802.17 Bridging Robert Castellano David James Bob Sultan Spencer Dawkins 1/22/2002 rc_brdg_02.pdf 802-17-02-00152
Outline Bridging Requirements Simple Bridging Bridging with Destination Stripping Reference Models Common Frame Format / TX/RX Procedures Interoperability Examples Flooding Issues Why DSID/SSID is important to 802.17 Recommendations References 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 2
Bridging Requirements 5 Criteria 802 Overview and Architecture Compatible with relevant portions of 802.1D, 802.1Q, and 802.1F Allow for simple mapping between 802.3 frames and RPR frames and vice versa. Spatial Reuse of Unicast Traffic Motion 7 Pass 89/1/4 - Requirement: The MAC shall support destination removal for uni-cast packets during normal operation. 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 3
Simple Bridging Unicast Frame Transmitted from C1 to C2 All frames flooded to every station on the ring. Frame Stripped based on TTL No spatial reuse. MAC C2 3 2 4 TTL = 4 MAC C1 1 802.17 Ring 5 TTL = 0 TTL = 3 8 7 6 TTL = 0 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 4
SID Proposal Bridging w/destination Stripping Unicast Frame Transmitted from C1 to C2 Frame directed to intended destination Frames Stripped at 3 based on ID Spatial Reuse DSID = 3 2 3 MAC C2 4 MAC C1 1 802.17 Ring 5 8 6 7 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 5
SID Proposal implications on 802.17 end station Unicast Frame Transmitted from C1 to C2 Frame Stripped at 3 based on destination MAC address Spatial Reuse DA = C2 3 MAC C2 2 4 MAC C1 1 802.17 Ring 5 8 6 7 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 6
802.17 MAC in 802.1D Bridge Architectural Model 802.1 MAC Relay Entity Forwarding, Filtering, Learning M_UNITDATA.request M_UNITDATA.indication 802.17 Internal Sublayer Service (802.17 ISS) Bridge Port 802.17xx 1 Sublayer MAC Control 802.17 MAC Ringlet 0/1 Ringlet 1/0 R0 Receive R1 Transmit R1 Receive R0 Transmit 1. Sublayer above the MAC providing certain services specific to the ring. Concept similar to 802.3ad. 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 7
Transparent Bridging w/ Simple Bridge 802.1 MAC Relay Entity Forwarding, Filtering, Learning M_UNITDATA.request M_UNITDATA.indication 802.17 Internal Sublayer Service (802.17 ISS) 802.17xx Sublayer 802.17 MAC Pass Through Transmit Frames onto Both ringlets Copy all frames on ring TTL strip only Pass Through Frame Reception Frame Transmission Frame Reception Frame Transmission Ringlet 0/1 Ringlet 1/0 R0 Receive R1 Transmit R1 Receive R0 Transmit 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 8
Transparent Bridging w/ DSID SSID Stripping 802 MAC Relay Entity Forwarding, Filtering, Learning M_UNITDATA.request M_UNITDATA.indication 802.17 Internal Sublayer Service (802.17 ISS) TX Map Learning 802.17xx Sublayer RID, SSID 802.17 MAC MAC_DA RID, DSID RID, SID TX Map Table Copy/Strip frames when match on DSID, Copy all others) Pass Through Pass Through MAC Control Frame Reception Frame Transmission Frame Reception Frame Transmission Ringlet 0/1 Ringlet 1/0 R0 Receive R1 Transmit R1 Receive R0 Transmit 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 9
Comparison of Darwin Routed vs. Bridged PDUs for spatial reuse Routed PDU with Spatial Reuse Encapsulated Bridged PDU with spatial reuse Bridge 802.17 Packet needs to add 14 bytes more overhead than the routed equivalent to achieve same level of spatial reuse as routed packet. CTRL Encap MAC DA Encap MAC SA 48 Bit 48 Bit CTRL Encap Type 16 Bit MAC_DA 48 Bit MAC_DA 48 Bit MAC_SA 48 Bit MAC_SA 48 Bit SDU Type 16 Bit SDU Type 16 Bit MAC SDU Additional 14 byte overhead is required To achieve the network scaleability benefits of encapsulation bridging (double encapsulation). MAC SDU FCS 32 Bit FCS 32 Bit 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 10
Low overhead Common Frame Format Destination ID Source ID SID provides spatial reuse for bridging 48 bit 48 bit 16 bit 8 bit 8 bit 8 bit 24 bit 16 bit 32 bit MAC_DA MAC_SA Type DSID SSID TTL CTL/CID HEC PDU FCS 802.17 End s can still strip frames based on their MAC Address DSID value of FF indicates a broadcast frame SSID value of FF indicates Null DSID/SSID MAC Address used to uniquely address the end station Common frame format provides interoperability between end stations (routers) and bridges on an 802.17 ring. 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 11
Common Frame Procedures Destination Stripping type Bridges Transmission Encapsulate a frame DSID based on the MAC_DA for all frames being transmitted onto the ring. Frame transmitted onto single ringlet. DSID set to B_cast address for all broadcast/multicast/unknown traffic. Frame transmitted onto both ringlets. SSID set to the transmitting station s station address Perform DSID aging Reception Copy/Strip frame if DSID matches station address Copy frame of all other receive/transit frames to MAC relay for learning and forwarding Learn all DSID in mapping table. 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 12
Common Frame Procedures Simple type Bridges Transmission DSID set to B_cast address for all traffic. SSID set to the transmitting station s station address Frame transmitted onto both ringlets Reception Copy/Strip frame if DSID matches station address Copy all other receive/transit frames to MAC relay for learning and forwarding 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 13
Common Frame Procedures 802.17 End s Transmission DSID set to B_cast address for all traffic. SSID set to the transmitting station s station address Frame transmitted onto both ringlets Reception Copy/Strip frame if DSID or MAC destination address matches station address Copy frame if broadcast/multicast 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 14
C1 to C2 Spatial Reuse (DSID) C2 to C1 Frame Flooded Interoperability Simple Bridge / DSID Stripping Bridge C1 to C2 2 3 C2 Simple Bridge 4 C1 Dest Stripping Bridge 1 802.17 Ring 5 C2 to C1 8 6 7 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 15
Interoperability End / DSID Stripping Bridge C1 to C2 Spatial Reuse (DSID) C2 to C1 Frame Flooded C1 to C3 Spatial Reuse (MAC DA) 3 C2 End C1 to C2 2 C2 to C3 4 C2 to C1 C1 1 802.17 Ring 5 C3 DSID Stripping Bridge 8 6 7 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 16
Interoperability End / Simple Bridge C1 to C2 Frame Flooded C2 to C1 Frame Flooded C2 to C3 Spatial Reuse 3 C2 End C1 to C2 2 C2 to C3 4 C2 to C1 C1 Simple Bridge 1 802.17 Ring 5 C3 8 6 7 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 17
Bridging Correctness Requirements 802.17 Operation needs to be robust to station adds/moves/changes Needs to be robust to sub ms reconfigurations 802.17 operation shall not broken by reconfigurations and cross connects made at the optical level (ie. optical cross connects and optical switches). 802.17 operation shall not result in frame duplication. (802.1D section 6.3.4, MAC service does not permit duplication of frames ). 802.17 operation shall not result in traffic loss exceeding 50ms during network reconfiguration 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 18
TTL Stripping needs careful attention Bridging correctness affected by topology changes Adding a station(s) results in traffic loss until new topology converges Removing a station(s) results in multiple copies being received until new topology converges 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 19
Flooding / TTL Stripping Coherency Affected by Topology Changes 1 Receives Multiple frames from station 7 5 Receives Multiple frames from station 6 5 MAC 1 3 TTL = 3 3 Receives Multiple frames from station 8 8 Receives Multiple frames from station 4 Need to Solve This Problem 802.17 Ring 8 4 4 Receives Multiple frames from station 5 TTL = 4 7 Receives Multiple frames from station 2 7 2 6 6 Receives Multiple frames from station 8 Pass Through Switch 2 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 20
Maintaining Coherency during Topology Changes Possible Solutions Topology Discovery and Initialization Procedures s must recognize and manage neighbor changes Adds complexity to topology algorithm and initialization procedures Selective source station ID filtering (Bridges) Filtering done based on station ID. Does not rely on TTL stripping keeps track of transmissions received on both ringlets If station ID x is received on ringlet 0, then it filters traffic received from station ID x on ringlet 1 and vice versa Each station maintains a 50ms timer to allow traffic to be received on the other ringlet due to protection switch TTL can be set to MAX_TTL 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 21
SSID Filtering Addresses Bridging Correctness Ringlet 0 Ringlet 1 Filter List SSID Ringlet 0 Ringlet 1 Timer Filter State 1 2 3 4 1 0 1 0 0 1 0 0 5ms 50ms 10ms 0 ms Ringlet 1 Ringlet 0 Ringlet 1 No Filter Traffic Received from ringlet having a matching filter state is discarded. N 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 22
Why DSID/SSID Important to 802.17? SID Proposal Spatial Reuse for Bridged Networks SID Proposal - Common low overhead (2 octet) frame format for Bridges/Routers SID Proposal Addresses bridging correctness requirements Darwin Routed networks have a distinct spatial reuse advantage over bridged networks. Darwin Special frame format (Encapsulation PDU) required for 802.17 bridging adds 14 more octets overhead than routed PDU to gain spatial reuse. Darwin Encapsulation PDU poses interoperability problems between 802.17 routers and other 802 end stations connected through 802.17 bridges. Encapsulation PDU should not be required to transmit across a single LAN. Does not preserve MAC service defintion, [802.1D, 6.2a] Darwin puts bridged 802.17 networks at a disadvantage to routed networks. SID Frame overcomes these deficiencies!! 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 23
Conclusions Common Frame Format forward compatible with Destination Stripping Supports Simple Bridging for compatibility with 802.1D/Q bridging Meets the 5 Criteria / 802.17 Technical Motion Requirements for spatial reuse Supports Interworking Simple / Destination Stripping Bridges / Routers / End s Reduces transparent bridging overhead by 12 bytes vs. full 14byte encapsulation header Encapsulation bridging frame format can be supported for network scaleability Minimal impact to routers/clients directly attached to ring Topology discovery algorithm performs unique station ID assignment ID assignment can be done manually or via topology discovery 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 24
Recommendations to 802.17 WG Incorporate DSID/SSID into 802.17 frame format to support simple bridging and provide forward compatibility with destination stripping bridging Define ID Assignment Algorithm used by all 802.17 type stations Define a robust method addressing the flooding / stripping issues. Draft Proposal - 802.17 Bridging, Castellano, rc_brdgdraft_01, January 2002 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 25
References 802.17 Bridging, rc_brdgdraft_01, January 2002 802.17 Bridging, R. Castellano et.al, rc_bridge, November 2001 802.17 MAC Compatibility with 802.1D/Q, M. Holness et. al., mh_brcom, November 2001 Draft Proposal for Resilient packet ring access method & physical layer specifications, David James editor, dvj_rprdraft, November 2001 Encapsulation Bridging and 802.17, R. Castellano, rc_ebridge, September 2001 RPR Bridging Compliance, M. Holness, September 2001 ANSI/IEEE 802.1D 1998 edition [ISO/IEC 15802-3: 1998] 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 26
Thank You! 1/22/2002 rc_brdg_02.pdf 802-17-02-00152 Slide 27