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Based on notes from D. Hollinger |
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7
Application |
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6
Presentation |
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5
Session |
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4
Transport |
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3
Network |
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2
Data-Link |
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1
Physical |
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In OSI reference model terminology -the IP
protocol covers the network layer. |
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IP can be used on many data-link layers (can
support many network hardware implementations). |
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It will be useful to discuss a real data-link
layer. |
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Ethernet (really IEEE 802.3) is widely used. |
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Supported by a variety of physical layer
implementations. |
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Multi-access (shared medium). |
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Every Ethernet interface has a unique 48 bit
address (a.k.a. hardware address). |
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Example:
C0:B3:44:17:21:17 |
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The broadcast address is all 1’s. |
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Addresses are assigned to vendors by a central
authority. |
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Carrier Sense: can tell when another host is
transmitting |
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Multiple Access: many hosts on 1 wire |
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Collision Detection: can tell when another host
transmits at the same time. |
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The preamble is a sequence of alternating 1s and
0s used for synchronization. |
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CRC is Cyclic Redundancy Check |
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Each interface looks at every frame and inspects
the destination address. If the address does not match the hardware address
of the interface or the broadcast address, the frame is discarded. |
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Some interfaces can also be programmed to
recognize multicast addresses. |
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IP is the network layer |
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packet delivery service (host-to-host). |
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translation between different data-link
protocols. |
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IP provides connectionless, unreliable delivery
of IP datagrams. |
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Connectionless: each datagram is independent of
all others. |
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Unreliable: there is no guarantee that datagrams
are delivered correctly or at all. |
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IP addresses are not the same as the underlying
data-link (MAC) addresses. |
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Why ? |
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IP is a network layer - it must be capable of
providing communication between hosts on different kinds of networks
(different data-link implementations). |
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The address must include information about what network
the receiving host is on. This makes routing feasible. |
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IP addresses are logical addresses (not
physical) |
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32 bits. |
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Includes a network ID and a host ID. |
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Every host must have a unique IP address. |
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IP addresses are assigned by a central authority
(Internet Corporation for Assigned Names and Numbers -- ICANN) |
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Class A |
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128 possible network IDs |
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over 4 million host IDs per network ID |
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A Network ID is assigned to an organization by a
global authority. |
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Host IDs are assigned locally by a system
administrator. |
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Both the Network ID and the Host ID are used for
routing. |
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IP Addresses are usually shown in dotted decimal
notation: |
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1.2.3.4
00000001 00000010 00000011 00000100 |
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cs.rpi.edu is
128.213.1.1 |
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10000000 11010101 00000001 00000001 |
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A single network interface is assigned a single
IP address called the host address. |
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A host may have multiple interfaces, and
therefore multiple host addresses. |
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Hosts that share a network all have the same IP network
address (the network ID). |
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An IP broadcast addresses has a host ID of all
1s. |
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IP broadcasting is not necessarily a true
broadcast, it relies on the underlying hardware technology. |
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An IP address that has a host ID of all 0s is called a network
address and refers to an entire network. |
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An organization can subdivide it’s host address
space into groups called subnets. |
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The subnet ID is generally used to group hosts
based on the physical network topology. |
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Subnets can simplify routing. |
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IP subnet broadcasts have a hostID of all 1s. |
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It is possible to have a single wire network
with multiple subnets. |
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IP Addresses are not recognized by hardware. |
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If we know the IP address of a host, how do we
find out the hardware address ? |
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The process of finding the hardware address of a
host given the IP address is called |
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Address
Resolution |
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The process of finding out the IP address of a
host given a hardware address is called |
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Reverse Address Resolution |
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Reverse address resolution is needed by diskless
workstations when booting. |
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The Address Resolution Protocol is used by a
sending host when it knows the IP
address of the destination but
needs the Ethernet address. |
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ARP is a broadcast protocol - every host on the
network receives the request. |
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Each host checks the request against it’s IP
address - the right one responds. |
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ARP does not need to be done every time an IP
datagram is sent - hosts remember the hardware addresses of each other. |
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Part of the ARP protocol specifies that the
receiving host should also remember the IP and hardware addresses of the
sending host. |
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Connectionless Delivery (each datagram is
treated individually). |
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Unreliable (delivery is not guaranteed). |
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Fragmentation / Reassembly (based on hardware
MTU). |
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Routing. |
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Error detection. |
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Each fragment (packet) has the same structure as
the IP datagram. |
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IP specifies that datagram reassembly is done
only at the destination (not on a hop-by-hop basis). |
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If any of the fragments are lost - the entire
datagram is discarded (and an ICMP message is sent to the sender). |
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If packets arrive too fast - the receiver
discards excessive packets and sends an ICMP message to the sender (SOURCE
QUENCH). |
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If an error is found (header checksum problem)
the packet is discarded and an ICMP message is sent to the sender. |
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ICMP is a protocol used for exchanging control
messages. |
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ICMP uses IP to deliver messages. |
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ICMP messages are usually generated and
processed by the IP software, not the user process. |
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Echo Request |
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Echo Response |
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Destination Unreachable |
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Redirect |
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Time Exceeded |
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Redirect (route change) |
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there are more ... |
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IP/BYE-BYE is a lecture protocol used to signal
the class that we have just finished our discussion of IP - the network
layer of UDP/IP and TCP/IP. |
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The appropriate response to an IP/BYE-BYE
request is immediate applause, although simply opening your eyes is enough
(known as a WAKEUP response). |
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UDP is a transport-layer protocol |
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communication between processes |
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UDP uses IP to deliver datagrams to the right
host. |
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UDP/IP uses an abstract destination point called
a protocol port. |
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Ports are identified by a positive integer. |
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Operating systems provide some mechanism that
processes use to specify a port. |
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Datagram Delivery |
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Connectionless |
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Unreliable |
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Minimal |
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TCP is an alternative transport layer protocol
supported by TCP/IP. |
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TCP provides: |
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Connection-oriented |
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Reliable |
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Full-duplex |
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Byte-Stream |
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Q: Which protocol is better ? |
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A: It depends on the application. |
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TCP provides a connection-oriented, reliable
byte stream service (lots of overhead). |
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UDP offers minimal datagram delivery service (as
little overhead as possible). |
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Internet commerce ? |
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Video server? |
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File transfer? |
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Email ? |
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Chat groups? |
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Robotic surgery controlled remotely over a
network? |
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