LLC and Bridges
LLCLLC andand BridgesBridges Raj Jain Professor of CIS The Ohio State University Columbus, OH 43210 [email protected] This presentation is available on-line at http://www.cis.ohio-state.edu/~jain/cis677-98/
The Ohio State University Raj Jain 1 OverviewOverview q Logical Link Control q Bridges q Path determination: Spanning tree, source routing
The Ohio State University Raj Jain 2 IEEEIEEE 802802 q 802.1 Network management and bridging q 802.2 Logical link control q 802.3 Ethernet (CSMA/CD) q 802.4 Token Bus q 802.5 Token Ring q 802.6 DQDB q 802.7 Broadband technical advisory group q 802.8 Fiber-optic technical advisory group q 802.9 Integrated data and voice q 802.10 Security and privacy The Ohio State University Raj Jain 3 IEEEIEEE 802802 (Cont)(Cont) q 802.11 Wireless LANs q 802.12 100VG-AnyLAN q 802.13 ?Bad Luck q 802.14
The Ohio State University Raj Jain 4 FrameFrame FormatFormat q Ethernet IP IPX AppleTalk Dest. Source Type Info CRC Address Address 6 6 2 4 Size in bytes q IEEE 802.3 IP IPX AppleTalk Dest. Source Length LLC Info Pad CRC Address Address 6 6 2 Length 4
The Ohio State University Raj Jain 5 LLCLLC TypeType 11 q Unacknowledged connectionless (on 802.3) No flow or error control. Provides protocol multiplexing. Uses 3 types of protocol data units (PDUs): UI = Unnumbered informaton XID = Exchange ID = Types of operation supported, window Test = Loop back test
The Ohio State University Raj Jain 6 LLCLLC TypeType 2,2, 33 q Type 2: Acknowledged connection oriented (on 802.5) Provides flow control, error control. Uses SABME (Set asynchronous balanced mode), UA (unnumbered ack), DM (disconneced mode), DISC (disconnect) q Type 3: Acknowledged connectionless Uses one-bit sequence number AC command PDUs acked by AC response PDUs
The Ohio State University Raj Jain 7 LLCLLC MultiplexingMultiplexing q Multiplexing allows multiple users (network layer protocols) to share a datalink q Each user is identified by a “service access point (SAP)” DSAP SSAP Control Info 8 8 8 Size in bits q Eight-bit SAP Þ Only 256 standard values possible q Even IP couldn’t get a standard SAP. Use Subnetwork Access Protocol SAP (SNAP SAP)
The Ohio State University Raj Jain 8 SNAPSNAP SAPSAP q SubNetwork Access Protocol Service Access Point q When DSAP=AA, SSAP=AA, Control=UI, protocol ID field is used for multiplexing DSAP SSAP Control AA AA 03 Protocol ID Info 40 bits q Protocol ID is 40 bit long. The first 24 bits are Organizationally Unique Identifiers (OUI). OUI of 0 is used. The Ethernet type values are used in the last 16 bits. Protocol ID = 00-00-00-xx-xx The Ohio State University Raj Jain 9 BridgesBridges
LAN A
Frames with addresses 11 through 20 are accepted and Station 1 Station 2 • Station 10 repeated on LAN B
Bridge
Frames with addresses 1 through 10 are accepted and repeated on LAN A LAN B
Station 11 Station 12 • Station 20
The Ohio State University Fig 14.1 Raj Jain 10 Bridge:Bridge: FunctionsFunctions q Monitor all frames on LAN A q Pickup frames that are for stations on the other side q Retransmit the frames on the other side q Knows or learns about stations are on various sides q Makes no modification to content of the frames. May change headers. q Provides storage for frames to be forwarded q Improves reliability (less nodes per LAN) q Improves performance (more bandwidth per node) q Security (Keeps different traffic from entering a LAN) q May provide flow and congestion control The Ohio State University Raj Jain 11 InterconnectionInterconnection DevicesDevices q Repeater: PHY device that restores data and collision signals q Hub: Multiport repeater + collision detection, notification and signal broadcast q Bridge: Datalink layer device connecting two or more collision domains q Router: Network layer device (does propagate MAC multicasts) Extended LAN =Broadcast LAN= domain B Collision H H H H Domain Router
The Ohio State University Raj Jain 12 DataData EncaptulationEncaptulation byby BridgesBridges
Station Station
USER USER LLC LLC MAC 3 4 PHY LAN LAN t1 t8 Bridge t2 t7 MAC MAC t t t5 t6 PHY PHY PHY (a) Architecture
t8 User data t
t t7 LLC-H User data
t
t t t6 MAC-H LLC-H User data MAC-T
(b) Operation The Ohio State University Fig 14.2 Raj Jain 13 BridgesBridges forfor Point-to-pointPoint-to-point linkslinks
Station USER Bridge Bridge USER 1 t 9 LLC LLC 2 t 8 MAC Link Link MAC t t LAN LAN
(a) Architecture
User data LLC-H User data MAC-H LLC-H User data LLC-T Link-H MAC-H LLC-H User data LLC-T Link-T
(b) Operation
The Ohio State University Fig 14.3 Raj Jain 14 PathPath DeterminationDetermination ByBy BridgesBridges Station 1 Station 2 Station 3
LAN A
Bridge Bridge 101 102
LAN B LAN C
Bridge Bridge Bridge Bridge 103 104 105 106
LAN D LAN E LAN F LAN G
Station 4 Station 5 Station 6 Station 7 Fig 14.5 The Ohio State University Raj Jain 15 1.1. FixedFixed RoutingRouting
Fig 14.7 The Ohio State University Raj Jain 16 2.2. SpanningSpanning TreeTree StationStationStation 123
LAN A
BridgeBridge 101 102
LAN B LAN C
BridgeBridgeBridgeBridge 103 104 105 106
LAN D LAN E LAN F LAN G
StationStationStationStation 4567 The Ohio State University Fig 14.5 Raj Jain 17 SpanningSpanning TreeTree (Cont)(Cont) StationStationStation 123
LAN A
BridgeBridgeBridge 101 107 102
LAN B LAN C
BridgeBridgeBridgeBridge 103 104 105 106
LAN D LAN E LAN F LAN G
StationStationStationStation 4 567 The Ohio State University Fig 14.6 Raj Jain 18 SpanningSpanning Tree:Tree: TerminologyTerminology q Bridge Identifier: MAC address plus a priority level q Port identifier: For each port of a bridge q Path cost: Cost transmitting through a port q Root Bridge: The bridge with the lowest identifier q Root port: Port with minimum cost to the root bridge q Root path cost: Cost of the path to the root bridge q Designated bridge: One per LAN. Provides minimum cost path from the LAN to the root bridge. q Designated Port: Connects designated bridge to LAN
The Ohio State University Raj Jain 19 SpanningSpanning TreeTree AlgorithmAlgorithm q All bridges multicast to “All bridges” m My ID m Root ID m My cost to root q The bridges update their info using Dijkstra’s algorithm and rebroadcast q Initially all bridges are roots but eventually converge to one root as they find out the lowest Bridge ID. q On each LAN, the bridge with minimum cost to the root becomes the Designated bridge q All ports of all non-designated bridges are blocked.
The Ohio State University Raj Jain 20 SpanningSpanning TreeTree ExampleExample LAN2 C=10 C=5 Bridge 3 Bridge 4 C=10 C=10 C=5 Bridge 1 LAN5 C=10 C=5 Bridge 5 C=5 LAN1 C=10 Bridge 2 C=5 C=5
LAN3 LAN4 The Ohio State University Raj Jain 21 SpanningSpanning TreeTree ExampleExample (Cont)(Cont) LAN2 C=10 C=5 Bridge 3 Bridge 4 C=10 C=10 C=5 Bridge 1 LAN5 C=10 C=5 Bridge 5 C=5 LAN1 C=10 Bridge 2 C=5 C=5
LAN3 LAN4 The Ohio State University Raj Jain 22 3.3. SourceSource RoutingRouting q The frame header contains the complete route: LAN 1 - Bridge B1 - LAN 3 - Bridge B3 - LAN 2 - Dest q Bridges are simple, end systems do the routing q Four types of destination addressing: m Null: Destination on the same LAN m Non-broadcast: Includes a route to destination m All-route Broadcast: Flooded. Bridges record route in the frame. m Single-route Broadcast: Once and only once on each LAN. Spanning tree used for broadcast
The Ohio State University Raj Jain 23 RouteRoute DiscoveryDiscovery q Manually on small internets q Route server q Dynamic route discovery m Transmit “All-route request frame” to destination The destination sends back “non-broadcast response” on each frame. Source knows all routes to the destination. Selects one. m Transmit “single-route request frame” to dest. The destination responds with one “All-routes response.” The source receives many responses and discovers all routes. The Ohio State University Raj Jain 24 ExampleExample
The Ohio State University Fig 14.12 Raj Jain 25 SummarySummary
q Ethernet bridges learn source addresses q Spanning tree algorithm q Token ring bridges use source route
The Ohio State University Raj Jain 26 HomeworkHomework
q Read chapter 14.1, 14.2
The Ohio State University Raj Jain 27 ThankThank You!You!
The Ohio State University Raj Jain 28