A WLAN allows users to move around the coverage area, often a home or small office, while maintaining a network connection. In the early s, WLANs were very expensive and were only used when wired connections were strategically impossible. WLAN prices also began to decrease significantly. However, not every Wi-Fi device actually receives Wi-Fi Alliance certification, although Wi-Fi is used by more than million people through about , Internet connection hot spots.
Every component that connects to a WLAN is considered a station and falls into one of two categories: access points APs and clients. APs transmit and receive radio frequency signals with devices able to receive transmitted signals; they normally function as routers. Clients may include a variety of devices such as desktop computers, workstations, laptop computers, IP phones and other cell phones and Smartphones.
All stations able to communicate with each other are called basic service sets BSSs , of which there are two types: independent and infrastructure. Toggle navigation Menu. Home Dictionary Tags Networking. Link failure detection via Much of the information in this section is summarized from the Data Center Infrastructure 2. While the rest of the campus network uses Layer 3 routing EIGRP all the way to the access layer, the unique requirements of data center deployments require a Layer 2 connection to the data center.
A Layer 2 access topology provides the following unique capabilities required in the data center:. The list of applications used in a clustered environment is growing, and Layer 2 adjacency is a common requirement. This can create challenges in a Layer 3 IP access topology. These servers usually depend on Layer 2 adjacency with other servers and may require rewriting of code when changing IP addresses. The active-standby modes of operation used by service modules require Layer 2 adjacency with the servers that use them.
The triangle looped topology utilized in the network used for this document is currently the most widely implemented in the enterprise data center. Otherwise, traffic flows can hop back and forth between aggregation switches, creating undesirable conditions and difficulty in troubleshooting. In the network used for this chapter, multiple access layer blocks are connected to a single distribution block.
This was done to reduce the number of distribution layer switches required. In a production deployment, the data center access-block would connect to a dedicated distribution block. In a production network, the distribution block dedicated to the data center access-block would run a variety of service modules supporting data center access.
This shows that due to low bandwidth a WLAN network is unable to support voice communication at vehicular speed. Clipping is a handy way to collect important slides you want to go back to later. A 20 percent or higher overlap can still be used if desired. It has a fixed bit rate of 64kbps. The main objectives of this study are; To define, describe, and forecast the global voice over WLAN market on the basis of solution, end user, application and geography. The shadow fading components varies randomly from one terminal location to another within any given macro-cell. The voice over WLAN market has been segmented on the basis of solution, end-user, application, and geography.
Example service modules include:. While some combination of these would be expected in a production distribution layer block, our test network is not specifically focused on data center testing, and we have implement the network without any of these service modules. QoS refers to the set of tools and techniques used to manage network resources. QoS technologies allow different types of traffic to contend inequitably for network resources.
Voice Over WLANS: The Complete Guide (Communications Engineering ( Paperback)) [Michael F. Finneran] on ykoketomel.ml *FREE* shipping on qualifying. Cover for Voice Over WLANS. Voice Over WLANS. The Complete Guide. Book • To operate on a wireless LAN, each user device (PC, PDA, voice handset, etc.) .
Using QoS, some network traffic such as Voice, video, or critical data may be granted priority or preferential services from network devices; this prevents lower priority background traffic from degrading the quality of these strategic applications. Until recently, QoS was not a great concern in the enterprise campus due to the large amount of available bandwidth as well as the asynchronous nature of data traffic and the ability of applications to tolerate the effects of buffer overflows and packet loss.
However, with new applications such as voice and video, which are sensitive to packet loss and delay it is important to utilize quality of service features to protect high priority traffic. Many campus links are underutilized. Some studies have shown that 95 percent of campus access layer links are used at less than 5 percent of their capacity.
This means that you can design campus networks to accommodate oversubscription between access, distribution and core layers.
Oversubscription allows for uplinks to be used more efficiently and more importantly, reduces the overall cost of building the campus network. The potential for congestion exists in campus uplinks because of oversubscription ratios and speed mismatches in campus downlinks for example, GigabitEthernet to FastEthernet links. The only way to provision service guarantees in these cases is to enable advanced interface queuing at these points.
For a given input or output interface, Cisco IOS can manage multiple queues. Traffic of a particular priority is mapped into the appropriate queue for that traffic class. Cisco IOS queue scheduling algorithms can then be configured to service those queues, giving more priority to servicing the queues containing higher priority traffic. In this way, higher priority traffic is protected from queue overruns caused by lower priority traffic.
This section is specific to wired Ethernet-attached IP phone. Cisco wired IP phones perform an intelligent exchange of information between the phone and the switchport it is plugged into using Cisco Discovery Protocol CDP. The last one configured overwrites the previous configuration. Because of the above limitation, policing will not be discussed in the configuration section of this document. When designing multicast networking, a routed access design has advantages over a design that has Layer 2 to the distribution layer. In the Layer 2 design, there are two routers on the same subnet as the multicast hosts.
This results in the following;. In the routed access design, this need for synchronized configuration is removed because there is only one router on the local segment, which by default results in synchronization of the unicast and multicast traffic flows.
Additionally, with the migration of the multicast router from the distribution to the access, there is no longer a need to tune the PIM hello timers to ensure rapid convergence between the distribution nodes in the case of a failure. The same remote fault indicator mechanisms that trigger rapid unicast convergence drive the multicast software and hardware recovery processes, and there is no need for Layer 3 detection of path or neighbor failure across the Layer 2 access switch.
The presence of a single router for each access VLAN also removes the need to consider non-reverse path forwarding non-RPF traffic received on the access side of the distribution switches. A multicast router drops any multicast traffic received on a non-RPF interface.
In the Layer 3 access design, there is a single router on the access subnet and no non-RPF traffic flows. Although the current generation of Cisco Catalyst switches can process and discard all non-RPF traffic in hardware with no performance impact or access list configuration required, the absence of non-RPF traffic simplifies operation and management. In our lab the core routers represented the best location. Refer to the above document as well as the relevant access-layer switch documentation for more details.
Layer 2 switched environments can prove easy targets for security attacks. The rich set of integrated security features on Cisco Catalyst Switches CISF protect your critical network infrastructure with easy-to-use tools that effectively prevent the most common—and potentially damaging— Layer 2 security threats. This type of attack floods the switch with so many MAC addresses that the switch does not know which port an end station or device is attached to.
When the switch does not know which port a device is attached to, it broadcasts the traffic destined for that device to the entire VLAN. In this way, the attacker is able to see all traffic that is coming to all the users in a VLAN. An untrusted port is a user-facing port that should never make any reserved DHCP responses. Therefore, rogue DHCP servers will be prevented from responding.
However, legitimately attached DHCP servers or uplinks to legitimate servers must be trusted. The binding information is recorded in a table on the Cisco Catalyst switch. Gratuitous ARP can be exploited by malicious programs that want to illegitimately take on the identity of another station.
When a malicious station redirects traffic to itself from two other stations that were talking to each other, the hacker who sent the GARP messages becomes the man-in-the-middle. Hacker programs such as ettercap do this with precision by issuing "private" GARP messages to specific MAC addresses rather than broadcasting them.
In this way, the victim of the attack does not see the GARP packet for its own address. IP address spoofing is commonly used to perform DoS attacks on a second party. The ping response will be directed to the second party from the third-party system. An essential element of network management, troubleshooting, and security operations is to have all network elements including routers switches and servers synchronized to a common clock source.
By synchronizing the clocks across the network it is possible to examine the exact sequence in which events occurred. This ability to analyze and correlate the sequence of events across multiple network elements makes it much easier to determine the root cause of network problems or security issues. The configuration section of this document shows the commands used in our network to have NTP synchronize to an external time source.
In most production the external time source used would be redundant, dedicated hardware that synchronizes via a GPS receiver to a clock source that is itself directly synchronized to an atomic clock. UDLD detects these physical misconfigurations and disables the ports in question. Throughout the configuration section of this chapter, many configuration examples are shown from actual routers and switches used in the lab build-out used to test and write this document. There is no special routing policy applied to the core routers; their configuration is left as simple as possible so as to not interfere with their primary function of routing packets.
The auto qos voip commands shown below are macros. They generate many configuration statements that configure CoS-to-DSCP mappings, interface queue discard thresholds, the mapping of specific CoS and DSCP values to a particular queue and threshold, and queue buffer sizes as well as generating the specific interface QoS trust policies.
The commands generated can be observed by entering the debug auto qos command before beginning the configuration. This section provides the configuration required for the campus network with the exception of the connection to the datacenter where slightly different configuration is required for the Layer 2 connections from the distribution to the access layers. This section provides the configuration required for the datacenter where slightly different configuration is required for the Layer 2 connections from the distribution to the access layers.
The configuration below is applied to all access layer switches that will have end-users or APs connected to them. Skip to content Skip to footer. Voice over Wireless LAN 4. Book Contents Book Contents. Find Matches in This Book. PDF - Complete Book CL sh ip route Route Filters The discussion on EIGRP stub above noted that in the structured campus model, the flow of traffic follows the hierarchical design.
D3L sh run begin router eigrp router eigrp CEF Switching Per-destination load balancing is enabled by default when you enable CEF, and is the load balancing method of choice for most situations. Adjusting EIGRP timers The recommended best practice for campus design is to use point-to-point fiber connections for all links between switches.
Spanning Tree Triangle Looped Topology The triangle looped topology utilized in the network used for this document is currently the most widely implemented in the enterprise data center. Lab Implementation Deviations from Standard Design Principals in the Data Center In the network used for this chapter, multiple access layer blocks are connected to a single distribution block. Can be used by services like NTP and multicast.
Also a good telnet address. Add any other non-routing interfaces. Use the Loopback1 address for this. In a point-point L3 campus design the EIGRP timers are not the primary mechanism used for link and node failure detection physical detection of fiber breaks are. They are intended to provide a fail-safe mechanism only. EIGRP Configuration Specific to Core Routers There is no special routing policy applied to the core routers; their configuration is left as simple as possible so as to not interfere with their primary function of routing packets.
Make one of the Distribution layer switches the STP root by configuring it with priority When debugging is enabled, the switch displays the QoS configuration that is automatically generated when auto-QoS is enabled. By default, it is enabled. Campus Routed Multicast configuration This section provides the configuration required for the campus network with the exception of the connection to the datacenter where slightly different configuration is required for the Layer 2 connections from the distribution to the access layers.
All RPs can use this address concurrently. The DRs use whichever RP its unicast routing protocol finds closest. The unicast routing protocol will automatically provide failover if a RP fails. The command defines the peer routers MSDP address its loopback1 and uses this routers loopback1 as the source IP address ip msdp cache-sa-state Cache SA-pairs learnt from MSDP peer even when there is no registered receiver for that multicast group ; this sacrifices some router memory in order to reduce join latency.
Optional interface VLAN 50 ip pim query-interval msec Increase the speed with which the router will detect other multicast routers on the same subnet; and then elect a designated router for IGMP queries and to send source registration messages to the rendezvous point RP.