Upload
akirank1
View
149
Download
2
Tags:
Embed Size (px)
DESCRIPTION
Internetworking with TCP/IP, Vol. I Principles, Protocols, & Architecture
Citation preview
© 2002 JW Ryder
CS 428 Computer Networks
1
Ethernet Properties
• 10Mbps/100Mbps broadcast bus technology– Bus: all stations share single
channel– Broadcast: all transceivers receive
every transmission
• Transceiver passes all packets from bus to host adapter
• Host adapter chooses some and filters others
© 2002 JW Ryder
CS 428 Computer Networks
2
Ethernet Properties
• Best-effort delivery: hardware provides no information to the sender about whether packet was actually delivered
• Destination machine powered down, packets will be lost
• TCP/IP protocols accommodate best-effort delivery
© 2002 JW Ryder
CS 428 Computer Networks
3
CSMA/CD• Carrier Sense Multiple Access /
Collision Detect
• When transceiver begins transmission– Not all parts of network reached
simultaneously– 80% speed of light speed
• Free for all transmission yields possibility of 2 transceivers sensing idle bus and beginning transmission simultaneously
• Draw picture
© 2002 JW Ryder
CS 428 Computer Networks
4
CSMA/CD
• Each transceiver monitors cable while transmitting in an attempt to detect foreign signals (interference)
• Monitoring called Collision Detection
• If collision detected, a host adapter– aborts transmission– waits predictable number of
arbitrary length time units– tries again
© 2002 JW Ryder
CS 428 Computer Networks
5
Binary Exponential Backoff
• Show BEB example
• Many stations try to transmit at exactly the same time yields a non-recoverable traffic jam
• Ethernet capacity– 10Mbps means for everyone– Highway system can manage a
max amount of traffic
© 2002 JW Ryder
CS 428 Computer Networks
6
• WinIPCfg find and view
• 48-bit addressing scheme
• Ethernet manufacturers buy ‘lot’s of addresses – Unique address in the universe
• Fixed in machine readable form on host interface hardware
• Ethernet Address belong to hardware devices– Physical addr., Hardware addr.
Ethernet Hardware Address
© 2002 JW Ryder
CS 428 Computer Networks
7
Ethernet Addresses
• Moving hardware interface to another machine changes the original machine’s physical address
• Host interface examines packets and decides which ones to send ‘up’ – Destination address used– CPU could perform check but
what would happen?
© 2002 JW Ryder
CS 428 Computer Networks
8
• 48-bit address is one of 3 types– Unicast– Broadcast (All 1’s)– Multicast (Group)
• Host interface recognizes more that just its physical address
• Not all forms of addressing implemented by all host adapter manufacturers– Usually unicast and broadcast,
multicast is newest idea
Ethernet Address
© 2002 JW Ryder
CS 428 Computer Networks
9
• (Data) Link level connection among machines
• “Phil Daily Never Took Sarah Prentice Anywhere” -- jwr
• Variable length, no smaller than 64 octets or larger than 1518 octets– See figure 2.7 on page 30
• Preamble extra - used for synchronization
• Sender computes CRC, receiver regenerates and checks
Ethernet Frame
© 2002 JW Ryder
CS 428 Computer Networks
10
Internet Services
• Read Chapter 11
• 3 layers
• Connectionless Delivery Service– Provides foundation
• Reliable Transport Service– Applications depend on this
• Application Service
© 2002 JW Ryder
CS 428 Computer Networks
11
Need for Multiple Protocols
• “… protocols allow one to specify or understand communication without knowing the details of a particular vendor’s network hardware.”
• Same or different?– Ethernet frame format, network
access policy, frame error handling
– IP addresses, datagram format, unreliable delivery
© 2002 JW Ryder
CS 428 Computer Networks
12
Conceptual Layering
• Heterogeneous network transport protocols require a buffering between actual network implementation view of implementation
• See figure 11.1 on page 179
• Protocol software more complex than simple model
• See figure 11.2 on page 180
• See figure 11.3 on page 180
© 2002 JW Ryder
CS 428 Computer Networks
13
ISO 7 Layer Reference Model
• Application - 7
• Presentation - 6
• Session - 5
• Transport - 4
• Network - 3
• Data Link - 2
• Physical - 1
See figure 11.4 on page 181
© 2002 JW Ryder
CS 428 Computer Networks
14
Physical Layer
• Level 1
• Physical interconnection to the network
• Includes electrical characteristics of voltage, current
© 2002 JW Ryder
CS 428 Computer Networks
15
Data Link Layer
• Level 2
• Handles transmission errors– Frame checksum– Transmission is unreliable
• Specifies exchange of acknowledgements between machines to know when frame transferred successfully
• Does not mean content is right!!
© 2002 JW Ryder
CS 428 Computer Networks
16
Network Layer
• Level 3
• Defines basics unit of transfer across network
• Includes concepts of destination addressing, routing
© 2002 JW Ryder
CS 428 Computer Networks
17
Transport Layer
• Level 4
• End to End reliability
• Destination host communicates with the source host
• Even though lower level layers provide reliable checks at each transfer, end to end layer double checks
© 2002 JW Ryder
CS 428 Computer Networks
18
Session Layer
• Level 5
• Remote terminal access
• Terminal to host connection
© 2002 JW Ryder
CS 428 Computer Networks
19
Presentation Layer
• Level 6
• Provides network functions that many applications use
• Text compression, graphic images to bit stream formats etc.
© 2002 JW Ryder
CS 428 Computer Networks
20
Application Layer
• Level 7
• Application programs that use the network
• Electronic mail, File transfer programs, finger, daytime, echo
© 2002 JW Ryder
CS 428 Computer Networks
21
TCP/IP Internet Layering Model
• Looked at as 4 layers plus a 5th hardware layer
• Application
• Transport
• Internet
• Network Interface
• Hardware
© 2002 JW Ryder
CS 428 Computer Networks
22
Application Layer
• Highest layer
• Application programs that access services available across TCP/IP internet
• Interacts with one of the transport layer protocols– Sequence of individual messages– Continuous stream of bytes
© 2002 JW Ryder
CS 428 Computer Networks
23
Transport Layer• Messages or Streams pass
between AL and TL
• Provides communication from one application program to another– Called End-to-End
• May regulate flow of information
• May provide reliable transport– Arranges for receiving side to
send back acknowledgements– Can retransmit packets with errors
• Must be able to service many applications
© 2002 JW Ryder
CS 428 Computer Networks
24
Internet Layer
• Transport Protocol Packets pass between TL and IP
• Handles communication from one machine to another
• Encapsulates packet into IP datagram
• IP Security implemented here
• Handles incoming datagrams
© 2002 JW Ryder
CS 428 Computer Networks
25
Network Interface Layer
• IP Datagrams pass between IP and NL
• Responsible for accepting datagrams and transmitting them over a specific network– Device driver when attaching to
LAN
© 2002 JW Ryder
CS 428 Computer Networks
26
• One way of extending an Ethernet network.
• Max cable length = 500 meters
• Repeater is a hardware device that relays electronic signals from one cable to another
• At most, 2 repeaters can be placed between any 2 machines
• Total length - 3 segments at 500m each
Ethernet Bridges
© 2002 JW Ryder
CS 428 Computer Networks
27
Repeater Example
Floor 1
Floor 2
Floor 3
RepeaterComputer (Host)
| 500 Meters |
© 2002 JW Ryder
CS 428 Computer Networks
28
• Superior because they do not replicate– Noise– Errors– Malformed frames
• Frame must be completely valid to retransmit on another wire
• Follow CSMA/CD rules– Collisions, Propagation delays
remain isolated on 1 wire
Ethernet Bridges
© 2002 JW Ryder
CS 428 Computer Networks
29
• Almost arbitrary number of bridges can be connected
• Why? What is different?
Bridges
Hide details of the interconnection
Acts like single huge Ethernet
© 2002 JW Ryder
CS 428 Computer Networks
30
Bridges
• Adaptive, Learning bridges
• 1 computer, 2 Ethernet interfaces
• Software keeps 2 address lists
• Frame arrives from E1 , adds 48-bit source addr. to list associated with E1
• Learns topology of each wire
• Check destination addr. If on frame from whence it came, disregard
© 2002 JW Ryder
CS 428 Computer Networks
31
Adaptive Bridges• Helps improve performance by
isolating traffic
• If there exists a natural dichotomy between computers which communicate, then there is major gain
• From TCP/IP pov, bridged Ethernets simply another form of physical network connection
• Modern bridges use distributed spanning tree algorithms to figure how to forward frames - Why? (Cycles & packets in 2 directions simultaneously!)
© 2002 JW Ryder
CS 428 Computer Networks
32
Reading
• Make sure you read all of chapter 2 & 3