Chapter 5 1

MIS 430

Chapter 5 – Network and Transport Layers

Chapter 5 2

I. Overview Layers are very close – move messages

from end to end in a network Transport Layer – accepts outgoing

messages from the application layer 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

Chapter 5 3

Introduction

See fig 5-1 p. 145 for 5 OSI layers 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

Chapter 5 4

II. Transport and Network Protocols

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 must analyze the packet to determine

the protocol

Chapter 5 5

TCP/IP: Internet Standard

TCP/IP originally developed for ARPANET – DoD network Produce error-free transmissions Compatible with variety of data link

protocols TCP/IP is world’s most popular

TCP=transmission control protocol (TL) IP=Internet protocol (NL)

Chapter 5 6

TCP: Transport Control Protocol

Performs packetizing 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

Chapter 5 7

IP: Internet Protocol

Network layer protocol 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)

Chapter 5 8

IPX/SPX: Novell

ISU still uses IPX/SPX but newer Novell Netware now uses TCP/IP SPX: TL protocol and like TCP IPX: NL protocol and like IP

Chapter 5 9

X.25 Packet Switching WAN global ITU standard for packet

switched networks of common carriers 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

Chapter 5 10

System network architecture-SNA

IBM standard intended for end to end IBM network 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

Chapter 5 11

III. Transport Layer Functions

Each application layer program has a unique TCP/IP port number 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

Chapter 5 12

Packetizing

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

Chapter 5 13

Connection oriented routing

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

Chapter 5 14

Connectionless routing Each packet is treated separately

and could take different paths May arrive out of sequence TCP packet replaced by UDP packet

User Datagram Protocol packet is much smaller that TCP packet

Often used when entire message fits one packet (control messages)

Chapter 5 15

Quality of service (QoS) routing

Special type of connection oriented routing Different connections are assigned

different priorities Email is low priority,

videoconferencing high priority to assure smooth images

Chapter 5 16

IV. Network Addresses Application Layer URL: misnt.indstate.edu

at C:>type Ping misnt.indstate.edu to see if active Network Layer IP: 139.102.31.12 Data Link Layer MAC: SMC network card 00-E0-

29-92-24-54 (12 hex digits) 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

Servers have fixed (static) addresses, clients usually not

Chapter 5 17

Internet Addresses Network Solutions is the agent that

provides domain names (called domain registrar) http://www.networksolutions.com

.com, .org, .net, .mil, .gov plus several new extensions (.biz, .info, .bz, and .tv) latter two were originally country codes

Country extensions: .us, .ca, .il, .jp, .de, .iq http://www.isi.edu/in-notes/iana/assignments/country-codes

Chapter 5 18

Subnets Subnet refers to logical group of computers,

often same physical network ISU uses 139.102.x.y Class B addresses

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

Chapter 5 19

Static vs. Dynamic Addresses Static IP address: always same, coded into

the Network TCP/IP properties DHCP and bootp give out dynamic

addresses at client boot up time 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)

Register: http://ithelp.indstate.edu/forms/bootp.html

Chapter 5 20

IP Address Lease 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)

Chapter 5 21

Address Resolution Server name resolution: DNS stands for Domain

Name Service 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!

DNS name is associated with domain name: www.indstate.edu=139.102.15.15

DNS servers replicate automatically

Chapter 5 22

Process of determining path through network of a message

Implement via a Routing Table (for computer B)

How many paths from A to G? ABCG, ADEFCG, ADEBCG, ABEFCG,

V. Routing

A B

DE

C

F

G

Destinat.

Route

A A

C C

D A

E E

F E

G C

Chapter 5 23

Routing - 2 Router points in the general direction of

destination 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

Chapter 5 24

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 8 156 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.

Chapter 5 25

Types of Routing 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.

Chapter 5 26

Routing Protocols

How routers exchange information to build, maintain routing tables

Autonomous system – network operated by one organization Routing protocols inside such systems

are interior routing protocols Routing protocols between autonomous

systems are exterior routing protocols

Chapter 5 27

Internet Routing Protocols

ICMP-Internet Control Message Protocol

RIP-Routing Information Protocol

BGP-Border Gateway Protocol

OSPF-Open Shortest Path First

EIGRP-Enhanced Interior Gateway Routing Protocol

For the test: know ICMP and RIP

Chapter 5 28

Multicasting

Unicast message: sent from one client to another client

Multicast message: sent from one node to a group of computers at same time Ex: Ghost for imaging hard drives; rebuild

all computers with same packets Ex: hearing a broadcast on the Internet –

like a seminar or workshop

Chapter 5 29

VI. TCP/IP Example A computer needs four TCP/IP settings:

Its IP address Subnet mask IP address of DNS server IP address of gateway leading outside subnet

Can get these values automatically or they can be static values typed into TCP/IP

Properties in Network control panel

Chapter 5 30

Example Network: fig 5-14 Four subnets: 98, 95, 50, 75 DNS server: 128.192.254.4 4 Gateways, each with at least two

IP addresses (internal/external) Bldg A: 128.192.98.1 129.192.254.3

(error) Router: 128.192.254.7 next to

Internet cloud

Chapter 5 31

Resolving Addresses Known Address, Same Subnet

Search IP address table, find Hand to Data Link layer, send packet

Known Address, Different Subnet Search IP address table, find Go through gateway to other subnet

Unknown Addresses Search IP address table, not found Perform DNS request, return address to table May go through gateway or out via router

Chapter 5 32

Bruce’s Router My home network has a Belkin

wireless router: http://139.102.180.53 with a special TCP port number

It has the following ports: WAN (connects to DSL modem) 4 wired LAN ports – inside firewall Wireless LAN ports – inside firewall

More in chapters 6-7 with LANs