computer network n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Computer Network PowerPoint Presentation
Download Presentation
Computer Network

Loading in 2 Seconds...

play fullscreen
1 / 150

Computer Network - PowerPoint PPT Presentation


  • 97 Views
  • Uploaded on

Computer Network. Andrew S. Tanenbaum. Outline. The mobile telephone system Cable television Wireless LANS Broadband wireless Bluetooth Data Link layer switching Quality of service. Outline. The mobile telephone system Cable television Wireless LANS Broadband wireless Bluetooth

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Computer Network' - kirra


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
computer network

Computer Network

Andrew S. Tanenbaum

outline
Outline
  • The mobile telephone system
  • Cable television
  • Wireless LANS
  • Broadband wireless
  • Bluetooth
  • Data Link layer switching
  • Quality of service
outline1
Outline
  • The mobile telephone system
  • Cable television
  • Wireless LANS
  • Broadband wireless
  • Bluetooth
  • Data Link layer switching
  • Quality of service
wireless telephones
Wireless telephones
  • Cordless phones

-Never used for networking

  • Mobile phones – through three generations with different technologies:

-Analog voice

-Digital voice

-Digital voice and data

the mobile telephone system
The mobile telephone system
  • First-generation mobile phones: analog voice

-IMTS

-AMPS

  • Second-generation mobile phones: digital voice

-D-AMPS

-GSM

-CDMA

  • Third-generation mobile phones: digital voice and data

-W-CDMA

-CDMA2000

  • 2.5G scheme

-GPRS

first generation mobile phones analog voice
First-generation mobile phones: analog voice
  • 1946 push-to-talk system

-A single channel for both sending and receiving

  • 1960 IMTS (Improved Mobile Telephone System)

-High-powered transmitter

-Two frequencies (sending/receiving)

-23 channels spread out from 150 MHz to

450 MHz

imts drawbacks
IMTS drawbacks
  • Due to the small number of channels, users often had to wait a long time before getting a dial tone.
  • Due to the lager power of the hilltop transmitter, adjacent systems had to be several hundred kilometers apart to avoid interference.
amts advanced mobile phone system
AMTS (Advanced Mobile Phone System)
  • In all mobile phone systems, a geographic region is divided up into cells.
  • Key idea:

-increases the system capacity (reuse of transmission frequencies)

-less power is needed.

mtso mobile telephone switching office
MTSO (Mobile Telephone Switching Office)
  • Handoff

- soft handoff

-no loss of continuity

-telephone needs to be able to

tune to two frequencies at the

same time

- hard handoff

amts channels
AMTS Channels
  • The AMPS system uses 832 full-duplex channels, each consisting of a pair of simplex channels

-832 simplex transmission channels

from 824 to 849 MHz

-832 simplex receive channels

from 869 to 894 MHz

  • AMPS uses FDM to separate the channels
amps call management
AMPS call management
  • When a phone switch on
  • When a caller makes a call
second generation mobile phones digital voice
Second-generation mobile phones: digital voice
  • D-AMPS is fully digital
  • D-AMPS is designed to co-exist with AMPS
  • Upstream channels are in the

1850-1910 MHz

  • Downstream channels are in the 1930-1990 MHz
d amps
D-AMPS
  • The voice signal is digitized and compressed
  • Users can share a single frequency pair using TDM
gsm the global system for mobile communications
GSM (The Global System for Mobile Communications)
  • GSM versus D-AMPS:

-FDM is used with each mobile transmitting on one frequency receiving on a higher frequency

-A single frequency pair is split by TDM into time slot shared by multiple mobiles

-GSM has a much higher data rate per user than D-AMPS

cdma code division multiple access
CDMA (Code Division Multiple Access)
  • D-AMPS , GSM use both FDM and TDM.
  • CDMA allows each station to transmit over the entire frequency spectrum all the time.
  • Multiple simultaneous transmissions are separated using coding theory.
cdma coding theory
CDMA coding theory
  • Each bit time is subdivided into m short intervals called chips (There are 64 or 128 chips per bit).
  • Each station is assigned a unique

m-bit code called a chip sequence.

- To transmit 1 bit , a station sends

its chip sequence

- To transmit 0 bit , a station sends

the one’s complement of its chip

sequence

third generation mobile phones digital voice and data
Third-generation mobile phones: digital voice and data
  • WCDMA (Wideband CDMA)

-uses direct sequence spread spectrum

-runs in a 5 MHz bandwidth

-has been designed to interwork with GSM

  • CDMA2000

-not be designed to interwork with GSM

-has the differences between WCDMA : chip rate, frame time, spectrum used, the way to do time synchronization

2 5 g schema gprs general packet radio service
2.5 G schema GPRS (General Packet Radio Service)
  • Is an overlay packet network on top of D-AMPS or GSM.
  • Allows mobile stations to send and receive IP packets in a cell running a voice system
outline2
Outline
  • The mobile telephone system
  • Cable television
  • Wireless LANS
  • Broadband wireless
  • Bluetooth
  • Data Link layer switching
  • Quality of service
cable television
Cable television
  • Community antenna television
  • Internet over cable
  • Spectrum allocation
  • Cable modems
  • ADSL versus cable
cable modems
Cable modems
  • Internet access requires a cable modem
  • Cable modem is always on
  • Cable operators do not charge for connect time
what happens when a cable modem is plugged in and powered up 1 2
What happens when a cable modem is plugged in and powered up? (1/2)
  • The modem scans the downstream channels looking for a special packet periodically put out by the headend to provide system parameters to modems.
  • Modem announces its presence on one of the upstream channels
  • The headend responds by assigning the modem to its upstream and downstream channels
what happens when a cable modem is plugged in and powered up 2 2
What happens when a cable modem is plugged in and powered up? (2/2)
  • The modem determines its distance from the headend –ranging
  • During initialization, the headend also assigns each modem to a minislot to use for requesting upstream bandwidth
  • What happens when a computer wants to send a packet?
adsl versus cable
ADSL versus cable
  • Both use fiber in the backbone, but they differ on the edge
  • The increasing numbers have different effects on existing users on the two system
  • Availability and security and reliability are issues on which ADSL and cable differ
outline3
Outline
  • The mobile telephone system
  • Cable television
  • Wireless LANS
  • Broadband wireless
  • Bluetooth
  • Data Link layer switching
  • Quality of service
wireless lans
Wireless LANS
  • The 802.11 protocol stack
  • The 802.11 physical layer
  • The 802.11 MAC sublayer protocol
  • The 802.11 frame structure
  • services
the 802 11 protocol stack
The 802.11 protocol stack
  • MAC sublayer determines how the channel is allocated, that is, who gets to transmit next
  • LLC sublayer hides the differences between the different 802 variants
  • 802.11 specifies three transmission techniques allowed in the physical layer

-infrared method

-short-range radio (FHSS/DSSS)

the 802 11 physical layer 1 7
The 802.11 physical layer(1/7)
  • Infrared option

-uses diffused transmission at 0.85

or 0.95 microns

-two speeds are permitted: 1 Mbps,

2Mbps

-infrared signals can’t penetrate walls

the 802 11 physical layer 2 7
The 802.11 physical layer(2/7)
  • FHSS (Frequency Hopping Spread Spectrum)

-uses 79 channels, each 1 MHz wide,

starting at the low end of the

2.4GHz ISM band

-A pseudorandom number generator

is used to produce the sequence of

frequencies hopped to

the 802 11 physical layer 3 7
The 802.11 physical layer(3/7)

-The amount of time spent at each

frequency—dwell time

-advantages:

1.a fair way to allocate spectrum

2.security

3.good resistance to multipath fading

4.relatively insensitive to radio

interference

-disadvantage: low bandwidth

the 802 11 physical layer 4 7
The 802.11 physical layer(4/7)
  • DSSS (Direct Sequence Spread Spectrum)

-restricts to 1 or 2 Mbps

-has some similarities to the CDMA

system

-each bit is transmitted at 11 chips,

using Barker sequence

-uses phase shift modulation

the 802 11 physical layer 5 7
The 802.11 physical layer(5/7)
  • High-speed wireless LANs, 802.11a, uses OFDM (Orthogonal Frequency Division Multiplexing)

-deliver up to 54 Mbps in the wider

5GHz ISM band

-advantages:

1.good immunity to multipath fading

2.using noncontiguous bands (good

spectrum efficiency)

the 802 11 physical layer 6 7
The 802.11 physical layer(6/7)
  • 802.11b uses HR-DSSS (High Rate Direct Sequence Spread Spectrum)

-uses 11 million chips/sec to achieve

11Mbps in the 2.4GHz band

-data rate 1,2 Mbps use phase shift

modulation (compatibility with DSSS)

-data rate 5.5,11Mbps use

Walsh/Hadamard codes

the 802 11 physical layer 7 7
The 802.11 physical layer(7/7)
  • Although 802.11b is slower than 802.11a, its range is about 7 times greater.
  • 802.11g uses OFDM modulation of 802.11a, but operates in the narrow 2.4GHz ISM band along with 802.11b
the 802 11 mac sublayer protocol
The 802.11 MAC sublayer protocol
  • The 802.11 MAC sublayer protocol is quite different from that of Ethernet due to the inherent complexity of the wireless environment compared to that of a wired system
802 11 supports two modes of operation to deal with the problem
802.11 supports two modes of operation to deal with the problem
  • DCF (Distributed Coordination Function)

-uses a protocol CSMA-CA

1.physical channel sensing

2.virtual channel sensing (based on

MACAW)

  • PCF (Point Coordination Function)
fragment frame
Fragment frame
  • The probability of a frame making it through successfully decreases with frame length
  • To deal with the problem of noisy channels, 802.11 allows frames to be fragmented into smaller pieces, each with its own checksum
slide55
PCF
  • The base station polls the other stations, asking them if they have any frames to send
  • Transmission order is completely controlled by the base station in PCF mode, no collisions ever occur
  • The basic mechanism is for the base station to broadcast a beacon frame periodically
services 1 2
Services (1/2)
  • Distribution services-manage cell membership and interact with stations outside the cell

1.association

2.disassociation

3.reassociation

4.distribution

5.integration

services 2 2
Services (2/2)
  • Station services- activity within a single cell

1.authentication

2.deauthentication

3.privacy

4.data delivery

outline4
Outline
  • The mobile telephone system
  • Cable television
  • Wireless LANS
  • Broadband wireless
  • Bluetooth
  • Data Link layer switching
  • Quality of service
broadband wireless
Broadband wireless
  • Comparison of 802.11 with 802.16
  • The 802.16 protocol stack
  • The 802.16 physical layer
  • The 802.16 MAC sublayer protocol
  • The 802.16 frame structure
comparison of 802 11 with 802 16 1 2
Comparison of 802.11 with 802.16 (1/2)
  • 802.11 and 802.16 are very different as they try to solve different problems

-similar :they were designed to provide high-bandwidth wireless communications

-differ:802.16 provides service to buildings

1.buildings are not mobile

2.buildings can have more than one

computer in them

comparison of 802 11 with 802 16 2 2
Comparison of 802.11 with 802.16 (2/2)

802.16(wireless MAN) properties:

-Because of distances, the perceived power at the base station vary widely from station to station (affects the signal-to-noise ratio)

-802.16 operate in the much higher 10-to-66 GHz frequency range

-These millimeter waves have different physical properties than the longer waves in the ISM bands (requires a completely different physical layer).

-802.16 provide QoS.

the 802 16 physical layer
The 802.16 physical layer
  • Because signal strength in the millimeter band falls off sharply with distance from the base station, the signal-to-noise ratio also drops with distance from the base station
  • 802.16 employs three different modulation schemes, depending on how far the subscriber station is from the base station

-the farther the subscriber is from the base station, the low the data rate

802 16 provides a more flexible way to allocate the bandwidth
802.16 provides a more flexible way to allocate the bandwidth
  • Two schemes:

-FDD (Frequency Division Duplexing)

-TDD (Time Division Duplexing)

the 802 16 mac sublayer protocol
The 802.16 MAC sublayer protocol
  • Downstream and upstream maps

-tell what is in which time slot and which time slots are free

  • Downstream channel

-base station simply decides what to put in which subframe

  • Upstream channel

-there are competing uncoordinated subscribers that need access to it

-Its allocation is tied closely to the QoS issue

four classes of service
Four classes of service
  • Constant bit rate service
  • Real-time variable bit rate service
  • Non-real-time variable bit rate service
  • Best-efforts service
outline5
Outline
  • The mobile telephone system
  • Cable television
  • Wireless LANS
  • Broadband wireless
  • Bluetooth
  • Data Link layer switching
  • Quality of service
bluetooth
Bluetooth
  • Bluetooth architecture
  • Bluetooth application
  • The Bluetooth protocol stack
  • The Bluetooth radio layer
  • The Bluetooth baseband layer
  • The Bluetooth L2CAP layer
  • The Bluetooth frame structure
bluetooth1
Bluetooth
  • A wireless standard for interconnecting computing and communication devices and accessories using short-range, low-power, inexpensive wireless radios
  • Bluetooth specification is for a complete system, from the physical layer to the application layer
bluetooth architecture
Bluetooth architecture
  • The basic unit of a Bluetooth system is a piconet, which consists of a master node and up to seven active slave nodes within a distance of 10 meters
  • An interconnected collection of piconets is called a scatternet
master slave design
Master/slave design
  • The reason is that the designers intended to facilitate the implementation of complete Bluetooth chips for under $5
  • Slaves are fairly dumb, doing whatever the master tells them to do
  • A piconet is a centralized TDM system, with master controlling the clock and determining which device gets to communicate in which time slot
the bluetooth radio layer 1 2
The Bluetooth radio layer (1/2)
  • The radio layer moves the bits from master to slave, or vice versa
  • Bluetooth is a low-power system with a range of 10 meters operating in the 2.4-GHz ISM band
  • The band is divided into 79 channels of 1MHz each
  • To allocate the channels fairly, frequency hopping spread spectrum is used with 1600 hops/sec and a dwell time of 623μsec
the bluetooth radio layer 2 2
The Bluetooth radio layer (2/2)
  • All the nodes in a piconet hop simultaneously, with the master dictating the hop sequence
  • 802.11 and Bluetooth operate in the 2.4GHz ISM band on the same 79 channels, they interfere with each other
the bluetooth baseband layer 1 2
The Bluetooth baseband layer (1/2)
  • The baseband layer turns the raw bit stream into frames and defines some key formats
  • Longer frames are much more efficient then single-slot frames
  • Each frame is transmitted over a logical channel, called a link, between the master and a slave
the bluetooth baseband layer 2 2
The Bluetooth baseband layer (2/2)
  • Two kinds of links :

-ACL (Asynchronous Connection-Less)

1.It is used for packet-switched

data available at irregular intervals

2.traffic is delivered on a best-

efforts basis

-SCO (Synchronous Connection Oriented)

1.It is used for real-time data

2.the type of channel is allocated a fixed slot in

each direction

the bluetooth l2cap layer
The Bluetooth L2CAP layer
  • It accepts packets of up to 64KB from the upper layers and breaks them into frames for transmission
  • It handles the multiplexing and demultiplexing of multiple packet sources
  • It handles the quality of service requirements
outline6
Outline
  • The mobile telephone system
  • Cable television
  • Wireless LANS
  • Broadband wireless
  • Bluetooth
  • Data Link layer switching
  • Quality of service
data link layer switching
Data link layer switching
  • Bridges from 802.x to 802.y
  • Local internetworking
  • Spanning tree bridges
  • Remote bridges
  • Repeaters, hubs, bridges, switches, routers, gateways
  • Virtual LANs
why a single organization may end up with multiple lans 1 2
Why a single organization may end up with multiple LANs?(1/2)
  • The goal of the various of departments differ, different departments choose different LANs.
  • The organization may be geographically spread over several buildings separates by considerable distances.
  • It may be necessary to split what is logically a single LAN into separate LANs to accommodate the load.
why a single organization may end up with multiple lans 2 2
Why a single organization may end up with multiple LANs?(2/2)
  • A single LAN would be adequate in terms of load, but the physical distance between the most distant machines is too great
  • There is the matter of reliability
  • Bridges can contribute to the organization’s security
some difficulties when trying to build a bridge between the various 802 lans
some difficulties when trying to build a bridge between the various 802 LANs
  • Each of the LANs uses a different frame format
  • Interconnected LANs don’t necessarily run at the same data rate
  • Different 802 LANs have different maximum frame lengths
  • Another problems are security and quality of service
local internetworking
Local internetworking
  • The bridges should be completely transparent
  • When a frame arrives, a bridge must decide whether to discard or forward it
  • The decision is made by looking up the destination address in a hash table inside the bridge
  • The algorithm used by the transparent bridges is backward learning
the routing procedure for an incoming frame
The routing procedure for an incoming frame
  • If destination and source LANs are the same, discard the frame
  • If the destination and source LANs are different, forward the frame
  • If the destination LAN is unknown, use flooding
spanning tree bridges
Spanning tree bridges
  • To increase reliability, some sites use two or more bridges in parallel between pairs of LANs, however, introduce some problems because it creates loops in the topology
  • The solution to this difficulty is for the bridges to communicate with each other and overlay the actual topology with a spanning tree that reached every LAN
repeaters
Repeaters
  • There are analog devices that are connected to two cable segments
  • A signal appearing on one of them is amplified and put out on the other
  • Repeaters understand volts
slide103
Hubs
  • Frames arriving on any of the lines are sent out on all the others
  • If two frames arrive at the same time, they will collide
bridges
Bridges
  • A bridge connects two or more LANs
  • When a frame arrives, software in the bridge extracts the destination address from the frame header and looks it up in a table to see where to send the frame
switches
Switches
  • Switches are similar to bridges in that both route on frame addresses
  • The main difference is that a switch is most often to connect individual computers
  • Since each port is its own collision domain, switches never lose frames to collisions
routers
Routers
  • When a packet comes into a router, the frame header and trailer are stripped off and the packet located in the frame’s payload field is passed to the routing software
  • The software uses the packet header to choose an output line
transport gateways
Transport gateways
  • These connect two computers that use different connection-oriented transport protocols
application gateways
Application gateways
  • Application gateways understand the format and contents of the data and translate messages from one format to another
virtual lans
Virtual LANs
  • With hubbed (switched) Ethernet, it was often possible to configure LANS logically rather than physically
why use virtual lans
Why use virtual LANs?
  • Security
  • Load
  • Broadcasting
  • In response to user requests for more flexibility-rewire building entirely in software
slide113
VLAN
  • VLANs are based on specially-designed VLAN-aware switches
  • To make the VLANs function correctly, configuration tables have to be set up in the bridges or switches
  • These tables tell which VLANs are accessible via which ports (lines)
the ieee 802 1q standard 1 3
The IEEE 802.1Q standard (1/3)
  • What actually matters is the VLAN of the frame itself, not the VLAN of the sending machine
  • If there were some way to identify the VLAN in the frame header, them the need to inspect the payload would vanish
  • How about 802.11, 802.16, Ethernet?
the ieee 802 1q standard 2 3
The IEEE 802.1Q standard (2/3)
  • The new format (change the Ethernet header) was Published in IEEE standard 802.1Q
  • The key to the solution is to realize that the VLAN fields actually used by bridges and switches and not by the user machines
the ieee 802 1q standard 3 3
The IEEE 802.1Q standard (3/3)
  • The first VLAN-aware bridge or switch to touch a frame adds the VLAN fields, and the last one down the road removes them
  • Switches have to know which VLANs are reachable on each port
conclusion
Conclusion
  • To use VLANs property, each frame carries a new special identifier that is used as an index into a table inside the switch to look up where the frame is supposed to be sent
  • That is precisely what happens in connection-oriented networks
outline7
Outline
  • The mobile telephone system
  • Cable television
  • Wireless LANS
  • Broadband wireless
  • Bluetooth
  • Data Link layer switching
  • Quality of service
quality of service
Quality of service
  • Requirements
  • Techniques for achieving good quality of service
  • Integrated services
  • Differentiated services
  • Label switching and MPLS
requirements
Requirements
  • The needs of each flow can be characterized by four primary parameters: reliability, delay, jitter, and bandwidth.
  • Together these determine the QoS the flow requires.
techniques for achieving good quality of service
Techniques for achieving good quality of service
  • Overprovisioning
  • Buffering
  • Traffic shaping
  • The leaky bucket algorithm
  • The token bucket algorithm
  • Resource reservation
  • Admission control
  • Proportional routing
  • Packet sheduling
overprovisioning
Overprovisioning
  • Theorem: An easy solution is to provide so much router capacity, buffer space, and bandwidth that the packets just fly through easily.
  • Disadvantage : It is expensive.
  • Application: The telephone system is overprovisioned.
buffering
Buffering
  • Flows can be buffered on the receiving side before being delivered.
  • Buffering them

-does not affect the reliability or bandwidth.

-increases the delay.

-smoothes out the jitter.

  • The source outputs the packets with a uniform spacing between them.
traffic shaping
Traffic shaping
  • How about if the server is handling many streams at once?

-No uniform output is common.

  • Traffic shaping smoothes out the traffic on the server side. (server transmits at a uniform rate)
the leaky bucket algorithm
The leaky bucket algorithm
  • It is a single server queueing system with constant service time and finite queue.
  • The leaky bucket algorithm enforces a rigid output pattern at the average rate, no matter how bursty the traffic is.
the token bucket algorithm 1 2
The token bucket algorithm(1/2)
  • It is better to allow the output to speed up somewhat when large bursts arrive.
  • The token bucket algorithm:

-For a packet to be transmitted, it must capture and destroy one token.

-It provides a different kind of traffic shaping.

the token bucket algorithm 2 2
The token bucket algorithm(2/2)

-The token bucket algorithm throws away tokens when the bucket fills up but never discards packets.

-A packet can only be transmitted if enough tokens are available to cover its length in bytes.

resource reservation
Resource reservation
  • A virtual circuit has to be set up from the source to the destination, and all the packets that belong the flow must follow this route.
  • Three kinds of resources can be potential be reserved:

-bandwidth

-buffer space

-CPU cycles

admission control
Admission control
  • A router has to decide whether to admit or reject the flow based on its capacity and how many commitments it has already made for other flows.
  • The sender, receiver, and all the routers along the path between them may be involved in the flow negotiation.
proportional routing
Proportional routing
  • To provide a higher quality of service by splitting the traffic for each destination over multiple paths.
packet sheduling
Packet sheduling
  • Fair queueing algorithm

-routers have separate queues for each output line, one for each flow.

-the round robin is done in such a way as to simulate a byte-by-byte round robin.

  • Weighted fair queueing algorithm

-the weight is equal to the number of flows coming out of a machine.

integrated services rsvp the resource reservation protocol
Integrated services-RSVP (the resource reservation protocol)
  • RSVP (Flow-based algorithm)

-It offer good quality of service to one or more flows by reserving whatever resources are needed along the path.

-It requires an advance setup to establish each flow. (not scalable)

differentiated services
Differentiated services
  • Differentiated services (Class based QoS)

-It defines a set of service classes with corresponding forwarding rules.

-It requires no advance setup, no resource reservation, and no time-consuming end-to-end negotiation for each flow.

  • Expedited forwarding
  • Assured forwarding
label switching and mpls
Label switching and MPLS
  • This work focused on adding a label in front of each packet and doing the routing based on the label rather than on the destination address.