Download Lecture 17

CS 453
Computer Networks
Lecture 17
Medium Access Control Sublayer
Bluetooth, Switching and VLAN
Bluetooth
Developed out of an interest by a cell phone
manufacturer for a way for cell phone to connect
to other devices sans cables
SIG created from Erricson, IBM, Intel, Nokia,
and Toshiba…
… to develop standards
Bluetooth SIG standards in 1999
IEEE jumped in later
…became 802.15
Bluetooth
Ever wonder where the name came from?
Harold Gormson (Harold I of Denmark), a
Viking king
Bluetooth
802.11 intended to serve buildings
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Range ~ hundred meters
Bluetooth intended to serve a room
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Much more of a personal area network
Short run cable replacement (at least
originally)
Range: 10 meter (that was the idea anyway)
Bluetooth
Bluetooth architecture
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Small radio cell – piconet
Piconet about 10 meters
Multiple piconets can be bridged
Cell has one master node…
… and up to seven slave nodes
Can have up to 255 parked nodes
Master does all parking (valet?)
Bluetooth
Bluetooth architecture
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Master does all control
Slave only does what Master says
This allow very cheap slave electronics (plan
was for under $5 per chip
All communications must be master/slave,
slave/master…
Never slave/slave
Bandwidth allocation via TDM
Bluetooth
Bluetooth architecture
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3 classes of radios used in Bluetooth
Class 3 radios – have a range of up to 1 meter or 3
feet
Class 2 radios – most commonly found in mobile
devices – have a range of 10 meters or 30 feet
Class 1 radios – used primarily in industrial use
cases – have a range of 100 meters or 300 feet
From: http://www.bluetooth.com/bluetooth/
Bluetooth
Bluetooth architecture
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Uses 2.4 Ghz ISM band
Uses FHSS
1600 Hops/second
Dwell time 625 microseconds
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79 channels 1 Mhz each
FSK modulation
Uses same band/same channels as
802.11, garage door remotes, cordless phones,
etc.
Bluetooth
Bluetooth application profiles
From: Tanenbaum, 2003, pg. 312
Bluetooth
Bluetooth links
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ACL – Asynchronous Connection Less
Packet switching irregular data
Slave can only have one ACL link with master
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Synchronous Connection Oriented
Real-time data
Like voice, etc.
Slave can have up to 3 SCO links to master
Bluetooth
Bluetooth
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SCO payload always 240 bits
ACL payload 80, 160, 240
Master uses even slots
Slave uses odd slots
Bluetooth
Bluetooth frames
Addr = address of one of eight active devices
Ack = piggybacking Ack on frame
Type = ACL, SCO, Polling, null
Seq = number frames (one bit?)
Flow = slave wants pause
Header repeated 3 times
Bluetooth
More Information:
http://www.bluetooth.com/bluetooth/
http://en.wikipedia.org/wiki/Bluetooth
Logical Link Control - LLC
Let’s backup a bit
Recall that we have discussed the Medium
Access Control Sublayer…
And that it is a sublayer of the Data Link
Layer…
…the bottom half, in fact
The top half is another sublayer known as
the Logical Link Control sublayer or LLC
Logical Link Control - LLC
The MAC sublayer can take several forms
depending the the physical medium used
at the physical layer, protocols, etc.
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Remember the different bandwidth allocation
schemes/protocols for IEEE 802.11?
These are the MAC sublayer
LLC takes care of error correction, flow
control,…
Logical Link Control - LLC
LLC also provides a consistent interface to the
Network Layer
For Ethernet and other IEEE 802 protocols…
LLC receives packet from Network layer…
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And prepends an LLC header to the packet…
This goes in the payload field of the frame
LLC header contains a
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source process address,
destination process address
Control field (sequence and acknowledgement
numbers)
Logical Link Control - LLC
LLC is standardized as IEEE 802.2
Data Link Layer Switching
We have briefly discussed hubs and
switches…
And mentioned repeaters, and routers…
…there are more…
So what is the difference?
Data Link Layer Switching
Bridges – interconnect LANs
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Operate at the DLL level
Repeaters on pass on traffic (electrically)
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Extend network medium range
Never looks at frames
Bridges examine frame – decide to
forward frame from one LAN to another
Can translate from one LAN type to
another
Data Link Layer Switching
Reasons for Bridges
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Network Autonomy – departments, organizational
units
Geography – different buildings – employ different
medium
Distance exceeds medium max – stretch network
past cable length limits
Load Balancing – keeping local traffic local
Isolation of bad traffic - keep bad traffic burst from
saturating network – limit to seqment
Security - prevent frames from being propagated
(and snooped) across the entire network
Data Link Layer Switching
Frame formats for 802.3, 802.11, 802.16
From: Tanenbaum (2003), pg. 321
Data Link Layer Switching
802.11 to 802.3 Bridge
From: Tanenbaum (2003), pg. 321
Data Link Layer Switching
Bridge
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Bridge sees all frames on both LANs
A to B frames seen by bridge, but not forwarded
A to C frames seen by bridge and forwarded
A
B
C
Bridge
From: Tanenbaum (2003), pg. 321
D
Data Link Layer Switching
So, what’s the difference between Bridges and
Switches?
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Not much
Bridges connect LANs
Switches connect stations
Both operate at the DLL level
Bridges may only have a few ports –
For connecting LAN segments
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Switches usually have many ports
For connecting stations
From: Tanenbaum (2003), pg. 321
Hubs, Switches, Routers, etc.
Layer
Device Class
Role
Physical Layer
Hubs, Repeater
Propagate medium,
same collision domain
Data Link Layer
Bridges, Switches
Routing, translation at
frame level, DLL
Network Layer
Router
Routing Packets. IP
Transport Layer
Transport gateway
Bridge between different
connection protocols,
TCP-ATM
Application
Application Gateway
Translate messages –
email to SMS
VLANs
Virtual Local Area Network
Remember that having a network broken
down into multiple LANs and connected
with bridges had some advantages
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Political “territory”
Security
Load control
Fault isolation
..and others
VLANs
A
B
C
D
Bridge
That is based on the physical topology of the
network
Wouldn’t it be nice if you could accomplish the
same thing logically rather than physically
That is a VLAN
VLANs
A
B
C
D
Bridge
For example, supple that station A and D are in
the research department…
…and B and C in accounting
You would want A and D to be in the research
VLAN while B and C should be in the accounting
VLAN
VLANs
Oh, and we need this to be transparent…
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Meaning that we should be able to move a station
from one physical LAN to another and it still be in its
appropriate VLAN
A few ways to accomplish this
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Have switches and bridges keep track of machine in a
VLAN by MAC address
Have switches and bridges keep track of machines in
a VLAN by port (this gets sticky)
Have stations announce their VLAN – changing the
802 spec?
VLANs
IEEE did just that … changed the 802
frame format ---IEEE 802.1Q
From: Tanenbaum, 2003, pg 335