Wireless LANs Standards. Overview of Standardization. IEEE Architecture

Transcription

1 Wireless LANs Standards 2003, Cisco Systems, Inc. All rights reserved , Cisco Systems, Inc. All rights reserved. 2-2 Overview of Standardization IEEE Architecture Standardization of networking functions has done much to further the development of affordable, interoperable networking products. This is true for wireless products as well. Prior to the development of standards, wireless systems were plagued with low data rates, incompatibility, and high costs. Standardization provides all of the following benefits: Interoperability among the products of multiple vendors Faster product development Stability Ability to upgrade Cost reductions 2003, Cisco Systems, Inc. All rights reserved. BCMSN v is a family of protocols, including the original specification, , b, a, g and others. Officially called the IEEE Standard for WLAN MAC and PHY specifications is just another link layer for is sometimes called wireless Ethernet, because of its shared lineage with Ethernet, The wired network side of the network could be Ethernet, Token Ring, etc.(we will always use Ethernet in our examples) Access Points and Bridges act as translation bridges between and (or other other protocol) 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

2 Overview of WLAN Topologies Overview of WLAN Topologies 2003, Cisco Systems, Inc. All rights reserved. 2-5 Three types of WLAN Topologies: Independent Basic Service Sets (IBSS) Basic Service Set (BSS) Extended Service Set (ESS) Service Set A logical grouping of devices. WLANs provide network access by broadcasting a signal across a wireless radio frequency. Transmitter prefaces its transmissions with a Service Set Identifier (SSID) A station may receive transmissions from transmitters with the same or different SSIDs. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Independent Basic Service Sets (IBSS) Basic Service Set (BSS) IBSS consists of a group of stations directly communicating with each other. No Access Point used Also known as an ad-hoc network. Our focus will be BSSs and ESSs. BSS, also known as an Infrastructure BSS (never called IBSS) Requires an Access Point (AP) Converts frames to Ethernet and visa versa Known as a translation bridge Stations do not communicate directly, but via the AP APs typically have an uplink port that connects the BSS to a wired network (usually Ethernet), known as the Distribution System (DS). 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v

3 Extended Service Set (ESS) Access Points Multiple BSSs can be connected together with a layer 2 backbone network to form an Extended Service Set (ESS) does not specify the backbone network The backbone network is also known as the Distribution System (DS) and could be wired or wireless. Stations are associated with only one AP at a time. Access Point (AP) Translates (converts) frames to Ethernet and visa versa Known as a translation bridge Typically provides wireless-to-wired bridging function All BSS communications must go through the AP, even between two wireless stations 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v Quick Preview: Station/AP Connectivity SSID (Service Set Identity) At a minimum a client station and the access point must be configured to be using the same SSID. An SSID is: Between 2 and 32 alphanumeric characters Spaces okay Must match EXACTLY, including upper and lower case Sometimes called the ESSID Not the same as BSSID (MAC address of the AP, later) Looking for an AP? Using NetStumbler 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v

4 Frames This isn t Ethernet! IP Packet Distribution System (DS) Medium Access Mechanisms General Frame L IP Packet L C has some similarities with Ethernet but it is a different protocol. Access Points are translation bridges. 2003, Cisco Systems, Inc. All rights reserved , Cisco Systems, Inc. All rights reserved. BCMSN v Frames Frames Data Frames (most are PCF) Data Null data Data+CF+Ack Data+CF+Poll Data+CF+Ac+CF+Poll CF-Ack CF-Poll CF-Cak+CF-Poll Control Frames RTS CTS ACK CF-End CF-End+CF-Ack Management Frames Beacon Probe Request Probe Response Authentication Deauthentication Association Request Association Response Reassociation Request Reassociation Response Disassociation Announcement Traffic Indication 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Medium Access CSMA/CA All stations detect the collision CSMA/CD Both CSMA/CD and CSMA/CA are half-duplex architectures Ethernet uses CSMA/CD Collision Detection CSMA/CA ACK Ethernet devices detect a collision as when the data is transmitted uses CSMA/CA Collision Avoidance devices only detect a collision when the transmitter has not received an Acknowledgement. Stations also use CS/CCA Stations also use a virtual carrier-sense function, NAV 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

5 Medium Access CSMA/CA DCF and PCF All stations detect the collision CSMA/CD ACK CSMA/CA The standard makes it mandatory that all stations implement the DCF (Distributed Coordination Function), a form of carrier sense multiple access with collision avoidance (CSMA/CA). The main goal of CSMA/CA is to avoid having stations transmit at the same time, which will then result in collisions and eventual retransmissions. However, collisions may still occur and when they do stations may or may not be able to detect them (hidden node problem). 2003, Cisco Systems, Inc. All rights reserved. BCMSN v IEEE mandated access mechanism for is DCF (Distributed Coordination Function) Basis for CSMA/CA There is also the PCF (Point Coordination Function) 2003, Cisco Systems, Inc. All rights reserved. BCMSN v DCF Operation Duration Field An example will be coming! An example will be coming! General Frame (more on this later) In DCF operation, a station wanting to transmit : Checks to see if radio link is clear, CS/CCA Carrier Sense, Clear Channel Assessment Checks its NAV timer (coming) to see if someone else is using the medium. If medium is available DCF uses a random backoff timer to avoid collisions and sends the frame. Transmitting station only knows the frame got there if it receives an ACK. May also use RTS/CTS to reduce collisions 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Duration/ID field The number of microseconds (millionths of a second) that the medium is expected to remain busy for transmission currently in progress. Transmitting device sets the Duration time in microseconds. Includes time to: Transmit this frame to the AP (or to the client if an AP) The returning ACK The time in-between frames, IFS (Interframe Spacing) All stations monitor this field! 2003, Cisco All Systems, stations Inc. All rights reserved. update their NAV (Network Allocation Vector) 20 timer. BCMSN v

6 NAV Timer Broadcast-based shared medium An example will be coming! General Frame (more on this later) All stations have a NAV (Network Allocation Vector) timer. Virtual carrier-sensing function Protects the sequence of frames from interruption. Martha sends a frame to George. Since wireless medium is a broadcast-based (not broadcast frame) shared medium, all stations including Vivian receive the frame. Vivian updates her NAV timer with the duration value. Vivian will not attempt to transmit until her NAV is decremented to 0. Stations will only update their NAV when the duration field value received is greater than their current NAV. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Host A is sending frames to another host via the AP. All other devices in BSS (on this channel) and within range of the signal will see the frame framing provides addressing, so only the AP knows it is the next- hop receiver. Other devices within this BSS can sense that the medium is in use and will update their NAV values. What if a station is in range of the AP but not the Host A? (Hidden node problem see WLAN pres.) 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Interframe Spacing (IFS) Example An example will be coming! I m waiting uses four different interframe spaces used to determine medium access (note: microsecond = millionth of a second): DIFS DCF Interface Space Minimum amount of medium idle time until contention-based services begin. PIFS PCF Interframe Space Used by PCF (See WLAN pres.) SIFS Short Interframe Space Used for highest priority transmission, ACKs, RTS, CTS (See WLAN pres.) EIFS Extended Interframe Space Not a fixed interval and used only when there is an error in frame transmission. (See WLAN pres.) 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Scenario: I m waiting Both Vivian and George want to transmit frames. Both stations have same NAV values and physically sense when the medium is idle. Both are waiting for Martha s transmission to end and the medium to become available. The medium now becomes available. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

7 Example Example Random backoff slots Vivian (7), George (31) George and Vivian are both wanting to transmit. Both perform the following: Both sense that medium is available using Physical and Virtual Carriers Sensing: Physical: Physically senses medium is idle (CS/CCA). Virtual: NAV timer is 0 Both waits DIFS (DCF Interface Space) Contention window begins. Uses random backoff algorithm to determine when it can attempt to access the medium. (next) 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Both Vivian and George calculate their random backoff algorithm to randomly selects a value from 0 to 255. Vivian has a slot time of 7 George a slot time of 31. Vivian wins! The destination of her frame is George (could have been a station on the wired network.) 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Example Example Others update NAV Martha and George receive broadcastbased frame. ( ( ( ) ) ) General Frame (more on this later) Vivian transmits, setting the Duration ID to the time needed to transmit, ACK and IFSs. George with a higher slot will see the frame from Vivian and wait to transmit. Assuming their was not a collision from another station, Martha and George update their NAVs. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v The frame arrives at the AP. After the SIFS: The AP sends an ACK back to Vivian, which is how Vivian knows the frame was received by the AP. The AP now has the frame and must contend for access to the medium like all other stations. Remember, uses a half-duplex, shared medium and the AP has to contend for access just like all other devices! 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

8 Ethernet MAC Addressing X xxx Distribution System (DS) Y yyy Data Frames and Addressing Access Point 1 Access Point 2 A B C D xxx yyy Pseudo MAC address of hosts xxx yyy IP Packet 2003, Cisco Systems, Inc. All rights reserved , Cisco Systems, Inc. All rights reserved. BCMSN v MAC Addressing MAC Addressing Frame Control Field The LLC encapsulation will be explained later in this presentation. General Frame General Frame Four address fields The address of these fields is dependent upon the source and destination for the frame. Address 4 is optional and not commonly used, except for WDS (wireless distribution system, bridge to bridge). To DS: indicates if frame is destined for the DS or AP (1 bit). From DS: indicates if frame is sourced from the DS or AP (1bit). 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v

9 MAC Addressing Frame Control Field MAC Addressing General Frame X xxx Distribution System (DS) Y Access Point 1 Access Point 2 A aaa 111 B C D bbb aaa bbb 111 Pseudo MAC address of hosts and BSSID of AP1 Function ToDS FromDS IBSS (no AP) 0 0 To AP 1 0 From AP 0 1 Wireless bridge to bridge 1 1 Note: Some documentation is misleading stating that the ToDS is set to 1 only when the destination is on the wired side of the AP. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Let s look at these options: Host A to Host B Host A to Host X Host X to Host A 2003, Cisco Systems, Inc. All rights reserved. BCMSN v MAC Addressing X xxx Distribution System (DS) Y BSSID Cisco 1200 The BSSID General Frame Access Point 1 Access Point 2 A aaa 111 B bbb C D Each BSS is assigned a BSSID. Not to be confused with SSID or ESSID. BSSID 48 bit identifier which distinguishes it from other BSSs in the network, used for filtering. In a BSS, the BSSID is the MAC address of the wireless interface. Remember, normal switches (bridges) may have MAC addresses, but these addresses are only used for management purposes and not for layer 2 frame forwarding (addressing). 2003, Cisco Systems, Inc. All rights reserved. BCMSN v BSSID BSSID for a WLAN 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

10 MAC Addressing X xxx Distribution System (DS) Y MAC Addressing X xxx Distribution System (DS) Y Host A to Host B General Frame Access Point 1 Access Point 2 A aaa 111 B bbb C D Host A to Host B aaa Host A to AP 1 Rec. Trans. DA 111 aaa bbb Access Point 1 Access Point 2 A 111 B bbb C D 1 0 Address 1 Receiver address Address 2 Transmitter address Address 3 Ethernet/wireless SA, Ethernet/wireless DA, or BSSID 0 1 AP1 to Host B Rec. bbb Trans. 111 SA aaa Receiver: Receives a frame on the wireless medium, but may not be the final destination, i.e. AP Transmitter: Sends a frame on to the wireless medium, but may not be the original source (didn t necessarily create the frame), i.e. AP 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Address 1 Receiver address Address 2 Transmitter address Address 3 Ethernet/wireless SA, Ethernet/wireless DA, or BSSID 2003, Cisco Systems, Inc. All rights reserved. BCMSN v MAC Addressing MAC Addressing X xxx Distribution System (DS) Y IP Packet Distribution System (DS) Host A to Host X Host A to AP Frame Access Point 1 Access Point 2 A aaa 111 B Rec. Trans. DA bbb 111 aaa xxx C D 1 0 General Frame L IP Packet L C AP 1 to Host X xxx aaa Access Points are translation bridges. From to Ethernet, and from Ethernet to The data/frame body is re-encapsulated with the proper layer 2 frame (Ethernet or ). Certain addresses are copied between the two types of frames. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v The Ethernet DA and SA are the source and destination addresses just like on traditional Ethernet networks. Destination Address Host X 2003, Cisco Systems, Source Inc. All rights reserved. Address Host A BCMSN v

11 MAC Addressing X xxx Distribution System (DS) Y MAC Addressing 1 0 Host A to Host X Host A to AP Frame Access Point 1 Access Point 2 A aaa 111 B Rec. Trans. DA bbb 111 aaa xxx xxx aaa AP 1 to Host X C D Host X to Host A X xxx Distribution System (DS) 111 Access Point 1 Access Point 2 A B C aaa bbb Y D The AP (bridge) knows which MAC addresses are on on its wireless interface and maintains a table with those MAC addresses. (from the Association process later) When the AP receives an frame, it examines the Address 3 address. If Address 3 is not in its table of wireless MACs it knows it needs to translate the frame to an Ethernet frame. The AP copies the Address 3 address to the Ethernet Destination Address, and Address 2 (Transmitter address) is copied to the Ethernet Source Address. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v MAC Addressing X xxx Distribution System (DS) Y MAC Addressing Host X to Host A Host X to AP 1 AP 1 to Host A Frame aaa xxx copied Trans. Access Point 1 Access Point 2 aaa A Rec. SA aaa 111 xxx 111 B bbb C D Destination Address Host X Source Address Host A xxx aaa xxx 1 aaa The AP (bridge) knows which MAC address on on its wireless interface and maintains a table with those MAC addresses. (via Association process later) When the AP receives an Ethernet frame, it examines the Destination address. If Destination Address is in its table of wireless MACs it knows it needs to translate the frame to an frame. The AP copies the Destination address to the Address 1, and Ethernet Source is copied to the Address 3 address (SA in this case). 2003, Cisco Systems, Inc. All rights reserved. BCMSN v So how do Ethernet switches know where the wireless stations are? Just like wired stations using the source address of frames that came from the wireless station via the access point. Here the switch learns from the incoming Ethernet frame that Source Address aaa is on port 2 and enters that in its MAC address table. Any frames coming into the switch (ex. port 1) with a Destination Address of aaa, the switch knows to forward those frames out port 2 (towards the AP). 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

12 Station Connectivity Successful Authentication Successful Association State 1 State 2 State 3 Unauthenticated Authenticated Authenticated Unassociated Unassociated Associated Deauthentication Disassociation MAC Layer Operations Station connectivity is a explanation of how stations select and communicate with APs. 2003, Cisco Systems, Inc. All rights reserved , Cisco Systems, Inc. All rights reserved. BCMSN v Station Connectivity Station Connectivity Probe Process Probe process State 1 Unauthenticated Unassociated Three processes: Authentication process Successful Authentication Deauthentication Probe Process (or scanning) The Authentication Process The Association Process State 2 Authenticated Unassociated Association process Successful Association Disassociation State 3 Authenticated Associated Only after a station has both authenticated and associated with the access point can it use the Distribution System (DS) services and communicate with devices beyond the access point. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v The Probe Process (Scanning) done by the wireless station Passive - Beacons Active Probe Requests Used by client to determine: SSID Supported data rates Security Depends on device drive of wireless adapter or the software utility you are using. Cisco adapters do active scanning when associating, but use passive scanning for some tests. In either case, beacons are still received and used by the wireless stations for other things besides scanning (coming). 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

13 Station Connectivity Passive Scanning Passive Scanning Saves battery power Station moves to each channel and waits for Beacon frames from the AP. Records any beacons received. Beacon frames allow a station to find out every thing it needs to begin communications with the AP including: SSID Supported Rates Station Connectivity Active Scanning Active Scanning: Probe Request This process is not mandatory on with A Probe Request frame is sent out on every channel (1 11) by the client. APs that receive Probe Requests must reply with a Probe Response frame if: From the client From the AP 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v Station Connectivity Authentication Process Probe process State 1 Unauthenticated Unassociated Authentication process Successful Authentication Deauthentication State 2 Authenticated Unassociated Association process Successful Association Disassociation State 3 Authenticated Associated Station connectivity processes: Probe Process (or scanning) The Authentication Process The Association Process Only after a station has both authenticated and associated with the access point can it use the Distribution System (DS) services and communicate with devices beyond the access point. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v On a wired network, authentication is implicitly provided by the physical cable from the PC to the switch. Authentication is the process to ensure that stations attempting to associate with the network (AP) are allowed to do so specifies two types of authentication: Open-system Shared-key (WEP, WPA, WPA2, etc.) 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

14 Station Connectivity Association Process Probe process State 1 Unauthenticated Unassociated Authentication process Successful Authentication Deauthentication Station connectivity processes: Probe Process (or scanning) The Authentication Process The Association Process State 2 Authenticated Unassociated Association process Successful Association Disassociation State 3 Authenticated Associated Only after a station has both authenticated and associated with the access point can it use the Distribution System (DS) services and communicate with devices beyond the access point. 1. Association Request 2. Association Response The association process is logically equivalent to plugging into a wired network. Once this process is completed, the wireless station can use the DS and connect to the network and beyond. A wireless station can only associate with one AP ( restriction) During the association process the AP maps a logical port known as the Association Identifier (AID) to the wireless station. The AID is equivalent to a port on a switch and is used later in Power Save Options. The association process allows the DS to keep track of frames destined for the wireless station, so they can be forwarded. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v Power Save (PS) Operations Power Save (PS) Operations A key factor in wireless is mobility, which implies batteries. To preserve battery power the specification provides for power saving operations on the wireless clients categories for power savings refer to: Unicast frames Broadcast/Multicast frames 2003, Cisco Systems, Inc. All rights reserved. BCMSN v The Cisco ACU has three options for Power Saving: CAM (Constantly Awake Mode) MAX PSP (Max Power Savings) Fast PSP (Fast Power Saving Mode) (see WLAN pres). 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

15 Power Save (PS) Operations I m awake. Let me listen for a beacon to see if there is any traffic for me. If not, I can go back to sleep. beacon A client enters low-power mode by turning off its radio. The AP buffers (holds) frames destined for that station while it is in PS mode. At a certain interval the client wakes up to listen for a beacon from the AP. The beacon contains information on whether or not there are frames for this station at the AP. If there are no frames buffered for this station it can return to PS mode. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Power Save (PS) Operations The basics: There are frames for me! Please send them to me. Beacon (frames buffered) PS-Poll (send them to me) ACK Frame 1 If there are frames buffered for this station it will poll the AP for those frames. The AP will then send the frames to the station. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Frame Formats (Some of them) Frames Data Frames (most are PCF) Data Null data Data+CF+Ack Data+CF+Poll CF-Cak+CF-Poll Data+CF+Ac+CF+Poll CF-Ack CF-Poll Control Frames RTS CTS ACK CF-End CF-End+CF-Ack Management Frames Beacon Probe Request Probe Response Authentication Deauthentication Association Request Association Response Reassociation Request Reassociation Response Disassociation Announcement Traffic Indication Integrating WLANs 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. 2-60

16 Mapping VLANs to SSIDs WLAN Cells VLAN 10 VLAN 10 VLAN 20 Access VLAN 10 Trunk VLAN 10, 20 SSID Marketing SSID Marketing SSID Engineering AP is a translational bridge, bridging tow dissimilar mediums. AP is in charge of mapping a VLAN to an SSID. For multiple VLANs (SSIDs) a trunk will need bo be created between the AP and the switch. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v When APs overlap, adjacent APs cannot use identical frequencies otherwise you have interference. Roaming: A client moving from one AP to another. Any data that the client was sending needs to be relayed from one AP to the new AP. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Roaming Layer 2 roaming: A WLAN device moves, the original and the new AP offer coverage for the same IP subnet, so the device s IP address is still be valid after the roam. Layer 3 roaming: Client moves from an AP that covers one IP subnet to an AP that covers another IP subnet. Would mean a new IP address and default gateway that are valid within the new AP s IP subnet Causes existing data sessions or voice sessions to fail. Solution: Cisco Unified Wireless Network and Intercontroller roaming. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v WLAN Architecture 2003, Cisco Systems, Inc. All rights reserved. 2-64

17 Traditional WLAN Architecture Traditional WLAN Architecture Traditional WLAN each AP serves as the central hub for its own BSS. Each AP must be configured individually for network policies including: Radio frequency (RF) Security policies Authentication and association Monitoring traffic QoS Bandwidth policing Rogue AP detection Cisco calls this an autonomous mode AP. Traffic patterns for an autonomous AP are completely handled by the AP. BSS Range 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Switched Routed AP can support multiple SSIDs if multiple VLANs are extended to it over a trunk link. If you want to offer the same SSIDs from several automous APs, the VLANS must be extended to the APs in a contiguous manner. Problem is that the SSID and its VLAN would have to be extended everywhere the user could possibly roam. This would cause end-to-end or campus-wide VLANs which is not good network design practice. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Cisco Unified Wireless Network Architecture Cisco Unified Wireless Network Architecture Real-time Processes RF Transmit/Receive MAC Management Encryption Management Processes RF Management Association & Roaming Management Client Authentication Security Management QoS Real-time Processes RF Transmit/Receive MAC Management Encryption Management Processes RF Management Association & Roaming Management Client Authentication Security Management QoS Real-time Processes RF Transmit/Receive MAC Management Encryption Management Processes RF Management Association & Roaming Management Client Authentication Security Management QoS Real-time Processes RF Transmit/Receive MAC Management Encryption Management Processes RF Management Association & Roaming Management Client Authentication Security Management QoS Traditional WLAN LWAPP or CAPWAP Tunnel Cisco Unified Wireless Network Cisco Unified Wireless Network Architecture centralizes many traditional capabilities moving many functions to a central location including: WLAN security WLAN deployment WLAN management WLAN control 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Traditional WLAN Real-time processes include: LWAPP or CAPWAP Tunnel Cisco Unified Wireless Network Sending/receiving frames, AP beacons, probes, data encryption. Management processes include: RF management, roaming management, QoS, security. Including all those association, authentication, power saving, etc. tasks we saw previously. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

18 Cisco Unified Wireless Network Architecture Cisco Unified Wireless Network Architecture LWAPP or CAPWAP Control Messages LAP WLC LAP or LWAP (Lightweight Access Point) Performs only the real-time operations. Layer 1 and 2 operations LWAPP or CAPWAP Encapsulated Data The IOS image and local intelligence is stripped down compared to autonomous APs. Dependent upon the WLC for all other operations. WLC (Wireless LAN Controller) Performs all management functions This is known as split-mac architecture 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Two devices have a LWAPP or CAPWAP tunnel to exchange messages and client data. LAP and WLC can be in the same VLAN/IP subnet or different ones. The LWAPP or CAPWAP tunnel allows user data to be switched or routed across the campus network. LWAPP (Lightweight Access Point Protocol) Developed by Cisco, submitted as draft RFC 4118 CAPWAP (Control and Provisioning Wireless Access Points protocol) The resulting standard. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Cisco Unified Wireless Network Architecture Cisco Unified Wireless Network Architecture Control messages are authenticated and encrypted so the LAP is securely controlled by the WLC. This also prevents rogue APs from being introduced into the network. Data Packets to and from wireless clients associated with the LAP are encapsulated with the LWAPP or CAPWAP tunnel but are not encrypted or otherwise secured between the LAP and WLC. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v WLC (Wireless LAN Controller) functions: Dynamic channel assignment Chooses and configures RF channel for each LAP. Transmit power optimization Sets transmit power for each LAP based on size of coverage area needed. Self-healing wireless coverage If a LAP radio dies other LAPs can have their power increased. Flexible client roaming Manages Layer 2 and 3 roaming. Dynamic client load balancing If multiple LAPs are in same coverage area, WLC can associate clients with the least used LAP. RF monitoring Scans channels to monitor RF usage, interference, noise, and signals from regue APs. Security management Require clients to get their IP address from a trusted DHCP server before allowing them to associate. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

19 Cisco Unified Wireless Network Architecture Cisco Unified Wireless Network Architecture WCS WLC available on several platforms including WLC module for ISR routers (2800 and 3800). The easiest way to distinguish between a regular AP and a LAP is to look at the part number of the AP. LAP (Lightweight AP Protocol [LWAPP]) Part numbers always begin with AIR- LAPXXXX. Autonomous AP (Cisco IOS Software) Part numbers always begin with AIR-APXXXX. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Cisco Wireless Control System (WCS) Optional - Allows for easier management of several WLCs. Server platform which uses a GUI front-end. Uses floor plans to display dynamic representations of wireless coverage. Can be used with Cisco Wireless Location Appliance to track the location of thousands of clients. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Cisco Unified Wireless Network Architecture HREAP DHCP Server WLC LAPs (Lightweight Access Point) are designed to be zero touch configuration. Gets is configuration parameters from the WLC Do not need to configure it through its console port or over the network. LAP Operations Step 1: LAP obtains an IP address from DHCP server Step 2: LAP learns IP address of an available WLCs DHCP server adds option 43 to its reply containing a list of WLCs, or LAP broadcasts a join request message (as long as the WLC on the local subnet) Step 3: LAP sends a join request to the first WLC in its list. Step 4: WLC compares IOS image number stored to the one stored on the WLC. If they differ the LAP download the code on the WLC and reboots. Step 5: WLCP and LAP build a secure LWAPP or CAPWAP tunnel for management traffic, and LWAPP or CAPWAP tunnel (not secured) for wireless client data. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v When LAP is cut off from WLC client associations are dropped and no data can pass over the WLAN. Cisco Hybrid Remote Edge Access Point (HREAP) is used when LAPs are separated from WLCS over a WAN link. The LAPs can keep operating even while the WAN link is down and the WLC is not available like an autonomous AP. Allows wireless clients to keep communicating within the remote site. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

20 Single VLANs Traffic Patterns Traffic patterns differ than traditional WLANs. Client data passes: From Client A to LAP From LAP to WLC From WLC back to LAP From LAP to Client B Encryption is still handled between the LAP and the client. BSS Range 2003, Cisco Systems, Inc. All rights reserved , Cisco Systems, Inc. All rights reserved. BCMSN v Multiple VLANs With traditional WLANs the access VLANs must be extended or trunked between APs and multilayer switch. This is not the case with LAPs and WLCs. There are two VLANs A and B with their respective SSIDs A and B. The VLANs exist on the trunk between the MLC and SW2 but go no further. The LAPs and the WLC are connected by VLAN Z which is can be totally isolated from VLANs A and B. VLANs A and B are carried over the LWAPP tunnel so they are logically connected between the LAP and the WLC. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Roaming in a Cisco Unified Wireless Network 2003, Cisco Systems, Inc. All rights reserved. 2-80

21 Traditional Roaming Traditional Roaming IAPP: Please send buffered frames for IAPP: Ok! * Packet - Source MAC of client A WLAN designer must determine whether clients will require seamless roaming from access point to access point. IEEE IAPP (Inter-Access Point Protocol). Initial Association: Probing (Probe Request, Probe Response) Authentication (Authentication Request, Authentication Response) Association (Association Request, Association Response) does not allow associating with more than one AP. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v The client initiates the roaming (re- association) process. As the client is moving out of range of its associated AP, the signal strength will start to drop off. At the same time, the strength of another AP will begin to increase. The re-association process then occurs, including authentication. * AP(B) must update MAC address tables on infrastructure switches to prevent to loss of data. AP(B) sends an Ethernet frame to AP(A) with the source MAC address of the client so all the switches can update their SAT/MAC tables. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Roaming in a Cisco Unified Wireless Network Intracontroller Roaming With autonomous APs when a client roams its association moves from one AP to another. Client must negotiate the move independently and the APs must also make sure any buffered data from the client is passed along with the association. WLC supports both Layer 2 and Layer 3 roaming. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Both LAP1 and LAP2: Use SSID MyWLAN Joined to the same WLC Client roams into area covered by AP2. Although the AP has changed the same controller is providing the association with through the LWAPP or CAPWAP tunnel. This is known as intracontroller roaming. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

22 Intracontroller Roaming Intercontroller Roaming (same subnet) Same Subnet Same IP address Intracontroller roaming. The WLC (controller) simply updates its tables to begin using the LWAPP or CAPWAP tunnel to LAP2. Any leftover data that was buffered for the prior association with LAP1 is easily shifted to new association with LAP , Cisco Systems, Inc. All rights reserved. BCMSN v Intercontroller roaming: When LAPs are supported by multiple WLCs (controllers) for redundancy, load balancing or scalability. Client moves to LAP2 s cell the same SSID is found. Client moves it association to WLC2. As long as WLC1 and WLC2 are in the same subnet they can easily hand off the clients association. Uses a mobility message to exchange information about the client. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Intercontroller Roaming (same subnet) Intercontroller Roaming (different subnet) Same Subnet Mobility Exchange Mobility Exchange Same IP address Same IP address When the mobility exchange occurs the client begins using the LWAPP or CAPWAP tunnel between LAP2 and WLC2. Client IP address has not changed. Roaming process completely transparent to the client. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v WLC controllers are in different subnets (VLANs A and B). Do not have to have end-to-end or campus wide VLANs. Client begins in cell with association to WLC1. Obtains an IP address within VLAN A LAP1 offers VLAN A on its SSID MyWLAN All traffic passes between LAP1 and WLC1 onto VLAN A. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

23 Intercontroller Roaming (different subnet) Intercontroller Roaming (different subnet) Mobility Exchange Mobility Exchange L3 Mobility Tunnel Client roams into cell provided by LAP2. Same IP address LAP2 offers access to a different VLAN, VLAN B. The client s IP address remains the same. But WLC1 and WLC2 are in different subnets (VLANs A and B). Client IP address has moved into a foreign subnet. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Same IP address Two WLCs (controllers) begin to work together to provide continue service for the client without the client needing to obtain an new IP address. WLCs (controllers) bring up an Ether-IP tunnel (RFC 3378) between them. Carries some of the clients data traffic Encapsulates Ethernet frame inside an IP packet using protocol 97. WLC1 encapsulates packets and sends them to WLC2. WLC2 unencapsulates the packets into their original form. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Intercontroller Roaming (different subnet) Intercontroller Roaming (different subnet) Mobility Exchange L3 Mobility Tunnel Anchor Mobility Exchange L3 Mobility Tunnel Foreign Agent Same IP address Traffic leaving the client travels from LAP2 to WLC2 onto the network even though it is on a foreign subnet. It s just a packet in an Ethernet frame. Dest MAC Source MAC [ IP Packet: Source IP Dest IP - ] Traffic coming in towards the client takes a different path. Traffic enters MLS (L3 switch) Because the packet has an IP address on VLAN 3 it is routed/switched out VLAN A to WLC1. WLC1 accepts the traffic and forwards it to the appropriate WLC controller that has the current association with the client. WLC1 sends the traffic to WLC2 through the Ether-IP tunnel. WLC2 forwards the traffic to LAP2 and onto the client. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v Same IP address The client originally joined the WLAN on WLC1, so WLC1 is known as the anchor. WLC2 is serving a client on a different subnet so it is known as the foreign agent. As the client continues to roam the foreign agent will change but the anchor will remain the same. To do this WLCs are configured into logical mobility groups. Up to 24 WLCs Number of LAPs vary depending upon LAP platform. If a client must move between mobility groups, it s IP address and all of its session information maintained by the WLC will be dropped. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

24 Configuring Switchports for Autonomous APs gig 0/1 Configuring Switch Ports for WLAN Use Switch(config)# interface gig 0/1 Switch(config-if)# switchport trunk encapsulation dot1q Switch(config-if)# switchport trunk allowed vlan 10, 20 Switch(config-if)# switchport mode trunk Switch(config-if)# spanning-tree portfast trunk APs are normally at the access layer. Each SSID is supported by the AP mapped to a VLAN. When multiple SSIDs/VLANs are used need to configure switchport as a trunk. The is spanning-tree portfast trunk used to shorten the time required for STP to bring up the trunk link to forwarding state quickly. 2003, Cisco Systems, Inc. All rights reserved , Cisco Systems, Inc. All rights reserved. BCMSN v Configuring Switchports for Cisco Unified Wireless Network Configuring Switchports for Cisco Unified Wireless Network fa 0/2 Distribution(config)# vlan 10, 20, 50, 55 Distribution(config)# interface vlan 10 Configure the SVIs Distribution(config-if)# ip address Distribution(config)# interface vlan 20 Distribution(config-if)# ip address Distribution(config)# interface vlan 50 Distribution(config-if)# ip address Distribution(config)# interface vlan 55 Distribution(config-if)# ip address Access(config)# interface fa 0/1 Access(config-if)# switchport trunk encapsulation dot1q Access(config-if)# switchport mode trunk Access(config)# interface fa 0/2 Access(config-if)# switchport mode access Access(config-if)# switchport access vlan 50 Access(config-if)# spanning-tree portfast Distribution(config)# interface fa 0/1 <must carry vlan 50> Distribution(config-if)# switchport trunk encapsulation dot1q Distribution(config-if)# switchport mode trunk Distribution(config)# interface gig 1/2 <must carry vlans 10, 20 & 55> Distribution(config-if)# switchport trunk encapsulation dot1q Distribution(config-if)# switchport mode trunk VLAN 50 is created to access the LAPs. VLAN 55 is created to access the WLC. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v VLAN 50 is created to access the LAPs. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v

25 Antenna Concepts Antennas Directionality Omnidirectional antennas (360 degree coverage) Directional antennas (limited range of coverage) Gain Measured in dbi (gain over theoretical isotropic) More gain means focusing in certain directions, limited range of coverage Polarization Vertical polarization for WLAN 2003, Cisco Systems, Inc. All rights 2005 reserved. Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v Antenna Theory Omnidirectional Antenna: Dipole A theoretical isotropic antenna has a perfect 360-degree vertical and horizontal beamwidth. Reference for all antennas. Energy lobes pushed in from the top and bottom Higher gain Smaller vertical beamwidth Larger horizontal lobe Typical dipole pattern Side View (Vertical Pattern) Vertical Beamwidth New Pattern (with Gain) Top View (Horizontal Pattern) 2-dBi Dipole "Standard Rubber Duck" 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v

26 Directional Antenna Cisco Access Point/Bridge Antennas Lobes are pushed in a certain direction, causing the energy to be condensed in a particular area. Very little energy is in the back side of a directional antenna. Side View (Vertical Pattern) Top View (Horizontal Pattern) 6.5-dBi Diversity Patch Wall Mount 55 degrees Frequency Antenna Horizontal Beamwidth Vertical Beamwidth 2.4 GHz 2.2-dBi dipole 360 o 65 o 2.4 GHz 5.2-dBi omni 360 o 38 o 2.4 GHz 6-dBi diversity patch 80 o 55 o 2.4 GHz 9-dBi patch 60 o 60 o 2.4 GHz 10-dBi Yagi 47 o 55 o 2.4 GHz 13.5-dBi Yagi 30 o 25 o 2.4 GHz 21-dBi dish 12.5 o 12.5 o 5 GHz 3.5-dBi dipole 360 o 40 o 5 GHz 6-dBi omni 360 o 17 o 5 GHz 7-dBi patch 70 o 50 o 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v Multipath Distortion Definition of Decibel Multipath distortion (a form of radio degradation) occurs when radio signals bounce off metal objects in a room, such as metal cabinets or ceiling lights. OFDM overcomes multipath distortion through parallel frequency use. Multiple signals at receiver cause distortion of the signal. As radio waves bounce, they arrive at the receiver slightly delayed, combining with the original signal, causing distortion. Diversity systems use two antennas in different positions to reduce the degradation. Decibel (db) Ratio of one value to another dbm = Power based on 1 milliwatt 0 dbm = 1 mw dbi = Antenna gain based on isotropic antenna [db] = 10 log 10 (Ratio) 0 db 1:1 10 db 10:1 +3 db Multiply by 2 3 db Divide by db Multiply by db Divide by db = = 10 * 2 20 db = = 10 * db = = 100 / , Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v

27 Effective Isotropic Radiated Power Antenna Cable Loss Transmit power is rated in dbm or mw. Power coming off an antenna is Effective Isotropic Radiated Power (EIRP). FCC and ETSI use EIRP for power limits in regulations for 2.4-GHz and 5-GHz WLANs. EIRP [dbm] = Power [dbm] cable_loss [db] + antenna_gain [dbi] Use cable that is supplied with the antenna, avoiding long cable runs when possible. Cisco offers these cables: LMR400-style cables 20 and 50 feet Total loss of 1.3 and 3.4 db, respectively LMR600-style cables 100 and 150 feet Total loss of 4.4 and 6.6 db, respectively LMR400 LMR600 Cable Type 2.4-GHz 5.8-GHz Loss (db/100 Loss (db/100 feet) feet) LMR LMR , Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v GHz EIRP Rules for FCC-Governed Areas 2.4-GHz EIRP Rules for ETSI-Governed Areas Point-to-Multipoint Transmitter Transmitter Maximum Power dbm Gain EIRP FCC Maximum 1 W 30 dbm 6 dbi 36 dbm Cisco Maximum 100 mw 20 dbm 16 dbi 36 dbm Reduced Tx Power 20 mw 13 dbm 23 dbi 36 dbm The above values reflect the 1:1 rule. Point-to-multipoint FCC allows increasing the gain of an antenna/cable system if the transmitter power is reduced below 30 dbm in a 1:1 ratio. Reduce transmit power below maximum of 30 dbm by 1 dbm and increase antenna/cable system gain by 1-dBi. Transmitter Power Transmitter dbm Maximum Gain EIRP ETSI Maximum 50 mw 17 dbm 3 dbi 20 dbm Cisco Maximum 50 mw 17 dbm 2.2 dbi 19.2 dbm Reduced Tx Power 20 mw 13 dbm 7 dbi 20 dbm Reduced Tx Power 10 mw 10 dbm 10 dbi 20 dbm Reduced Tx Power 1 mw 0 dbm 20 dbi 20 dbm Currently ETSI allows a maximum of 20 dbm EIRP on point-to-multipoint and point-to-point installations 17 dbm maximum transmitter power with 3 dbi in gain attributed to antenna and cable combination. Reduce transmit power below maximum of 17 dbm by 1 dbm and increase antenna/cable system gain by 1 dbi. 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved. BCMSN v

28 EIRP Rules: Summary Frequency [GHz] No. of Channels (26 total) Channel Identifier Usage TX Power FCC Ant. Gain EIRP ETSI EIRP , 6, 11 Indoor Outdoor 30 dbm 6 dbi 36 dbm 20 dbm Indoor only Indoor Outdoor 16 dbm 6 dbi 22 dbm 23 dbm 24 dbm 6 dbi 30 dbm 23 dbm Wireless LANs Indoor Outdoor 24 dbm 6 dbi 30 dbm 30 dbm The End Indoor Outdoor 30 dbm 6 dbi 36 dbm n/a MHz and above currently not allowed in most of Europe 2003, Cisco Systems, Inc. All rights reserved. BCMSN v , Cisco Systems, Inc. All rights reserved