Chương 2

Mạng Ethernet là một mạng cục bộ (LAN) sử dụng công nghệ Ethernet để kết nối các thiết bị điện tử với nhau. Ethernet là một họ các tiêu chuẩn định nghĩa cách truyền dữ liệu qua cáp xoắn đôi hoặc cáp quang. Các thiết bị được kết nối với mạng Ethernet thường bao gồm máy tính, máy tính xách tay, máy in, máy chủ và thiết bị định tuyến.

 Cơ bản về mạng

What Is a Network?

A network is a connected collection of devices that can

communicate with each other Networks carry data in many kinds

of environments, including homes, small businesses, and large enterprises

Common Physical Components of a Network

Interpreting a Network

Diagram

Network User Applications

 Web browser (IE, Firefox, and so on)

 Instant messaging (Yahoo IM, Microsoft Messenger, and so on)

 Collaboration (Whiteboard, Netmeeting, WebEx, and so on)

 Databases (file servers)

Impact of User Applications

on the Network

 Batch applications

 FTP, TFTP, inventory updates

 No direct human interaction

 Bandwidth important, but not

 Because a human is waiting for a

response, response time is important but not critical, unless the wait becomes excessive.

Physical Topology Categories

Logical Topologies

Bus Topology

All devices receive the signal.

Star Topology

Transmission through a central point.

Single point of failure.

Extended-Star Topology

More resilient than star topology.

Ring Topology

Signals travel around ring.

Single point of failure.

Dual-Ring Topology

Signals travel in opposite directions.

More resilient than single ring.

Full-Mesh Topology

Highly fault-tolerant

Partial-Mesh Topology

Trade-off between fault tolerance and cost

Connection to the Internet

Local Area Network

LAN Sizes

2.1 Giới thiệu về mạng

Ethernet.

started a project, called Project 802, to set

standards to enable intercommunication

among equipment from a variety of

manufacturers Project 802 does not seek to replace any part of the OSI or the Internet

model Instead, it is a way of specifying

functions of the physical layer and the data

2.1 Giới thiệu về mạng

Ethernet.

into two sublayers: logical link control

(LLC) and media access control (MAC).

IEEE has also created several physical layer standards for different LAN protocols.

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2.1 Giới thiệu về mạng

Ethernet.

traditional OSI model

LAN Standards

2.1 Giới thiệu về mạng Ethernet.

2.1 Giới thiệu về mạng

Ethernet.

 Data Link Layer:

1)Logical Link Control (LLC) :

 In IEEE Project 802, flow control, error control, and part of the framing duties are collected into one sublayer called the

logical link control

 The LLC provides one single data link control protocol for all IEEE LANs.

 A single LLC protocol can provide interconncctivity between different LANs because it makes the MAC sublayer transparent.

 The purpose of the LLC is to provide flow and error control for the upper layer protocols that actually demand these

2.1 Giới thiệu về mạng

Ethernet.

 IEEE Project 802 has created a sublayer called

media access control that defines the specific access method for each LAN

 For example, it defines CSMA/CD as the media

access method for Ethernet LANs and the token

passing method for Token Ring and Token Bus

LANs

 In contrast to the LLC sublayer, the MAC sublayer contains a number of distinct modules; each defines the access method and the framing format specific to the corresponding LAN protocol.

MAC Address Components

2.1 Giới thiệu về mạng

Ethernet.

MAC addresses:

2.1 Giới thiệu về mạng

Ethernet.

on the implementation and type of physical

specifications for each LAN implementation.

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Ethernet Evolution 2.1 Giới thiệu về mạng

Ethernet.

CSMA/CD

Ethernet Frame Structure

Communicating Within the

LAN

2.1 Giới thiệu về mạng

Ethernet.

1) Standard Ethernet :

2.1 Giới thiệu về mạng

Ethernet.

- Frame Length :

2.1 Giới thiệu về mạng

Ethernet.

- Addressing : Each station on an Ethernet network (such as a

PC, workstation, or printer) has its own network interface card (NIC) The NIC fits inside the station and provides the station with a 6-byte physical address.

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Example of an Ethernet address in hexadecimal notation:

2.1 Giới thiệu về mạng

Ethernet.

Unicast, Multicast, and Broadcast Addresses: A source address is always a unicast address-the frame comes from only one station The destination address, however, can be unicast, multicast, or broadcast.

2.1 Giới thiệu về mạng

Ethernet.

- Access Method: CSMA/CD

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2.1 Giới thiệu về mạng

Ethernet.

2.1 Giới thiệu về mạng

Ethernet.

 Encoding in a Standard Ethernet implementation:

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2.1 Giới thiệu về mạng

Ethernet.

2) Fast Ethernet

The goals of Fast Ethemet can be summarized:

 Upgrade the data rate to 100 Mbps.

 Make it compatible with Standard Ethernet.

 Keep the same 48-bit address.

 Keep the same frame format.

 Keep the same minimum and maximum frame lengths.

2.1 Giới thiệu về mạng

Ethernet.

 MAC Sublayer

-Autonegotiation: is a new feature added to Fast

negotiate the mode or data rate of operation

- Autonegotiation was designed particularly for the following purposes:

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2.1 Giới thiệu về mạng

Ethernet.

-Implementation

2.1 Giới thiệu về mạng

Ethernet.

-Encoding

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 Upgrade the data rate to 1 Gbps.

 Make it comoatible with Standard or Fast Ethernet.

 Use the same 48-bit address.

 Use the same frame format.

 Keep the same minimum and maximum frame lengths.

 To support autonegotiation as defined in Fast Ethernet

 The maximum length of the cable is determined by the signal attenuation in the cable

 The half-duplex approach uses CSMA/CD.

 The maximum length of the network in this approach is totally dependent on the minimum frame size Three methods have been defined: traditional, carrier extension, and frame bursting

2.1 Giới thiệu về mạng

Ethernet.

-Implementation

2.1 Giới thiệu về mạng

Ethernet.

-Encoding

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2.2 Kết nối mạng cục bộ

Ethernet.

-Passive hub is just a connector.

-Passive hub connects the wires coming from different branches.

- In a star-topology Ethemet LAN, a passive hub is just a point where the signals coming from different stations collide; the hub is the collision point This type of a hub is part of the media; its location in the Internet model is below the physical layer.

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2.2 Kết nối mạng cục bộ

Ethernet.

-A repeater connects segments of a LAN

capability

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2.2 Kết nối mạng cục bộ

Ethernet.

2.2 Kết nối mạng cục bộ

Ethernet.

repeater It is normally used to create connections between stations in a physical star topology Hubs can also be used to create multiple levels of hierarchy

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addresses in a frame

2.2 Kết nối mạng cục bộ

Ethernet.

 Routers

A router is a three-layer device that routes packets

based on their logical addresses (host-to-host addressing) A router normally connects LANs and WANs in the Internet and has a routing table that is used for making decisions about the route The routing tables are normally dynamic and are updated using routing protocols

be connected to another network using the Internet model The gateway connecting the two systems can take a frame as

it arrives from the first system, move it up to the OSI application layer, and remove the message

2.2 Kết nối mạng cục bộ

Ethernet.

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 Operate at Layer 2 of the OSI model

 Forward, filter, or flood frames

 Have few ports



2.2 Kết nối mạng cục bộ

Ethernet.

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LAN Switch

 High port density

 Large frame buffers

 Mixture of port speeds

 Fast internal switching

 Switching modes:

– Cut-through

– Store-and-forward

– Fragment-free

2.2 Kết nối mạng cục bộ

Ethernet.

Transmitting Frames through a Switch

2.2 Kết nối mạng cục bộ

Ethernet.

How Switches Learn Host Locations

2.2 Kết nối mạng cục bộ

Ethernet.

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• Station A sends a frame to Station C

• Switch caches station A MAC address to port E0 by learning the source address of data frames

• The frame from station A to station C is flooded out to all ports except port E0 (unknown unicasts are flooded)

2.2 Kết nối mạng cục bộ

Ethernet.

• Station D sends a frame to station C

• Switch caches station D MAC address to port E3 by learning the source Address of data frames

• The frame from station D to station C is flooded out to all

ports except port E3 (unknown unicasts are flooded)

2.2 Kết nối mạng cục bộ

Ethernet.

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How Switches Filter Frames

• Station A sends a frame to station C

• Destination is known, frame is not flooded

2.2 Kết nối mạng cục bộ

Ethernet.

Broadcast and Multicast Frames

• Station D sends a broadcast or multicast frame

• Broadcast and multicast frames are flooded to all ports other than the originating port

2.2 Kết nối mạng cục bộ

Ethernet.

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Loops

2.2 Kết nối mạng cục bộ

Ethernet.

Spanning tree protocol

2.4 Quá trình phân phối gói tin

từ host to host thông qua switch

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Layer 2 Addressing

Assigned to end devices

Layer 3 Devices and Their

Function

The network layer provides connectivity and

path selection between two host systems.

In the host, this is the path between the data link layer and the upper layers of the NOS

In the router, it is the actual path across the

network

Layer 3 Addressing

OSI uses NSAP

TCP/IP uses IP

Host-to-Host Packet Delivery

(1 of 10) -UDP

Host-to-Host Packet Delivery

(2 of 10)

Host-to-Host Packet Delivery

(3 of 10)

Host-to-Host Packet Delivery

(4 of 10)

Host-to-Host Packet Delivery

(5 of 10)

Host-to-Host Packet Delivery

(6 of 10)

Host-to-Host Packet Delivery

(7 of 10)

Host-to-Host Packet Delivery

(8 of 10)

Host-to-Host Packet Delivery

(9 of 10)

Host-to-Host Packet Delivery

(10 of 10)

Host-to-Host Packet Delivery

(1 of 22)-TCP

Host-to-Host Packet Delivery

(2 of 22)

Host-to-Host Packet Delivery

(3 of 22)

Host-to-Host Packet Delivery

(4 of 22)

Host-to-Host Packet Delivery

(5 of 22)

Host-to-Host Packet Delivery

(6 of 22)

Host-to-Host Packet Delivery

(7 of 22)

Host-to-Host Packet Delivery

(8 of 22)

Host-to-Host Packet Delivery

(9 of 22)

Host-to-Host Packet Delivery

(10 of 22)

Host-to-Host Packet Delivery

(11 of 22)

Host-to-Host Packet Delivery

(12 of 22)

Host-to-Host Packet Delivery

(13 of 22)

Host-to-Host Packet Delivery

(14 of 22)

Host-to-Host Packet Delivery

(15 of 22)

Host-to-Host Packet Delivery

(16 of 22)

Host-to-Host Packet Delivery

(17 of 22)

Host-to-Host Packet Delivery

(18 of 22)

Host-to-Host Packet Delivery

(19 of 22)

Host-to-Host Packet Delivery

(20 of 22)

Host-to-Host Packet Delivery

(21 of 22)

Host-to-Host Packet Delivery

(22 of 22)

Default Gateway