Transcript Chapter 5 - Indiana State University

MIS 430
Chapter 5 – Network and
Transport Layers
Chapter 5
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I. Overview
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Layers are very close – move messages from
end to end in a network
Transport Layer – accepts outgoing messages
from the application layer
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Packetizes them
Addresses them
Network layer – takes messages from the
transport layer and routes them through the
network
Data Link Layer – produces error-free delivery
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Introduction
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See fig 5-1 p. 145 for 5 OSI layers
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Note path of packets
Note additional headers added at each
layer: encapsulation
Remember that each layer “talks to” its
counterpart layer at the other end
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II. Transport and Network
Protocols
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Many similar protocols here can do the
same thing: TCP/IP, IPX/SPX, X.25, etc.
Multiprotocol stacks (software) will
process each protocol’s packets
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must analyze the packet to determine the
protocol
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TCP/IP: Internet Standard
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TCP/IP originally developed for
ARPANET – DoD network
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Produce error-free transmissions
Compatible with variety of data link
protocols
TCP/IP is world’s most popular
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TCP=transmission control protocol (TL)
IP=Internet protocol (NL)
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TCP: Transport Control Protocol
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Performs packetizing
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Breaks message into packets
Numbers them (for reassembly later)
Assures packets are delivered reliably
Puts packets in order at destination
See figure 5-2 p. 147 for TCP packet: 192-bit header
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IP: Internet Protocol
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Network layer protocol
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Performs addressing and routing
IP SW must be at every node
IP packet in figure 5-3 p. 147: 192-bit header
IPv4: 32 bits=4.3B IP addresses
IPv6: 128 bits=3.4x1038 addresses! Simpler header structure
but requires ALL computers be revised (Microsoft has upgrade)
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IPX/SPX: Novell
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ISU still uses IPX/SPX but newer Novell
Netware now uses TCP/IP
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SPX: TL protocol and like TCP
IPX: NL protocol and like IP
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X.25 Packet Switching
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WAN global ITU standard for packet switched
networks of common carriers
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Seldom used in North America
Maps to lowest 3 levels of OSI model
DTE (data terminal equipment or end
devices) vs. DCE (data communications
equipment or communications devices)
PAD – packet assembler/disassembler
X. means digital data carried on digital
network in ITU-T notation
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System network architecture-SNA
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IBM standard intended for end to end
IBM network
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Used only on IBM compatible mainframes
Uses proprietary protocols: important
concept in open standards environment
Experts predict SNA will be replaced by
TCP/IP and this will decline
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III. Transport Layer Functions
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Each application layer program has a
unique TCP/IP port number
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16-bit (2 byte) number up to 65536
FTP=21, Telnet=23, HTTP=80, SMTP=25
Can choose non standard port numbers
and give application program that port #
http://someplace.com:4567/index.htm
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Packetizing
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Given maximum packet size, most
messages are split into >1 packet
Web browsers build page a packet at a
time, especially streaming and graphics
Email clients wait until all packets have
arrived and are reassembled
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Connection oriented routing
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Sets up TCP connection as a virtual
circuit between sender and receiver
Once established, packets flow in same
order until connection is closed
Reassembling message is simple here
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Connectionless routing
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Each packet is treated separately and
could take different paths
May arrive out of sequence
TCP packet replaced by UDP packet
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User Datagram Protocol packet is much
smaller that TCP packet
Often used when entire message fits
one packet (control messages)
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Quality of service (QoS) routing
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Special type of connection oriented
routing
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Different connections are assigned
different priorities
Email is low priority, videoconferencing
high priority to assure smooth images
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IV. Network Addresses
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Application Layer URL: misnt.indstate.edu
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Network Layer IP: 139.102.31.12
Data Link Layer MAC: SMC network card 00-E0-2992-24-54 (12 hex digits)
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at C:>type Ping misnt.indstate.edu to see if active
at C:> type winipcfg (Windows 95, 98, ME)
at C:> type ipconfig (Windows NT, 2000, XP)
Must have an approved address to attach a computer
to the Internet
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Servers have fixed (static) addresses, clients usually not
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Internet Addresses
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Network Solutions is the agent that provides
domain names (called domain registrar)
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http://www.networksolutions.com
.com, .org, .net, .mil, .gov plus several new
extensions (.biz, .info, .bz, and .tv) latter two
were originally country codes
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Country extensions: .us, .ca, .il, .jp, .de, .iq
http://www.isi.edu/innotes/iana/assignments/country-codes
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Subnets
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Subnet refers to logical group of computers, often
same physical network
ISU uses 139.102.x.y Class B addresses
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X is the subnet and y is the computer
SB 403 and servers: 139.102.31.y
 SB faculty and staff: 139.102.67.y and
139.102.69.y
Subnet mask: 255.255.255.0 vs 255.255.0.0 – parts
refer to clients on the same subnet
Partial-byte subnets: 255.255.255.240 allows for 16
computers per subnet: 11111111 11111111
11111111 11110000
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Static vs. Dynamic Addresses
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Static IP address: always same, coded into
the Network TCP/IP properties
DHCP and bootp give out dynamic addresses
at client boot up time
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Can reuse dynamic IP addresses
In TCP/IP Properties, Obtain an IP address automatically
Cannot assign a dynamic address to a server!
At ISU, even though we use bootp you always get
the same IP address; (ISU is replacing bootp with
DHCP for roaming)
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Register: http://ithelp.indstate.edu/forms/bootp.html
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IP Address Lease
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Client is given an IP address for a
certain length of time
After that time expires, the IP address
lease expires and someone else can use
that IP address
At C> prompt, type ipconfig /all to see
IP address lease information. (In
Windows 9x, type winipcfg)
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Address Resolution
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Server name resolution: DNS stands for Domain
Name Service
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Any time your computer does not know the IP address of a
server, it calls the DNS to get it
DNS may have to go to root DNS to get IP
139.102.48.35, 139.102.7.102, 139.102.1.10 are ISU DNS
Once learned, this address is stored inside your computer
until you shut down. Hint: you may need to do a DNS Flush
if your computer is acting up. Ask about this in class!
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DNS name is associated with domain name:
www.indstate.edu=139.102.15.15
DNS servers replicate automatically
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V. Routing
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Process of determining path
through network of a
message
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Implement via a Routing
Table (for computer B)
B
A
D
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E
C
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How many paths from A to
G? ABCG, ADEFCG,
ADEBCG, ABEFCG,
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Destinat.
Route
A
A
C
C
D
A
E
E
F
E
G
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Routing - 2
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Router points in the general direction of
destination
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Ex: for all IP 126.x.x.x addresses, go here
Ex: for all Texas destinations go here, otherwise
go there
Router contains software and builds routing
tables dynamically to accommodate
congestion, cuts, etc.
Cisco – has best dynamic routing software
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Tracing Your Route(rs)
C:\WINDOWS\Desktop>tracert www.kelley.indiana.edu
Tracing route to kelley.iu.edu [129.79.121.231]
over a maximum of 30 hops:
1
27 ms
26 ms
38 ms 139.102.180.1 (this was from my home!)
2
26 ms
33 ms
28 ms 139.102.7.3
3
30 ms 2981 ms
29 ms 139.102.1.254
4
45 ms 2971 ms
54 ms ind-ag-2-atm6-0-1-12m.ind.net
[157.91.9.174]
5 1982 ms 2965 ms
69 ms ihets-gw-1-atm-ind-ag-2.ind.net
[199.8.76.250]
6 1970 ms
*
59 ms iupui-atm6-0-100.ind.net [157.91.6.34]
7 1818 ms 2976 ms
56 ms 156.56.249.13
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156 ms 2952 ms
148 ms wcc6-gw.ucs.indiana.edu [129.79.8.6]
9 1969 ms
182 ms
140 ms kelley.iu.edu [129.79.121.231]
Trace complete.
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Types of Routing
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Centralized routing: all decisions made by
central computer
Static routing: all decisions made are fixed. If
break in network, messages are held until
routes refigured. Good for small networks
with few alternative paths.
Dynamic: adapts to network conditions in
decentralized fashion. Default mode with
many paths, but requires lots of calculations
by routers including network coordination
traffic between routers.
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Routing Protocols
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How routers exchange information to
build, maintain routing tables
Autonomous system – network
operated by one organization
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Routing protocols inside such systems are
interior routing protocols
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Routing protocols between autonomous
systems are exterior routing protocols
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Internet Routing Protocols
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ICMP-Internet Control Message Protocol
RIP-Routing Information Protocol
BGP-Border Gateway Protocol
OSPF-Open Shortest Path First
EIGRP-Enhanced Interior Gateway Routing Protocol
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For the test: know ICMP and RIP 
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Multicasting
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Unicast message: sent from one client
to another client
Multicast message: sent from one node
to a group of computers at same time
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Ex: Ghost for imaging hard drives; rebuild
all computers with same packets
Ex: hearing a broadcast on the Internet –
like a seminar or workshop
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VI. TCP/IP Example
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A computer needs four TCP/IP settings:
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Its IP address
Subnet mask
IP address of DNS server
IP address of gateway leading outside subnet
Can get these values
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automatically or
they can be static values typed into TCP/IP
Properties in Network control panel
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Example Network: fig 5-14
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Four subnets: 98, 95, 50, 75
DNS server: 128.192.254.4
4 Gateways, each with at least two IP
addresses (internal/external)
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Bldg A: 128.192.98.1 129.192.254.3
(error)
Router: 128.192.254.7 next to Internet
cloud
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Resolving Addresses
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Known Address, Same Subnet
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Known Address, Different Subnet
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Search IP address table, find
Hand to Data Link layer, send packet
Search IP address table, find
Go through gateway to other subnet
Unknown Addresses
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Search IP address table, not found
Perform DNS request, return address to table
May go through gateway or out via router
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Bruce’s Router
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My home network has a Belkin wireless
router: http://139.102.180.53 with a
special TCP port number
It has the following ports:
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WAN (connects to DSL modem)
4 wired LAN ports – inside firewall
Wireless LAN ports – inside firewall
More in chapters 6-7 with LANs
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