cs 453 computer networks

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

Ever wonder where the name came from?

Harold Gormson (Harold I of Denmark), a Viking king

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.

BluetoothBluetooth application profiles

From: Tanenbaum, 2003, pg. 312

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?


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


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


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


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


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


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

cs 453 computer networks

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