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
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Andrew S. Tanenbaum
-Never used for networking
-Digital voice and data
-A single channel for both sending and receiving
-Two frequencies (sending/receiving)
-23 channels spread out from 150 MHz to
-increases the system capacity (reuse of transmission frequencies)
-less power is needed.
- soft handoff
-no loss of continuity
-telephone needs to be able to
tune to two frequencies at the
- hard handoff
-832 simplex transmission channels
from 824 to 849 MHz
-832 simplex receive channels
from 869 to 894 MHz
-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
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
-uses direct sequence spread spectrum
-runs in a 5 MHz bandwidth
-has been designed to interwork with GSM
-not be designed to interwork with GSM
-has the differences between WCDMA : chip rate, frame time, spectrum used, the way to do time synchronization
-short-range radio (FHSS/DSSS)
-uses diffused transmission at 0.85
or 0.95 microns
-two speeds are permitted: 1 Mbps,
-infrared signals can’t penetrate walls
-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 amount of time spent at each
1.a fair way to allocate spectrum
3.good resistance to multipath fading
4.relatively insensitive to radio
-disadvantage: low bandwidth
-restricts to 1 or 2 Mbps
-has some similarities to the CDMA
-each bit is transmitted at 11 chips,
using Barker sequence
-uses phase shift modulation
-deliver up to 54 Mbps in the wider
5GHz ISM band
1.good immunity to multipath fading
2.using noncontiguous bands (good
-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
-uses a protocol CSMA-CA
1.physical channel sensing
2.virtual channel sensing (based on
-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
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 farther the subscriber is from the base station, the low the data rate
-FDD (Frequency Division Duplexing)
-TDD (Time Division Duplexing)
-tell what is in which time slot and which time slots are free
-base station simply decides what to put in which subframe
-there are competing uncoordinated subscribers that need access to it
-Its allocation is tied closely to the QoS issue
-ACL (Asynchronous Connection-Less)
1.It is used for packet-switched
data available at irregular intervals
2.traffic is delivered on a best-
-SCO (Synchronous Connection Oriented)
1.It is used for real-time data
2.the type of channel is allocated a fixed slot in
-does not affect the reliability or bandwidth.
-increases the delay.
-smoothes out the jitter.
-No uniform output is common.
-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 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.
-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.
-the weight is equal to the number of flows coming out of a machine.
-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)
-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.