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Bluetooth and Mobile IP
Bluetooth
Consortium: Ericsson, Intel, IBM, Nokia, Toshiba…
Scenarios:
connection of peripheral devices
loudspeaker, joystick, headset
support of ad-hoc networking
small devices, low-cost
bridging of networks
e.g., GSM via mobile phone - Bluetooth - laptop
Simple, cheap, replacement of IrDA, low range, lower data rates, low-power
Worldwide operation: 2.4 GHz
Resistance to jamming and selective frequency fading:
FHSS over 79 channels (of 1MHz each), 1600hops/s
Coexistence of multiple piconets: like CDMA
Links: synchronous connections and asynchronous connectionless
Interoperability: protocol stack supporting TCP/IP, OBEX, SDP
Range: 10 meters, can be extended to 100 meters
Documentation: over 1000 pages specification: bluetooth.com
Bluetooth Application Areas
Data and voice access points
Real-time voice and data transmissions
Cable replacement
Eliminates need for numerous cable attachments for connection
Low cost < $5
Ad hoc networking
Device with Bluetooth radio can establish connection with another when in range
Protocol Architecture
Bluetooth is a layered protocol architecture
Core protocols
Cable replacement and telephony control protocols
Adopted protocols
Core protocols
Radio
Baseband
Link manager protocol (LMP)
Logical page link control and adaptation protocol (L2CAP)
Service discovery protocol (SDP)
Protocol Architecture
Cable replacement protocol
RFCOMM
Telephony control protocol
Telephony control specification – binary (TCS BIN)
Adopted protocols
PPP
TCP/UDP/IP
OBEX
WAE/WAP
Protocol Architecture
BT Radio (2.4 GHZ Freq. Band):
Modulation: Gaussian Frequency Shift Keying
Baseband: FH-SS (79 carriers), CDMA (hopping sequence from the node MAC address)
Audio: interfaces directly with the baseband. Each voice connection is over a 64Kbps SCO link. The voice coding scheme is the Continuous Variable Slope Delta (CVSD)
Link Manager Protocol (LMP): page link setup and control, authentication and encryption
Host Controller Interface: provides a uniform method of access to the baseband, control registers, etc through USB, PCI, or UART
Logical Link Control and Adaptation Layer (L2CAP): higher protocols multiplexing, packet segmentation/reassembly, QoS
Service Discover Protocol (SDP): protocol of locating services provided by a Bluetooth device
Telephony Control Specification (TCS): defines the call control signaling for the establishment of speech and data calls between Bluetooth devices
RFCOMM: provides emulation of serial links (RS232). Upto 60 connections
Usage Models
File transfer
Internet bridge
LAN access
Synchronization
Three-in-one phone
Headset
Piconets and Scatternets
Piconet
Basic unit of Bluetooth networking
Master and one to seven slave devices
Master determines channel and phase
Scatternet
Device in one piconet may exist as master or slave in another piconet
Allows many devices to share same area
Makes efficient use of bandwidth
Wireless Network Configurations
Network Topology
Piconet = set of Bluetooth nodes synchronized to a master node
The piconet hopping sequence is derived from the master MAC address (BD_ADDR IEEE802 48 bits compatible address)
Scatternet = set of piconet
Master-Slaves can switch roles
A node can only be master of one piconet. Why?
Scatternets
Each piconet has one master and up to 7 slaves
Master determines hopping sequence, slaves have to synchronize
Participation in a piconet = synchronization to hopping sequence
Communication between piconets = devices jumping back and forth between the piconets
Radio Specification
Classes of transmitters
Class 1: Outputs 100 mW for maximum range
Power control mandatory
Provides greatest distance
Class 2: Outputs 2.4 mW at maximum
Power control optional
Class 3: Nominal output is 1 mW
Lowest power
Frequency Hopping in Bluetooth
Provides resistance to interference and multipath effects
Provides a form of multiple access among co-located devices in different piconets
Frequency Hopping
Total bandwidth divided into 1MHz physical channels
FH occurs by jumping from one channel to another in pseudorandom sequence
Hopping sequence shared with all devices on piconet
Piconet access:
Bluetooth devices use time division duplex (TDD)
Access technique is TDMA
FH-TDD-TDMA
Frequency Hopping
Physical Links
Synchronous connection oriented (SCO)
Allocates fixed bandwidth between point-to-point connection of master and slave
Master maintains page link using reserved slots
Master can support three simultaneous links
Asynchronous connectionless (ACL)
Point-to-multipoint page link between master and all slaves
Only single ACL page link can exist
Bluetooth Packet Fields
Access code – used for timing synchronization, offset compensation, paging, and inquiry
Header – used to identify packet type and carry protocol control information
Payload – contains user voice or data and payload header, if present
Bluetooth Piconet MAC
Each node has a Bluetooth Device Address (BD_ADDR). The master BD_ADDR determines the sequence of frequency hops
Types of connections:
Synchronous Connection-Oriented page link (SCO) (symmetrical, circuit switched, point-to-point)
Asynchronous Connectionless Link (ACL): (packet switched, point-to-multipoint, master-polls)
Packet Format:
Access code: synchronization, when piconet active derived from master
Packet header (for ACL): 1/3-FEC, MAC address (1 master, 7 slaves), page link type, alternating bit ARQ/SEQ, checksum
Types of Access Codes
Channel access code (CAC) – identifies a piconet
Device access code (DAC) – used for paging and subsequent responses
Inquiry access code (IAC) – used for inquiry purposes
Preamble+sync+trailer
Packet Header Fields
AM_ADDR – contains “active mode” address of one of the slaves
Type – identifies type of packet
ACL: Data Medium (DM) or Data High (DH), with different slot lengths (DM1, DM3, DM5, DH1, DH3, DH5)
SCO: Data Voice (DV) and High-quality voice (HV)
Flow – 1-bit flow control
ARQN – 1-bit acknowledgment
SEQN – 1-bit sequential numbering schemes
Header error control (HEC) – 8-bit error detection code
Payload Format
Payload header
L_CH field – identifies logical channel
Flow field – used to control flow at L2CAP level
Length field – number of bytes of data
Payload body – contains user data
CRC – 16-bit CRC code
Error Correction Schemes
1/3 rate FEC (forward error correction)
Used on 18-bit packet header, voice field in HV1 packet
2/3 rate FEC
Used in DM packets, data fields of DV packet, FHS packet and HV2 packet
ARQ
Used with DM and DH packets
ARQ Scheme Elements
Error detection – destination detects errors, discards packets
Positive acknowledgment – destination returns positive acknowledgment
Retransmission after timeout – source retransmits if packet unacknowledged
Negative acknowledgment and retransmission – destination returns negative acknowledgement for packets with errors, source retransmits
Types of packets
SCO packets: Do not have a CRC (except for the data part of DV) and are never retransmitted. Intended for High-quality Voice (HV).
ACL packets: Data Medium-rate (DM) and Data High-rate (DH)
Channel Control
Major states
Standby – default state
Connection – device connected
Interim substates for adding new slaves
Page – device issued a page (used by master)
Page scan – device is listening for a page
Master response – master receives a page response from slave
Slave response – slave responds to a page from master
Inquiry – device has issued an inquiry for identity of devices within range
Inquiry scan – device is listening for an inquiry
Inquiry response – device receives an inquiry response
State Transition Diagram
Inquiry Procedure
Potential master identifies devices in range that wish to participate
Transmits ID packet with inquiry access code (IAC)
Occurs in Inquiry state
Device receives inquiry
Enter Inquiry Response state
Returns FHS (Frequency Hop Synchrnonization) packet with address and timing information
Moves to page scan state
Inquiry Procedure Details
Goal: aims at discovering other neighboring devices
Inquiring node:
Sends an inquiry message (packet with only the access code: General Inquiry Access Code: GIAC or Dedicated IAC: DIAC). This message is sent over a subset of all possible frequencies.
The inquiry frequencies are divided into two hopping sets of 16 frequencies each.
In inquiry state the node will send upto NINQUIRY sequences on one set of 16 frequencies before switching to the other set of 16 frequencies. Upto 3 switches can be executed. Thus the inquiry may last upto 10.24 seconds.
To be discovered node:
Enters an inquiry_scan mode
When hearing the inquiry_message (and after a backoff procedure) enter an inquiry_response mode: send a Frequency Hop Sync (FHS) packet (BD_ADDR, native clock)
After discovering the neighbors and collecting information on their address and clock, the inquiring node can start a page routine to setup a piconet
Page Procedure
Master uses devices address to calculate a page frequency-hopping sequence
Master pages with ID packet and device access code (DAC) of specific slave
Slave responds with DAC ID packet
Master responds with its FHS packet
Slave confirms receipt with DAC ID
Slaves moves to Connection state
Page Procedure Details
Goal: e.g., setup a piconet after an inquiry
Paging node (master):
Sends a page message (i.e., packet with only Device Access Code of paged node) over 32 frequency hops (from DAC and split into 2*16 freq.)
Repeated until a response is received
When a response is received send a FHS message to allow the paged node to synchronize
Paged node (slave):
Listens on its hopping sequence
When receiving a page message, send a page_response and wait for the FHS of the pager
Slave Connection State Modes
Active – participates in piconet
Listens, transmits and receives packets
Sniff – only listens on specified slots
Hold – does not support ACL packets
Reduced power status
May still participate in SCO exchanges
Park – does not participate on piconet
Still retained as part of piconet
States of a Bluetooth Device
Bluetooth Audio
Voice encoding schemes:
Pulse code modulation (PCM)
Continuously variable slope delta (CVSD) modulation
Choice of scheme made by page link manager
Negotiates most appropriate scheme for application
Bluetooth Link Security
Elements:
Authentication – verify claimed identity
Encryption – privacy
Key management and usage
Security algorithm parameters:
Unit address
Secret authentication key (128 bits key)
Secret privacy key (4-128 bits secret key)
Random number
Link Management
Manages master-slave radio link
Security Service: authentication, encryption, and key distribution
Clock synchronization
Exchange station capability information
Mode management:
switch master/slave role
change hold, sniff, park modes
QoS
L2CAP
Provides a link-layer protocol between entities with a number of services
Relies on lower layer for flow and error control
Makes use of ACL links, does not support SCO links
Provides two alternative services to upper-layer protocols
Connectionless service
Connection-oriented service: A QoS flow specification is assigned in each direction
Exchange of signaling messages to establish and configure connection parameters
Flow Specification Parameters
Service type
Token rate (bytes/second)
Token bucket size (bytes)
Peak bandwidth (bytes/second)
Latency (microseconds)
Delay variation (microseconds
Mobile IP
Motivation for Mobile IP
Routing
based on IP destination address, network prefix (e.g. 129.13.42) determines physical subnet
change of physical subnet implies change of IP address to have a topological correct address (standard IP) or needs special entries in the routing tables
Specific routes to end-systems?
change of all routing table entries to forward packets to the right destination
does not scale with the number of mobile hosts and frequent changes in the location, security problems
Changing the IP-address?
adjust the host IP address depending on the current location
almost impossible to find a mobile system, DNS updates take too much time
TCP connections break, security problems
Mobile IP Requirements
Transparency
mobile end-systems keep their IP address
continuation of communication after interruption of page link possible
point of connection to the fixed network can be changed
Compatibility
support of the same layer 2 protocols as IP
no changes to current end-systems and routers required
mobile end-systems can communicate with fixed systems
Security
authentication of all registration messages
Efficiency and scalability
only little additional messages to the mobile system required (connection typically via a low bandwidth radio link)
world-wide support of a large number of mobile systems in the whole Internet
Terminology
Mobile Node (MN)
system (node) that can change the point of connection to the network without changing its IP address
Home Agent (HA)
system in the home network of the MN, typically a router
registers the location of the MN, tunnels IP datagrams to the COA
Foreign Agent (FA)
system in the current foreign network of the MN, typically a router
forwards the tunneled datagrams to the MN, typically also the default router for the MN
Care-of Address (COA)
address of the current tunnel end-point for the MN (at FA or MN)
actual location of the MN from an IP point of view
can be chosen, e.g., via DHCP
Correspondent Node (CN)
communication partner
Example network
Data transfer to the mobile
Data transfer from the mobile
Overview
Network integration
Agent Advertisement
HA and FA periodically send advertisement messages into their physical subnets
MN listens to these messages and detects, if it is in the home or a foreign network (standard case for home network)
MN reads a COA from the FA advertisement messages
Registration (always limited lifetime!)
MN signals COA to the HA via the FA, HA acknowledges via FA to MN
these actions have to be secured by authentication
Advertisement
HA advertises the IP address of the MN (as for fixed systems), i.e. standard routing information
routers adjust their entries, these are stable for a longer time (HA responsible for a MN over a longer period of time)
packets to the MN are sent to the HA,
independent of changes in COA/FA
Agent advertisement
Registration
Mobile IP registration request
Encapsulation
Encapsulation I
Encapsulation of one packet into another as payload
e.g. IPv6 in IPv4 (6Bone), Multicast in Unicast (Mbone)
here: e.g. IP-in-IP-encapsulation, minimal encapsulation or GRE (Generic Record Encapsulation)
IP-in-IP-encapsulation (mandatory in RFC 2003)
tunnel between HA and COA
Encapsulation II
Minimal encapsulation (optional) [RFC2004]
avoids repetition of identical fields
e.g. TTL, IHL, version, TOS
only applicable for unfragmented packets, no space left for fragment identification
Optimization of packet forwarding
Triangular Routing
sender sends all packets via HA to MN
higher latency and network load
“Solutions”
sender learns the current location of MN
direct tunneling to this location
HA informs a sender about the location of MN
big security problems!
Change of FA
packets on-the-fly during the change can be lost
new FA informs old FA to avoid packet loss, old FA now forwards remaining packets to new FA
this information also enables the old FA to release resources for the MN
Change of foreign agent
Reverse tunneling (RFC 2344)
Mobile IP with reverse tunneling
Routers accept often only “topological correct“ addresses (firewall)
a packet from the MN encapsulated by the FA is now topological correct
furthermore multicast and TTL problems solved (TTL in the home network correct, but MN is to far away from the receiver)
Reverse tunneling does not solve
problems with firewalls, the reverse tunnel can be abused to circumvent security mechanisms (tunnel hijacking)
optimization of data paths, i.e. packets will be forwarded through the tunnel via the HA to a sender (double triangular routing)
The new standard is backwards compatible
the extensions can be implemented easily and cooperate with current implementations without these extensions
Mobile IP and IPv6
security is integrated and not an add-on, authentication of registration is included
COA can be assigned via auto-configuration (DHCPv6 is one candidate), every node has address autoconfiguration
no need for a separate FA, all routers perform router advertisement which can be used instead of the special agent advertisement
MN can signal a sender directly the COA, sending via HA not needed in this case (automatic path optimization)
“soft” hand-over, i.e. without packet loss, between two subnets is supported
MN sends the new COA to its old router
the old router encapsulates all incoming packets for the MN and forwards them to the new COA
authentication is always granted
Problems with Mobile IP
Security
authentication with FA problematic, for the FA typically belongs to another organization
no protocol for key management and key distribution has been standardized in the Internet
patent and export restrictions
Firewalls
typically mobile IP cannot be used together with firewalls, special set-ups are needed (such as reverse tunneling)
QoS
many new reservations in case of RSVP
tunneling makes it hard to give a flow of packets a special treatment needed for the QoS
Security, firewalls, QoS etc. are topics of current research and discussions!