IBU CEN 263: Computer
International Burch University
Networks
Lecture 1
Dr. Elma Avdic
CEN 263: Computer
Networks
Introductory Lecture 1: Welcome to the Course
- Global network infrastructure and the Internet
- Robust protocols accommodating unforeseen applications
- Food for thought:
- How this global network infrastructure work?
- What are the design principles it is based on, did we compromise on the design principles and
how do we make it work better, how do we make sure it works in the future?
- How should Internet applications be written?
Routing
Subnetting
What you’ll learn Computer network
MAC address
ARP
Switches
Troubleshooting Node
● The Layered Network model(s) IP address
Protocols UDP
● How computers determine where to
send their messages Computer networks TCP/IP
● How network services like DNS and Routers Cables
DHCP work DHCP Hubs
DNS
● Tools to help you troubleshoot Layered network model(s): TCP/IP &
OSI/ISO
network issues
● Network design and analysis
○ Architecture
○ Protocols
...
○ Algorithms Computer... Computer Networks...
○ Analysis tools Diff kinds of questions - layers
Applications
Network
What the MAC addresses are?
Operating System Data Link layer
How it’s physically linked together?
Hardware What sort of cables you are using, Physical
how long they can be, etc.
Today’s Class
● Organisational Information
● Contents to Cover
● The Basics of Networking
○ TCP/IP and OSI/ISO layer network model
○ Networking Devices:
■ Cables
■ Hubs/switches
■ Routers
■ Servers and Clients
○ The Physical Layer
○ The Data Link Layer
Course Logistics
● Goals ● Course structure/material
○ To understand the network protocols, ○ LMS Course page
architectures and applications ■ Lectures (slides, videos)
○ To understand how networking research ■ The textbook (chapters readings
is done and investigate novel ideas in the + the textbook slides)
area ■ Labs
● Prerequisites ● Grading
○ The course covers basic networking ○ Quiz 10%
concepts ○ Lab Exam 20%
● Textbook ○ Exams: midterm 30%, final 40%
○ Kurose, J. and Ross, K., 2001. Computer ● Readings
networks: A top-down approach. Pearson ○ See Syllabus
Education, pp.419-420.
Contents to Cover
the TCP/IP and the
OSI/ISO network cables, hubs, switches, routers, servers
● Introduction: models,... and clients, setting up a network,...
● The Basics of Networking: moving bits across the wire, cabling,
network ports, Ethernet,...
● The Physical layer: MAC addresses, unicast, multicast,
● The Data Link Layer: broadcast, Ethernet frame,...
IP address, datagrams, encapsulation,
● The Network Layer: address classes, ARP,...
subnetting, masks, binary math, CIDR, routing concepts, routing
● Subnetting & Routing: tables, gateway protocols, RFCs and standards etc.
● Transportation and Application layers: transport layer, TCP segment, control flags and 3-way
handshake, protocols, firewalls, application layer
● Intro to Networking Services: DNS, NAT, DHCP, VPNs, Proxies
● Connecting to the Internet: security, protection, Wireshark, IP configuration, IP analysis
● Troubleshooting: ping and ICMP, traceroute, testing
connectivity, DNS, the cloud, IPv6,...
The Basics of Networking
What is the Internet?
- HW and SW components
- A networking infrastructure
Network Models: TCP/IP vs. OSI/ISO
# Layer Protocol Protocol Data Addressing Device
Unit
5 Application HTTP, SMTP, etc... Messages -
4 Transport TCP/UDP Segment Port #’s
3 Network IP Datagram IP address Router
2 Data Link Ethernet, Wi-Fi Frames MAC Address Switch
1 Physical 10 Base T, 802.11 Bits - Hub
Package delivery...
Layered Network Model
Cabling Physical Layer
Connectors Physical
And sending signals Data Link Network
Transport
Application
Workstation
Server
google.com
Routers Internet
IP
Network SW: client,
server
Network layer
Network Layer
The OSI Model: Overview
1984 OSI/ISO reference model
… to provide set of design standards for
equipment manufacturers so they
could communicate with each other.
The principles of layers:
A layer → new abstraction needed
A layer → well-defined function
The function of a layer → internationally standardised protocols
The layer boundaries → Min info flow across the interfaces
The number of layers →
The Basics of Networking Devices
Networking Devices: Cables
+
RJ45
+
TOOLS
Networking Devices: Cables
Networking Devices: Hubs (if you have them, throw them
away)
HUB
Workstation Workstation
Workstation
Workstation
Networking Devices: Collision Domain
Collision domain
Data
A network segment where
Collision
only one device can communicate
at a time.
HUB
Workstation Workstation
Workstation
Workstation
Networking Devices: Network Switch
Collision domain
A network segment where only one device can communicate at a time.
Data
Hub Collision
Sending data to
machine 3
HUB Sending data to
machine 4
Sending data to Switch Me neither
machine 4
Workstation 1 Workstation 4
Workstation 1
Workstation 4 Me.
Not me.
Workstation 2 Workstation 3 Workstation 2 Workstation 3
Networking Devices
# Layer Protocol Protocol Addressing Device
Data Unit
5 Application HTTP, SMTP, Messages -
etc...
4 Transport TCP/UDP Segment Port #’s
Router 3 Network IP Datagram IP address Router
2 Data Link Ethernet, Frames MAC Address Switch
Switch Wi-Fi
1 Physical 10 Base T, Bits - Hub
Hub 802.11
Networking Devices: Routers
Hubs and switches
Router
The primary devices used to connect computers
A device that knows how to forward on a single network, usually referred to as a LAN,
data between independent networks. or local area network.
Switch can inspect Ethernet data to
determine where to send things, a
Internet router can inspect IP data to Core routers making decisions on
determine where to send things.
where to send traffic
Core
routers
ISP
Router
Workstation
Laptop
Networking Devices: Routers (2) - Protocols
Border Gateway Protocol (BGP)
Routers share data with each other via this protocol, which lets them learn about the most
optimal paths to forward traffic.
Internet
Internet
Core
routers
ISP
Router
Workstation
Laptop
Networking Devices: Servers & Clients
Clients
DNS Server
Server
Workstation
Internet
Client
Laptop
Phone
Client Mail Server
Layered Network Model Components
● Protocols
● Protocol Data Units
● Addressing
● Devices
The Physical Layer
The Physical
Layer ●
●
Protocol
Data Unit
# Layer Protocol Protocol Addressing Device ● Addressing
Data
Unit ● Device
1 Physical 10 Base Bits - Hub,
T, 802.11 Switch
Sending digital information over a wire
voltage
5V
0V
1 0 0 1 0 0 1 0 =01461
Other media: fiber optics and RF encoding
The PHY Layer: Moving bits across the wire
Sender Receiver
Bit Line coding
The smallest representation of
data that a computer can
understand; 1 or 0.
Digital data Digital data
encoder decoder
Modulation
A way of varying the voltage of
the electrical charge moving
across the cable = line coding in
comp networks.
The PHY Layer: Twisted Pair Cabling and Duplexing
Duplexing
The concept of communication that
information can flow in both
directions across the cable
Simplex
communication Simplex
(only sends)
...is unidirectional.
10BASE5, 100BASE-TX,
1000BASE-SX Full-duplex
...baseband digital
simultaneous
transmission
The PHY Layer: Network Ports and Patch Panels
RJ45 port
RJ45 plug and port Activity Link LED
LED Cable properly
The concept of communication that Would flash connected to
when data is two devices
information can flow in both actively that are both
directions across the cable transmitted powered on
across the
cable
Simplex
communication
...is unidirectional.
10BASE5, 100BASE-TX,
1000BASE-SX
...baseband digital
transmission Patch panel
The Data Link
Layer ●
●
MAC addresses
Ethernet frame
# Layer Protocol Protocol Addressing Device ● Unicast, multicast, broadcast
Data
Unit ● CRC
2 Data Ethernet, Frames MAC Switch
Link Wi-Fi Address
1 Physical 10 Base Bits - Hub
T, 802.11
The Data Link Layer: Brief history of Ethernet
● Ethernet 1980s, Data
standards in 1983 Collision
● Collision domain
● CSMA/CD HUB
● MAC address
Workstation Workstation
Workstation A Workstation B
Workstation
Workstation
The Data Link Layer: MAC address
A globally unique identifier Organizational Unique Vendor Assigned (NIC
attached to an individual network Identifier Cards, Interfaces)
interface.
24 Bits 24 Bits Size in bits
● 48-bit number: 6 x 2 hex numbers
● 16 digits to represent numbers. >9 => A, B, 6 Hex Digits 6 Hex Digits Size in hex digits
C, D, E, and F represent 10, 11, 12, 13, 14,
and 15 00 60 2F 3A 07 BC Example
● Octet = any number represented in 8 bits
● Unique MAC adds: Total number = 2^48 = Cisco Particular Device Structure
281,474,976,710,656
● 2 sections: OUI (first 3 octets) and the last 3
octets
hexadecimal 0 1 2 3 4 5 6 7 8 9 A B C D E F
decimal 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
The Data Link Layer: Ethernet and MAC address
Ethernet uses MAC addresses to ensure that the data it sends has both and address for the
machine that sent the transmission, as well as the one address the transmission was intended
for.
→ each node on that network knows when traffic is intended for it (even on a network segment
acting as a collision domain)
The Data Link Layer: Unicast, multicast, broadcast
Unicast
UNICAST
Sender
… is always meant for just one receiving address.
If the least significant bit in the first octet of a destination address is set to zero,
it means that Ethernet frame is intended for only the destination address.
MULTICAST Receiver
… If the least significant bit in the first octet of a destination address is set to one,
it means we’re dealing with a multicast frame.
Broadcast Multicast
BROADCAST
…sent to every device on a LAN Sender Sender
Ethernet broadcast address
FF:FF:FF:FF:FF:FF
Receiver Receiver Receiver Receiver Receiver
The Data Link Layer: Ethernet Frame
Data packet
An all-encompassing term that represents any single set of binary data being sent across a network link.
Ethernet frame
A highly structured collection of information presented in a specific order.
Preamble
8 bytes (or 64 bits) long, and can itself be split into two sections.
Destination MAC address
The hardware address of the intended recipient.
Preamble SFD Source address Ether-type FCS
8 bytes 1 byte 6 bytes 2 bytes 4 bytes
Destination address VLAN header Payload
6 bytes 4 bytes 0 - 1,500 bytes
The Data Link Layer: Ethernet Frame (2) - VLAN
Virtual LAN (VLAN) Switch
A technique that lets you have multiple logical LANs
operating on the same physical equipment.
VLAN header
It indicates that the frame itself is a VLAN frame.
If a VLAN header is present, the EtherType field follows it.
VLAN 2 VLAN 1
Payload
In networking terms, is the actual data being transported,
which is everything that isn’t a header.
Frame Check Sequence
A 4-byte (or 32-bit) number that represents a checksum value
(calculated by doing a CRC against the frame) for the entire frame. VLAN 1
VLAN 2
Preamble SFD Source address Ether-type FCS
8 bytes 1 byte 6 bytes 2 bytes 4 bytes
Destination address VLAN header Payload
6 bytes
The Data Link Layer: Ethernet Frame (3)
4773099563521
CRC
Checksum
number
DATA
IP header /
TCP header
Checksum Checksum Checksum
number Ethernet number RNI number
Calculating IP Calculating IP
header TCP header TCP
header header
Checksum Checksum
number number
correct correct
Frame formats
Point to Point Multipoint / Broadcast
Ethernet
Switch
Ethernet Frame
6 bytes 6 bytes 2 bytes 46-1500 bytes 4 bytes
ff:ff:ff:ff:ff:ff:ff:ff
64 - 1500 bytes
Ethernet Switch MAC
addresses
68:e8:56:37:de:2e 80:f8:47:36:51:1a 68:56:35:8e:2c:2
1 2 3
Lecture 1 Summary
Ethernet Preamble frame gap HLDC
framing and flag bytes Ethernet LLC PPP LLC
frame formats
Manchester code NRZ QAM
encoding info
copper fiber radio
Additional Slides
How your network works: basic diagram of a network
Discussion points:
1. Physical vs.
Logical way
Websites 2. Speed
VPN
connections
Email
Internet ...
Switch Firewall Router Modem Internet Cloud
or The Cloud or
Splitter of the Does 1st Cloud
Internet networking device to Computing =
signal; all well: 1. allows connect Internet
devices computers to you to
connected to talk to each
Logically this is how
Internet
switch other, and 2. your network works:
get on the all these logical
Internet
devices are now in
one physical device.
Discussion points: Speed, Devices, Cabling,
Client-Server Architecture
● NETWORK DEVICES
Data is sized by two measurements: ○ MODEM
○ ROUTER
Bit → b → Kb 8b = 1B ○ HUB
○ SWITCH and PATCH
Byte → B → KB
PANELS
DL 16 Mb → 2MB (ISPs) ○ WiFi AP and 802.11
● NETWORK CABLING
UL 100 MB → 8x longer, 8b=1B
● CLIENTS and SERVERS
Trailer: Subnetting
Network and Host ID
Subnet Mask
192.68.40.55 IP address classes
Network ID = 192.68.40.0
11111111.11111111.00101000.00000000
255.255.255.0
11111111.11111111.11111111.00000000
/24 CIDR notation
Magic chart
128 64 32 16 8 4 2 1
27 26 25 24 23 22 21 20
Next Class
● The Network Layer
○ Introduction
○ IP Addresses
○ IP Datagrams and Encapsulation
○ IP Address Classes
○ ARP
○ Looking up IP addresses
● Subnetting
○ Subnet Masks
○ Binary Math
○ CIDR
● Routing
○ Introduction
○ Routing Tables
○
