cs671 advanced computer networking chen qian fall 2014 introduction cq (2014) 1-1

CS671 Advanced Computer Networking

Chen QianFall 2014

IntroductionCQ (2014)

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What you can learn

Basic knowledge of conventional Internet Protocols layers

Introduction of current hot topics in networking Wireless and mobile networks Data center networking Software defined networking Future Internet

Research skills in system and network area Presentation skills

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Wireless networks

IntroductionC. Q. (8/13)

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Cloud Computing


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Data centers


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Data centers


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Data center networks


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Future Internet

Content-based network? (YouTube, Netflix, etc.)

Most devices are mobile? (smartphones, laptops, touch pads, etc.)


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Lecture 1: Introduction

1.1 What is the Internet?1.2 Network edge

end systems, access networks, links

1.3 Network corepacket switching, network structure

1.4 Delay, loss and throughput in packet-switched networks

1.5 Protocol layers

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What’s the Internet: “nuts and bolts” view

millions of connected computing devices: hosts = end systems running network apps: Web

browser, YouTube, Skype, etc.

router

PC

server

wirelesslaptop

cellular handheld

wiredlinks

access points

communication links fiber, copper, radio, satellite transmission rate = bandwidth

routers: forward packets (chunks of data)

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What’s the Internet: “nuts and bolts” view Internet: “network of

networks” loosely hierarchical public Internet versus

private intranet

protocols control sending, receiving of msgs e.g., TCP, IP, HTTP, DNS,

Ethernet

Home network

Institutional network

Mobile network

Global ISP

Regional ISP

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What’s the Internet: a service view

communication services provided to apps: reliable data delivery

from source to destination

• File transfer, email, E-bank.

“best effort” (unreliable) data delivery

• Multimedia (cell phone, video streaming, VoIP)

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What’s a protocol?human protocols: “Homework

assignment” Turn in

“I have a question” Explain

… specific msgs sent… specific actions

taken when msgs received, or other events

network protocols: machines rather than

humans all communication

activity in Internet governed by protocols

protocols define format, order of msgs sent and

received among network entities, and actions taken on msg transmission, receipt

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What’s a protocol?a human protocol and a computer network protocol:

Hi

Hi

Got thetime?

2:00

TCP connection request

TCP connectionresponseGet http://www.cs.uky.edu/~qian

<file>time

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Chapter 1: roadmap





1.5 Protocol layers

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A closer look at network structure:

network edge: applications and hosts

access networks, physical media: wired, wireless communication links

network core: interconnected

routers network of networks

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The network edge: end systems (hosts):

run application programs e.g. Web, email at “edge of network”

client/server

peer-peer

client/server model client host requests, receives

service from always-on server e.g. Web browser/server;

email client/server peer-peer model:

minimal (or no) use of dedicated servers

e.g. Skype, BitTorrent

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Access networks and physical media

Q: How to connect end systems to edge router?

residential access nets institutional access

networks (school, company)

mobile access networks

Keep in mind: bandwidth (bits per

second) of access network?

shared or dedicated?

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100 Mbps

100 Mbps

100 Mbps1 Gbps

server

Ethernetswitch

Institutionalrouter

To Institution’sISP

Ethernet Internet access

Typically used in companies, universities, etc 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernet Today, end systems typically connect into

Ethernet switch

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Wireless access networks

shared wireless access network connects end system to router via base station aka “access

point”

wireless LANs: 802.11b/g (WiFi): 11 or 54

Mbps

wider-area wireless access provided by telco operators ~1 Mbps over cellular system

(3G) WiMAX promises 10’s Mbps

over wide area

basestation

mobilehosts

router

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Home networks

Typical home network components: DSL or cable modem router/firewall/NAT Ethernet wireless access point

wirelessaccess point

wirelesslaptops

router/firewall

cablemodem

to/fromcable

headend

Ethernet

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Chapter 1: roadmap



1.3 Network core packet switching, network structure


1.5 Protocol layers

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The Network Core

mesh of interconnected routers

the fundamental question: how is data transferred through net? circuit switching:

dedicated circuit per call: telephone net

packet-switching: data sent thru net in discrete “chunks”

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Packet Switching

Sequence of A & B packets does not have fixed pattern bandwidth shared on demand queueing delay, packet loss

A

B

C100 Mb/sEthernet

1.5 Mb/s

D E

statistical multiplexing

queue of packetswaiting for output

link

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store-and-forward

store and forward: entire packet must arrive at router before it can be transmitted on next link

A file/message larger than maximum packet size is transmitted as multiple packets

R R RL

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Network Core: Packet Switching

each end-end data stream divided into packets

packets of different users share network resources

each packet uses full link bandwidth

resources used as needed

resource contention: aggregate resource

demand can exceed amount available

congestion: packets queue, wait for link use

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Packet Switching versus Message Switching

Smaller end-to-end delay from pipelining Less data loss from transmission errors

Advantages of packet switching

More header bits Additional work to do segmentation

and reassembly

Disadvantages of packet switching

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Packet switching versus circuit switching

1 Mb/s link each user:

100 kb/s when “active”

active 10% of time (a “bursty” user)

circuit-switching: 10 users

packet switching: with 35 users,

probability > 10 active at same time is less than .0004

Packet switching allows more users to use network!

N users

1 Mbps link

Q: how did we get value 0.0004?

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Packet switching versus circuit switching

great for bursty data resource sharing simpler, no call setup

excessive congestion: packet delay and loss protocols needed for reliable data transfer,

congestion control Q: How to provide circuit-like behavior?

bandwidth guarantees needed for audio/video apps

solution may impact network neutrality

Is packet switching a “slam dunk winner?”

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Internet structure: network of networks

roughly hierarchical at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T,

Cable and Wireless), national/international coverage treat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1 providers interconnect (peer) privately

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Tier-1 ISP: e.g., Sprint

…

to/from customers

peering

to/from backbone

….

………

POP: point-of-presence

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

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet tier-2 ISP is customer oftier-1 provider

Tier-2 ISPs also peer privately with each other.

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“Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems)

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP



Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

Local and tier- 3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet

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a packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP



Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

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Chapter 1: roadmap





1.5 Protocol layers

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How do loss and delay occur?packets queue in router buffers packet arrival rate to link exceeds output link

capacity packets queue, wait for turn

A

B

packet being transmitted (delay)

packets queueing (delay)

free (available) buffers: arriving packets dropped (loss) if no free buffers

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Four sources of packet delay

1. nodal processing: check bit errors determine output link

A

B

propagation

transmission

nodalprocessing queueing

2. queueing time waiting at output

link for transmission depends on congestion

level of router

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Delay in packet-switched networks3. Transmission delay: R=link bandwidth

(bps) L=packet length (bits) time to send bits into

link = L/R

4. Propagation delay: d = length of physical

link s = propagation speed in

medium (~2x108 m/sec) propagation delay = d/s

A

B

propagation

transmission

nodalprocessing queueing

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End-to-End Delay Nodal delay (from when last bit of packet arrives at this

node to when last bit arrives at next node)

dnodal = dproc + dqueue + dtrans + dprop

End-to-end delay over N identical nodes/links from client c to server s (from when last bit of packet leaves client to when last bit arrives at server)

dc-s = dprop + Ndnodal

Round trip time (RTT)RTT = dc-s + ds-c + tserver

where tserver is server processing time

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Implications of end-to-end delay Relative importance of bandwidth and “distance”

for a small message (e.g. 1 byte), distance(1 ms vs. 100 ms propagation time) is moreimportant than bandwidth (1 Mbps vs. 100 Mbps)

for a large message (e.g., 25 Mbyte),bandwidth is more important than distance

Delay x Bandwidth productExample:

for 100 ms end to end delay and 45 Mbps bandwidth,there can be up to 560 Kbyte of data in flight

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Throughput

throughput: rate (bits/time unit) at which bits transferred between sender/receiver instantaneous: rate at given point in time average: rate over longer period of time

server, withfile of F bits

to send to client

link capacity

Rs bits/sec

link capacity

Rc bits/sec pipe that can carry

fluid at rate

Rs bits/sec

pipe that can carryfluid at rate

Rc bits/sec

server sends bits

(fluid) into pipe

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Throughput (more)

Rs < Rc What is average end-end throughput?

Rs bits/sec Rc bits/sec

Rs > Rc What is average end-end throughput?

Rs bits/sec Rc bits/sec

link on end-end path that constrains end-end throughput

bottleneck link

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Throughput: Internet scenario

10 connections (fairly) share backbone bottleneck link R

bits/sec

Rs

Rs

Rs

Rc

Rc

Rc

R

per-connection end-end throughput: min(Rc,Rs,R/10)

in practice: Rc or Rs is often bottleneck

Or the server is the bottleneck

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Chapter 1: roadmap





1.5 Protocol layers

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Protocol “Layers”Networks are

complex! many “pieces”:

hosts routers links of various

media applications protocols hardware,

software

Question: Is there any hope of organizing structure of

network?

Or at least our discussion of networks?

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Layered architecture Use abstraction to hide

complexity Each layer

• provides a service via its own internal actions as well as relying on service provided by layer below

• is a network of processes Can have alternative

abstractions at each layer (resulting in protocol graph rather than protocol stack)

Application programs

Process-to-process channels

Host-to-host connectivity

Hardware

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Each protocol

involves two or more peers two interfaces defined

• service interface: operations a local user can perform on a protocol entity and get results

• peer-peer interface: form and meaning of messages exchanged by protocol entities (also called peers) to provide protocol service

term “protocol” generally used to refer to peer-peer spec

High-level entity

High-level entity

Protocol entity

Protocol entity

Serviceinterface

Peer-to-peer

interface

Host 1 Host 2

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Internet protocol stack application: supporting network

applications FTP, SMTP, HTTP

transport: process-process data transfer TCP, UDP

network: routing of datagrams from source to destination IP, routing protocols

link: data transfer between neighboring network elements PPP, Ethernet

physical: bits “on the wire”

application

transport

network

link

physical

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ISO/OSI reference model presentation: allow applications

to interpret meaning of data, e.g., encryption, compression, machine-specific conventions

session: synchronization, checkpointing, recovery of data exchange

Internet stack “missing” these layers! these services, if needed, must

be implemented in application

application

presentation

session

transport

network

link

physical

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Logical communication between peers

E.g.: transport accept data from

application add addressing,

reliability check info to form a message

send message to peer via a delivery service

wait for peer’s reply (ack)

applicationtransportnetwork

linkphysical


linkphysical


linkphysical


linkphysical

networklink

physical

data

data

transport

transport

ack

data

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Physical path of dataEach layer takes data (service data unit) from above adds header to create its own protocol data unit passes protocol data unit to layer below

network

link

physical

network

link

physical

application

transport

network

link

physical

source

host

destination

host

message

segment

datagram

frame

M

MH 4

MH 4H 3

MH 4H 3H 2 T2

bits

application

transport

network

link

physical

router routerprotocol data units

...

More terminology: A switch is a relay with two layers (physical and link). A repeater is a relay with only the physical layer.

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Introduction: SummaryCovered a “ton” of material! Internet components: hosts, links, routers,

Internet what’s a protocol? network edge, core, access network

packet-switching versus circuit-switching

Internet structure: ISPs performance: loss, delay, throughput layering

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End of Lecture01

cs671 advanced computer networking chen qian fall 2014 introduction cq (2014) 1-1

Documents

network structure

network apps

network entities

computer network protocol

network core packet

events network protocols

time slide

voip slide