TSIN02 Internetworking

Lecture 1

Outline● Course info● Internet history and management● TCP/IP protocol stack● Physical layer: modulation● Link layer: Error control, access control● Application of the above in standards

People involved in the course● Daniel Persson ‒ danielp@isy.liu.se

Lecturer, examiner

● Victor Cheng ‒ hei.cheng@liu.se Teaching assistant, project responsible

● Possible second project responsible will be announced later

Course organization● Lectures & Problem Classes ● Examination

– Written exam (4.5 hp)– Home assignment (written report) (1.5 hp)

● All info is at course web page: www.commsys.isy.liu.se/en/student/kurser/TSIN02 www.commsys.isy.liu.se/TSIN02

– Guidelines for the report– Reading guide– Relation between lectures and lessons– Lecture slides – Problems for the problem classes– Schedule

● Guest lecture, to be announced later (included in exam)

Literature● TCP/IP Protocol Suite, 4th Ed, Behrouz A. Forouzan● Networked Life, 20 Questions and Answers, Mung

Chiang, Cambridge University Press.● Lecture material and problem classes material are

most important!● Guest lecture, to be announced, is part of examination

● Alternative literature: ● TCP/IP Protocol Suite, 3rd Ed, Behrouz A. Forouzan● See course home page

Getting the book

Copies promised by course start at Bokakademin, Kårhuset, Valla

Lectures and problem classes times

Times may at occasions be subject to change, keep an eye on the course homepage and the schedule regularly!

What to expect from the course

● No prior networking knowledge needed. ● The course is broad, from the physical layer to mobile phone apps.● After the course, you will understand the main principles of today's and future

computer networks such as Internet. You will also have some specific insight into pricing, robustness, clouds, fairness, and source coding for packet networks a la Skype.

● Just enough learning of inter-networking language, words, and abbreviations, to be able to communicate with the people in the networking field. Few protocol details.

● We learn networking in this course, keeping the mathematical descriptions as simple as possible.

● The lessons may be treating complementary material, not treated in the lectures, and vice versa. All the material is covered in the reading guide.

Home assignment: online Pac-Man game

● Detailed guidelines on homepage

● Find partners, you work in groups of 4 students

● Not later than Monday, November 11: Announce your group using our lab sign-up system.

● Victor will get back to you as soon as possible per email to tell who will be your supervisor, as well as the email of your supervisor.

● Checkpoint, not later than November 21: Send an outline of the report, marked with your group number, by mail to your supervisor as a pdf file attachment.

- The purpose of the outline is to show that you have started to work with the assignment and has some initial plan.

- Your supervisor will get back to you as soon as possible with an OK or comments about things to take into consideration. You may book a shorter meeting with your supervisor for further discussion.

Home assignment cont...

● Not later than December 6: Print out the final report to your supervisor. Leave the report in the cupboard in the D corridor between entrances B25 and B27 (close to Café Java) in the B-house. Half of the shelves in the cupboard have glassed fronts. Put your report in one of the glassed shelves that are marked "TSIN02".

● The hand-in of the report will be graded P=Pass, C=Complement or F=Fail. The graded report will be handed back to you on December 13 at the latest.

● If you need to complement your report, the complemented report must be handed in not later than January 22. You are allowed to book a short meeting with your supervisor until December 20 (no meetings after December 20), if you have some questions regarding improvement of the report. The graded reports will be handed back to you on January 31.

● Detailed info on course homepage!

Questions

Contact us via mail, or book a time to come and see us! This should not be a substitute for visiting the lectures and lessons though.

Course evaluation people

Task: Collecting comments from students and relaying these to me.

TSIN02 collection of formulas

● Will be posted on the web● You must bring the TSIN02 collection of formulas

yourself to the exam!

Lectures and lessons

● Turn off mobile phones and similar.

● Do not read newspapers in class.

What is inter-networking?

Inter-networking“The art and science of connecting individual local-area networks (LANs) to create wide-area networks (WANs), and connecting WANs to form even larger WANs.”

from the Webopedia Computer Dictionary

One example: The Internet

Inter-networking terms

● Connecting two entities (computers=hosts): a link

● Connecting several entities: a network

● Connecting networks: inter-networking (verb)

● An inter-network (inter-net): a network of networks (noun)● Internet: the world's biggest inter-network● A protocol: A set of rules for communication● A standard: An agreed-upon protocol

● Name for the protocols that are the fundament of the Internet: The Transmission Control Protocol (TCP)/Internet Protocol (IP) protocol suite, cf., course book title.

Connectionless and connection-oriented services

● Circuit-switched network: Physical resources along the propagation path are reserved.● Quality of service (QoS): to guarantee a certain level of performance to a data flow. Some

services, e.g., delay and bandwidth, are guaranteed

● Packet-switched network: Packets are used.

● A packet-switched network can be either

connection-less

connection-oriented/the virtual circuit approach● Connection-less: Resources along the propagation path are not reserved.

● Connection-oriented: A connection service that may not cover all demands on a full circuit-switched network

Inter-networks today

● The Public Switched Telephone Network (PSTN)Circuit-switched: bandwidth, delay, and error rate guarantees

● The InternetPacket-switched, connection-less, no Quality of service (QoS)

Why focus on Internet / the TCP/IP protocol suite in this course?

● The Internet carries by far more data than PSTN today.

● Internet provides more services than PSTN. You can use voice over IP (VoIP=name for technology and protocols for voice over IP).

● We will however discuss circuit-switched networks also, e.g., IPv6, the new version of the IP protocol, is becoming connection-oriented...

Brief history of the Internet

● 1969: (Advanced Research Projects Agency Network) (ARPANET), four nodes at American universities

● 1974: V. Cerf and B. Kahn, Transmission Control Protocol (TCP). Cerf and Kahn worked in a project called the Inter-netting project, wanting to connect different networks

● 1977: First internet with three different nets: ARPANET, packet radio, and packet satellite

● Late 70's: TCP divided into TCP and the Internet protocol (IP)!

● 1980's–: The Internet – a collection of networks, communicating using the TCP/IP protocols

● 1995: Companies known as Internet service providers (ISP)s started (offers users access to the Internet)

Number of Internet hosts

● 1981: 213 hosts● 2001: 100 million ● 2012:1 billion

Communication standards

● Standardization organizations: governmental/companies/international● Internet Engineering Task Force, (IETF), part of the Internet Society, non-profit

organization, V. Cerf and B. Kahn involved in the startup● IETF publishes Request for Comment (RFC), see www.rfc-editor.org, protocol

may become standard after different maturity levels● RFC 2026: specifies the process for the standardization of all protocols● RFC 675: ”Specification of internet Transmission Control Program”, The first TCP

version● Institute of Electrical and Electronics Engineers (IEEE): Ethernet, WIFI● International Telecommunications Union (ITU), United nations, e.g., IMT-

Advanced, requirements which 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) tries to fulfill.

Internet management

- Internet society, with, e.g., IETF

- Internet Corporation for Assigned Names and Numbers (ICANN), nonprofit private organization. E.g.:-IP address block allocations to Internet service providers (ISP)s- mapping between human- and computer- readable addresses...

Layered protocols

Layer 1

Layer 2

● Division of the complicated communication task: finding the route to the right host, i.e., routing, human-friendly graphical user interface (GUI), etc.

● Typically, a process, i.e., computer program is run in each layer.

● The computer program communicates with its upper and lower layer through interfaces, i.e, a set of commands, and does not need to know the specific details behind the interface.

Interface

TCP/IP protocol suiteUser application, e.g., http with Mozilla

Communication for each appl. layer process on computer

Find the route over the planet tothe destination

Computer/network entity to computer/network entity, access control,error control, addressing

Map digital bits to analog waveforms (modulation), and let these propagate to destination

Good name for our book!

Encapsulation

H5 DataData

H4 Data

H3 Data

H2 Data

Physical link layer

Every new layer encapsulates previous layer data with a header

Waveform Now

Modulation

The process of sending a (digital here) message signal, with an analog signal that can be physically transmitted.

See whiteboard!

Error control

-Error control = Error detection or correction-Error correction can be either forward error correction (FEC) or automatic repeat request (ARQ)

Error detection main principle

● Add extra bits describing the message on the sender side, e.g., repetition code: 0: 000

● On the receiver side, the received message is checked to deduce if something has gone wrong.

000: ok!

100: something wrong!

FEC main principle

● Add extra bits describing the message on the sender side, as for detection, e.g., repetition code: 0: 000

● On the receiver side, the received message is checked to deduce if some errors can be corrected (FEC).

● Binary symmetric channel describes the digital modulation and the channel reasonably well in most cases: You send and receive zeros and ones. The transition probability from 0 to 1 is the same as the transition probability from 1 to 0 (i.i.d. transitions). For this channel, if the codewords are equally likely and the transition probability is less than 0.5, the maximum likelihood (ML) decision is to decode 0 if there are more received zeros than ones, and vice versa. If there are as many zeros and ones, you have to guess.

ARQ

● Send an acknowledgement (ACK) packet to the sender if you think the received packet is OK. If the sender has not received an ACK after a while, the sender resends.

● Bit error example: Add error detection bits describing on the sender side: 0 => 000. 001 received. ARQ may ask the sender to resend. In this case, an ACK is not transmitted.

● Loss example: The whole packet was lost. The receiver does not know that the packet was transmitted, does not send ACK, and after a while, the sender resends.

● If the sender does not receive ACK, it can thus be because of bit errors, or because the receiver did not receive the packet, or because the ACK was lost

● Sometimes ARQ is referred to as backward error correction.● ARQ causes delay!

Access control:

Split the channel between users

Access control: two classes

● Channel partitioning: centrally controlled: TDM, FDM

● Random access: CSMA-CD, CSMA-CA, each host transmits using the whole channel when it thinks the channel is free. This may lead to collisions.

time

frequency

Frequency division multiplexing (FDM),

User 2

User 1

time

frequency

Time division multiplexing (TDM)

Random access methods

Carrier Sense Multiple Access (CSMA) with collision detection: CSMA-CD

Send and listen for collision. If no collision, ok! Otherwise wait a random time and try again a few times.

CSMA-CD

Wireless CSMA

● For CSMA-CD, the hosts need to send and receive at the same time. This is judged too costly for wireless systems.

● We need a new protocol!

Carrier Sense Multiple Access (CSMA) with collision avoidance: CSMA-CA, method I

● Listen if someone else is sending. Wait a random time interval if someone else is sending. Go on like this and send when the channel is free.

● Wait for acknowledgement packet (ACK) (packet sent from receiver as confirmation) (ARQ!)

● If no ACK, wait a random time interval, before trying to resend. Repeat a few times or until ACK received.

Hidden terminal problem

● Sending hosts A and B may reach their destination D, but without hearing each other- this can result in both hosts contacting D at the same time- the hidden terminal problem

● New method again!

CSMA-CA, method II, flow diagram

random

Standards

ADSL● Asymmetric digital subscriber line (ADSL)● Example at home: Telia/Tele2 ADSL modem● Access control: FDM/TDM● Use of frequencies not used during PSTN voice

call● FEC

DOCSIS● Data Over Cable Service Interface Specification

(DOCSIS)● Example at home: Comhem● Access control: FDM/TDM● Use of bandwidth not used by cable TV● FEC

DOCSIS illustration

home

cable headend

cable distributionnetwork

Channels

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

DATA

DATA

CONTROL

1 2 3 4 5 6 7 8 9

FDMA:

Traditional Ethernet, IEEE 802.3

● Home/office local area networks (LANs): e.g., from Asymmetric Digital Subscriber Line (ADSL) modem to a computer

● 100BASE-TX flavor common, 100 Mbit/s● Over cupper wire● Access control: CSMA-CD (error detection, ARQ)

IEEE 802.11 = WIFI● CSMA-CA method 2● FEC ● example at home: wireless home network

(from, e.g., ADSL wireless modem, to your mobile phone)

Global System for Mobile Communications (GSM), and Long Term Evolution (LTE)

● GSM: TDM, FEC

● LTE: TDMA/FDM, FEC

Fiber optic communication

● Internet core: SONET OC-768: 40 Gbit/s

● FEC

Fiber-optic cables under seas