Computer Networking Note1

8/13/2019 Computer Networking Note1

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Computer Networking

a Top-Down Approach Featuring the Internet

Chapter1: Computer Networks and the In ternet

Introduction Chapter goal

get context, overview, and feel of computer networking more depth, detail laterin the course approach:

descriptive use I nternetas example

This chapter describes the overall computer network and Internet, and its purpose is through the computernetwork / Internet composition, critical understanding of computer network technology, the overall situation (see theforest through the trees.) Same time, involving more involved in the knowledge point, this chapter also guide the

introduction of the specific details will be given in later chapters.

Roadmap What is the Internet? The Network edge The Network core Access networks and physical media ISPs and Internet backbones Delay & loss in packet-switched networks Protocol layers and their service models History of networking and the Internet

First, from two perspectives to understand what Internet: Internet and the specific composition of the servicesprovided, as well as the concept of network protocols.Part of the learning at the network edge-to-end systems, network applications, architecture, connectionless andconnection-oriented services and so on.Section involving the computer network switching technology, which circuit switching and packet switching, andcomputer network of the type / classification.Access network to learn the classification of the fourth quarter, the main form of access networks and physicalmedia.Part of the ISP and Internet backbone connection between the compositions of the Internet to learn the structure ofISP.Section VI study the delay in packet switched networks and packet loss, delay involved in the type of packet losscaused by the main reason.VII, the main contents on computer networks / Internet architecture, namely, computer network protocols accordingto levels of components, layers and protocols is a collection of network architecture.The last part is about the development of computer networks and Internet history. Their own learning.

1.1Whats the Internet? Nuts-and-bolts description

The basichardwareand softwarecomponents that make up the Internet. Computing devices, communication links, switches

A service description Describing the Internet in terms of a networking inf rastructurethat provides servicesto distributed

applications. Connection-oriented reliable service Connectionless unreliable service

Internet difficult word to define. We introduce the following two perspectives from what is the Internet.1, nuts and bolts: "Nuts and bolts" of the internet is the basic hardware and software components that make up the

Internet.

2, service-oriented view: describing the Internet in terms of a networking infrastructure that provides services todistributed applications.


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1 A Nuts-and-Bolts view

End systems public Internet is a worldwidecomputer networkthat connects millions of computing devices

Pcsworkstations, servers, PDAs phones, even toasters.

hosts The term computer networkis being to sound a bit dated!Public Internet is a global computer network, connected to the distribution in many parts of the world's

computing devices (Computing devices), such as traditional PC, Unix-based workstations and servers, PDA, mobilephones, environmental sensing equipment, and even home appliances (household appliances) and other equipment.

Thus, in a sense, Computer Networks concept some old, out of date.All of these Computing devices are called host or end system. Currently, the number of Internet hosts has nearly

500 million.

Host Count in the Internet

communication l inks connect the end systems together to form a network Fiber, copper, radio, satellite transmission rate: bits per second (bps)

End systems are usually connected to each other through packet switches. forwardarrival packetsfrom input to output

A packet is a chunkof data. Router andLi nk-layer switch

forward packets thru network according to the value of header field


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Packet switches packets arriving from the input link from the output link forwards them.

Packet switch there are two categories, one is called a router, a class called the link layer switches. The role ofthe two similar groups are forwarded, the difference is forwarding packets based on different information. Router'sIP address according to packet forwarding packets, link layer packet switch according to the destination MACaddress to forward packets.

Example-A Packet

route/ path

li nks and switches sequencethat a packet traversed from a source to the destination endsystem

In the Internet, the routeis dynamic, and not dedicated. packet switching

Allows multiple communicating end systems to sharea link, a switch, or the whole path.

Routing and path: packet from sender to receiver through the transmission process of the sequence ofcommunication links and switches.

Packet Switched Network (Packet Switching Network), this path is not fixed, but dynamic, that is, between the

source and destination host may send multiple packets.

End system access the Internet through theI SP. Internet Service Provider Each ISP is a networkof packet switchesand communication l inks.

Protocolscontrol the sending and receiving of information within the Internet. Protocols are rules must be obeyed. TCP/IP

TCP: transmission control protocol IP: Internet protocol

Internet standards RFC:Request for comments IETF: Internet Engineering Task Force IEEE:Institute of Electrical and Electronics Engineers

Protocol: the two sides abide by the rules of communication, mainly used to specify the packet format, and

each packet is received after the implementation of the action

collectively referred to as Internet Protocol TCP / IP protocols, including TCP, IP, DNS, HTTP, PPP, etc.Protocol for the Internet is extremely important, the organizations responsible for developing protocol standards are:

IETF Internet Engineering Task Force RFC: Request for CommentsIEEE (Institute of Electrical and Electronics Engineers): IEEE802.3


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public I nternetvs. private in tranet Internetis a network of networks public Internet:the network that one typically refers to astheInternet, that is, the global network of

networks extranet

private Internet:heir hosts cannot exchange messages with hosts outside of the private network intranet

Brief summary

End systems/hosts Communication links Packet switches Route or Path ISP Protocols Public Internet and private Intranet

2A Service Description The Internet enables distributedapplications

WWW, email, e-commerce, database, voting, Everything over I P! connection-oriented reliable service

guarantees that data transmitted from a sender to a receiver will eventually be delivered tothe receiver in order and in its entirety

Connectionless unreliable service without any guarantees about the eventually delivery

Internet allows distributed applications running on their end systems to communicate with each other, with the"Everything over IP" the trend, more and more types of network applications. For example, Web surfing, instantmessaging (QQ, MSN, etc.), Video-on-demand, streaming media and so on.

Internet services provided in two ways:Reliable connection-oriented service: to ensure that from the sender sends the data to the receiver will

eventually order to reach the receiver intactConnectionless unreliable service: does not provide any guarantee for the transmissionThe current Internet provides only a service model, "best effort": the network to do their best to transfer the

application packet, but not a packet transmission delay without any warranty. Internet is also not willing to pay morefor the users with better service. The Internet without QoS (Quality of Service) capabilities.

3Whats a protocol?human protocols:

Whatsthe time? I have a question Introductionsthere are specific msgswe send, and specific actionswe take in response to the received reply msgs orother events

What's a protocol? Protocol is a buzzword in computer networkingwhat does a protocol do?

To facilitate understanding of the term protocol, we take the example of people talking to each other toexplain. For example: Inquiry time, ask questions.

Clearly, the message sent or received and when these messages are sent or received when the action taken, inthe human protocol plays the most important role. If you talk to both sides saying the other side cannotunderstand the language, you cannot communicate, which is the same network protocol, but received not a

human entity to send a message, but in the host's hardware and software entities only.

Network protocols: machines, rather than humans, exchange msgs all communication activity in Internet governed by protocols

Protocols define format,orderof msgs exchanged between network entities, and actionstaken on msg transmission,receipt or other events


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Humanprotocol and computernetworkprotocol:

1.1Whats the Internet?-summary Nuts-and-bolts description

The basichardwareand softwarecomponents that make up the Internet. A service description

Describing the Internet in terms of a networking inf rastructurethat provides servicesto distributedapplications.

Protocols Define format, orderof msgs exchanged between network entities, andactionstaken on msg

transmission, receipt or other events.1-2 The Network edge

Introduction

network edge: hosts and applications services

network core: routers and switches Circuit/Packet switching

access networks, physical media: physical media access types

The edge of the network, we understand the main host, applications, etc., we also detail connectionless andconnection-oriented services. In the network and the core part, the main understanding of circuit switching andpacket switching technology, multiplexing. Part in the access network, we mainly need to understand the way access

networks and access networks using a variety of physical media

1 End systems

Computersconnected to the Internet are referred to as end systems. sit at the edge of the Internet Run application programs, so also referred to as host.

e.g., WWW, email Access to the Internet computer (computing device) in the network at the end is generally called the end

system. End system is also called the host, because they hold the application.

1 Clients, and Servers

Two categories of hosts : Clientsand Servers Cli ent (program)host requests, receives service from server (program) Client/Server Internet applications are distr ibuted applications

Client program runs on one PC, and the server program runs on anotherPC.


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Host client and server are generally divided into two categories. Clients refer to the processing power ingeneral, request and receive resources or services equipment; and the server refers to have a strong capacity toprovide resources or services equipment. This client-server model is the most mainstream of the web applicationmodel, this time; Internet can be seen as a black box.

Peer to Peer model (P2P)

host interaction symmetric e.g.:

teleconferencing emule

In fact, a host can be both a client and a server; even both client and server. For example, in P2P, a host ofother peers as a client to request resources or services to another host and can provide resources or services.

2Services End system programs use the servicesof the Internet to exchange messages.

Connectionless service UDP:user datagram protocol User Datagram Protocol

Connection-orientedservice TCP:transmission control protocol Transmission Control Protocol

End system using the Internet to communicate with each other provided services. The Internet provides two

types of services:Connection-oriented: the communicating parties before a formal data transmission to send control packets to

establish a connection establish and notify the parties about the connection status. The relationship between thecommunicating parties to establish a relatively loose, packet transmission path / route through which the packetswitches are not maintenance-related condition, which is called "connection-oriented" and not directly called

"Connect" service reasons.Connectionless Service: connectionless service. No handshake.

2Connection-Oriented Service Connection-Or iented service

handshaking setup (prepare for) data transfer ahead Sends control packetsto each other to establi sh the connection.

end system al locates resour ces for the connection buffer/bandwidth/states

Whyconnection-or ientedand notjustconnection? Connection established between hosts is very looseand only the end systems are aware of the

connection.

Only the end system allocates buffers, state, fort the connection TCP

reliable, in-order byte-streamdata transfer Connection is equivalent to a water pipe loss: acknowledgements and retransmissions

fl ow control: a sender wont overwhelm the receiver

Congestion Contr ol senders slow down sending rate when network congested


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TCP (Transmission Control Protocol, Transmission Control Protocol) is a connection-oriented protocol, beforethe data transmission through three-way handshake to establish a full duplex connection, before the real data.

In addition to TCP is a connection-oriented protocol, but also to provide reliable, on-demand to reach the bytestream data transfer, flow control and congestion control.

1, reliable - in sequence - a stream of bytes transmitted: through the recognition and retransmission to ensurereliable data transmission; TCP entity in order to submit the application data; each byte has its own number, butwhether each byte meaning.

2, flow control: The main thing to avoid low-end system will not be sending data to the end overwhelmed. The

basic mechanism is the buffer.3, congestion control: to avoid the network into a state called Gridlock, which detects when the network iscongested conditions to reduce their sending rate.

Gridlock is a situation that ultimately comes from a region such that all intersections are blocked by vehicles,

no vehicle can move such a state; dining philosophers problem with this possibility.

2Connectionless Service Connectionless Service = no handshaking UDP (User Datagram Protocol)

Connectionless service is sending the data connection is not established before the process of application tosend data on what time to send data, so applications using this service, the data from the source to the target side of

the time may be short. However, this service generally does not guarantee reliable data transmission, does notprovide flow control and congestion control. Generally not used to losing some of the lethal effects of dataapplications such as IP telephony, video conferencing.

2Services TCP or UDP?

Apps using TCP WWW, FTP, E-mail

Apps using UDP Internet Phone, video-conferencing

If the apps want control whatandwhenthe data sent, choose UDP.

If apps want reliable data transfer, choose TCP.Summary End systems/hostsare sit at the edgeof the Internet, and host applications.

Client/Server P2P

End systems use the servicesof the Internet to send msgs to each other Connection-oriented serviceTCP Connectionless serviceUDP

Applications choose transport service according to their requirements.

1-3 The Network core

Introduction

Network coreis a meshof routers and links that interconnectthe hosts.

The main task of the core network from the edge of the network to reach its

destination packet forwarding. For the network core switching technology is mainly two:

1. Switching techniques

Two approaches to build a network core circui t switching:dedicatedcircuitper call

telecommunication network packet-switching:data sent thru net in discrete chunks (packets)

Internet


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Circuit Switched (circuit switching): In the communication process, the network for data

transmission in the transmission path reserve resources, these resources can only be the Communication

used by both sides; Packet switching (packet switching): Data is divided into a one group, each group have

to carry the destination address, not for the packet transmission network in Reserve resources along the

packet switches, packet switches for each packet independently to determine the forwarding direction.

Circuit Switching Reserveresources needed along a path for any call for the duration of the session.

bandwidthand/or switch capacity dedicatedresources allocation guaranteedperformance call setuprequired

Circuit switching network, communicating parties must be established before sending data in a dedicatedcircuit, to reserve resources along the way, including bandwidth and switching capacity

Packet Switchi ng Resources are used on demand Resources are sharedwith other sessions Noperformance guarantee

Circuit Switching

For circuit-switched technology brief.The slide chart:

1) the use of four four-link circuit switches to connect to the network. Each link has n circuits (circuit),

can support n-connected.2) Host and a switch. When two hosts pre-communication, the network between the host to establish a

dedicated end to end connection. For example, the host communication between A and B before, eachlink in the network first reserve a circuit (circuit).

3) As a link up to the n circuits, each circuit using the link bandwidth 1 / n.

Multiplexing in Circuit Switched Networks

There are lots of circuitsin a link. How to implement a circuit? network resources (e.g., bandwidth) divided into pieces

a piece allocated to one call resource piece idleif not used by the owning call (no sharing)

In a physical link on a number of circuits (circuit), the basic approach is to achieve the circuitresources into multiple small pieces, a small piece points to a call (call), when this piece of free resourcesto other call cannot be used, that is resources are exclusive. Circuit-switched data in the resourceexclusive cause low utilization, which is the computer network using packet switching the main reason.


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Whats multiplexing Multiplexing is sending multiplesignalson a carrierat the same timein the form of a complex

signaland then recovering the separate signals at the receiving end.

frequency-division multiplexing-FDM Wavelength division multiplexing-WDM

time-division multiplexing-TDM code-division multiplexing-CDM

"Multiplex multiplexing" is the term commonly used in communications technology, is in the sametransmission medium can transmit multiple signals simultaneously in the technology, aims to improve the utilizationof communication lines. Commonly used methods are frequency-division multiplexing, TDM, CDM code divisionmultiplexing, etc.

FDM

The frequency spectrumof a link is divided into bandsand shared amongthe connectionsestablished across the link. Bandwidth: the widthof the band

FDM (Frequency Division Multiplexing, Frequency Division Multiplexing): frequency-division multiplexingis the use of different frequencies to transmit different signals simultaneously without any interference. Spectrum of

the physical link is shared by multiple circuits, but use different frequencies for each circuit only. For example, thevoice frequency range 4 KHz, a link will be divided into a spectrum of 4 KHz wide frequency band, a band assignedto a Call to use, as a Circuit.Bandwidth: The width of the band is called the bandwidth (bandwidth).

Interference

TDM

For a TDM link, timeis divided into framesof fixed duration, and each frame is divided into afixed number of time slots. The network dedicates one time slotin every frame to the connection.


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TDM (Time Division Multiplexing, Time Division Multiplexing): time division multiplexing is the

use of different time slots send different signals. The time is divided into a fixed long Frame (structural,

frame, etc.), each Frame is divided into a fixed number of time slots (time slot). When the connection is

established, the network connection for each Frame in a fixed allocation of time slots (slot).

Multiplexing in Circuit Switched Networks

Circuit switching is wastefulbecause the dedicated circuits are idleduring silent periods.

Example: Calculate the time to transfer a file from A to B (in the slide) Suppose

file size: 640,000 bits setup time:500 msec; link rate:1.536Mbps; a frame=24slot

time=640000/(1.536Mbps/24)+0.5s=10.5sPacket Switching

Long msgsare broken into packets. There has a destinati on addressof the destination in each packet and used by the packetswitchesto

determine output link Packets are transmitted over each link at fullrateof the link resources used asneeded, no setup

Resources are shared among multiple user

The basic idea of packet switching: the data into a one packet, the destination address of each packet arecarried along by the packet through the packet switches based on the destination address carried by the decision of itsoutput link. And circuit switching, link, switch / routers and other resources shared by multiple users, the switchforwards a packet to its output link speed full speed.

Packet Switching:

Store-and-Forward transmission

Packet Switches mustreceive the enti re packetbefore it can beginto transmit the first bit ofthe packet onto the outbound link. it introduces a store-and-forward delayat the inputto each link along the path. The delay is proportionalto the packets length

Packet Length = L bits and the link rate =R bps Store-and-forward delay=L/R s

Generally use packet switching Store and Forward (Store and Forward) technology, that switch must

receive a complete packet before the packet transmitted on the outbound link first. Using Store and

Forward will introduce a delay, this delay and packet length is proportional to the speed and inversely

proportional to the output link.

Packet length: L bits Qlinks from source to destination link rate: Rbps no queuing delay and no propagations delay store and forward delay in each link is L /Rs end to end delay is QL/Rs

Packet Switching:

Buffering in Packet Switches

If a packet needs to be transmitted across a link that is busy now, it must be stored in the

buffertemporarily and wait for its turn. Queuing delay Packet loss: if the buffer overflows

Packet switching in storage group to use buffer (buffer / cache), cache is generally set at the switch

output (this switch is called the output buffer switch). When arriving from multiple input links from the


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same output link packet forwarding, the switch can only transmit a packet on the output link, the other

group waiting in the buffer required output link is idle. Can be seen in the packet switches in the group will

go through a line (queuing) delay. Queuing delay on busy with the switch, the size variable.

If the cache is full when the packet arrives, the switch will discard a packet.

Statistical Multiplexing of Packet Switched Network

Sequence of A & B packets does not have fixed pattern statistical multi plexing. In TDM each host gets same slot in revolving TDM frame.

The picture shows a simple packet switch network. Suppose A, B also sends to the E group.

Statistical multiplexing "is actually a time-division multiplexing technology. Full name is called" statistical

time division multiplexing ", referred to as STDM, also known as" asynchronous time-division

multiplexing. "

The so-called "asynchronous" or "statistics" because it uses common channel "slot" method and the

traditional time-division multiplexing methods, the traditional time-division multiplexing access terminals

are fixed to each assigned a common channel of a time slot, is pigeon-holing. Because of the terminal and

the slot is "condemnation", so they are "synchronous". The asynchronous time division multiplexing or

statistical time division multiplexing is to implement public channel time slot, "according to need", that is

only for those who need to transmit information or termination to work before being assigned to the slot,

thus making all of the time slots are can get full use.

Statistical analysis, statistical multiplexing than traditional time-division multiplexing to improve

transmission efficiency 2-4 times. The main features of this multiplexing is to dynamically allocate channel

time slot, so the statistical multiplexing can be called "dynamic multiplexing."

Packet switching vs. Circuit switching

Packet switching allows more usersto use network than circuit switching! For Example:

1 Mbps link each user:

100 kbps when active active 10% of time

circuit-switching: 10 users

packet switching: with 35 users, probability > 10 active less than .0004


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Packet switches can send data at full r ateof the outbound link. Example

10users, one suddenly generates one 1000-bit packet, while others remain silent. Link rate is 1Mbps, each user 100kbps

Under circuit switching 1000/100000=10msec

Under packet switching 1000/1000000=1msec

2. Packet Switched Networks datagram network:

destination address determines next hop routes may change during session analogy: driving, asking directions

vir tual cir cuit network : Each packet carries tag (virtual circuit ID), tag determines next hop. And fixed path

determined at call setup time, remains fixed thru call routers maintain per-call state

There are two types of packet-switched network, classification is based on packet-based switch

forwards the packet destination address or Virtual circuit identifier:1, Datagram (packet) network: According to the packet destination address to forward packet network, eg

Internet. Each packet contains the destination address and other information are

Interest in the head, when the packet arrives the switch, the switch according to the packet destination

address and a routing table to determine the packet forwarding direction.

2, Virtual Circuit virtual circuit network: number of forward packets according to virtual circuit network,

eg, X.25, ATM, etc. Virtual circuit network, data transmission before

Need to use signaling to establish a virtual circuit end to end, with the VC ID to identify and fill in each

packet, called a tag. Switch according to the

Group in the tag to determine its forward direction, which is no longer checks the destination address. Each

virtual circuit switches the connection needs to maintain ongoing

Access information.

Network Taxonomy

Summary of the network core

Network core is a mesh of r outers move packet from source to destination

Circuit switching and packet switching multiplexing in circuit switched networks store-and-forward (delay) buffering and queuing delay circuit switching vs. packet switching

packet switched networks Network Taxonomy


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1-4Access networks and physical mediaIntroduction

Access Networksis the physical l ink(s) that connect a host to its edge rou ter edge router:the firstrouter on a path from a source host to the destination host. Categories:

Residential access Company access wireless access

Keep in mind:

bandwidthof access network sharedor dedicated

Host access network is connected to the border router of the physical link (last mile), divided into the

home access, access, and wireless access to three types of units.

1.1Residential Access

Connect home end systemsinto the Network (edge router). Dial-up MODEM

ordinary analog telephone line + modem up to 56Kbps direct access to router (conceptually) access network= a host-side modem + a telephone line + a router-side model Cant surf and phone at same time The link isdedicated!

Early home Internet access is usually dial-up networking, using ordinary telephone line modem (UTP

cat.3) up to a maximum data transfer rate of 56kbps, this time at the border routers also need a MODEM.

Therefore, at this time is the access network includes a point of the MODEM and a telephone line. As the

lower rate, cannot make phone calls and Internet access. Broadbandresidential access

DSL:(digi tal subscriber l ine) a kind of new modem technologyrunning over traditional telephone line.

restricting transmission distance to achieve higher rate DSLs link isdedicated The data rate are typically asymmetricalin the two directions. ADSL: (asymmetric digital subscriber l ine)

Download:10Mbps Upload:1Mbps

HFC:(hybri d fi ber-coaxial cable)Many households use broadband access technologies such as xDSL and HFC.

xDSL is the analog telephone lines to transmit digital signals, it uses a new modem technology and limits themaximum transmission distance, it can transfer data at higher speeds. The use of ADSL, phone and Internet can be,

both independently of each other.ADSL uplink and downlink speeds of different. Uplink speeds of up to 1Mbps, downlink speeds of up to 10Mbps.

xDSL uses FDM 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream 0 kHz - 4 kHz for telephone

DSL uses frequency division multiplexing, the communications link is divided into three frequencychannels and do not cover, namely:

1,0 ~ 4KHz two-way voice channels

2,4 KHz ~ 50KHz uplink data channel

3,50 KHz ~ 1MHz downlink data channel


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HFChybrid fiber-coaxial cable ) extended from broadcasting cable television. require cable modemto convert signal also asymmetric

up to 1 Mbps upstream >= 10 Mbps downstream

sharedlink bandwidth with other users

Television system is a broadcasting systemIn the cable TV system, cable head stations located all users to radio and television signals, television

signals along the station -> the user the direction of transmission and amplification.

HFC (hybrid fiber coaxial cable network), Host Modem need to use the device called a cable access

network, Cable Modem uplink and downlink will link into two channels. As the channel is shared among

multiple users, so there is network congestion and the size of the problem.

Similar to ADSL, HFC upstream channel rate is lower than the downlink channel rate, and the entire

channel is shared by all users. While ADSL uses Point to Point Channel, is the dedicated channel.

1.1 Residential Access - HFC


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1.2Company AccessLAN

company/units typically use LANto connect end systems to edge router LANLocal Area Network Ethernetis by far the most prevalent technology for company access 10/100Mbps, Gigabit Ethernet, 10GE shared mediatwist pair ,coaxial cable, fiber

Press coverage of computer network, divided into LAN, MAN and WAN. (Emphasis needs to know

according to the classification of computer network coverage)

LAN: local area network: a few hundred meters to several kilometers covered

WAN: wide area network:

MAN: Metropolitan Area Network: a city covered

1.3Wireless Access Wireless LAN

transmit/receive packets to/from a base station(access point, AP) base station connected to a wired router Wireless LAN standard:

802.11a(2Mbps) 802.11b(11Mbps) 802.11g(54Mbps)

In addition to WLAN, but also can use the wireless WAN technology, access to Internet, such as mobilephones. WAN technologies on the use of unlimited access, see p30 ~ 31

wider-area wireless access provided by Telco operator 3G ~ 384 kbps

Will it happen? WAP/GPRS in Europe

wireless access protocol General Packet Radio Service


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1.3Wireless Access-Home networks

Typical home network components: ADSL or cable modem router/firewall/NAT Ethernet wireless access point (AP)

Head end Data Repeater

2.1 Physical Media

One bitpasses through a series of transmitter-receiver pair For each transceiver pair, the bit is sent by propagating electromagneticwavesor optical

pulseacross a physical medium. physical l inklies between transmitter & receiver

2.2 Physical Media

Categories of physical medium

guided media The waves are guided along a solid mediumsuch as copper, fiber or coax.

unguided media The waves propagate in the atmosphereand in outer space, such as in a wireless

LAN

Oriented media: media guide the direction of propagation of the signal

Non-oriented media: general spread of the signal through the air, it does not guide the direction of propagation forthe signal, such as short wave, microwave and infrared communications.

2.3 Twisted-Pair Copper Wire

two insulated copper wires twistedtogether (TP) Category 3: traditional phone wires, 10 Mbps Ethernet

Category 5: 100Mbps Ethernet Shield or Unshielded TP

STP-Shielded TP UTP-Unshielded TP

2.4 Coaxial Cable

two concentric(rather than parallel) copper conductors Base-band

single channel on cable Broadband: multiple channels on a cable HFC

Fiber Optics

glass fiber carrying light pulses, each pulserepresents a bit high-speed and lower error rate


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Radio

signal carried in electromagnetic spectrum no physical wire and bidirectional propagation environment effects:

reflection obstructionby objects interference

Radio Link Types

terrestrial microwave e.g. up to 45 Mbps channels

WLAN (e.g., Wi-Fi) 2Mbps, 11Mbps, 54Mbps

wide-area (e.g., cellular) e.g. 3G: hundreds of kbps

satellite up to 50Mbps channel (or multiple smaller channels)

250 msec end-end delay

1.4 Access Network and Physical Media

Access Networks is the physical link (s) that connect a host to edge router Residential, company and wireless access

Dial-up modem, xDSL, HFC LAN, Ethernet, Fast Ethernet, GE, 10GE WLAN, 802.11

the bit is sent by propagating electromagnetic waves or optical pulse across a medium. Guided media and unguided media Twisted-pair, coaxial cable, fiber optics and radio

1-5ISPs and Internet backbonesInternet Structure

ISPs connect to each other and form a tiered hierarchy logical topology

At very top of the hierarchy is a relatively small number of so-called Tier-1 ISPs.

Tier-1 ISPs

Tier-1 ISPs are special

Directly connected to each of the other Tier-1 ISPs Connected to a large number of Tier-2 ISPs International in coverage Link speed is high

known as I nternet Backbonenetworks


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Access network connected to the Internet via an ISP, ISP component hierarchy. The top level is

called Tier-1 ISP.

Tier-I ISPs are also called the Internet Backbone, which is characterized by:

1, with the other Tier-1 ISP is directly connected (to facilitate billing?)

2, with most Tier-2 ISP Internet

3, covering international, regional

POP (Point of Presence): the points at which the ISP connect to other ISPs; POP belongs to a provider's

network; A POP is a group of routers

NAP (Network Access Point, not nap): are complex high speed switching networks, often concentrated in a

single building, and can be owned and operated by the third party exchange huge quantities of traffic

among many ISPs

Increasingly, tier-1 ISPs interconnect with each other at POPs

Tier-2 ISPs

Tier-2 ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier-2 ISP's coverage area, but a region or country. Tier-2 ISP usually with one or more Tier-1ISP

connected, you can also connect with other Tier2 ISP.


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Tier-3 ISPs and Local ISPs

last hop (access) network (closest to end systems)

Internet Structure

a packet passes through many networks!

1.6Delay & loss in packet-switched networksHow do loss and delay occur?

packetsqueuedin switch buffers and wait their turns to output packet arrival rateexceeds links capacity packets en-queue, wait for turn

Packet switching network, a router uses storage - forwarding technology. Input from the router to

reach the group may need to wait in the queue the output link is idle. When the packet arrives at thelocation when the queue is not idle, the packet might be discarded.

Packet source to the destination in the transmission process, in each node will experience delay. Packet

delay in a node includes the node processing delay, queuing delay, send delay, propagation delay.


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1. Types of Delay

Nodal processing delay Time required to examine the header and determine where to direct the packet

Queuing delay Time a packet waits to be transmitted in queue

Transmission delay Time required to push all bits of a packet into link

Propagation delay Time required to propagate from one end to another end of the link

1.1 Processing Delay

nodal processing determine output link check bit errors on the order of microseconds or less after nodal processing, the router directs the packet to the queue

After a node packet processing to the next node in the process, the delay experienced, there are four:

1, nodal processing delay (processing delay): refers to the router / switch, check the packet header to

determine which output port to forward from the time required. Node processing delays may also include

checking whether an error packet the time required. After processing delays, the packets are cached in the

queue.

1.2 Queuing Delay

Wait timefor the packets turn to be transmitted onto the link depends on congestionlevel of router on the order of microseconds to milliseconds

queuing delay (queuing delay): grouping the output link is idle waiting for the time required. From

the beginning to the grouping of packets into the queue to leave when the time difference. Queuing delay

experienced by packets already in the queue depends on the total length of the packet and queue strategy.

1.3 Transmission Delay

Time to push all of the packet bitsonto the link Also call store-and-forwarddelay

R=link bandwidth (bps) L=packet length (bits) time to send bits into link = L/R

Transmission delay: the packet is sent to link all the bits on the time required, also known as Store

and Forward Delay.

1.4 Propagation Delay

propagation delay dprop= d / s s=2.0~3.0108m/s


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Propagation delay: bit transmitted from one point to another time experienced, and the distance between twopoints and the signal propagation speed.Delay and propagation delay on sending easily confused. Need to remember that a packet transmission delay refersto the bit sent to the link on all the time, and the packet length and transmission rate, and the distance between twopoints is not in any way. The propagation delay refers to a communication from one end of the link to the other endof the time, and the link length and signal propagation speed.

1.4 Transmission vs. Propagation Delay

The transmission delayis the amount of time required for the router to push outthe packet. function of the packets lengthand links transmission rate

The propagation delayis the time it takesa bit to propagate from one router to the next. function of thedistancebetween the two routers

1.4Transmission vs. Propagation Delay Caravan analogycar ~ bit ; caravan ~ packet ; tollbooth ~ router; highway ~ link

car travels at rate of 100km/h; tollbooth takes 12s to serve a car propagation speed and transmission time

Suppose:when the first car arrives at a tollbooth, it waitsat the entrance until the others havearrived.

Q: How long until caravan is lined up before the 2ndtollbooth? time to pushentire caravan through the tollbooth onto highway = 12*10 = 120 sec time for last car to propagate from 1st to 2nd tollbooth: 100km/(100km/hr)= 1 hr A: 62 minutes car travels at rate of 1000km/h; tollbooth takes 60s to serve a car Q: Will the 1st car arrive to 2nd booth before all other cars served at 1st booth? Yes!After 7 min, 1stcar arrives at 2ndtollbooth and 3 cars still wait at 1sttollbooth. 1stbit of packet can arrive at 2ndrouter beforepacket is fully transmitted at 1st router!

Nodal Delay

Node delay and the delay of the four parts.

Processing delay (dproc) typically a few microsecs or less

queuing delay (dqueue) depends on congestion

transmission delay (dtrans) = L / R, significant for low-speed links

propagation delay (dprop) a few microsecs to hundreds of msecs

2. Queuing delay

Traffic intensity = La/R

R: link bandwidth (bps) L: packet length (bits) a: average packet arrival rate


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La/R ~ 0: average queuing delay small La/R 1: delays become large La/R > 1: more work arriving than can be serviced, average delay infinite! Design your system so that the traf fi c in tensity is no greater than 1 ! ! !

Node queuing delay is the delay of the most complex and most interesting part. The reason why the mostinteresting, or refer to the current research work is carried out for the queuing delay, including scheduling, cachingstrategies.

Queuing delay and the load status of network devices is closely related to different groups experienced queuingdelay will change with the load.

2. End-to-End Delay

End-to-End delay is a a packets delay form source end-system to destination end system.dend-end= (dproc+dtrans+dprop+dqueu)

RealInternet delays and routes

What do realInternet delay & loss look like? trace route( tracer t (XP)):

Measurement delay from source to routeralong end-end path towards destination. for allI:

sends three packets that will reach router ion path towards destination routerIwill return packets to sender Sender times interval between transmission and reply.

Summary

type of delays processing, transmission, queuing and propagating delay

End-to-End delay from source to destination buffering and queuing delay buffering and packet loss delay and routes in the Internet


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1.7Protocol layers and their service modelsIntroduction

Networks are complex!

many pieces: Hosts and packet switches links of various media applications protocols hardware, software

Question:Is there any hope of organizingstructure of network? Or at least for our discussionof networks?

The Internet is a very complex system; there are many different types of applications, protocol, end systems,connections.

Is there a problem is structured to describe something / build Internet?

Layering of airline functionality

Layers:each layer implements a or some service(s) via its own internal-layer actions relying on services provided by layer(s) below

Hierarchical structure is conducive to modular processing of complex systems, is conducive to the realization

of system services. For a complex system, the system may continue to implement changes in the hierarchy will helpto adapt to these changes.

Air passenger transport functions are divided into different levels; we discuss a framework to provide air travel.Each layer with the following features provided by the combination of level, have achieved a certain function,

and called Service (Service).

Layer in the ticket: to provide a passenger service counter to counter, as long as you buy a ticket, your airlinecan use the aircraft to the destination.

Layer in the baggage: Passengers can check-in baggage, arrive at your destination can retrieve their luggage.Note, baggage only purchased tickets for passenger's baggage service.

Why layering?

Dealing with complex systems:

explicit structureallowsidenti fi cation relationship of complex systems pieces layered reference modelfor discussion

modularizationeases maintenance, updating of system change of implementation of layers service transparent to rest of system e.g., change in gate procedure doesnt affect rest of system

Agreement with the concept of layering and structural benefits. First, the agreement provides a discussion of

hierarchical structured approach to complex problems; modular system to achieve beneficial updates and changes.Protocol layer has its disadvantages: 1) protocol layer may result in duplication of certain functions to achieve;

2) a layer of some services may need to use it with some of the other layers of information,in violation of the principle of layering. Such as TCP checksum calculation on the IP layer need some information.


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Internet protocol stack

application: supporting network applications transport: process-process data transfer network: host-to-host data transfer, routing of datagram's from source to destination link: data transfer between neighboring network elements physical: bits on the wire

The Internet is a very complex system, including hardware and software, including application, protocol, end

systems, different types of communication media, routers / switches. The Internet architecture is also used inhierarchical structure, with the previously mentioned examples of similar passenger; Internet use for each layer is thelayer of the upper or lower function to provide one or more services.

Each protocol layer can use the software, hardware or a combination of both to achieve.Architecture: a collection of protocols and layers.Collection of the agreement also called protocol stack (Protocol Stack), Internet protocol stack, including: the

application layer, transport layer, network layer, link layer and physical layer.Application Layer: contains a large number of applications generally require the agreement; application of

the message called the message.Transport Layer: responsible for receiving messages from the application layer and transport the application

layer message, the message will be handed over to the destination application. The group is called the transport layersegment.

Network layer: the transport layer is responsible for the source Host segment to the network layer, networklayer is responsible for the segment transmitted to the destination host's transport layer.

Link layer: network layer is responsible for passing data between the source and destination, Link layer isresponsible for packet transmission from one node to the next node. Link layer data transmission unit is called theFrame.

Physical Layer: Link layer is responsible for a Frame from a Node to pass to the next Node, is responsiblefor the physical layer of each Frame (bit) transmitted from one end of the link to the other side.

Applications send and receive data is a complex process, the source data by the application layer vertical top-down pass, will message to the Transport layer, fill out the message that the application of information, fitted intosegments, to the network layer; network layer protocol entities included in the segment to add the destination address

outside of the head, loaded into a datagram (we used to call packet, packet) and turned over to the link layer; linklayer in the packet's neighbor on the outside package node's link-layer address information, pretending to convert the

physical layer frame by light signals transmitted on the media. After the middle of switches, routers forward theequipment to reach the destination after the data and then submit up layer by layer, each corresponding to submit theprotocol headers are removed, and the final message to the application.

It can be seen; the data transmission layer in the source Host to have a package (encapsulation) process, thedestination Host opened a layer of the process.

Data transmission may take one or more switches and routers. Both devices call Packet switch, but the highestlevel of different work. Routers work at the highest level of network layer; link layer switches work at the highest

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Computer Networking Note1