Networking Concepts

LAN

• Concepts– Attenuation, Noise

• Hardware– Repeater, Amplifier– Bridge, Router, Gateway, Switch, Hub– Twisted pair, Coaxial cable, Fiber optics– Server, Workstation– Wireless access point

• Topology– Bus, Tree, Star, Ring

LAN

• Standard– OSI (Open Systems Interconnection)– IEEE (Institute of Electrical and Electronic Engineers)– ITU-T (Int’l Telephone Union – Telecom. Sector)– ISO (International Standards Organization)– EIA (Electronic Industries Association)– ETS (European Telecom. Standard)

Communications Hardware

• Repeater– Extends distance limitation on networks (both voice

and data)– Filters noise– Regenerates signals– For twisted pair wire, repeaters are placed every 100

meters

• Amplifier– Extends distance limitation on networks (both voice

and data)– Amplifies both signal and noise

Communications Hardware

• Bridge– Connects two LANs using same protocol– Single path between LANs– Minimal sophistication

• Router– Connects multiple LANs using same protocol– Choice of paths between LANs– Mainstay of internetworking

Communications Hardware

• Gateway– Connects multiple LANs using any protocol– Very sophisticated– Supports today’s internet by providing access

points to several networks

• Hub– Connects nodes to a network– Sometimes acts as repeater

Communications Hardware

• Switch– Connects multiple LAN segments using the

same protocol– Connections may use twisted pair, coaxial

cable, or fiber optics wiring– Faster than bridges– Enables simultaneous communication between

multiple network segments

Ethernet• Ethernet was developed jointly by Xerox, Intel,

and DEC in 1980• DEC (Digital Equipment Corporation) a computer

company that specialized in mini-computers in the 1970s. It was acquired by Compaq and Compaq merged with HP.

• This was the first commercial LAN system• Ethernet is a simple protocol to implement• Ethernet addresses the layers 1 and 2 functionality

for the OSI model• Ethernet standard is very close to IEEE 802.3

standard, but has some minor differences

Ethernet• Ethernet uses bus topology (which we will discuss

next)• Ethernet transmits a baseband signal at 10 Mbps• Baseband signals are digital and bidirectional• Ethernet allows the user data to have a variable

length up to 1500 bytes• Unlike HDLC and SDLC protocols, ethernet uses

a length field in the header to identify the length of the user data in bytes. Because of this, no special bit pattern is needed to recognize the start and end of the user data.

Ethernet frame format

6-bytes 6-bytes 2-bytes Variable length 4-bytes

Destination address

Source address

length User data CRC-32

Ethernet diagramPC1

PC2

PC3

Segment 1

Repeater

PC-B

PC-A

PC-C

Segment 2

Bus topology• It is a contention-based topology, which means that each

node on the network must contend for access

• Each node listens to traffic on the network

• When a node has packets to transfer and the bus is not busy, then the packets are put on the bus in both directions, with the destination address marked on the packets

• All nodes listen to traffic on the network and the node that has packets addressed to it, receives the packets

• No routing or switching is involved in data transfer

Bus topology diagram

PC1 PC3PC2 PC4

Tap for a new node

Tree topology• Tree topology is a variation on bus topology• A special node is designated as root• The primary reason for this topology is to

segment nodes so that not all nodes need to listen to packets broadcast on a segment

• This adds a layer of security in the form of unwanted nodes not listening to the network traffic

• Speeds up data transfer since there will be fewer nodes on each segment

Tree topology diagram

Root

PC 1 PC 2PC 3

PC 4PC 5

PC 6

PC 7

Star topology• This is another variation on bus topology• This has a central hub, a passive device• Star is a logical bus and a physical ring• Hub has ports in multiples of 8. Multiple hubs can be

connected in a daisy chain format• Easy to add nodes to the network and remove nodes from

the network• Central node does switching between nodes• Multiple nodes can communicate simultaneously without

collision• Potential problem is the single point of failure for the

network when the central node fails

Star topology diagram

HubPC 1 PC 5

PC 3

PC 7

PC 4PC 2

PC 8 PC 6

Ring topology• The nodes are connected in a ring pattern• Unlike bus topology, each node on the ring acts as a

repeater on the network• Nodes access the network using a token, which eliminates

the need for contention as in bus topology• Token is a series of bits that identifies the node that has the

right to transmit at any given time• Example of a token: Assume that there are 6 nodes on the

network. The nodes are labeled 1 through 6 and the token would consist of 3 bits. The token 100 will indicate that node 4 has the token.

• Tokens circulate in a single direction from a node to its neighbor

Ring topology diagram

PC 1

PC 2

PC 3

PC 4

PC 5

PC 6

OSI 7-layer model

Source Destination

Application

Presentation

Session

Transport

Network

Data link

Physical

Application

Presentation

Session

Transport

Network

Data link

Physical

IEEE 802• 802.1 General LAN management of OSI

layers 3 through 7• 802.2 LLC sublayer• 802.3 Ethernet• 802.4 Token bus• 802.5 Token ring• 802.6 MAN• 802.7 Broadband, in general

IEEE 802

• 802.10 Network Security

• 802.11 Wireless LAN

• 802.12 100VG-AnyLAN (Voice Grade)

• 802.13 unused

• 802.14 Cable Modem

WAN

• Concepts– Gateway, Frame Relay, ATM, DSL, T1, T3,

STS (Synchronous Transport Signal)

• Standard– TCP/IP (Transmission Control Protocol

/Internet Protocol)– IETF (Internet Engineering Task Force)– ATM Forum (Asynchronous Transfer Mode)

STS, STM, OC equivalencies

STS level STM level OC level Data Rate

STS-1 -- OC-1 52 Mbps

STS-3 STM-1 OC-3 155 Mbps

STS-9 STM-3 OC-9 467 Mbps

STS-12 STM-4 OC-12 622 Mbps

STS-18 STM-6 OC-18 933 Mbps

STS-24 STM-8 OC-24 1.2 Gbps

STS-36 STM-12 OC-36 1.9 Gbps

STS-48 STM-16 OC-48 2.5 Gbps

ATM VPI and VCIV P I 1 V P I 5

V P I 3

V C I 1V C I 2

V C I 1V C I 2

V P I 3

V P I 2V C I 2V C I 6

V C I 2V C I 6

V C I 4

V C I 7

V C I 7

V C I 4

V P Sw i t c h

V P I 6

TCP/IP functions• Establish a connection between nodes• Manage data flow on the network• Handle transmission errors• Terminate connection at the end• TCP is a connection-oriented protocol, meaning that a

packet sent to the next node is monitored for proper receipt• IP is a connection-less protocol, meaning that a packet sent

to the next node is not monitored for proper delivery• Since TCP and IP work together, the packet delivery is

reliable• Connection-less mode is known as User Datagram

Protocol (UDP)

TCP/IP 5-layer model

• TCP/IP protocol is divided into 5 layers– Application layer– Transport layer– Network layer– Data link layer– Physical layer

IP Addressing

• IP address consists of 4 octets: n.n.n.n where n is in the range 0 to 255

• This form of IP address is known as IPv4, denoting IP address Version 4

• A new form of IP address known as IPv6, denoting IP address Version 6, has been proposed. It uses 128-bit addressing instead of 32-bit addressing.

IP Address Hierarchy

• There are 3 main classes of IP addresses in use and two additional classes of IP addresses available for multicast and testing

• Class A First octet range: 1 – 126– IBM, AT&T, HP, Merck, Stanford University

• Class B First octet range: 128 – 191– U of L and most other universities

• Class C First octet range: 192 – 223– IGLOU, Louisville’s first ISP

UDP• User Datagram Protocol is a ‘best effort’ protocol• ‘best effort’ means no guarantee of delivery• This is a connection-less protocol• UDP does not provide reliability• UDP sends out packets without first establishing a

connection• RFC 768 describes UDP• UDP header consists of source port, destination port,

length, checksum• Example of UDP: TFTP (Trivial File Transfer Protocol).

TFTP is used when bootsrapping diskless system• TFTP is on UDP port 69