Networking—Networklayer

Threeconcepts

• Naming

• Awaytoidentifythesource/destination• E.g.,houseaddress

• Routing• Finding“howto”movetowardsthedestination

• E.g.,whichairplaneshouldthestuffgoon

• Forwarding• Actually“moving”towardsthedestination

• E.g.,Usingairplane/truck/rail

Networklayer—Forwarding

Networklayer—Forwarding

Letscomeupwithanapproach?GeneralizeEthernetideas?

Networklayer—Forwarding

Attempt1:Broadcast

Networklayer—Forwarding

Attempt1:Broadcast

• Sendtoeverybody

Networklayer—Forwarding

Attempt1:Broadcast

• Sendtoeverybody• Goods

Networklayer—Forwarding

Attempt1:Broadcast

• Sendtoeverybody• Goods

• Oh,well,simplicity

Networklayer—Forwarding

Attempt1:Broadcast

• Sendtoeverybody• Goods

• Oh,well,simplicity

• Not-so-goods

Networklayer—Forwarding

Attempt1:Broadcast

• Sendtoeverybody• Goods

• Oh,well,simplicity

• Not-so-goods• Oh,well,everythingelse

Networklayer—Forwarding

Attempt1:Broadcast

• Sendtoeverybody• Goods

• Oh,well,simplicity

• Not-so-goods• Oh,well,everythingelse

• Bandwidthoverheads

Networklayer—Forwarding

Networklayer—Forwarding

Attempt2:TimedivisionMultiplexing

Networklayer—Forwarding

Attempt2:TimedivisionMultiplexing

• Eachsource-destinationpairassignedatimeslot

Networklayer—Forwarding

Attempt2:TimedivisionMultiplexing

• Eachsource-destinationpairassignedatimeslot

• Cansenddataonlyduringthatslot

Networklayer—Forwarding

Attempt2:TimedivisionMultiplexing

• Eachsource-destinationpairassignedatimeslot

• Cansenddataonlyduringthatslot

• Goods

Networklayer—Forwarding

Attempt2:TimedivisionMultiplexing

• Eachsource-destinationpairassignedatimeslot

• Cansenddataonlyduringthatslot

• Goods• Nocollisions

Networklayer—Forwarding

Attempt2:TimedivisionMultiplexing

• Eachsource-destinationpairassignedatimeslot

• Cansenddataonlyduringthatslot

• Goods• Nocollisions

• Not-so-goods

Networklayer—Forwarding

Attempt2:TimedivisionMultiplexing

• Eachsource-destinationpairassignedatimeslot

• Cansenddataonlyduringthatslot

• Goods• Nocollisions

• Not-so-goods• Underutilizationofresources

Networklayer—Forwarding

Networklayer—Forwarding

Attempt3:FrequencydivisionMultiplexing

Networklayer—Forwarding

Attempt3:FrequencydivisionMultiplexing

• Eachsource-destinationpairassignedasubsetofresources

Networklayer—Forwarding

Attempt3:FrequencydivisionMultiplexing

• Eachsource-destinationpairassignedasubsetofresources• Canuseonly“assigned”resources(e.g.,bandwidth)

Networklayer—Forwarding

Attempt3:FrequencydivisionMultiplexing

• Eachsource-destinationpairassignedasubsetofresources• Canuseonly“assigned”resources(e.g.,bandwidth)

• Goods

Networklayer—Forwarding

Attempt3:FrequencydivisionMultiplexing

• Eachsource-destinationpairassignedasubsetofresources• Canuseonly“assigned”resources(e.g.,bandwidth)

• Goods• Predictableperformance

Networklayer—Forwarding

Attempt3:FrequencydivisionMultiplexing

• Eachsource-destinationpairassignedasubsetofresources• Canuseonly“assigned”resources(e.g.,bandwidth)

• Goods• Predictableperformance

• Not-so-goods

Networklayer—Forwarding

Attempt3:FrequencydivisionMultiplexing

• Eachsource-destinationpairassignedasubsetofresources• Canuseonly“assigned”resources(e.g.,bandwidth)

• Goods• Predictableperformance

• Not-so-goods• Underutilizationofresources

Networklayer—Forwarding

Networklayer—Forwarding

Attempt2and3:CircuitSwitching

Networklayer—Forwarding

Attempt2and3:CircuitSwitching

• Sourceestablishesconnection

Networklayer—Forwarding

Attempt2and3:CircuitSwitching

• Sourceestablishesconnection• Resourcesalongthepatharereserved

Networklayer—Forwarding

Attempt2and3:CircuitSwitching

• Sourceestablishesconnection• Resourcesalongthepatharereserved

• Sourcesendsdata

Networklayer—Forwarding

Attempt2and3:CircuitSwitching

• Sourceestablishesconnection• Resourcesalongthepatharereserved

• Sourcesendsdata• Transmitdatausingthereservedresources

Networklayer—Forwarding

Attempt2and3:CircuitSwitching

• Sourceestablishesconnection• Resourcesalongthepatharereserved

• Sourcesendsdata• Transmitdatausingthereservedresources

• Sourcetearsdownconnection

Networklayer—Forwarding

Attempt2and3:CircuitSwitching

• Sourceestablishesconnection• Resourcesalongthepatharereserved

• Sourcesendsdata• Transmitdatausingthereservedresources

• Sourcetearsdownconnection• Freeresourcesforotherstouse

Networklayer—Forwarding

Networklayer—Forwarding

CircuitSwitching

Networklayer—Forwarding

CircuitSwitching

• Goods:

Networklayer—Forwarding

CircuitSwitching

• Goods:• Predictableperformance

Networklayer—Forwarding

CircuitSwitching

• Goods:• Predictableperformance

• Reliabledelivery

Networklayer—Forwarding

CircuitSwitching

• Goods:• Predictableperformance

• Reliabledelivery• Simpleforwardingmechanism

Networklayer—Forwarding

CircuitSwitching

• Goods:• Predictableperformance

• Reliabledelivery• Simpleforwardingmechanism

• Not-so-goods

Networklayer—Forwarding

CircuitSwitching

• Goods:• Predictableperformance

• Reliabledelivery• Simpleforwardingmechanism

• Not-so-goods• Resourceunderutilization

Networklayer—Forwarding

CircuitSwitching

• Goods:• Predictableperformance

• Reliabledelivery• Simpleforwardingmechanism

• Not-so-goods• Resourceunderutilization• Blockedconnections

Networklayer—Forwarding

CircuitSwitching

• Goods:• Predictableperformance

• Reliabledelivery• Simpleforwardingmechanism

• Not-so-goods• Resourceunderutilization• Blockedconnections• Connectionsetupoverheads

Networklayer—Forwarding

CircuitSwitching

• Goods:• Predictableperformance

• Reliabledelivery• Simpleforwardingmechanism

• Not-so-goods• Resourceunderutilization• Blockedconnections• Connectionsetupoverheads• Per-connectionstateinswitches(scalabilityproblem)

Networklayer—Forwarding

Networklayer—Forwarding

Attempt4:PacketSwitching

Networklayer—Forwarding

Attempt4:PacketSwitching

• Dividethemessageintopackets

Networklayer—Forwarding

Attempt4:PacketSwitching

• Dividethemessageintopackets

• Putdestinationaddressintheheaderofeachpacket

Networklayer—Forwarding

Attempt4:PacketSwitching

• Dividethemessageintopackets

• Putdestinationaddressintheheaderofeachpacket• Justlikeshippingstuff

Networklayer—Forwarding

Attempt4:PacketSwitching

• Dividethemessageintopackets

• Putdestinationaddressintheheaderofeachpacket• Justlikeshippingstuff

• Eachdevicestoresa“look-uptable”

Networklayer—Forwarding

Attempt4:PacketSwitching

• Dividethemessageintopackets

• Putdestinationaddressintheheaderofeachpacket• Justlikeshippingstuff

• Eachdevicestoresa“look-uptable”• Whatsthenexthoptowardsthedestination?

Networklayer—Forwarding

Attempt4:PacketSwitching

• Dividethemessageintopackets

• Putdestinationaddressintheheaderofeachpacket• Justlikeshippingstuff

• Eachdevicestoresa“look-uptable”• Whatsthenexthoptowardsthedestination?

• Destinationreceivesthepacket(s)

Networklayer—Forwarding

Attempt4:PacketSwitching

• Dividethemessageintopackets

• Putdestinationaddressintheheaderofeachpacket• Justlikeshippingstuff

• Eachdevicestoresa“look-uptable”• Whatsthenexthoptowardsthedestination?

• Destinationreceivesthepacket(s)• Andreconstructsthemessage

Networklayer—Forwarding

Networklayer—Forwarding

PacketSwitchedforwarding

Networklayer—Forwarding

PacketSwitchedforwarding

• Hop-by-hopforwarding

Networklayer—Forwarding

PacketSwitchedforwarding

• Hop-by-hopforwarding• Eachrouterhasa“look-uptable”(forwardinginformationbase)

Networklayer—Forwarding

PacketSwitchedforwarding

• Hop-by-hopforwarding• Eachrouterhasa“look-uptable”(forwardinginformationbase)

• Whatshouldbestoredinthistable?

Networklayer—Forwarding

PacketSwitchedforwarding

• Hop-by-hopforwarding• Eachrouterhasa“look-uptable”(forwardinginformationbase)

• Whatshouldbestoredinthistable?

Networklayer—Forwarding

PacketSwitchedforwarding

• Hop-by-hopforwarding• Eachrouterhasa“look-uptable”(forwardinginformationbase)

• Whatshouldbestoredinthistable?

• Prefix-basedforwarding(longest-prefixmatching)

Networklayer—Forwarding

PacketSwitchedforwarding

• Hop-by-hopforwarding• Eachrouterhasa“look-uptable”(forwardinginformationbase)

• Whatshouldbestoredinthistable?

• Prefix-basedforwarding(longest-prefixmatching)

• Mapsprefixestothenext-hop

Networklayer—Forwarding

Networklayer—Forwarding

PacketSwitching

Networklayer—Forwarding

PacketSwitching

• Goods:

Networklayer—Forwarding

PacketSwitching

• Goods:• Noresourceunderutilization

Networklayer—Forwarding

PacketSwitching

• Goods:• Noresourceunderutilization

• Asourcecansendmoreifothersdon’tuseresources

Networklayer—Forwarding

PacketSwitching

• Goods:• Noresourceunderutilization

• Asourcecansendmoreifothersdon’tuseresources

• Noblockedconnectionproblem

Networklayer—Forwarding

PacketSwitching

• Goods:• Noresourceunderutilization

• Asourcecansendmoreifothersdon’tuseresources

• Noblockedconnectionproblem• Noper-connectionstate

Networklayer—Forwarding

PacketSwitching

• Goods:• Noresourceunderutilization

• Asourcecansendmoreifothersdon’tuseresources

• Noblockedconnectionproblem• Noper-connectionstate• Noset-upcost

Networklayer—Forwarding

PacketSwitching

• Goods:• Noresourceunderutilization

• Asourcecansendmoreifothersdon’tuseresources

• Noblockedconnectionproblem• Noper-connectionstate• Noset-upcost

• Not-so-goods:

Networklayer—Forwarding

PacketSwitching

• Goods:• Noresourceunderutilization

• Asourcecansendmoreifothersdon’tuseresources

• Noblockedconnectionproblem• Noper-connectionstate• Noset-upcost

• Not-so-goods:• Packetheaderoverhead

Networklayer—Forwarding

PacketSwitching

• Goods:• Noresourceunderutilization

• Asourcecansendmoreifothersdon’tuseresources

• Noblockedconnectionproblem• Noper-connectionstate• Noset-upcost

• Not-so-goods:• Packetheaderoverhead• Networkfailuresbecomeaproblem

Networklayer—Forwarding

Networking—Networklayer

Threeconcepts

• Naming

• Awaytoidentifythesource/destination• E.g.,houseaddress

• Routing• Finding“howto”movetowardsthedestination

• E.g.,whichairplaneshouldthestuffgoon

• Forwarding• Actually“moving”towardsthedestination

• E.g.,Usingairplane/truck/rail

Networklayer—Example

C

1

23

17

B

A

Dest.

Networklayer—Routing

Letscomeupwitharoutingscheme

Networklayer—Routing

Networklayer—Routing

C

1

23

17

B

A

Dest.

Networklayer—Routing

C

1

23

17

B

A

Dest.

Awantsto

findapathto

Dest.

{(A,0)}

Networklayer—Routing

C

1

23

17

B

A

Dest.

Awantsto

findapathto

Dest.

{(A,0)}

Awantstofinda

pathtoDest.

{(A,0),(B,2)}

Networklayer—Routing

C

1

23

17

B

A

Dest.

Awantsto

findapathto

Dest.

{(A,0)}

Awantstofinda

pathtoDest.

{(A,0),(B,2)}

Awantstofinda

pathtoDest.

{(A,0),(C,7)}

Networklayer—Routing

C

1

23

17

B

A

Dest.

Awantsto

findapathto

Dest.

{(A,0)}

Awantstofinda

pathtoDest.

{(A,0),(B,2)}

Awantstofinda

pathtoDest.

{(A,0),(C,7)}

Pathto

Dest.

{(A,0),(B,2),

(D,3)}

Networklayer—Routing

C

1

23

17

B

A

Dest.

Awantsto

findapathto

Dest.

{(A,0)}

Awantstofinda

pathtoDest.

{(A,0),(B,2)}

Awantstofinda

pathtoDest.

{(A,0),(C,7)}

Pathto

Dest.

{(A,0),(B,2),

(D,3)}

Pathto

Dest.

{(A,0),(C,7),

(D,1)}

Networklayer—Routing

C

1

23

17

B

A

Dest.

Awantsto

findapathto

Dest.

{(A,0)}

Awantstofinda

pathtoDest.

{(A,0),(B,2)}

Awantstofinda

pathtoDest.

{(A,0),(C,7)}

Pathto

Dest.

{(A,0),(B,2),

(D,3)}

Awantstofinda

pathtoDest.

{(A,0),(B,2),(C,1)}

Pathto

Dest.

{(A,0),(C,7),

(D,1)}

Networklayer—Routing

C

1

23

17

B

A

Dest.

Awantsto

findapathto

Dest.

{(A,0)}

Awantstofinda

pathtoDest.

{(A,0),(B,2)}

Awantstofinda

pathtoDest.

{(A,0),(C,7)}

Pathto

Dest.

{(A,0),(B,2),

(D,3)}

Awantstofinda

pathtoDest.

{(A,0),(B,2),(C,1)}

Pathto

Dest.

{(A,0),(C,7),

(D,1)}Path

toDest.

{(A,0),(B,2),

(C,1),

(D,1)}

Networklayer—Routing

Attempt1:DynamicSourceRouting

Networklayer—Routing

Attempt1:DynamicSourceRouting

• BroadcastaRouteRequestPacketfordestinationd

Networklayer—Routing

Attempt1:DynamicSourceRouting

• BroadcastaRouteRequestPacketfordestinationd• PutsourceIDinthepacketheader

Networklayer—Routing

Attempt1:DynamicSourceRouting

• BroadcastaRouteRequestPacketfordestinationd• PutsourceIDinthepacketheader

• Ateachrouter

Networklayer—Routing

Attempt1:DynamicSourceRouting

• BroadcastaRouteRequestPacketfordestinationd• PutsourceIDinthepacketheader

• Ateachrouter• Ifapathnotknowntothedestination

Networklayer—Routing

Attempt1:DynamicSourceRouting

• BroadcastaRouteRequestPacketfordestinationd• PutsourceIDinthepacketheader

• Ateachrouter• Ifapathnotknowntothedestination

• Putits{ID,cost}inthepacketheader

Networklayer—Routing

Attempt1:DynamicSourceRouting

• BroadcastaRouteRequestPacketfordestinationd• PutsourceIDinthepacketheader

• Ateachrouter• Ifapathnotknowntothedestination

• Putits{ID,cost}inthepacketheader• BroadcasttheRouteRequestPacket

Networklayer—Routing

Attempt1:DynamicSourceRouting

• BroadcastaRouteRequestPacketfordestinationd• PutsourceIDinthepacketheader

• Ateachrouter• Ifapathnotknowntothedestination

• Putits{ID,cost}inthepacketheader• BroadcasttheRouteRequestPacket

• Else

Networklayer—Routing

Attempt1:DynamicSourceRouting

• BroadcastaRouteRequestPacketfordestinationd• PutsourceIDinthepacketheader

• Ateachrouter• Ifapathnotknowntothedestination

• Putits{ID,cost}inthepacketheader• BroadcasttheRouteRequestPacket

• Else• RespondwithaRouteReplypacket

Networklayer—Routing

Attempt1:DynamicSourceRouting

• BroadcastaRouteRequestPacketfordestinationd• PutsourceIDinthepacketheader

• Ateachrouter• Ifapathnotknowntothedestination

• Putits{ID,cost}inthepacketheader• BroadcasttheRouteRequestPacket

• Else• RespondwithaRouteReplypacket• Putknownpathinthepacketheader

Networklayer—Routing

Attempt1:DynamicSourceRouting

• BroadcastaRouteRequestPacketfordestinationd• PutsourceIDinthepacketheader

• Ateachrouter• Ifapathnotknowntothedestination

• Putits{ID,cost}inthepacketheader• BroadcasttheRouteRequestPacket

• Else• RespondwithaRouteReplypacket• Putknownpathinthepacketheader

• Challenge?

Networklayer—Routing

Networklayer—Routing

C

1

23

17

B

A

Dest.

Networklayer—Routing

C

1

23

17

B

A

Dest.

{(A-B,0),

(A-C,7)}

Networklayer—Routing

C

1

23

17

B

A

Dest.

{(A-B,0),

(A-C,7)}

{(A-B,2),

(B-C,1),

(B-D,3)}

Networklayer—Routing

C

1

23

17

B

A

Dest.

{(A-B,0),

(A-C,7)}

{(A-B,2),

(B-C,1),

(B-D,3)}

{(A-C,7),

(B-C,1)}

Networklayer—Routing

C

1

23

17

B

A

Dest.

{(A-B,0),

(A-C,7)}

{(A-B,2),

(B-C,1),

(B-D,3)}

{(A-C,7),

(B-C,1)}

{(B-D,3),

(C-D,1)}

Networklayer—Routing

C

1

23

17

B

A

Dest.

{(A-B,0),

(A-C,7)}

{(A-B,2),

(B-C,1),

(B-D,3)}

{(A-C,7),

(B-C,1)}

{(B-D,3),

(C-D,1)}

{(A-B,0),

(A-C,7)}

Networklayer—Routing

C

1

23

17

B

A

Dest.

{(A-B,0),

(A-C,7)}

{(A-B,2),

(B-C,1),

(B-D,3)}

{(A-C,7),

(B-C,1)}

{(B-D,3),

(C-D,1)}

{(A-B,0),

(A-C,7)}

{(B-D,3),

(C-D,1)}

Networklayer—Routing

C

1

23

17

B

A

Dest.

{(A-B,0),

(A-C,7)}

{(A-B,2),

(B-C,1),

(B-D,3)}

{(A-C,7),

(B-C,1)}

{(B-D,3),

(C-D,1)}

{(A-B,0),

(A-C,7)}

{(B-D,3),

(C-D,1)}

{(A-C,7),

(B-C,1)}

Networklayer—Routing

Attempt2:LinkStateRouting

Networklayer—Routing

Attempt2:LinkStateRouting

• Eachroutermaintainsitslocal“linkstate”(LS)

Networklayer—Routing

Attempt2:LinkStateRouting

• Eachroutermaintainsitslocal“linkstate”(LS)

• Eachrouterperiodically“floods”itsLS

Networklayer—Routing

Attempt2:LinkStateRouting

• Eachroutermaintainsitslocal“linkstate”(LS)

• Eachrouterperiodically“floods”itsLS• AndforwardsalltheLSreceivedfromotherrouters

Networklayer—Routing

Attempt2:LinkStateRouting

• Eachroutermaintainsitslocal“linkstate”(LS)

• Eachrouterperiodically“floods”itsLS• AndforwardsalltheLSreceivedfromotherrouters

• Atonepoint

Networklayer—Routing

Attempt2:LinkStateRouting

• Eachroutermaintainsitslocal“linkstate”(LS)

• Eachrouterperiodically“floods”itsLS• AndforwardsalltheLSreceivedfromotherrouters

• Atonepoint• Everyrouterknowstheentiretopology

Networklayer—Routing

Attempt2:LinkStateRouting

• Eachroutermaintainsitslocal“linkstate”(LS)

• Eachrouterperiodically“floods”itsLS• AndforwardsalltheLSreceivedfromotherrouters

• Atonepoint• Everyrouterknowstheentiretopology

• Runashortestpathalgorithm(e.g.,Dijkstra)locally

Networklayer—Routing

Attempt2:LinkStateRouting

• Eachroutermaintainsitslocal“linkstate”(LS)

• Eachrouterperiodically“floods”itsLS• AndforwardsalltheLSreceivedfromotherrouters

• Atonepoint• Everyrouterknowstheentiretopology

• Runashortestpathalgorithm(e.g.,Dijkstra)locally

• Findpathtothedestination

Networklayer—Routing

Attempt2:LinkStateRouting

• Eachroutermaintainsitslocal“linkstate”(LS)

• Eachrouterperiodically“floods”itsLS• AndforwardsalltheLSreceivedfromotherrouters

• Atonepoint• Everyrouterknowstheentiretopology

• Runashortestpathalgorithm(e.g.,Dijkstra)locally

• Findpathtothedestination

• Moreimportantly,findnext-hoptothedestination

Networklayer—Routing

Attempt2:LinkStateRouting

• Eachroutermaintainsitslocal“linkstate”(LS)

• Eachrouterperiodically“floods”itsLS• AndforwardsalltheLSreceivedfromotherrouters

• Atonepoint• Everyrouterknowstheentiretopology

• Runashortestpathalgorithm(e.g.,Dijkstra)locally

• Findpathtothedestination

• Moreimportantly,findnext-hoptothedestination

• Challenge?

Networklayer—Routing

Networklayer—Routing

Attempt3:DistanceVectorRouting

Networklayer—Routing

Attempt3:DistanceVectorRouting

• Eachrouter

Networklayer—Routing

Attempt3:DistanceVectorRouting

• Eachrouter• maintainsits“currentdistancetodestination”

Networklayer—Routing

Attempt3:DistanceVectorRouting

• Eachrouter• maintainsits“currentdistancetodestination”

• Periodicallyannouncesittoallitsneighbors

Networklayer—Routing

Attempt3:DistanceVectorRouting

• Eachrouter• maintainsits“currentdistancetodestination”

• Periodicallyannouncesittoallitsneighbors• Updateitslocaltable

Networklayer—Routing

Attempt3:DistanceVectorRouting

• Eachrouter• maintainsits“currentdistancetodestination”

• Periodicallyannouncesittoallitsneighbors• Updateitslocaltable

• d(A,dest)=min{d(A,neighbor)+d(neighbor,dest)}

Networklayer—Routing

Attempt3:DistanceVectorRouting

• Eachrouter• maintainsits“currentdistancetodestination”

• Periodicallyannouncesittoallitsneighbors• Updateitslocaltable

• d(A,dest)=min{d(A,neighbor)+d(neighbor,dest)}

• {dest—distance,neighbor-that-minimizes-distance}

Networklayer—Routing

Attempt3:DistanceVectorRouting

• Eachrouter• maintainsits“currentdistancetodestination”

• Periodicallyannouncesittoallitsneighbors• Updateitslocaltable

• d(A,dest)=min{d(A,neighbor)+d(neighbor,dest)}

• {dest—distance,neighbor-that-minimizes-distance}

• Broadcasttoallitsneighbors

Networklayer—Routing