cs 453 computer networks lecture 17 medium access control sublayer bluetooth, switching and vlan
TRANSCRIPT
CS 453CS 453Computer NetworksComputer Networks
Lecture 17Lecture 17
Medium Access Control SublayerMedium Access Control Sublayer
Bluetooth, Switching and VLANBluetooth, 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
802.11 intended to serve buildings Range ~ hundred meters
Bluetooth intended to serve a room 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 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 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 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 Uses 2.4 Ghz ISM band Uses FHSS
1600 Hops/secondDwell time 625 microseconds
79 channels 1 Mhz each FSK modulation Uses same band/same channels as
802.11, garage door remotes, cordless phones, etc.
Bluetooth
Bluetooth links ACL – Asynchronous Connection Less
Packet switching irregular data
Slave can only have one ACL link with master Synchronous Connection Oriented
Real-time data
Like voice, etc.
Slave can have up to 3 SCO links to master
Bluetooth
Bluetooth 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
Type = ACL, SCO, Polling, null
Flow = slave wants pause
Ack = piggybacking Ack on frame
Seq = number frames (one bit?)
Header repeated 3 times
Bluetooth
More Information:
http://www.bluetooth.com/bluetooth/
http://en.wikipedia.org/wiki/Bluetooth
Logical Link Control - LLCLogical Link Control - LLC
Let’s backup a bitLet’s backup a bit
Recall that we have discussed the Medium Recall that we have discussed the Medium Access Control Sublayer…Access Control Sublayer…
And that it is a sublayer of the Data Link And that it is a sublayer of the Data Link Layer…Layer…
……the bottom half, in factthe bottom half, in fact
The top half is another sublayer known as The top half is another sublayer known as the Logical Link Control sublayer or LLCthe Logical Link Control sublayer or LLC
Logical Link Control - LLCLogical Link Control - LLC
The MAC sublayer can take several forms The MAC sublayer can take several forms depending the the physical medium used depending the the physical medium used at the physical layer, protocols, etc.at the physical layer, protocols, etc. Remember the different bandwidth allocation Remember the different bandwidth allocation
schemes/protocols for IEEE 802.11?schemes/protocols for IEEE 802.11? These are the MAC sublayerThese are the MAC sublayer
LLC takes care of error correction, flow LLC takes care of error correction, flow control,…control,…
Logical Link Control - LLCLogical Link Control - LLCLLC also provides a consistent interface to the LLC also provides a consistent interface to the Network LayerNetwork Layer
For Ethernet and other IEEE 802 protocols…For Ethernet and other IEEE 802 protocols…
LLC receives packet from Network layer…LLC receives packet from Network layer… And prepends an LLC header to the packet…And prepends an LLC header to the packet… This goes in the payload field of the frameThis goes in the payload field of the frame
LLC header contains aLLC header contains a source process address, source process address, destination process addressdestination process address Control field (sequence and acknowledgement Control field (sequence and acknowledgement
numbers)numbers)
Logical Link Control - LLCLogical Link Control - LLCLLC is standardized as IEEE 802.2LLC is standardized as IEEE 802.2
Data Link Layer SwitchingData Link Layer Switching
We have briefly discussed hubs and We have briefly discussed hubs and switches…switches…
And mentioned repeaters, and routers…And mentioned repeaters, and routers…
……there are more…there are more…
So what is the difference?So what is the difference?
Data Link Layer SwitchingData Link Layer Switching
Bridges – interconnect LANsBridges – interconnect LANs Operate at the DLL levelOperate at the DLL level
Repeaters on pass on traffic (electrically) Repeaters on pass on traffic (electrically) Extend network medium rangeExtend network medium range Never looks at framesNever looks at frames
Bridges examine frame – decide to forward Bridges examine frame – decide to forward frame from one LAN to anotherframe from one LAN to another
Can translate from one LAN type to anotherCan translate from one LAN type to another
Data Link Layer SwitchingData Link Layer Switching
Reasons for BridgesReasons for Bridges Network Autonomy – departments, organizational Network Autonomy – departments, organizational
unitsunits Geography – different buildings – employ different Geography – different buildings – employ different
mediummedium Distance exceeds medium max – stretch network past Distance exceeds medium max – stretch network past
cable length limitscable length limits Load Balancing – keeping local traffic localLoad Balancing – keeping local traffic local Isolation of bad traffic - keep bad traffic burst from Isolation of bad traffic - keep bad traffic burst from
saturating network – limit to seqmentsaturating network – limit to seqment Security - prevent frames from being propagated Security - prevent frames from being propagated
(and snooped) across the entire network(and snooped) across the entire network
Data Link Layer SwitchingData Link Layer Switching
Frame formats for 802.3, 802.11, 802.16Frame formats for 802.3, 802.11, 802.16
From: Tanenbaum (2003), pg. 321
Data Link Layer SwitchingData Link Layer Switching802.11 to 802.3 Bridge802.11 to 802.3 Bridge
From: Tanenbaum (2003), pg. 321
Data Link Layer SwitchingData Link Layer SwitchingBridgeBridge Bridge sees all frames on both LANsBridge sees all frames on both LANs A to B frames seen by bridge, but not forwardedA to B frames seen by bridge, but not forwarded A to C frames seen by bridge and forwardedA to C frames seen by bridge and forwarded
From: Tanenbaum (2003), pg. 321
A B C D
Bridge
Data Link Layer SwitchingData Link Layer SwitchingSo, what’s the difference between Bridges and Switches?So, what’s the difference between Bridges and Switches? Not muchNot much Bridges connect LANsBridges connect LANs Switches connect stationsSwitches connect stations Both operate at the DLL levelBoth operate at the DLL level Bridges may only have a few ports – Bridges may only have a few ports –
For connecting LAN segmentsFor connecting LAN segments
Switches usually have many portsSwitches usually have many portsFor connecting stationsFor connecting stations
From: Tanenbaum (2003), pg. 321
Hubs, Switches, Routers, etc.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 NetworkRemember that having a network broken down into multiple LANs and connected with bridges had some advantages Political “territory” Security Load control Fault isolation ..and others
VLANs
That is based on the physical topology of the networkWouldn’t it be nice if you could accomplish the same thing logically rather than physicallyThat is a VLAN
A B C D
Bridge
VLANs
For example, supple that station A and D are in the research department……and B and C in accountingYou would want A and D to be in the research VLAN while B and C should be in the accounting VLAN
A B C D
Bridge
VLANs
Oh, and we need this to be transparent… 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 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