Spatial Reuse Ring Networks Chun-Hung Chen Department of Computer Science and Information Engineering National Taipei University of Technology

Outlines  Ring Networks  Spatial Reuse  Spatial Reuse Protocol  Resilient Packet Ring

Ring Networks  All nodes chained in a loop is called a ring  Data flow in one direction  Suitable for Backbone Connection  Bandwidth is increased with more rings  Two types of ring  Token ring  Slotted ring

Token Ring

Slotted Ring Sense

Spatial Reuse  Destination Stripping Mechanism  Node B has the right to transmit data  Node B transmits data to Node D  Node D receives data and strip data  If Node D has data to send out, Node D sends it immediately or Node D will leave it free for other nodes to send data, ex: Node E-> Node A-> …  While multicast, packets are source stripped  Problems  Fairness issue  Starvation

Fairness Issue  If Node C is the hot switch in the networks and Node A, D both have lots of packets to Node C 1. Node A sends a packet to Node C 2. Node C strips a packet and has no packet to send 3. Node D has a packet for Node C, and once Node D senses free media, it sends it out immediately 4. Node C strips a packet and has no packet to send 5. Node D has no packet to send at the time 6. Node A has a packet for Node C, and once Node A senses free media, it sends it out immediately

Spatial Reuse Protocol (SRP)  Developed by Cisco  SRP is the underlying technology used in Cisco Dynamic Packet Transport (DPT) which is optimized for packet-based optical transport

SRP Background  Bidirectional Dual Counter-rotation ring  “Inner” and “Outer” Rings  Both rings are utilized for transporting data and SRP control packets  SRP control packets:  Topology Discovery  Protection Switching  Bandwidth Control

Spatial Reuse Node C has full bandwidth access to Node D, while Node B to Node A and Node C to Node A are sharing the bandwidth

Receive-Side Packet Handling  Stripped  Received and Stripped  Received and Forwarded  Forwarded (data packets)  Wrapped  Pass Through (control packets)

SRP Fairness Algorithm (SRP-fa)  Global Fairness  Each node controls the rate of forwarding packets for upstream or downstream nodes in relations to packets sourced by itself  Local Optimization  Maximally leverage spatial reuse properties to utilize more than their fair share  Scalability  Rapidly adapt to changing traffic conditions

 For each node, there are three types of packet:  High-Priority Packets  Put in High-Priority Transit Buffer  Low-Priority Packets  Put in Low-Priority Transit Buffer (LPTB)  Self-Generated Packets  Put in High (Low)-Priority Transmit Queue  Packet Priority in Nodes  High-Priority Transit Buffer  High-Priority Transmit Queue  Low-Priority Transit Buffer  Low-Priority Transmit Queue

 Packet delivery order  High-Priority Forwarded Packets are sent first  High-Priority Generated Packets are sent if the LPTB is not full  Low-Priority Forwarded Packets are sent with Forward Rate  Low-Priority Generated Packets are sent if LPTB is not crossed the low-priority threshold and SRP-fa rules allow it  my_usage < allow_usage

Updated every clock cycle  my_usage (bytes) is increased as the generated low- priority packet inserted in the ring  fwd_rate (bytes) is increased as the forwarded low- priority packet inserted in the ring  my_usage should be smaller than allow_usage & MAX_USAGE and fwd_rate is larger than my_usage or LPTB is empty, the host is permitted to send its packets

Calculated every DECAY_INTERVAL  DECAY_INTERVAL = 8000 bytes for OC-12s/STM-4; bytes for OC-48s/STM-16  AGECOEFF = 4  LP_MY_USAGE = 512  LP_FWD_RATE = 64  LP_ALLOW = 64  MAX_LINE_RATE = AGECOEFF * DECAY_INTERVAL If LPTB is larger than ½ THRESHOLD, then it is congested If receiving not NULL usage packet, allow_usage is set to usage packet, otherwise, allow_usage is increased 8000 bytes * 8 = bits = 6.4 Mb OC-12 = 51.84*12 = (Mbps) => (6.4) / (622.08) = (sec) bytes * 8 = bits = 25.6 Mb OC-48 = 51.84*48 = (Mbps) => (25.6) / ( ) = (sec)

When congested  If lp_my_usage > received_usage (smaller is set to advertise usage packet)  advertise usage packet is set to received_usage

If not congested  If received_usage is not NULL  Advertise usage packet is set to received_usage  Otherwise  Advertise usage packet is NULL

SRP-fa Procedure  Extract usage information from incoming packets  Periodically update the allow_usage threshold based on the received fairness value as well as parameter aging  Calculate the SRP-fa signaling information to send in the usage field by using the values of the allow_usage, fwd_rate and my_usage parameter.  Send fairness message to upstream neighbor

SRP-fa Simulation  Node 4 starts to send packets to Node 1 via outer ring at 1 second  Node 3 starts to send packets to Node 1 via outer ring at 2 second  Node 2 starts to send packets to Node 1 via outer ring at 3 second

SRP-fa Simulation  Node 4 sends traffic at full speed during 1~2 seconds  Node 3 wants to send traffic at 2 second, then Node 3 sends a fairness (usage) packet to Node 4  Node 4 slows down its transmitting rate  Node 3 starts to send traffic and the bandwidth is shared by Node 3 and Node 4  Node 2 wants to send traffic at 3 second, then Node 2 sends a fairness (usage) packet to Node 3 and Node 4  Node 3 and Node 4 slow down its transmitting rate  Node 2 starts to send traffic and the bandwidth is shared by Node 2, Node 3 and Node 4

Intelligent Protection Switching (IPS)  IPS provides SRP rings with powerful self-healing capabilities that allow them to automatically recover from fiber facility or node failure by wrapping the traffic on the failed span  Proactive fault and performance monitoring, and event detection and reporting  Signal processing and propagation to communicate information on detected faults and fault clearances  Topological knowledge independence  Network operator may add or remover nodes from the rings  Ring wrapping to by-pass failed fiber facility or nodes while delivering packets to the intended destination  Protection switching is transparent to Layer 3  Protection switching event hierarchy  Handling of concurrent multiple events  Procedures which minimize IPS-related signaling traffic under normal conditions

IPS Request Type  Automatic request  Signal Fail (SF) 2  Signal Degrade (SD) 3  Wait-to-Restore (WTR) 5  Manual request  Forced Switch (FS) 1  Manual Switch (MS) 4  Path Indicator  Short Path IPS Messages: one-hop away  Long Path IPS Messages: sent around the ring

Thank you