March, 2004Dr. Paul Chen1 Wireless LAN MSTP Dr. Paul Chen [email protected]

March, 2004 Dr. Paul Chen 1

Wireless LAN MSTP

Dr. Paul [email protected]


IEEE802.11 Wireless LAN

• 802.11b was defined in an attempt to increase the original bandwidth of 802.11 (1-2 Mbps) in the range of 2.4GHz operational frequency using direct sequence spread spectrum (DSSS). Its bandwidth capacity is set to be between 5.5Mbps and 11Mbps.

• 802.11a As the need for bandwidth grew, 802.11a was specified in 1999 as a Physical Layer (PHY) standard to operate at 5GHz frequency band with possible data rates between 6-54 Mbps. Those products are slowly becoming available to a wider public. The additional advantage of 802.11a over 802.11b is that there is also much less interference with radio at its 5GHz frequency in comparison to 802.11b and 802.11g.


IEEE802.11 Wireless LAN (continued)

• 802.11cTo help define the standard of development of access points (APs) for wireless technologies to bridge the information flow, 802.11c was established and its work has already been concluded.

• 802.11dAs the operation, especially in the 5GHz range, may differ from country to country (or domain to domain), the 802.11d protocol was established. It also better defined interoperability issues.

• 802.11eWith the expansion of wireless device technologies and the feature-rich applications already in development for video and audio (voice), it was apparent that the 802.11 PHYs were not quite optimized to fulfill such tasks. This lead to the development of 802.11e which refines a 802.11 medium access layer (MAC) to prioritize traffic to improve quality of service (QoS) for support of video and audio



• 802.11fThis protocol specification addresses the roaming need for transmission for a user from one access point (AP) to another and ensures the continuity of transmission; it would ultimately provide inter-access point protocol.

• 802.11gThe "g" technology specification is still in the works and is the most recent redefinition for 802.11. Its goal is defined as extension to 20+ Mbps rate by adding one more channel to the current three in the operation spectrum of 2.4GHz, which would compete with 802.11a rates.

• 802.11h802.11h is an extension of 802.11a to satisfy regulations in Europe for the spectrum band of 5GHz by providing dynamic channel selection (DCS) and transmit power control (TPC).



• 802.11iSecurity Enhancements

• 802.11jExtending 802.11a to Japanese brand

• 802.11k Radio Resource Measurement

• 802.11m Maintenance

• 802.11n High Throughput (100 Mbps)


The Problems of RF

• Fixed resources / shared media

• Coverage extends outside the physical building

• RF problems are statistical in nature

• The air space is constantly changing

- signal strength

- interference

- signal to noise ratio

- coverage area

- throughput

- load


Taking A System Level Approach for Wireless Networks

• Mobility

• RF Physical layer security

• Layer 2 security (802.1x, WPA, 802.1i)

• Layer 3 security (VPN)

• Client security

• Physical layer management / visibility

• Client management

• Planning / deployment

• Location


802 Architecture and Relation to Bluetooth


Functions of 802.15.1 lower layer protocols

• RF layerThe air interface is based on antenna power range starting from 0 dBm up to 20 dBm. Bluetooth operates in the 2.4 GHz band and the link range is anywhere from 10 centimeters to 10 meters.

• Baseband layerThe Baseband layer establishes the Bluetooth physical link between devices forming a piconet -- a network of devices connected in an ad hoc fashion using Bluetooth technology. A piconet is formed when two Bluetooth devices connect, and can support up to eight devices. In a piconet one device acts as the master and the other devices act as slaves.

• Link managerThe link manager sets up the link between Bluetooth devices. Other functions of the link manager include security, negotiation of Baseband packet sizes, power mode and duty cycle control of the Bluetooth device, and the connection states of a Bluetooth device in a piconet.


Functions of 802.15.1 lower layer protocols (continued)

• Logical Link Control and Adaptation Protocol (L2CAP)This layer provides the upper layer protocols with connectionless and connection-oriented services. The services provided by this layer include protocol multiplexing capability, segmentation and reassembly of packets, and group abstractions.


Differences Between WPAN (802.15) and WLAN (802.11)


IEEE 802.1w RSTP Overview

• RSTP significantly reduces the time to reconfigure the active topology of the network when changes

occur to the physical topology or its configuration parameters. RSTP selects one switch as the root of a

spanning tree-connected active topology and assigns port roles to individual ports of the switch,

depending on whether that port is part of the active topology.• RSTP provides rapid connectivity following the failure of a switch,

switch port, or a LAN. A new root

port and the designated port on the other side of the bridge transition to forwarding using an explicit

handshake between them. RSTP allows switch port configuration so that the ports can transition to

forwarding directly when the switch reinitializes.


IEEE 802.1w RSTP Overview (continued)

• RSTP as specified in 802.1w supersedes STP specified in 802.1D, but remains compatible with STP.

• RSTP selectively sends 802.1D-configured BPDUs and topology change notification (TCN) BPDUs

on a per-port basis.• When a port initializes, the migration-delay timer starts and RSTP

BPDUs are transmitted. While the migration-delay timer is active, the bridge processes all BPDUs received on that port.

• If the bridge receives an 802.1D BPDU after a port’s migration-delay timer expires, the bridge assumes it is connected to an 802.1D bridge and starts using only 802.1D BPDUs.

• When RSTP uses 802.1D BPDUs on a port and receives an RSTP BPDU after the migration-delay expires, RSTP restarts the migration-delay timer and begins using RSTP BPDUs on that port.


RSTP Port Roles

• Root—A forwarding port elected for the spanning tree topology.• Designated—A forwarding port elected for every switched LAN

segment.• Alternate—An alternate path to the root bridge to that provided by

the current root port.• Backup—A backup for the path provided by a designated port

toward the leaves of the spanning tree. Backup ports can exist only where two ports are connected together in a loopback by a point-to-point link or bridge with two or more connections to a shared LAN segment.

• Disabled—A port that has no role within the operation of spanning tree.

• Port roles are assigned as follows:- A root port or designated port role includes the port in the active topology.- An alternate port or backup port role excludes the port from the active topology.


RSTP Port States

• The port state controls the forwarding and learning processes and provides the values of discarding, learning, and forwarding.

• Comparison Between STP and RSTP Port States


RSTP Port States (continued)

• In a stable topology, RSTP ensures that every root port and designated port transition to forwarding, and ensures that all alternate ports and backup ports are always in the discarding state.


IEEE 802.1s MST (Multiple Spanning Tree Protocol)

• MST extends the IEEE 802.1w rapid spanning tree (RST) algorithm to multiple spanning trees. This extension provides both rapid convergence and load balancing in a VLAN environment.

• MST is backward compatible with 802.1D STP.

• MST allows you to build multiple spanning trees over trunks. You can group and associate VLANs to spanning tree instances. Each instance can have a topology independent of other spanning tree instances.

• This new architecture provides multiple forwarding paths for data traffic and enables load balancing.

• Network fault tolerance is improved because a failure in one instance (forwarding path) does not affect other instances.


IEEE 802.1s MST (continued)

• A spanning tree instance can exist only on bridges that have compatible VLAN instance assignments. You must configure a set of bridges with the same MST configuration information, which allows them to participate in a specific set of spanning tree instances.

• Interconnected bridges that have the same MST configuration are referred to as an MST region.

• MST runs a variant of spanning tree called internal spanning tree (IST). IST augments the common spanning tree (CST) information with internal information about the MST region. The MST region appears as a single bridge to adjacent single spanning tree (SST) and MST regions.

• CST (802.1Q) is a single spanning tree for all the VLANs.



• A bridge running MST provides interoperability with single spanning tree bridges as follows:– MST bridges run IST, which augments the common spanning tree (CST) information with internal information about the MST region.– IST connects all the MST bridges in the region and appears as a subtree in the CST that includes the whole bridged domain. The MST region appears as a virtual bridge to adjacent SST bridges and MST regions.– The common and internal spanning tree (CIST) is the collection of ISTs in each MST region, the CST that interconnects the MST regions, and the SST bridges. CIST is the same as an IST inside an MST region and the same as CST outside an MST region. The STP, RSTP, and MSTP together elect a single bridge as the root of the CIST.



• MST establishes and maintains additional spanning trees within each MST region. These spanning trees are referred to as MST instances (MSTIs). The IST is numbered 0, and the MSTIs are numbered 1,2,3, and so on. Any MSTI is local to the MST region that is independent of MSTIs in another region, even if the MST regions are interconnected. MST instances combine with the IST at the boundary of MST regions to become the CST as follows:

• – Spanning tree information for an MSTI is contained in an MSTP record (M-record).

M-records are always encapsulated within MST BPDUs (MST BPDUs). The original spanning trees computed by MSTP are called M-trees. M-trees are active only within the MST region. M-trees merge with the IST at the boundary of the MST region and form the CST.


Network with Interconnected SST and MST Regions


STP Default Configuration

Documents

March, 2004Dr. Paul Chen1 Wireless LAN MSTP Dr. Paul Chen [email protected]