1. 1-2 access networks and physical media q: how to connect end systems to edge router? residential...

1

Internet Access Overview

1-2

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?

1-3

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 Mbps) ADSL2+ 24Mbps

1-4

Residential access: cable modems

• HFC: hybrid fiber coax▫asymmetric: up to 30Mbps downstream, 2

Mbps upstream• network of cable and fiber attaches homes to ISP

router▫homes share access to router

• deployment: available via cable TV companies

1-5

Residential access: cable modems

Diagram: http://www.cabledatacomnews.com/cmic/diagram.html

1-6

Cable Network Architecture: Overview

home

cable headend

cable distributionnetwork (simplified)

Typically 500 to 5,000 homes

1-7


home

cable headend

cable distributionnetwork

server(s)

1-8


home

cable headend

cable distributionnetwork (simplified)

1-9


home

cable headend

cable distributionnetwork

Channels

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

VIDEO

DATA

DATA

CONTROL

1 2 3 4 5 6 7 8 9

FDM:

1-10

Company access: local area networks

• company/univ local area network (LAN) connects end system to edge router

• Ethernet: ▫shared or dedicated link

connects end system and router

▫10 Mbs, 100Mbps, Gigabit Ethernet

1-11

Wireless access networks

• shared wireless access network connects end system to router▫ via base station aka “access point”

• wireless LANs:▫ 802.11b/g (WiFi): 11 or 54 Mbps

• wider-area wireless access▫ provided by telco operator▫ 3G ~ 384 kbps

Will it happen??▫ GPRS ▫ WiMAX

basestation

mobilehosts

router

1-12

Home networks

Typical home network components: • ADSL or cable modem• router/firewall/NAT• Ethernet• wireless access point

wirelessaccess point

wirelesslaptops

router/firewall

cablemodem

to/fromcable

headend

Ethernet

1-13

Physical Media

• Bit: propagates betweentransmitter/rcvr pairs

• 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

Twisted Pair (TP)• two insulated copper

wires▫ Category 3: traditional

phone wires, 10 Mbps Ethernet

▫ Category 5: 100Mbps Ethernet

1-14

Physical Media: coax, fiber

Coaxial cable:• two concentric copper

conductors• bidirectional• baseband:▫ single channel on cable▫ legacy Ethernet

• broadband:▫ multiple channels on cable▫ HFC

Fiber optic cable: glass fiber carrying light pulses,

each pulse a bit high-speed operation:

high-speed point-to-point transmission (e.g., 10’s-100’s Gps)

low error rate: repeaters spaced far apart ; immune to electromagnetic noise

1-15

Physical media: radio

• signal carried in electromagnetic spectrum

• no physical “wire”• bidirectional• propagation environment

effects:▫ reflection ▫ obstruction by objects▫ interference

Radio link types: terrestrial microwave

e.g. up to 45 Mbps channels

LAN (e.g., Wifi) 11Mbps, 54 Mbps

wide-area (e.g., cellular) e.g. 3G: hundreds of kbps

satellite up to 45Mbps channel (or

multiple smaller channels) 270 msec end-end delay geosynchronous versus low

altitude

16

Teleports• A telecommunications port—or, more commonly, teleport—is

a satellite ground station with multiple parabolic antennas (i.e., an antenna farm) that functions as a hub connecting a satellite or geocentric orbital network with a terrestrial telecommunications network.

• Teleports may provide various broadcasting services among other telecommunications functions, such as uploading computer programs or issuing commands over an uplink to a satellite.

17

Teleports

Balambu Earth Station: Nepal Telecom=>Teleport

18

Satellites• Geostationary Satellites• Medium-Earth Orbit Satellites• Low-Earth Orbit Satellites

19

Geostationary Satellites• At altitude approx. 36000Km above equatorial plane, satellite

rotation period is 24hrs.• Satellite is stationary with respect to Earth.• With current technology, it is unwise to have geostationary

satellites spaced much closer than 2 degrees in the 360-degree equatorial plane, to avoid interference.

• With a spacing of 2 degrees, there can only be 360/2 = 180 of these satellites in the sky at once.

• However, each transponder can use multiple frequencies and polarizations to increase the available bandwidth.

20

Medium-Earth Orbit Satellites• At much lower altitudes, we find the MEO (Medium-Earth

Orbit) satellites.

• As viewed from the earth, these drift slowly in longitude, taking something like 6 hours to circle the earth. Accordingly, they must be tracked as they move through the sky. Because they are lower than the GEOs.

• GPS (Global Positioning System) satellites orbiting at about 18,000 km are examples of MEO satellites.

21

Low-Earth Orbit Satellites• Moving down in altitude, we come to the LEO (Low-Earth

Orbit) satellites.

• Due to their rapid motion, large numbers of them are needed for a complete system.

• On the other hand, because the satellites are so close to the earth, the ground stations do not need much power, and the round-trip delay is only a few milliseconds.

22

Satellite

23

Terrestrial Radio Links•Radio channels carry signals in the electromagnetic

spectrum.

•They are an attractive media because require no physical "wire“ to be installed, can penetrate walls, provide connectivity to a mobile user, and can potentially carry a signal for long distances.

•The characteristics of a radio channel depend significantly on the propagation environment and the distance over which a signal is to be carried.

24

Terrestrial Radio Links• those that operate as local area networks (typically spanning 10's to a few

hundred meters) e.g. WLAN and

• wide-area radio channels that are used for mobile data services (typically operating within a metropolitan region) e.g. WAP, 3G etc

25

Satellite frequency band• L-bank (1-2GHz)•C-Bank (4-8GHz)•KU-Band (12-18GHz)•KA-Band (26.5-40GHz)

26

Satellite frequency band• L-bank (1-2GHz)▫ Being a relatively low frequency, L-band is easier to process,

requiring less sophisticated and less expensive RF equipment.▫ L-Band is also used for low earth orbit satellites, military satellites,

and terrestrial wireless connections like GSM mobile phones. It is also used as an intermediate frequency for satellite TV where the Ku or Ka band signals are down-converted to L-Band at the antenna

• C-Bank (4-8GHz)▫ Satellite C-band usually transmits around 6 GHz and receives

around 4 GHz. It uses large (2.4- 3.7 meter) antennas▫ C-band is typically used by large ships that traverse the oceans on a

regular basis and require uninterrupted, dedicated, always on connectivity as they move from region to region.

▫ C-band is also used for terrestrial microwave links

27

Satellite frequency band• KU-Band (12-18GHz)

▫ Ku-Band is most commonly used for satellite TV and is used for most VSAT systems.

▫ There is much more bandwidth available in Ku -Band and it is therefore less expensive that C or L-band.

▫ Ku band coverage is generally by regional spot beams, covering major land areas with TV reception

▫ VSAT Antenna sizes typically range from the standard 1 meter, to 1.5 meters & as low as 60cm for spread spectrum operation

• KA-Band (26.5-40GHz)▫ is an extremely high frequency requiring great pointing accuracy and

sophisticated RF equipment. ▫ It is commonly used for high definition satellite TV. It is also used today

for terrestrial VSAT services

28

Internet Backbone Networks

29

Internet service provider• An Internet service provider (ISP) is an organization that provides access

to the Internet. Access ISPs directly connect clients to the Internet using copper wires, wireless or fiber-optic connections.

• Hosting ISPs are a kind of colocation center that leases server space to smaller businesses and other people. Transit ISPs provide large amounts of bandwidth for connecting hosting ISPs to access ISPs

30

ISPs• Tier1• Tier2 and • Tier3 ISPS

1-31

Internet structure: network of networks

• roughly hierarchical• at center: “tier-1” ISPs (e.g., MCI, Sprint, AT&T, Cable and

Wireless), national/international coverage▫treat each other as equals

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

Tier-1 providers interconnect (peer) privately

NAP

Tier-1 providers also interconnect at public network access points (NAPs)

1-32

Tier-1 ISP: e.g., SprintSprint US backbone network

Seattle

Atlanta

Chicago

Roachdale

Stockton

San Jose

Anaheim

Fort Worth

Orlando

Kansas City

CheyenneNew York

PennsaukenRelayWash. DC

Tacoma

DS3 (45 Mbps)OC3 (155 Mbps)OC12 (622 Mbps)OC48 (2.4 Gbps)

…

to/from customers

peering

to/from backbone

….

………

POP: point-of-presence

1-33


• “Tier-2” ISPs: smaller (often regional) ISPs▫ Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP

Tier-2 ISPTier-2 ISP

Tier-2 ISP Tier-2 ISP

Tier-2 ISP

Tier-2 ISP pays tier-1 ISP for connectivity to rest of Internet tier-2 ISP is customer oftier-1 provider

Tier-2 ISPs also peer privately with each other, interconnect at NAP

1-34


• “Tier-3” ISPs and local ISPs ▫ last hop (“access”) network (closest to end systems)

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP



Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

Local and tier- 3 ISPs are customers ofhigher tier ISPsconnecting them to rest of Internet

1-35


• a packet passes through many networks!

Tier 1 ISP

Tier 1 ISP

Tier 1 ISP

NAP



Tier-2 ISP

localISPlocal

ISPlocalISP

localISP

localISP Tier 3

ISP

localISP

localISP

localISP

36

Delays• As a packet travels from one node to the subsequent node

along the path, the packet suffers from several different types of delays at each node along the path.

• The most important of these delays are the▫Nodal processing delay /Processing Delay▫Queuing delay▫ Transmission delay and▫ Propagation delay

37

Delays• Nodal processing delay /Processing Delay

▫ The time required to examine the packet's header and determine where to direct the packet is part of the processing delay.

▫ The processing delay can also include other factors, such as the time needed to check for bit-level errors in the packet that occurred in transmitting the packet's bits from the upstream router to router

• Queuing delay▫ After this nodal processing, the router directs the packet to the queue that

precedes the link to router B. ▫ At the queue, the packet experiences a queuing delay as it waits to be

transmitted onto the link. ▫ The queuing delay of a specific packet will depend on the number of other,

earlier-arriving packets that are queued and waiting for transmission across the link; the delay of a given packet can vary significantly from packet to packet.

▫ If the queue is empty and no other packet is currently being transmitted, then our packet's queuing delay is zero

38

Delays• Transmission Delay

▫ The amount of time required to transmit all of the packet's bits into the link.

• Propagation Delay▫ The time required to send packet from one router to another router. The

bit propagates at the propagation speed of the link. ▫ The propagation speed depends on the physical medium of the link and

the distance from source to destination.• Total Delay

▫ Total Delay dtotal = dproc + dqueue + dtrans + dprop

• If there is N node and all the delays are same then the total delay is ▫ Total Delay dtotal = N (dproc + dqueue + dtrans + dprop)

1. 1-2 access networks and physical media q: how to connect end systems to edge router? residential...

Documents