What’s the Internet? What’s the Internet?
PC Mobile network connected computing Protocols control sending Mobile network server devices: hosts = end Global ISP and receiving Global ISP wireless systems . TCP, IP, HTTP, Ethernet laptop . running network cellular Home network handheld apps Internet: “network of Home network Regional ISP communication networks” Regional ISP
access links points . fiber, copper, Institutional network Internet standards wired Institutional network links radio . RFC: Request for comments . transmission . IETF: Internet Engineering rate = Task Force router bandwidth routers: forward packets Introduction 1-1 Introduction 1-2
What’s the Internet? Service view: What’s a protocol?
distributed applications: human protocols: network protocols: . Web, VoIP, email, “what’s the time?” machines rather than games, e-commerce, humans file sharing “I have a question” introductions all communication communication services activity in Internet provided to apps: governed by protocols . reliable data delivery . “best effort” protocols define format, (unreliable) data order of msgs sent and delivery received among network entities, and actions taken on msg transmission, receipt
Introduction 1-3 Introduction 1-4
What’s a protocol? A closer look at network structure:
a human protocol and a computer network protocol: network edge: applications and hosts Hi TCP connection request access networks, Hi TCP connection physical media: response Got the wired, wireless time? Get http://www.awl.com/kurose-ross communication links 2:00
1 The network edge: Access networks and physical media
end systems (hosts): Q: How to connect end . run application programs systems to edge router? . e.g. Web, email residential access nets peer-peer . at “edge of network” institutional access client/server model networks (school, . client host requests, receives company) service from always-on server mobile access networks client/server . e.g. Web browser/server; email client/server peer-peer model: . minimal (or no) use of dedicated servers . e.g. Skype, BitTorrent
Introduction 1-7 Introduction 1-8
Ethernet Internet access Wireless access networks
wireless access network 100 Mbps institutional router . via base station aka “access to institution’s Ethernet point” switch ISP router 100 Mbps wireless LANs: . 802.11 1 Gbps base wider-area wireless access station 100 Mbps . provided by telco operator server . 3G, 4G
typically used in companies, universities, etc mobile 10 Mbps, 100Mbps, 1Gbps, 10Gbps Ethernet hosts end systems typically connect into Ethernet switch
Introduction 1-9 Introduction 1-10
Home networks Physical Media Typical home network components: Twisted Pair (TP) DSL or cable modem physical link: what lies two insulated copper between transmitter & router/firewall wires receiver . Category 3: traditional Ethernet guided media (cables): phone wires, 10 Mbps wireless access point . signals propagate in solid Ethernet media: copper, fiber, coax . Category 5: 100Mbps Ethernet wireless unguided media: to/from laptops . signals propagate freely, cable router/ cable e.g., radio modem firewall headend wireless access Ethernet point
Introduction 1-11 Introduction 1-12
2 Physical Media: coax, fiber Physical media: radio
Coaxial cable: Fiber optic cable: signal carried in Radio link types: two concentric copper high-speed operation: electromagnetic terrestrial microwave conductors . high-speed point-to-point spectrum . e.g. up to 45 Mbps channels transmission (e.g., 10’s- no physical “wire” LAN (e.g., WiFi) 100’s Gpbs) . 11Mbps, 54 Mbps low error rate bidirectional wide-area (cellular) repeaters spaced far propagation . 3G, 4G apart environment effects: . reflection satellite immune to . obstruction by objects . 270 msec end-end delay electromagnetic noise . interference . geosynchronous versus low altitude
Introduction 1-13 Introduction 1-14
The Network Core Network Core: Circuit Switching
mesh of interconnected link bandwidth, switch routers capacity reserved for Two main principles: call . circuit switching: no sharing dedicated circuit per Guaranteed call: telephone net performance . packet-switching: data call setup required sent thru net in discrete “chunks”
Introduction 1-15 Introduction 1-16
Network Core: Circuit Switching Circuit Switching: FDM and TDM
Example: network resources dividing link bandwidth FDM (e.g., bandwidth) into “pieces” 4 users divided into “pieces” . frequency division pieces allocated to calls . time division frequency resource piece idle if not used by owning call time (no sharing) TDM
frequency
time Introduction 1-17 Introduction 1-18
3 Network Core: Packet Switching Packet switching
data stream divided into resource contention: great for bursty data packets demand can exceed . resource sharing packets share network capacity . simpler, no call setup resources congestion: packets congestion: packet delay and loss each packet uses full link queue . protocols needed for reliable data transfer, bandwidth store and forward: congestion control resources used as needed packets move one hop How to provide quality of service? at a time . bandwidth guarantees for audio/video apps . still an unsolved problem
Introduction 1-19 Introduction 1-20
Internet structure: network of networks Tier-1 ISP: e.g., Sprint roughly hierarchical at center: small # of well-connected large networks . “tier-1” commercial ISPs (e.g., Verizon, Sprint, AT&T, Qwest, Level3), national & international coverage . large content distributors (Google, Akamai, Microsoft) . treat each other as equals
IXP IXP
Tier-1 ISPs & Large Content Tier 1 ISP Large Content Content Distributor Distributor Distributors, (e.g., Akamai) (e.g., Google) interconnect (peer) privately … or at Internet Tier 1 ISP Tier 1 ISP Exchange Points IXPs
Introduction 1-21 Introduction 1-22
Internet structure: network of networks Internet structure: network of networks “tier-2” ISPs: smaller (often regional) ISPs “Tier-3” ISPs, local ISPs connect to one or more tier-1 (provider) ISPs customer of tier 1 or tier 2 network . each tier-1 has many tier-2 customer nets . last hop (“access”) network (closest to end systems) . tier 2 pays tier 1 provider tier-2 nets sometimes peer directly with each other
(bypassing tier 1) , or at IXP Tier 2 IXP ISP IXP Tier 2 Tier 2 Tier 2 IXP ISP IXP ISP ISP Tier 2 Tier 2 Large Content ISP ISP Large Content Tier 1 ISP Distributor Distributor Large Content Tier 1 ISP Large Content (e.g., Akamai) (e.g., Google) Distributor Distributor (e.g., Akamai) (e.g., Google) Tier 2 Tier 1 ISP Tier 1 ISP ISP Tier 2 Tier 2 Tier 2 Tier 2 Tier 2 Tier 2 Tier 1 ISP Tier 1 ISP ISP ISP ISP Tier 2 ISP ISP ISP Tier 2 Tier 2 Tier 2 Tier 2 ISP ISP ISP ISP ISP Introduction 1-23 Introduction 1-24
4 Internet structure: network of networks Protocol “Layers”
a packet passes through many networks from source Networks are complex, host to destination host with many “pieces”: hosts Question: routers Is there any hope of Tier 2 links of various organizing structure of IXP ISP IXP Tier 2 Tier 2 media network? ISP ISP Large Content applications Large Content Tier 1 ISP Distributor Distributor (e.g., Akamai) (e.g., Google) protocols Or at least our discussion hardware, of networks? Tier 2 Tier 1 ISP Tier 1 ISP software ISP Tier 2 Tier 2 Tier 2 Tier 2 Tier 2 ISP ISP ISP ISP ISP
Introduction 1-25 Introduction 1-26
Internet protocol stack ISO/OSI reference model
application: supporting network presentation: allow applications to applications application interpret meaning of data, e.g., application . FTP, SMTP, HTTP encryption, compression, machine- presentation transport: process-process data transport specific conventions transfer session: synchronization, session . TCP, UDP network checkpointing, recovery of data transport exchange network: routing of datagrams from network source to destination link Internet stack “missing” these link . IP, routing protocols layers! physical link: data transfer between . these services, if needed, must physical neighboring network elements be implemented in application . Ethernet, 802.11 (WiFi) physical: bits “on the wire” Introduction 1-27 Introduction 1-28
Exempel Vad händer?
Dator A Dator B 3 7
3 7 Message Message
7 Message 7 Message
B 7 Message B 7 Message B 7 Message B 7 Message
X B 7 Message X B 7 Message Y B 7 Message Y B 7 Message Router C Port Y
Port X
1-29 1-30
5 source Encapsulation message M application
segment Ht M transport datagram Hn Ht M network frame Hl Hn Ht M link physical
switch
H H M destination Hn Ht M network n t M application Hl Hn Ht M link Hl Hn Ht M physical Ht M transport
Hn Ht M network router Hl Hn Ht M link physical
Introduction 1-31
6