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 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

2.4 Ethernet Technology

Comer Figure 2.1 Ethernet using twisted pair wiring (with HUB)

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

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

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)

Figure 2.1 (with hub)

Figure 2.2 Format of an Ethernet frame (packet)

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

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

Figure 2.2 Ethernet Frame Format

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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

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

Figure 2.2 Ethernet Frame Format

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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!