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Internetworking Technology - Chapter 1 Computer Networks and the Internet (Cont.)

Chapter 1: roadmap 1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History

Access networks and physical media Q: How to connection end systems to edge router? Physical link(s) that connect an end system to its edge router, which is the first 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?

Residential access: point to point access Dialup via modem up to 56Kbps direct access to router (often less) Can t surf and phone at same time: can t be always on ADSL: asymmetric digital subscriber line up to 1 Mbps upstream (today typically < 256 kbps) up to 8 Mbps downstream (today typically < 1.5 Mbps) FDM: 50 khz - 1 MHz for downstream; 4 khz - 50 khz for upstream; 0 khz - 4 khz for ordinary telephone By restricting the distance between user and ISP modem

Residential access: cable modems HFC: hybrid fiber coaxial cable asymmetric: upstream is less than downstream network of cable and fiber attaches homes to ISP router shared access to router among home E.g. In the case that all the users are downloading MP3 file at the same time. issues: congestion, dimensioning deployment: available via cable companies, e.g., MediaOne

Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

Cable Network Architecture: Overview A cable head end broadcasts through a distribution network of coaxial cable and amplifiers to residence. Fiber optics connect the cable head end to neighborhoodlevel junctions, from which traditional coaxial cable is used to reach individual houses. Typically 500 to 5,000 homes cable headend cable distribution network (simplified) home

Cable Network Architecture: Overview Special modem is needed Purchase or lease Connects to the home PC through a Ethernet port cable headend cable distribution network (simplified) home

Cable Network Architecture: Overview server(s) cable headend cable distribution network home

Cable Network Architecture: Overview Channels V I D E O V I D E O V I D E O V I D E O V I D E O V I D E O D A T A D A T A C O N T R O L 1 2 3 4 5 6 7 8 9 FDM: cable headend home cable distribution network

HFC versus DSL Shared or Dedicated? As with DSL, the downstream channel is typically allocated more bandwidth Hence, a faster transmission rate With HFC, the rates are shared among the homes (shared broadcast medium) If reasonably dimensioned, it provides higher bandwidths than DSL. The battle between two mediums has clearly begun However, the common attractive feature is always on

Company access: local area networks company/univ local area network (LAN) connects end system to edge router Ethernet: Currently by far, the most prevalent tech. for LAN shared or dedicated link connects end system and router 10 Mbps, 100Mbps, Gigabit Ethernet deployment: institutions, home LANs happening now LANs: chapter 5

Wireless access networks shared wireless access network connects end system to router via base station aka access point for roaming PC a router interconnects the BS and the stationary PC with a cable model for Internet -> two household members can use Internet wireless LANs (Wireless Ethernet): 802.11b (WiFi): 11 Mbps (few meters) wider-area wireless access 3G ~ 384 kbps Will it happen?? WAP/GPRS in Europe : Internet access over the portable phones router base station mobile hosts

Home networks Typical home network components: ADSL or cable modem router/firewall Ethernet wireless access point to/from cable headend cable modem router/ firewall Ethernet (switched) wireless access point wireless laptops

Physical Media Bit: propagates between transmitter/rcvr pairs (electromagnetic waves or optical pulses) physical link: what lies between transmitter & receiver guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., radio : wireless LAN, digital satellite channel Twisted Pair (TP) two common insulated copper wires Category 3: traditional phone wires, 10 Mbps Ethernet (Office buildings are prewired with two or more parallel pairs of category 3 TPs Category 5 TP: 100Mbps Ethernet (For new recent office buildings)

Physical Media: coax, fiber Coaxial cable: two concentric copper conductors (rather than parallel in TP) Bidirectional (T-connector) baseband: single channel on cable legacy Ethernet broadband: multiple channel on cable HFC (common in cable TV) Fiber optic cable: glass fiber carrying light pulses, each pulse a bit high-speed operation: high-speed point-to-point transmission (e.g., 5 Gps) low error rate: repeaters spaced far apart ; immune to electromagnetic noise (overseas links) Prevalent in the backbone of the Internet

Physical media: radio signal carried in electromagnetic spectrum no physical wire bidirectional propagation environment effects: reflection Shadow fading (decrease the signal strength as the signal travels over a distance and through obstructing objects Interference (due to other radio channels or electromagnetic signals) Radio link types: terrestrial microwave LAN e.g. up to 45 Mbps channels Ten to a few hundred meters wide-area Tens of kilometers (e.g. 3G) satellite up to 50Mbps channel (or multiple smaller channels) 250 msec end-end delay: substantial Geostationary ersus Lowaltitude (for the Internt access soon)

Internet structure: network of networks roughly hierarchical (tiered hierarchy) at center: tier-1 ISPs (e.g., UUNet, BBN/Genuity, Sprint, AT&T), national/international in coverage treat each other as equals Internet backbone networks Tier-1 providers interconnect (peer) privately Tier 1 ISP Tier 1 ISP NAP Tier 1 ISP Tier-1 providers also interconnect at public network access points (NAPs)

Tier-1 ISP: e.g., Sprint Sprint US backbone network often, 622Mbps or the 2.5-10Gbps range recently

Internet structure: network of networks Tier-2 ISPs: smaller (often regional) ISPs Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet tier-2 ISP is customer of tier-1 provider Tier-2 ISP Tier-2 ISP Tier 1 ISP NAP Tier 1 ISP Tier 1 ISP Tier-2 ISPs also peer privately with each other, interconnect at NAP Tier-2 ISP Tier-2 ISP Tier-2 ISP

Internet structure: network of networks Tier-3 ISPs and local ISPs last hop ( access ) network (closest to end systems) Dozens of tier-1 and tier-2 ISPs and thousands of lower-tier ISPs Local and tier- 3 ISPs are customers of higher tier ISPs connecting them to rest of Internet local ISP local ISP Tier 3 ISP Tier-2 ISP Tier 1 ISP Tier-2 ISP local ISP local ISP Tier 1 ISP local ISP Tier-2 ISP NAP Tier 1 ISP Tier-2 ISP local ISP local ISP Tier-2 ISP local ISP

Internet structure: network of networks a packet passes through many networks! Now anyone of us can become an access ISP local ISP Tier 3 ISP Tier-2 ISP local ISP Tier 1 ISP local ISP Tier-2 ISP NAP local ISP local ISP Tier 1 ISP Tier-2 ISP local ISP Tier 1 ISP Tier-2 ISP local ISP Tier-2 ISP local ISP

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 packet being transmitted (delay) A B packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers

Four sources of packet delay 1. nodal processing: check bit errors determine output link 2. queuing time waiting at output link for transmission depends on congestion level of router A transmission propagation B nodal processing queueing

Delay in packet-switched networks 3. 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 (~2x10 8 m/sec) propagation delay = d/s A transmission Note: s and R are very different quantities! propagation B nodal processing queueing

Caravan analogy 100 km 100 km ten-car caravan Cars propagate at 100 km/hr toll booth Toll booth takes 12 sec to service a car (transmission time) car~bit; caravan ~ packet Q: How long until caravan is lined up before 2nd toll booth? toll booth Time to push entire caravan through toll booth onto highway = 12*10 = 120 sec Time for last car to propagate from 1st to 2nd toll both: 100km/(100km/hr)= 1 hr A: 62 minutes

Caravan analogy (more) 100 km 100 km ten-car caravan toll booth Cars now propagate at 1000 km/hr Toll booth now takes 1 min to service a car Q: Will cars arrive to 2nd booth before all cars serviced at 1st booth? toll booth Yes! After 7 min, 1st car at 2nd booth and 3 cars still at 1st booth. 1st bit of packet can arrive at 2nd router before packet is fully transmitted at 1st router! This situation arises often in packet-switched networks.

Nodal delay d = d + d + d + nodal proc queue trans d prop d proc = processing delay typically a few microsecs or less d queue = queuing delay depends on congestion d trans = transmission delay = L/R, significant for low-speed links d prop = propagation delay a few microsecs to hundreds of msecs

Queueing delay (revisited) R=link bandwidth (bps) L=packet length (bits) a=average packet arrival rate traffic intensity = La/R La/R ~ 0: average queueing delay small La/R -> 1: delays become large La/R > 1: more work arriving than can be serviced, average delay infinite!

Real Internet delays and routes What do real Internet delay & loss look like? Traceroute program: provides delay measurement from source to router along end-end Internet path towards destination. For all i: sends three packets that will reach router i on path towards destination router i will return packets to sender sender times interval between transmission and reply. 3 probes 3 probes 3 probes

Real Internet delays and routes traceroute: gaia.cs.umass.edu to www.eurecom.fr Three delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * 18 * * * 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms trans-oceanic link * means no response (probe lost, router not replying)

Packet loss queue (aka buffer) preceding a link has finite capacity when packet arrives to full queue, packet is dropped (aka lost) lost packet may be retransmitted by previous node, by source end system, or not retransmitted at all

Protocol Layers Networks are complex! many pieces : hosts routers various types of link-media applications protocols hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks?

Organization of air travel ticket (purchase) baggage (check) gates (load) runway takeoff ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing airplane routing a series of steps

Organization of air travel: a different view ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing airplane routing Layers: Divided the airline functionality into layers Each layer implements a service via its own internal-layer actions relying on services provided by layer below

Why layering? Dealing with complex systems: Allows us to discuss a well-defined, specific part of a large and complex system. modularization eases maintenance, updating of system change of implementation of layer s service transparent to rest of system e.g., change in gate procedure doesn t affect rest of system Can layering be harmful? One layer may duplicate lower-layer functionality Functionality on one layer may need information which is present only in another-layer, this violates the goal of separation of layers.

Internet protocol stack application: supporting network applications FTP, SMTP, STTP transport: host-host 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

Layering: logical communication Each layer: distributed entities implement layer functions at each node E.g.: transport data application transport network link physical application transport network link physical data ack application transport network link physical network link physical data application transport network link physical

Protocol layering and data Each layer takes data from above adds header information to create new data unit passes new data unit to layer below source destination Hl Ht HnHt HnHt M M M M application transport network link physical application transport network link physical Hl Ht HnHt HnHt M M M M message segment datagram frame

Problems # 8, 9 #2, 10 in Discussion Questions Using the 802.11b wireless LAN tech., design a home network for your home or your parents home. List the specific product models in your home network along with their costs. Surf the Web to find a company that is offering HFC Internet access. What is the transmission rate of the cable modem? Is this rate always guaranteed for each user on the network?