COMPLETE COMPUTER NETWORK

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Computer Networks

LMR

What is….. It ?

• A computer network consists of end systems, which are sources of information, which are sources of information, which communicate through the transit systems interconnecting them. The transit system is also called an interconnect subsystem or a subnetwork.

Topology:

– Topology refers to the way the network is laid out, either physically or logically. Two or more devices connect to a link, two or more links form a topology.

A

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Central Controller

B A

HUB

HUBHUB

C D D DD

A B

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A

ARing interface

unit

The OSI Model

TCP/IP Protocol :

DSL BLOCK DIAGRAM

Asymmetrical DSL (ADSL)

• ADSL divides up the available frequencies in a line on the assumption that most Internet users look at, or download, much more information than they send, or upload. – Under this assumption, if the connection speed

from the Internet to the user is three to four times faster than the connection from the user back to the Internet, then the user will see the most benefit (most of the time).

Asymmetrical DSL (ADSL)

• ADSL is an adaptive technology.

• The system uses a data rate based on the condition of the local loop line.

• Speed:Most existing local loops can handle

bandwidths up to 1.1 MHz.

ADSL Modem

OTHER TYPES OF DSL:

• Symmetric DSL (SDSL)• High-bit-rate DSL (HDSL)• Very high bit-rate DSL (VDSL)

Symmetric DSL (SDSL)

• Used mainly by small businesses & residential areas

• Bit rate of downstream is higher than upstream

High-bit-rate DSL (HDSL)

• Used as alternative of T-1 line• Uses 2B1Q encoding• Less susceptible to attenuation at higher

frequencies• Unlike T-1 line (AMI/1.544Mbps/1km), it can

reach 2Mbps @ 3.6Km

Very high bit-rate DSL (VDSL)

• Uses DMT modulation technique• Effective only for short distances(300-1800m)• Speed:

downstream : 50 - 55 Mbpsupstream : 1.5-2.5 Mbps

DATA LINK LAYER

• chacter count

• Starting and ending characters with character stuffing

• Starting end ending flags with bit stuffing.

Flow Control

• STOP N WAIT• SLIDDING WINDOW

– SLIDDING WINDOW GO BACK N ARQ– SELECTIVE REJECT ARQ

Error control :

• Cyclic redundancy check :• If Original Data to be transmitted is 110101010• Divisor is 10101• The data is appended with 4 zeros and divided by the divisor.• The remainder is added to the dividend in order to obtain the data to be transmitted.• 1101010100000• 1011• 1101010101011• Therefore, transmitted data : 1101010101011

10101 1101010100000

10101

11111

10101

10100

10101

11000

10101

11010

10101

11110

10101

1011 REMANIDER

• HAMMING CODE

CS757© Jörg Liebeherr, 2000-2003

• Communication networks can be classified based on the way in which the nodes exchange information:

Taxonomy of Networks

Communication Network

Circuit-SwitchedNetwork

Packet-SwitchedNetwork

Datagram Network

Virtual Circuit NetworkFrequency

DivisionMultiplexing

Time DivisionMultiplexing

Wavelength Division

Multiplexing


• In a circuit-switched network, a dedicated communication path (“circuit”) is established between two stations through the nodes of the network

• The dedicated path is called a circuit-switched connection or circuit

• A circuit occupies a fixed capacity of each link for the entire lifetime of the connection. Capacity unused by the circuit cannot be used by other circuits

• Data is not delayed at the switches

Circuit Switching


• Circuit-switched communication involves three phases:

1. Circuit Establishment2. Data Transfer3. Circuit Release

• “Busy Signal” if capacity for a circuit not available

• Most important circuit-switching networks:• Telephone networks• ISDN (Integrated Services Digital Networks)

Circuit Switching


Circuit Switching

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circuit 2

circuit 1


Implementation of Circuit-Switching

• There are two ways to implement circuits– Frequency Division Multiplexing (FDM)– Time Division Multiplexing (TDM)– Wavelength Division Multiplexing (WDM)

• Example: Voice in (analog) telephone network: Needed bandwidth: 3000 Hz

Allocated bandwidth: 4000 HzTherefore, a channel with 64 kHz can carry 16 voice conversations


Frequency Division Multiplexing (FDM)

Channel 1 (f1)

Channel 2 (f2)

Channel 3 (f3)

Channel 4 (f4)

Channel 5 (f5)

Channel 6 (f6)

Source 1

Source 2

Source 3

Source 4

Source 5

Source 6

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Switch

Switch

Approach: Divide the frequency spectrum into logical channels and assign each information flow one logical channel


Frequency Division Multiplexing (FDM)

CircuitSwitch

End-system

End-system

End-system

CircuitSwitch

End-system

• A circuit switch bundles (multiplexes) multiple voice calls on a high-bandwidth link

• Frequency-Division-Multiplexing (FDM): Each circuit receives a fixed bandwidth. The frequency of each call is shifted, so that multiple calls do not interfere


Source 1

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Source 6

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Time Division Multiplexing (TDM) Approach: Multiple signals can be carried

on a single transmission medium by interleaving portions of each signal in time


CircuitSwitch

end-system

end-system

end-system

CircuitSwitch

end-system

Time Division Multiplexing (TDM)

• Time is divided into frames of fixed length • Each frame has a fixed number of constant-sized “slots” • Each circuit obtains one or more “slots” per frame

frames

slots


Circuit Switch

memory

switchfabric

•A circuit switch relays a circuit from an input to an output link

•A switch may reassign frequencies (FDM) or time slot allocation (TDM)

•No queueing delays are experienced


Packet Switching• Data are sent as formatted bit-sequences, so-called packets • Packets have the following structure:

• Header and Trailer carry control information

• Each packet is passed through the network from node to node along some path (Forwarding/Routing)

• At each node the entire packet is received, stored briefly, and then forwarded to the next node (Store-and-Forward Networks)

• Packet transmission is never interrupted (no preemption)• No capacity is allocated for packets

Header Data Trailer


A Packet Switch

memory

outputqueues

inputqueues

switchfabric


Transmissionline

Packets from differentstreams

1 12N

1

N

2

output buffer

Statistical Multiplexing

• Packet transmission on a link is referred to as statistical multiplexing – There is no fixed allocation of packet transmissions– Packets are multiplexed as they arrive


Datagram Packet Switching

• The network nodes process each packet independentlyIf Host A sends two packets back-to-back to Host B over a datagram packet network, the network cannot tell that the packets belong together In fact, the two packets can take different routes

• Packets are called datagrams

• Implications of datagram packet switching: • A sequence of packets can be received in a different order than it

was sent• Each packet header must contain the full address of the destination


Virtual-Circuit Packet Switching

• Virtual-circuit packet switching is a hybrid of circuit switching and packet switching– All data is transmitted as packets– Emulates a circuit-switched network

• All packets from one packet stream are sent along a pre-established path (=virtual circuit)– Guarantees in-sequence delivery of packets– Note: Packets from different virtual circuits may be

interleaved



• Communication with virtual circuits (VC) takes place in three phases:

1. VC Establishment2. Data Transfer3. VC Disconnect

• Note: Packet headers don’t need to contain the full destination address of the packet

• Circuit-switched and virtual-circuit packet-switched networks are said to provide a connection-oriented service.


Packet Forwarding and Routing

• There are two parts to the routing problem:1. How to pass a packet from an input interface to the

output interface of a router (packet forwarding)? 2. How to calculate routes (routing algorithm)?

• Packet forwarding is done differently in datagram and virtual-circuit packet networks

• Route calculation is similar in datagram and virtual-circuit packet networks



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Packet Forwarding of Datagrams

• Recall: In datagram networks, each packet must carry the full destination address

• Each router maintains a routing table which has one row for each possible destination address

• The lookup yields the address of the next hop (next-hop routing)to

x

w v n

n

via(next hop)

d

Routing Table of node v

d


Packet Forwarding of Datagrams

• When a packet arrives at an incoming link, ...1. The router looks up the routing table2. The routing table lookup yields the address of the

next node (next hop)3. The packet is transmitted onto the outgoing link

that goes to the next hopto

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w v n

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via(next hop)

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ForwardingDatagrams

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To Next hop

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To Next hop

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To Next hop

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To Next hop

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To Next hop

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Packet Forwarding with Virtual Circuits

• Recall: In VC networks, the route is setup in the connection establishment phase

• During the setup, each router assigns a VC number (VC#) to the virtual circuit

• The VC# can be different for each hop• VC# is written into the packet headers

3dx

w v n

2w


dfrom VC# to VC#

path of virtualcircuit

2 31


Packet Forwarding of Virtual Circuits• When a packet with VCin in header arrives from router nin, ...

1. The router looks up the routing table for an entry with (VCin, nin)

2. The routing table lookup yields (VCout, nout)

3.The router updates the VC# of the header to VCout and transmits the packet to nout

3dx

w v n

2w


dfrom VC# to VC#

path of virtualcircuit

2 31

2 3 1


Forwarding with VCs

X

EA

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nin Vin nout Vout

- - C 5

nin Vin nout Vout

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nin Vin nout Vout

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nin Vin nout Vout

D 5 E 3

nin Vin nout Vout

B 3 - -

Part 1: VC setup from X to E


Forwarding with VCs

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nin Vin nout Vout

- - C 5

nin Vin nout Vout

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Part 2: Forwarding the packet


Comparison

Dedicated transmission path

Continuous transmission

Path stays fixed for entire connection

Call setup delay Negligible

transmission delay No queueing delay Busy signal overloaded

network Fixed bandwidth for

each circuit No overhead after call

setup

Circuit Switching

No dedicated transmission path

Transmission of packets

Route of each packet is independent

No setup delay Transmission delay

for each packet Queueing delays at

switches Delays increase in

overloaded networks Bandwidth is shared

by all packets Overhead in each

packet


No dedicated transmission path

Transmission of packets

Path stays fixed for entire connection

Call setup delay Transmission delay

for each packet Queueing delays at

switches Delays increase in

overloaded networks Bandwidth is shared

by all packets Overhead in each

packet

VC Packet Switching

HDLC Overview

Broadly HDLC features are as follows:• Reliable protocol

– selective repeat or go-back-N• Full-duplex communication

– receive and transmit at the same time• Bit-oriented protocol

– use bits to stuff flags occurring in data• Flow control

– adjust window size based on receiver capability• Uses physical layer clocking and synchronization to

send and receive frames

HDLC Overview• Defines three types of stations

– Primary– Secondary– Combined

• Defines three types of data transfer mode– Normal Response mode– Asynchronous Response mode– Asynchronous Balanced mode

• Three types of frames– Unnumbered– information– Supervisory

HDLC• The three stations are :

– Primary station • Has the responsibility of controlling the operation of data flow the

link. • Handles error recovery• Frames issued by the primary station are called commands.

– Secondary station, • Operates under the control of the primary station. • Frames issued by a secondary station are called responses.• The primary station maintains a separate logical link with each

secondary station.– Combined station,

• Acts as both as primary and secondary station.• Does not rely on other for sending data

HDLC

Primary

Secondary Secondary

Commands

Responses

Combined Combined

commands/Responses

Unbalanced Mode

Balanced mode

HDLC• The three modes of data transfer operations are

– Normal Response Mode (NRM) • Mainly used in terminal-mainframe networks. In this case, • Secondaries (terminals) can only transmit when specifically instructed by

the primary station in response to a polling• Unbalanced configuration, good for multi-point links

– Asynchronous Response Mode (ARM) • Same as NRM except that the secondaries can initiate transmissions

without direct polling from the primary station• Reduces overhead as no frames need to be sent to allow secondary nodes

to transmit• Transmission proceeds when channel is detected idle , used mostly in

point-to-point-links– Asynchronous Balanced Mode (ABM)

• Mainly used in point-to-point links, for communication between combined stations

Data Link Control HDLC frame structure

(a) Frame Format

(b) Control field format

11-7 POINT-TO-POINT PROTOCOL

Although HDLC is a general protocol that can be used for both point-to-point and multipoint configurations, one of the most common protocols for point-to-point access is the Point-to-Point Protocol (PPP). PPP is a byte-oriented protocol.

11.54

Figure 11.32 PPP frame format

11.55

PPP is a byte-oriented protocol using byte stuffing with the escape byte 01111101.

Note

11.56

Figure 11.33 Transition phases

Routing :

• 1) Centralized Routing :• 2) Distributed Routing :• 3) Static Routing or Non-adaptive routing :• 4) Dynamic Routing or Adaptive Routing :

• 1.Shortest path routing algorithm:

• Distance Vector Routing :

• . The count-to-infinity problem.

• Link State Routing– Discover its neighbors and learn their network

addresses.– Measure the delay or cost to each of its neighbors.– Construct a packet telling all it has just learned.– Send this packet to all other routers.– Compute the shortest path to every other router.

CS 640 62

CIDR Addresses

• Identifying a CIDR block requires both an address and a mask– Slash notation– 128.211.168.0/21 for addresses 128.211.168.0 – 128.211.175.255

• Here the /21 indicates a 21 bit mask– All possible CIDR masks can easily be generated

• /8, /16, /24 correspond to traditional class A, B, C categories

• IP addresses are now arbitrary integers, not classes• Raises interesting questions about lookups

– Routers cannot determine the division between prefix and suffix just by looking at the address

• Hashing does not work well• Interesting lookup algorithms have been developed and analyzed

CS 640 63

CIDR – A Couple Details

• ISP’s can further subdivide their blocks of addresses using CIDR

• Some prefixes are reserved for private addresses– 10/8, 172.16/12, 192.168/16, 169.254/16– These are not routable in the Internet

Traffic Shaping

Congestion control

• In Virtual-Circuit – Admission control

• In Datagram Subnets– The Warning Bit– Choke Packets– Hop-by-Hop Choke Packets– Load Shedding– Jitter Control

IP Addresses

HEADER

TRANSPORT LAYER

HAND SHAKE

T/TCP

HEADER-TCP

INTER NETWORKING DEVICES

Connecting Devices and the OSI Model

Connecting Devices

Connecting Devices

Repeaters

Hubs

Bridges

Two-Layer Switches

Connecting devices

Repeaters• A repeater (or regenerator) is an electronic device that

operates on only the physical layer of the OSI model.• A repeater installed on a link receives the signal before it

becomes too weak or corrupted, regenerates the original pattern, and puts the refreshed copy back on the link.

Repeaters• A repeater does not actually connect two LANS; it connects

two segments of the same LAN.

• A repeater forwards every frame; it has no filtering capability.

Hubs

• A Hub is a multiport repeater. It is normally used to create connections between stations in a physical star topology.

Bridges

• Bridges operate in both the physical and the data link layers of the OSI model.

Bridges

• Bridges can divide a large network into smaller segments. They contain logic that allows them to keep the traffic on each segment separate. When a frame (or packet) enters a bridge, the bridge not only regenerates the signal but checks the destination address and forwards the new copy only to the segment the address belong.

Bridges• A bridge operates in both the physical and the data link layers.• As a physical layer device, it regenerates the signal it receives.

• As a data link layer device, the bridge can check the physical

(MAC) address (source and destination) contained in the frame.

• A bridge has filtering capability. It can check the destination address of a frame and decide if the frame should be forwarded or dropped. If the frame is to be forwarded, the decision must specify the port.

• A bridge does not change the physical (MAC) addresses in a frame.

• A bridge has a table used in filtering decisions.

Bridge

Types of Bridges

• To select between segments, a bridge must have a look-up table that contains the physical addresses of every station connect to it. The table indicate to which segment each station belongs.

Simple Bridge• The address table must be entered manually, before a

simple bridge can be used.• Whenever a new station is added or removed, the table

must modified.• Installation and maintenance of simple bridges are time-

consuming and potentially more trouble than the cost savings are worth.

Routers• Routers have access

to network layer addresses and contain software that enables them to determine which of several possible paths between those addresses is the best for a particular transmission.

• Routers operate in the physical, data link, and network layers of the OSI model.

• Routers relay packets among multiple interconnected networks. They route packets from one network to any of a number of potential destination networks on an internet.

Gateways• Gateways potentially operate in all seven layers of the OSI

model.

Gateways

• A gateway is a protocol converter. A router by itself transfers, accepts, and relays packets only across networks using similar protocols.

A gateway can accept a packet formatted for one protocol (e.g. AppleTalk) and convert it to a packet for another protocol (e.g. TCP/IP).

Gateways• A gateway is generally software installed within a router.

The gateway understands the protocols used by each network linked into the router and is therefore able to translate from one to another.

What is SONET?

• Synchronous Optical Network standard

• Defines a digital hierarchy of synchronous signals• Maps asynchronous signals (DS1, DS3) to synchronous format• Defines electrical and optical connections between equipment• Allows for interconnection of different vendors’ equipment• Provides overhead channels for interoffice OAM&P

SONETNetworkElement

SONETNetworkElement

DigitalTributaries

DigitalTributaries

SONET Rates

STS-1 OC-1 51.840

STS-3 OC-3 155.520

STS-12 OC-12 622.080

STS-48 OC-48 2,488.320

STS-192 OC-192 9,953.280

Level OpticalDesignation

Bit Rate(Mb/s)

STS = SYNCHRONOUS TRANSPORT SIGNALOC = OPTICAL CARRIER (“..result of a direct optical conversions of the STS after synchronous scrambling” - ANSI)

SONET Network Layers

DS3etc

DS3etc

Path • Map Services & POH Into SPE• Path Protection/Restoration • Other Path OA&M Functions

Line • Combine SPE & LOH• Sync & Mux For Path Layer• Line Protection/Restoration• Other Line OA&M Functions

Section • Add SOH & Create STS Signal• Framing, Scrambling• Section OA&M Functions

Physical(Photonic)

• E/O Conversion• Line Code• Physical Signal[No additional overhead]

MUX LTE Regen MUXLTELTERegen

ServicesDS3, DS1, etc

SONET ADM

Path

Line Line

SectionSection Section Section

Functional Description of SONET Layers

OH: Overhead

Path Layer

Line Layer

SectionLayer

PhotonicLayer

Information Payload

PathOH

LineOH

SectionOH

E/O Conversion

Transmission over OC-N

Function

Payload MappingError Monitoring

SynchronizationMultiplexingError MonitoringLine MaintenanceProtection SwitchOrder Wire

FramingScramblingError MonitoringSection MaintenanceOrderwire

E/O ConversionPulse ShapingPower LevelWavelenght

Internet Protocol (IP)• Features:

– Layer 3 (Network layer)– Unreliable, Connectionless, Datagram– Best-effort delivery

• Popular version: IPv4• Major functions

– Global addressing– Datagram lifetime– Fragmentation & Reassembly

IPv4 Header

IPv4 companion protocols (1)

• ARP: Address Resolution Protocol– Mapping from IP address to MAC address

• ICMP: Internet Control Message Protocol– Error reporting & Query

• IGMP: Internet Group Management Protocol– Multicast member join/leave

• Unicast Routing Protocols (Intra-AS)– Maintaining Unicast Routing Table– E.g. RIP, OSPF (Open Shortest Path

First)

IPv4 companion protocols (2)

• Multicast Routing Protocols– Maintaining Multicast Routing Table– E.g. DVMRP, MOSPF, CBT, PIM

• Exterior Routing Protocols (Inter-AS)– E.g. BGP (Border Gateway Protocol)

• Quality-of-Service Frameworks– Integrated Service (ISA, IntServ)– Differentiated Service (DiffServ)

Why IPv6?• Deficiency of IPv4• Address space exhaustion• New types of service Integration

– Multicast– Quality of Service– Security– Mobility (MIPv6)

• Header and format limitations

Advantages of IPv6 over IPv4

• Larger address space• Better header format• New options• Allowance for extension• Support for resource allocation• Support for more security• Support for mobility

Header: from IPv4 to IPv6Changed Removed

IPv6 Header Format

Advantages of IPv6 over IPv4 (1)

Feature IPv4 IPv6

Source and destination address

32 bits 128 bits

IPSec Optional required

Payload ID for QoS in the header

No identification Using Flow label field

Fragmentation Both router and the sending hosts

Only supported at the sending hosts

Header checksum included Not included

Resolve IP address to a link layer address

broadcast ARP request

Multicast Neighbor Solicitation

message

Advantages of IPv6 over IPv4 (2)

Feature IPv4 IPv6

Determine the address of the best default gateway

ICMP Router Discovery(optional)

ICMPv6 Router Solicitation and

Router Advertisement

(required)

Send traffic to all nodes on a subnet

Broadcast Link-local scope all-nodes multicast

address

Configure address Manually or DHCP Autoconfiguration

Manage local subnet group membership

(IGMP) Multicast Listener Discovery (MLD)

Bluetooth Overview

• Wireless technology for short-range voice and data communication

• Low-cost and low-power• Provides a communication platform between a

wide range of “smart” devices• Not limited to “line of sight” communication

Motivation

PDACell Phone

Cordless PhoneBase Station

InkjetPrinter

Scanner

Home Audio System

Computer

Digital Camera

Bluetooth Applications

• Automatic synchronization between mobile and stationary devices

• Connecting mobile users to the internet using bluetooth-enabled wire-bound connection ports

• Dynamic creation of private networks

Ad Hoc Networks

• Up to 8 devices can be actively connected in master/slave configuration

• Piconets can be combined to form scatternets providing unlimited device connectivity

Bluetooth Radio

• Uses 2.4 GHz ISM band spread spectrum radio (2400 – 2483.5 MHz)

• Advantages– Free– Open to everyone worldwide

• Disadvantages– Can be noisy (microwaves, cordless phones,

garage door openers)

Frequency Hopping

• In order to mitigate interference, Bluetooth implements frequency hopping

• 1600 hops per second through 79 1MHz channels

• Spreads Bluetooth traffic over the entire ISM band

• All slaves in piconet follow the master for frequency hop sequence

Establishing Piconets

• Whenever there is a connection between two Bluetooth devices, a piconet is formed

• Always 1 master and up to 7 active slaves

• Any Bluetooth device can be either a master or a slave

• Can be a master of one piconet and a slave of another piconet at the same time (scatternet)

• All devices have the same timing and frequency hopping sequence

Scatternets

• Formed by two or more Piconets

• Master of one piconet can participate as a slave in another connected piconet

• No time or frequency synchronization between piconets

Berkeley Sockets

The socket primitives for TCP.

Technology

COMPLETE COMPUTER NETWORK