Chapter I: Introduction

UG3 Computer Communications & Networks (COMN)

Slides thanks to Myungjin Lee, and copyright of Kurose and Ross Whats the Internet: nuts and bolts view

PC mobile network v billions of connected computing server devices: wireless § hosts = end systems global ISP laptop § running network apps smartphone home v communication links network § fiber, copper, radio, regional ISP wireless links satellite wired § transmission rate: links bandwidth

v Packet switches: forward packets router (chunks of data) institutional network § routers and switches

2 Whats the Internet: nuts and bolts view

mobile network • Internet: network of networks – Interconnected ISPs global ISP • protocols control sending, home receiving of msgs network regional ISP – e.g., TCP, IP, HTTP, Skype, 802.11 • Internet standards – RFC: Request for comments – IETF: Internet Engineering Task Force institutional network

3 Whats the Internet: a service view

mobile network • Infrastructure that provides services to applications: global ISP – Web, VoIP, email, games, e- commerce, social nets, … home network • provides programming interface to regional ISP apps – hooks that allow sending and receiving app programs to connect to Internet – provides service options, institutional analogous to postal service network

4 Whats a protocol? human protocols: network protocols: • whats the time? • machines rather than • I have a question humans • introductions • all communication activity in Internet governed by … specific msgs sent protocols … specific actions taken when protocols define format, order msgs received, or other of msgs sent and received events among network entities, and actions taken on msg transmission, receipt

5 Whats a protocol? a human protocol and a computer network protocol:

Hi TCP connection request Hi TCP connection response Got the time? Get http://www.awl.com/kurose-ross 2:00 time

6 A closer look at network structure:

mobile network v network edge: §hosts: clients and servers global ISP §servers often in data centers

home v access networks, physical network regional ISP media: wired, wireless communication links v network core: §interconnected routers §network of networks institutional network

7 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?

8 Access net: digital subscriber line (DSL)

central office telephone network

DSL splitter modem DSLAM

ISP voice, data transmitted at different frequencies over DSL access dedicated line to central office multiplexer v use existing telephone line to central office DSLAM § data over DSL phone line goes to Internet § voice over DSL phone line goes to telephone net v < 2.5 Mbps upstream transmission rate (typically < 1 Mbps) v < 24 Mbps downstream transmission rate (typically < 10 Mbps)

9 Access net: cable network

cable headend …

cable splitter modem

C O V V V V V V N I I I I I I D D T D D D D D D A A R E E E E E E T T O O O O O O O A A L

1 2 3 4 5 6 7 8 9 Channels frequency division multiplexing: different channels transmitted in different frequency bands

10 Access net: cable network

cable headend …

cable splitter cable modem modem CMTS termination system

data, TV transmitted at different frequencies over shared cable ISP distribution network v HFC: hybrid fiber coax § asymmetric: up to 30Mbps downstream transmission rate, 2 Mbps upstream transmission rate v network of cable, fiber attaches homes to ISP router § homes share access network to cable headend § unlike DSL, which has dedicated access to central office 11 Access net: home network

wireless devices

to/from headend or central office often combined in single box

cable or DSL modem

wireless access router, firewall, NAT point (54 Mbps) wired Ethernet (100 Mbps)

12 Enterprise access networks (Ethernet)

institutional link to ISP (Internet) institutional router

Ethernet institutional mail, switch web servers

v typically used in companies, universities, etc v 10 Mbps, 100Mbps, 1Gbps, 10Gbps transmission rates v today, end systems typically connect into Ethernet switch

13 Wireless access networks

• shared wireless access network connects end system to router – via base station aka access point wireless LANs: wide-area wireless access § within building (100 ft) § provided by telco (cellular) § 802.11b/g (WiFi): 11, 54 Mbps operator, 10 s km transmission rate § between 1 and 10 Mbps § 3G, 4G: LTE

to Internet to Internet

14 Host: sends packets of data host sending function: v takes application message v breaks into smaller chunks, two packets, known as packets, of length L bits L bits each v transmits packet into access network at transmission rate R § link transmission rate, aka link 2 1 capacity, aka link bandwidth R: link transmission rate host

packet time needed to L (bits) transmission = transmit L-bit = delay packet into link R (bits/sec)

15 Physical media

• bit: propagates between transmitter/receiver pairs twisted pair (TP) • physical link: what lies • two insulated copper wires between transmitter & – Category 5: 100 Mbps, 1 Gpbs receiver Ethernet • guided media: – Category 6: 10Gbps – signals propagate in solid media: copper, fiber, coax • unguided media: – signals propagate freely, e.g., radio

16 Physical media: coax, fiber coaxial cable: fiber optic cable: v two concentric copper v glass fiber carrying light pulses, each conductors pulse a bit v bidirectional v high-speed operation: v broadband: § high-speed point-to-point § multiple channels on cable transmission (e.g., 10s-100s § HFC Gbps transmission rate) v low error rate: § repeaters spaced far apart § immune to electromagnetic noise

17 Physical media: radio

radio link types: v signal carried in electromagnetic v terrestrial microwave spectrum § e.g. up to 45 Mbps channels v no physical wire v LAN (e.g., WiFi) § 11Mbps, 54 Mbps v Bidirectional v wide-area (e.g., cellular) v propagation environment effects: § 3G cellular: ~ few Mbps § Reflection v satellite § obstruction by objects § Kbps to 45Mbps channel (or § interference multiple smaller channels) § 270 msec end-end delay § geosynchronous versus low altitude