Wireless Network Design Principles Mobility Addressing Capacity Security

Site Survey Floor plans are a useful aid to surveying a new site Help with the determination of coverage needs – this will show where communications is needed and therefore where APs will be installed

Site Survey Walk-through permits visual confirmation of the actual site (desks, office location, etc) Check for building construction - wall construction (concrete & steel vs partition walls) - hallways, open areas etc

Site Survey Optimum location of APs Coverage of APs once installed Actual bit and error rates in selected locations Number of APs

Site Survey Measurements may consist of frame error rates interfering signal strengths (noise) received signal strength multipath signal interference

Site Survey Antenna choices for coverage, diversity Signal amplifiers (if necessary – remember increasing signal power may cause interference to others and may increase the potential number of clients using the access point)

Site Survey Channel Layout APs will often overlap in coverage Selection of non-overlapping channels (1 6 11) Coverage must be in 3 dimensions if inside a building

Mobility DHCP Addressing - private addresses - NAT Mobile-IP

IP Addressing Many security plans require the use of privateaddresses - class A 10.x.x.x - class B x.x – x.x - class C x.x

IP Addressing Once a private address has been assigned, the network cannot access the external Internet To permit connection to outside world, Network Address Translation is necessary

DHCP (Dynamic Host Configuration Protocol) IP addresses offered by a server to hosts Static – MAC addresses in a table are mapped to a fixed IP address Dynamic – IP addresses are allocated from a pool (range of addresses)

DHCP Permits central point of control for management of IP addresses Allows efficient allocation of IP addresses

DHCP MAC addresses may be checked against a list of “approved” clients DHCP server may be local to client or may be centralised

Mobility Even with DHCP, addresses will tend to be static Since wireless devices can move about, fixed addresses may be unsuitable Even in a small network, use of subnet addressing will not suit static addressing

Mobility Mobile IP offers a more dynamic way of implementing an IP solution that can be used with wireless networks Mobile stations are allocated to a home network and have a static address in that network When the station operates in another foreign network it must use an address from that network

Mobility The mobile station registers with a foreign agent (commonly a router) Communications from and for the mobile station are carried between the foreign agent and a home agent using a care-of address given from the foreign network

Mobility Mobile IP is implemented using three basic functions: Discovery Router advertisement (ICMP) messages contain extensions that support their identification as a mobile agent

Mobility Registration A UDP-based registration process permits the mobile node to register with an available foreign agent (if none available, then a mobile node may become its “own” foreign agent) The process usually requires authentication

Mobility Tunneling Agents must carry the mobile node’s IP packets between the home and foreign networks The traffic between networks must be carried over the global Internet and so must be encapsulated This traffic should be secured by authentication and encryption

Mobility Tunneling Encapsulation can be: IP-within-IP encapsulation Minimal Encapsulation (specifically identified IP packets) GRE (Generic Router Encapsulation)

Capacity No. of clients depends upon the amount of traffic that users generate The capacity of an Access Point operating at 11 Mbps will be shared at around 6 Mbps Contemporary users using web, , file accesses will generate around kbps each

Connection RateNumber of 6Mbps 100 kbps kbps kbps20 Sustained Throughput Compared with Number of Clients

Security WEP -> WPA -> 11i SSL VPN