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WWW.AMARPANCHAL.COM
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
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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
CS757© Jörg Liebeherr, 2000-2003
• 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
CS757© Jörg Liebeherr, 2000-2003
• 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
CS757© Jörg Liebeherr, 2000-2003
Circuit Switching
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circuit 2
circuit 1
CS757© Jörg Liebeherr, 2000-2003
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
CS757© Jörg Liebeherr, 2000-2003
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
CS757© Jörg Liebeherr, 2000-2003
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
CS757© Jörg Liebeherr, 2000-2003
Source 1
Source 2
Source 3
Source 4
Source 5
Source 6
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M
U
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M
1 2 3 4 5 6 1 2
Time Division Multiplexing (TDM) Approach: Multiple signals can be carried
on a single transmission medium by interleaving portions of each signal in time
CS757© Jörg Liebeherr, 2000-2003
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
CS757© Jörg Liebeherr, 2000-2003
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
CS757© Jörg Liebeherr, 2000-2003
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
CS757© Jörg Liebeherr, 2000-2003
A Packet Switch
memory
outputqueues
inputqueues
switchfabric
CS757© Jörg Liebeherr, 2000-2003
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
CS757© Jörg Liebeherr, 2000-2003
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
CS757© Jörg Liebeherr, 2000-2003
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
CS757© Jörg Liebeherr, 2000-2003
Virtual-Circuit Packet Switching
• 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.
CS757© Jörg Liebeherr, 2000-2003
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
CS757© Jörg Liebeherr, 2000-2003
Datagram Packet Switching
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CS757© Jörg Liebeherr, 2000-2003
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Virtual-Circuit Packet Switching
VC 2
VC 1
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CS757© Jörg Liebeherr, 2000-2003
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
CS757© Jörg Liebeherr, 2000-2003
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
x
w v n
n
via(next hop)
d
Routing Table of node v
d
d d
CS757© Jörg Liebeherr, 2000-2003
ForwardingDatagrams
X
EA
C
B
D
To Next hop
A -
B B
C C
D C
E B
X C
To Next hop
A C
B C
C C
D C
E C
X -
To Next hop
A A
B -
C D
D D
E E
X D
To Next hop
A B
B B
C B
D B
E -
X B
To Next hop
A B
B B
C C
D -
E B
X C
To Next hop
A A
B -
C D
D D
E D
X E
EE
EE
EE
CS757© Jörg Liebeherr, 2000-2003
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
Routing Table of node v
dfrom VC# to VC#
path of virtualcircuit
2 31
CS757© Jörg Liebeherr, 2000-2003
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
Routing Table of node v
dfrom VC# to VC#
path of virtualcircuit
2 31
2 3 1
CS757© Jörg Liebeherr, 2000-2003
Forwarding with VCs
X
EA
C
B
D
nin Vin nout Vout
- - C 5
nin Vin nout Vout
X 5 D 3
nin Vin nout Vout
C 3 B 5
nin Vin nout Vout
D 5 E 3
nin Vin nout Vout
B 3 - -
Part 1: VC setup from X to E
CS757© Jörg Liebeherr, 2000-2003
Forwarding with VCs
X
EA
C
B
D
nin Vin nout Vout
- - C 5
nin Vin nout Vout
X 5 D 3
nin Vin nout Vout
C 3 B 5
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D 5 E 2
nin Vin nout Vout
B 3 - -5
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2
Part 2: Forwarding the packet
CS757© Jörg Liebeherr, 2000-2003
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
Datagram Packet Switching
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.