welcome to cs 334/534
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Welcome to CS 334/534. “Fig 1.5” – An internet. 4 LANs linked by a WAN. Comer Figure 1.1 – Growth of the Internet. 2.2 Two Approaches to Network Communication * circuit-switched networks (telephone) 3 phases: establish connection between end points use connection - PowerPoint PPT PresentationTRANSCRIPT
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Welcome
to
CS 334/534
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“Fig 1.5” – An internet
4 LANs linked by a WAN
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Comer Figure 1.1 – Growth of the Internet
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2.2 Two Approaches to Network Communication
* circuit-switched networks (telephone)
3 phases:establish connection between end pointsuse connection
relinquish connection
disadvantage: cost independent of use
* packet-switched networks (post office)
at source, data divided into packets
packets individually sent from sourceto destination
data reassembled at destination
advantage: can share transport facilities
\My Doc\cs\cs434\s04\circuit packet.doc
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2.4 Ethernet Technology
Comer Figure 2.1 Ethernet using twisted pair wiring (with HUB)
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2.4.5 Properties of an EthernetEthernet was “designed to be”
i.e. “classical” or “original” Ethernet
■ shared bus- shared bandwidth- only one station transmitting at a time- “half duplex”
(station transmits XOR receives)
■ broadcast technology- all stations receive all messages
■ best-effort delivery
■ distributed access control- CSMA/CD
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2.4.8 Ethernet Hardware Addresses
6 bytes total - globally unique
High-Order 3 bytes: assigned to manufacturer by IEEE
Low-Order 3 bytes: serial number assigned bymanufacturer
Destination address as filter
An Ethernet station receiving packet checks destination address
ignores packet if not intended for this station
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Ethernet Addresses – continued
Types of Destination address
An address can be used to specify■ a single, specific station
on this network (“unicast address”)■ all stations on this network
(“broadcast address”)■ a subset of stations on this network
(“multicast address”)Interface Modes of Operation
■ normal modeInterface processes only packets with destination * its own unicast address * the network broadcast address
■ promiscuous modeInterface process all received packets (including those addressed to other stations)
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Figure 2.1 (with hub)
Figure 2.2 Format of an Ethernet frame (packet)
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2.4.5 Properties of an EthernetEthernet was “designed to be”
i.e. “classical” or “original” Ethernet
■ shared bus- shared bandwidth- only one station transmitting at a time- “half duplex”
(station transmits XOR receives)
■ broadcast technology- all stations receive all messages
■ best-effort delivery
■ distributed access control- CSMA/CD
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Properties of a “switched” Ethernet
■ not shared bus- point-to-point connections- not shared bandwidth- “full duplex”
(station transmitting and receiving)
■ not broadcast technology- stations receive only their own messages
■ best-effort delivery
■ no access control needed- private frame buffer - no entrance collisions- not CSMA/CD- exit port collision
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Comer Figure 3.1 Two physical networks connected by a router
Comer Figure 3.2 Three networks connected by two routers
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Comer figure 3.3 (a) user’s view (b) structure of physical networks and routers
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“Fig 1.5” – An internet
4 LANs linked by a WAN
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Figure 4.1 The original classful IP addressing scheme
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Figure 4.4 Special forms of IP addresses
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Figure 4.5 Logical connection of
Two networks to the Internet backbone
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Figure 4.6 Example IP address assignment
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Figure 2.2 Format of an Ethernet Frame
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Figure 2.2 Ethernet Frame Format
0806
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Comer Section 5.10 ARP Implementation
■ action when sending an ARP requestdetain outgoing data message in queue
until ARP reply received
■ action when receiving an ARP message either request or reply contain mapping(s), so
look in ARP cache to see if receiver already has an entry for the sender.
if yes, overwrite physical address (quickest way) and reset timerif no, make new entry and start timer
further action depends on two sub-cases:
* incoming ARP message was a requestlook at target IP address; if it’s for this
machine, generate ARP reply
* incoming ARP message was a reply did this machine earlier send an ARP request
for the IP address in the reply?if yes, release outgoing data message from queue, incorporate packet into outgoing frame.if no, no further action
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Figure 5.3 ARP Message Format
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ARP Message
0806
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Chapter 6 – Internet Protocol: Connectionless Datagram Delivery
Chapter 6 is about this level
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Figure 6.3 Format of an IP Datagram
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Figure 6.3 Format of an IP Datagram
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Figure 2.2 Ethernet Frame Format
0800
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Figure 6.7 Where Fragmentation Occurs
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Figure 6.8 (a) Original Datagram carrying 1400 octets of data
(b) Three fragments for a network MTU of 620;
each fragment is a complete datagram, with header!
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