Transcript “Fig 1.5” – An internet

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
relinquish connection
disadvantage: cost independent of use
* packet-switched networks (post office)
at source, data divided into packets
packets individually sent from source
to destination
data reassembled at destination
advantage: can share transport facilities
\My Doc\cs\cs434\s04\circuit packet.doc
2.4 Ethernet Technology
Comer Figure 2.1 Ethernet using twisted pair wiring (with HUB)
2.4.5 Properties of an Ethernet
Ethernet 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
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 by
manufacturer
Destination address as filter
An Ethernet station receiving packet
checks destination address
ignores packet if not intended for this station
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 mode
Interface processes only packets with destination
* its own unicast address
* the network broadcast address
■ promiscuous mode
Interface process all received packets
(including those addressed to other stations)
Figure 2.1 (with hub)
Figure 2.2 Format of an Ethernet frame (packet)
2.4.5 Properties of an Ethernet
Ethernet 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
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
Comer Figure 3.1 Two physical networks connected by a router
Comer Figure 3.2 Three networks connected by two routers
Comer figure 3.3 (a) user’s view (b) structure of physical networks and routers
“Fig 1.5” – An internet
4 LANs linked by a WAN
Figure 4.1 The original classful IP addressing scheme
Figure 4.4 Special forms of IP addresses
Figure 4.5 Logical connection of
Two networks to the Internet backbone
Figure 4.6 Example IP address assignment
Figure 2.2 Format of an Ethernet Frame
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Figure 2.2 Ethernet Frame Format
Comer Section 5.10 ARP Implementation
■ action when sending an ARP request
detain 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 timer
if no, make new entry and start timer
further action depends on two sub-cases:
* incoming ARP message was a request
look 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
Figure 5.3 ARP Message Format
ARP Message
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Chapter 6 – Internet Protocol: Connectionless Datagram Delivery
Chapter 6 is about this level
Figure 6.3 Format of an IP Datagram
Figure 6.3 Format of an IP Datagram
0800
Figure 2.2 Ethernet Frame Format
Figure 6.7 Where Fragmentation Occurs
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!