Network Layer Protocols

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Network LayerProtocols
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Figure 20.1 Protocols at network layer
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Figure 20.2 ARP operation
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Note
An ARP request is broadcast an ARP reply is
unicast.
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Figure 20.7 IP datagram
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Note
The total length field defines the total length
of the datagram including the header.
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Figure 20.8 Multiplexing
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Figure 20.10 MTU
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Figure 20.12 ICMP encapsulation
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Note
ICMP always reports error messages to the
original source.
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Figure 20.13 Error-reporting messages
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Note
There is no flow control or congestion control
mechanism in IP.
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Unicast and Multicast Routing
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Figure 21.1 Unicasting
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Note
In unicast routing, the router forwards the
received packet through only one of its ports.
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Some Popular Unicast routing protocols
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Figure 21.3 Autonomous systems
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Table 21.1 A distance vector routing table
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Figure 21.7 Areas in an autonomous system
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Figure 21.14 Types of LSAs
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Figure 21.17 Summary link to network
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Figure 21.18 Summary link to AS boundary router
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Figure 21.19 External link
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Note
In OSPF, all routers have the same link state
database.
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Dijkstra Algorithm
1. Start with the local node (router) the root
of the tree. 2. Assign a cost of 0 to this node
and make it the first permanent node. 3. Examine
each neighbor node of the node that was the last
permanent node. 4. Assign a cumulative cost to
each node and make it tentative. 5. Among the
list of tentative nodes 1. Find the node with
the smallest cumulative cost and make it
permanent. 2. If a node can be reached from
more than one direction 1. Select the
direction with the shortest cumulative cost.6.
Repeat steps 3 to 5 until every node becomes
permanent.
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Table 21.2 Link state routing table for router A
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Figure 21.23 Multicasting
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Note
In multicast routing, the router may forward the
received packet through several of its ports.
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Note
IGMP is a group management protocol. It helps a
multicast router create and update a list of
loyal members related to each router interface.
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Wireless Networks
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Wireless networks in comparison to fixed
networksKey Characteristics

• Higher loss-rates due to interference
• emissions of, e.g., engines, lightning
• Restrictive regulations of frequencies
• frequencies have to be coordinated, useful
  frequencies are almost all occupied
• Low transmission rates
• local transmission in Mbps, regional currently,
  e.g., 9.6kbit/s with GSM
• Higher delays, higher jitter
• connection setup time with GSM in the second
  range, several hundred milliseconds for other
  wireless systems
• Lower security, simpler active attacking
• radio interface accessible for everyone, base
  station can be simulated, thus attracting calls
  from mobile phones
• Always shared medium
• secure access mechanisms important

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Frequencies for communication
coax cable
twisted pair
optical transmission
1 Mm 300 Hz
10 km 30 kHz
100 m 3 MHz
1 m 300 MHz
10 mm 30 GHz
100 ?m 3 THz
1 ?m 300 THz
visible light
VLF
LF
MF
HF
VHF
UHF
SHF
EHF
infrared
UV

• VLF Very Low Frequency UHF Ultra
  High Frequency
• LF Low Frequency SHF Super High
  Frequency
• MF Medium Frequency EHF Extra High
  Frequency
• HF High Frequency UV Ultraviolet
  Light
• VHF Very High Frequency
• Frequency and wave length ? c/f
• wave length ?, speed of light c ? 3x108m/s,
  frequency f

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Electromagnetic spectrum for wireless
communication
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Frequencies for mobile communication

• VHF-/UHF-ranges for mobile radio
• simple, small antenna for cars
• deterministic propagation characteristics,
  reliable connections
• SHF and higher for directed radio links,
  satellite communication
• small antenna, focusing
• large bandwidth available
• Wireless LANs use frequencies in UHF to SHF
  spectrum
• some systems planned up to EHF
• limitations due to absorption by water and oxygen
  molecules (resonance frequencies)
• weather dependent fading, signal loss caused by
  heavy rainfall etc.

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Note
Infrared signals can be used for short-range
communication in a closed area using
line-of-sight propagation.
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The Wireless Space
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Emerging Landscape
Who will be the winner ?
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Two options 802.11 and Bluetooth
Bluetooth
802.11
Cordless headset
Access Point
Designed for wired Ethernet replacement
Designed for cable replacement
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An Ad-Hoc Wireless Network (MANET)
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Vision of the Future
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WirelessLANs
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802.11 Market Evolution
802.11
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BSSs
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ESS
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Physical layer specifications
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IEEE 802.11 current status
LLC
MAC Mgmt
WEP
MAC
MIB
PHY
FH
IR
DSSS
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Piconet
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Scatternet
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Wireless Technology Current Landscape
72 Mbps
Turbo .11a
54 Mbps
802.11a,b
5-11 Mbps
.11 p-to-p link
802.11b
1-2 Mbps
802.11
Bluetooth
µwave p-to-p links
3G
384 Kbps
WCDMA, CDMA2000
2G
56 Kbps
IS-95, GSM, CDMA
Outdoor 50 200m
Mid range outdoor 200m 4Km
Long range outdoor 5Km 20Km
Long distance com. 20m 50Km
Indoor 10 30m
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Research Program
72 Mbps
Turbo .11a
54 Mbps
802.11a,b
5-11 Mbps
802.11b
.11b p-to-p link
1-2 Mbps
802.11
µwave p-to-p links
384 Kbps
WCDMA, CDMA2000, HDR
56 Kbps
IS-95, GSM, CDMA
Outdoor 50 200m
Mid range outdoor 200m 4Km
Long range outdoor 5Km 20Km
Long distance com. 20m 50Km
Indoor 10 30m
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Concluding Remarks

• IEEE 802.11
• Will continue to grow in
• Public spaces, home, industry vertical, and
  enterprise market
• 802.11 will provide a viable alternative to 3G in
  public places
• Offers a great promise for bringing low cost
  networking services to the Asia/Pacific mass
  market
• Bluetooth will be complimentary to WLANs, it will
  not be a competitor
• Interoperability between WLANs, WPANs and 3G
  networks will be critical !