Introduction cont. Some Structure in the Chaos Lecture goal: get context, overview, feel of ing more depth, detail later in course approach: o descriptive o use Internet as example Overview: access net, media performance: loss, delay protocol layers, service models backbones, NAPs, ISPs Datakommunikation & Internet, Datavetenskap, Umu - Introduction 1 Datakommunikation & Internet, Datavetenskap, Umu - Introduction 4 Packet switching versus circuit switching Is packet switching a slam dunk winner? Great for bursty o resource sharing o no call setup Excessive congestion: packet delay and loss o protocols needed for reliable transfer, congestion control Q: How to provide circuit-like behavior? o bandwidth guarantees needed for audio/video apps still an unsolved problem (chapter 6) Access s and media Q: How to connection end systems to edge router? residential access nets institutional access s (school, company) mobile access s Keep in mind: bandwidth (bits per second) of access? shared or dedicated? Datakommunikation & Internet, Datavetenskap, Umu - Introduction 2 Datakommunikation & Internet, Datavetenskap, Umu - Introduction 5 Packet-switched s: routing Residential access: point to point access Goal: move packets among routers from source to destination o we ll study several path selection algorithms (chapter 4) gram : o destination address determines next hop o routes may change during session o analogy: driving, asking directions virtual circuit : o each packet carries tag (virtual circuit ID), tag determines next hop o fixed path determined at call setup time, remains fixed thru call o routers maintain per-call state Dialup via modem o up to 56Kbps direct access to router (conceptually) ISDN: intergrated services digital : 128Kbps alldigital connect to router ADSL: asymmetric digital subscriber line o up to 1 bps home-to-router o up to 8 bps router-to-home o Ordinary PSTN Datakommunikation & Internet, Datavetenskap, Umu - Introduction 3 Datakommunikation & Internet, Datavetenskap, Umu - Introduction 6 1
Residential access: cable modems HFC: hybrid fiber coax o asymmetric: up to 10bps upstream, 1 bps downstream of cable and fiber attaches homes to ISP router o shared access to router among home o issues: congestion, dimensioning edia : transmitted bit propagates across guided media: o signals propagate in solid media: copper, fiber unguided media: o signals propagate freely e.g., radio Twisted Pair (TP) two insulated copper wires o Category 3: traditional phone wires, 10 bps ethernet o Category 5 TP: 100bps ethernet 1000bps ehternet Datakommunikation & Internet, Datavetenskap, Umu - Introduction 7 Datakommunikation & Internet, Datavetenskap, Umu - Introduction 10 Institutional access: local area s edia: coax, fiber company/univ local area (LAN) connects end system to edge router Ethernet: o shared or dedicated cable connects end system and router o 10 bs, 100bps, Gigabit Ethernet LANs: chapter 5 Coaxial cable: wire (signal carrier) within a wire (shield) o baseband: single channel on cable o broadband: multiple channel on cable bidirectional common use in 10bps Ethernet Fiber optic cable: glass fiber carrying light pulses high-speed operation: o 100bps Ethernet o high-speed point-to-point transmission (e.g., 5 Gbps) low error rate Datakommunikation & Internet, Datavetenskap, Umu - Introduction 8 Datakommunikation & Internet, Datavetenskap, Umu - Introduction 11 Wireless access s media: radio shared wireless access connects end system to router wireless LANs: o radio spectrum replaces wire o e.g., Lucent Wavelan 10 bps wider-area wireless access o GPRS (General Packet Radio Service) o 3G router base station mobile hosts signal carried in electromagnetic spectrum no wire bidirectional propagation environment effects: o reflection o obstruction by objects o interference Radio types: microwave o e.g. up to 45 bps channels LAN (e.g., wavelan) o 2bps, 11bps, 22bps, 54bps wide-area (e.g., cellular) o e.g. GPRS, 10 s Kbps satellite o up to 50bps channel (or multiple smaller channels) o 270 msec end-end delay Datakommunikation & Internet, Datavetenskap, Umu - Introduction 9 Datakommunikation & Internet, Datavetenskap, Umu - Introduction 12 2
Delay in packet-switched s Packet loss and End to End delay packets experience delay on end-to-end path four sources of delay at each hop A B transmission nodal processing propagation queuing nodal processing: o check bit errors o determine output queuing o time waiting at output for transmission o depends on congestion level of router Finite queue length o La/R > 1 -> The space in the queue decrease o Sooner or later no space on the queue for arriving packets o This will results in packet loss End to End delay o N(d proc +d tran +d prop ) o What about queuing delay? queue of packets waiting for output o traceroute Datakommunikation & Internet, Datavetenskap, Umu - Introduction 13 Datakommunikation & Internet, Datavetenskap, Umu - Introduction 16 Delay in packet-switched s Protocol Layers Transmission delay: R= bandwidth (bps) L=packet length (bits) time to send bits into = L/R A transmission propagation Propagation delay: d = length of s = propagation speed in medium (~2x10 8 m/sec) propagation delay = d/s Note: s and R are very different quantities! s are complex! many pieces : o hosts o routers o s of various media o s o protocols o hardware, software Question: Is there any hope of organizing structure of? Or at least our discussion of s? B nodal processing queueing Datakommunikation & Internet, Datavetenskap, Umu - Introduction 14 Datakommunikation & Internet, Datavetenskap, Umu - Introduction 17 Queuing delay (revisited) Organization of air travel R= bandwidth (bps) L=packet length (bits) a=average packet arrival rate traffic intensity = La/R ticket (purchase) baggage (check) gates (load) runway takeoff ticket (complain) baggage (claim) gates (unload) runway landing 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! a series of steps Datakommunikation & Internet, Datavetenskap, Umu - Introduction 15 Datakommunikation & Internet, Datavetenskap, Umu - Introduction 18 3
Organization of air travel: a different view ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing Layers: each layer implements a service o via its own internal-layer actions o relying on services provided by layer below Why layering? Dealing with complex systems: explicit structure allows identification, relationship of complex system s pieces o layered reference model for discussion modularization eases maintenance, updating of system o change of implementation of layer s service transparent to rest of system o e.g., change in gate procedure doesn t affect rest of system layering considered harmful? Datakommunikation & Internet, Datavetenskap, Umu - Introduction 19 Datakommunikation & Internet, Datavetenskap, Umu - Introduction 22 Layered air travel: services Internet protocol stack Counter-to-counter delivery of person+bags baggage-claim-to-baggage-claim delivery people transfer: loading gate to arrival gate runway-to-runway delivery of plane from source to destination : supporting s o ftp, smtp, http : host-host transfer o tcp, udp : routing of grams from source to destination o ip, routing protocols : transfer between neighboring elements o ppp, ethernet : bits on the wire N level Protocol Data Unit (n-pdu) Datakommunikation & Internet, Datavetenskap, Umu - Introduction 20 Datakommunikation & Internet, Datavetenskap, Umu - Introduction 23 Distributed implementation of layer functionality Layering: logical communication Departing airport ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing intermediate air traffic sites arriving airport Each layer: distributed entities implement layer functions at each node entities perform actions, exchange messages with peers Datakommunikation & Internet, Datavetenskap, Umu - Introduction 21 Datakommunikation & Internet, Datavetenskap, Umu - Introduction 24 4
Layering: logical communication E.g.: take from app add addressing, reliability check info to form gram send gram to peer wait for peer to ack receipt analogy: post office ack Layer functions Each layer perform one or more of the following generic tasks Error control - o Reliability Flow controlo Avoids overwhelming slower peer Segmentation and reassemblyo Transmission side divides o Receiving side reassembles ultiplexing - o allows several higher level session to share lower level connections Connection setup - o handshaking Datakommunikation & Internet, Datavetenskap, Umu - Introduction 25 Datakommunikation & Internet, Datavetenskap, Umu - Introduction 28 Layering: communication Datakommunikation & Internet, Datavetenskap, Umu - Introduction 26 ISO/OSI protocol stack Application Presentation Session Transport Data End host Data Data One or more nodes within the ISO: International Standards Organisation OSI: Open System Interconnection Application Presentation Session Transport Data End host Datakommunikation & Internet, Datavetenskap, Umu - Introduction 29 Protocol layering and Internet structure: of s Each layer takes from above adds header information to create new unit passes new unit to layer below Ht HnHt Hl HnHt source destination Ht HnHt Hl HnHt message segment gram frame roughly hierarchical national/international backbone providers (NBPs) o e.g. BBN/GTE, Sprint, AT&T, IB, UUNet o interconnect (peer) with each other privately, or at public Access Point (NAPs) regional ISPs o connect into NBPs local ISP, company o connect into regional ISPs NAP regional ISP local ISP NBP B NBP A local ISP regional ISP NAP Datakommunikation & Internet, Datavetenskap, Umu - Introduction 27 Datakommunikation & Internet, Datavetenskap, Umu - Introduction 30 5
SUNET Datakommunikation & Internet, Datavetenskap, Umu - Introduction 31 NORDUnet Datakommunikation & Internet, Datavetenskap, Umu - Introduction 32 Summary Covered a ton of material! Internet overview what s a protocol? edge, core, access performance: loss, delay layering and service models backbones, NAPs, ISPs You now hopefully have: context, overview, feel of ing more depth, detail later in course Datakommunikation & Internet, Datavetenskap, Umu - Introduction 33 6