of the stations are unnecessary.
• These bridges make use of two processes i.e. bridge forwarding and bridge learning.
• Source Routing Bridges: - In these bridges, routing operation is performed by source station and the frame specifies which route to follow. The hot can discover frame by sending a special frame called discovery frame, which spreads through the entire network using all possible paths to destination.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

58

• Switch – A switch is a multi-port bridge with a buffer and a design that can boost its efficiency (large number of ports imply less traffic) and performance. Switch is data link layer device. Switch can perform error checking before forwarding data, that makes it very efficient as it does not forward packets that have errors and forward good packets selectively to correct port only. In other words, switch divides collision domain of hosts, but broadcast domain remains same.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

59

• Routers – A router is a device like a switch that routes data packets based on their IP addresses. Router is mainly a Network Layer device.
• Routers normally connect LANs and WANs together and have a dynamically updating routing table based on which they make decisions on routing the data packets.
• Router divide broadcast domains of hosts connected through it.

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

60

Department of Electrical and Electronics Engineering, BVCOE New Delhi Subject: IDCN, Instructor: Dr.SUDHA.K

61