Wireless MAN

IEEE 802.16: Broadband Wireless MAN Standard (WiMAX)

The IEEE 802.16 defines the wireless metropolitan area network (MAN) technology which is branded as WiMAX. The 802.16 includes two sets of standards, 802.16-2004 (802.16d) for fixed WiMAX and 802.16-2005(802.16e) for mobile WiMAX. The WiMAX wireless broadband access standard provides the missing link for the "last mile" connection in metropolitan area networks where DSL, Cable and other broadband access methods are not available or too expensive. WiMAX also offers an alternative to satellite Internet services for rural areas and allows mobility of the customer equipment.

IEEE 802.16 standards are concerned with the air interface between a subscriber's transceiver station and a base transceiver station. The fixed WiMax standard IEEE 802.16-2004 (also known as 802.16d) is approved by the IEEE in June 2004, which provides fixed, point-to-multi point broadband wireless access service and its product profile utilizes the OFDM 256-FFT (Fast Fourier Transform) system profile. The fixed WiMAX 802.16-2004 standard supports both time division duplex (TDD) and frequency division duplex (FDD) services - the latter of which delivers full duplex transmission on the same signal if desired. In Dec. 2005, IEEE approved the mobile WiMax standard, the 802.16-2005 (also known as 802.16e). IEEE 802.16e, based on the early WiMax standard 802.16a, adds mobility features to WiMAX in the 2 to 11 GHz licensed bands. 802.16e allows for fixed wireless and mobile Non Line of Sight (NLOS) applications primarily by enhancing the OFDMA (Orthogonal Frequency Division Multiple Access).

IEEE 802.16 and WiMAX are designed as a complimentary technology to Wi-Fi and Bluetooth. The following table provides a quick comparison of 802.16 with to 802.11(WLAN) and 802.15.1

Parameters	IEEE802.16d (802.16-2004 Fixed WiMAX)	IEEE802.16e (802.16-2005 Mobile WiMAX)	802.11 (WLAN)	802.15.1 (Bluetooth)
Frequency Band:	2-66GHz	2 - 11GHz	2.4 – 5.8GHz	2.4GHz
Range	~31 miles	~31 miles	~100 meters	~10meters
Maximum Data rate:	~134 Mbps	~15 Mbps	~55 Mbps	~3Mbps
Number of users:	Thousands	Thousands	Dozens	Dozens

Protocol Structure -IEEE 802.16: Broadband Wireless MAN Standard (WiMAX)

IEEE 802.16 Protocol Architecture has 4 layers: Convergence, MAC, Trnamission and physical, which can be map to two OSI lowest layers: phusical and data link.

Metropolitan Area Network (MAN)

MANs (Metropolitan Area Networks) connect multiple geographically nearby LANs to one another (over an area of up to a few dozen kilometres) at high speeds. Thus, a MAN lets two remote nodes communicate as if they were part of the same local area network.

A MAN is made from switches or routers connected to one another with high-speed links (usually fibre optic cables). 

Switches

A switch is a multi-port bridge, meaning that it is an active element working on layer 2 of the OSI model.

The switch analyses the frames coming in on its entry ports and filters the data in order to focus solely on the right ports (this is called switching and is used in switched networks). As a result, the switch can act as both a port when filtering and as a hub when handling connections. Here is a diagram of a switch:

Switching

The switch uses a filtering/switching mechanism that redirects data flow to the most suitable machines, based on certain elements found in the data packets.

A layer-4 switch, operating on the transport layer of the OSI model, inspects the source and destination addresses of the messages, and creates a table that lets it find out which machine is connected to which port on the switch (in general this process is done automatically, but the switch manager can work differently if the right adjustments are made).

Once it knows the destination port, the switch only sends the message to the right port, and the other ports are then free for other transmissions which may be taking place at the same time. Consequently, each data exchange can run at the nominal transfer rate (more bandwidth sharing), without collisions, with the end result being a very significant increase in the network's bandwidth (at an equal nominal speed).

The most advanced switches, called layer 7 switches (corresponding to the application layer of the OSI model) can redirect data based on advanced application data contained in the data packets, such as cookies for HTTP, the type of the file being sent for FTP, etc. For this reason, a layer 7 switch can be used for load balancing, by routing the incoming data flow to the most appropriate servers, which have a lower load or are responding more quickly. 

Router

A router is a device for connecting computer networks to one another, used for handling the routing of packets between two networks, or to determine the path that a data packet shall take.

When a user enters a URL, the Web client (the browser) queries the domain name server, which shows it the IP address of the desired machine.

The workstation sends the request to the nearest router, i.e. to the default gateway on the network it is located on. This router determines the next machine to which the data will be forwarded, in such a way as to choose the best pathway possible. To do so, the routers keep up-to-date routing tables, which are like maps showing the paths that can be taken to get to the destination address. There are numerous protocols designed to handle this process.

In addition to their routing function, routers are also used to manipulate data travelling in the form of data-grams so that they can go from one kind of network to another. As not all networks are able to handle the same size of data packets, routers are tasked with fragmenting packets so they can travel freely.

Physical design of routers

The first routers were simply computers with multiple network cards, with each one linked to a different network. Current routers are mostly hardware designed for routing, generally in the form of 1U servers.

A router has several network interfaces, with each one connected to a different network. Therefore, it has one IP address for every network it is connected to.

Wireless router

A wireless router is the same in principle as a traditional router, the difference being that it lets wirelessWiFi stations) connect to the networks which the router is connected to by wired connections (usually Ethernet). 

Routing protocols

There are two major types of routing protocols:

• Distance vector routers generate a routing table that calculates the "cost" (in terms of the number of hops) of each route, then sends that table to nearby routers. Each time a connection request is made, the router chooses the least costly route.
• Link state routers listen to the network continuously, in order to identify the various elements surrounding it. With this information, each router calculates the shortest pathway (in terms of time) to each neighbouring router, and sends this information in the form of update packets. Finally, each router builds its own routing table by calculating the shortest pathways to all other routers (using the Dijkstra algorithm).  

Routers

Routers are devices which make it possible to "choose" the path that data-grams will take to arrive at the destination.
They are machines with several network interface cards each one of which is linked to a different network. So, in the simplest configuration, the router only has to "look at" what network a computer is located on to send data-grams to it from the originator.

However, on the Internet the schema is much more complicated for the following reasons:

• The number of networks to which a router is connected is generally large
• The networks to which the router is linked can be linked to other networks that the router cannot see directly

So, routers work using routing tables and protocols, according to the following model:

• The router receives a frame from a machine connected to one of the networks it is attached to
• Datagrams are sent on the IP layer
• The router looks at the datagram's header
• If the destination IP address belongs to one of the networks to which one of the router interfaces is attached, the information must be sent at layer 4 after the IP header has been unencapsulated (removed)
• If the destination IP address is part of a different network, the router consults its routing table, a table which establishes the path to take for a given address.
• The router sends the datagram using the network interface card linked to the network on which the router decides to send the packet.

So, there are two scenarios, either the originator and recipient belong to the same network in which case we talk about direct delivery, or there is at least one router between the originator and recipient, in which case we talk about indirect delivery.

In the case of indirect delivery, the role of the router and in particular that of the routing table is very important. So, the operation of a router is determined by the way in which this routing table is created.

• If the routing table is entered manually by the administrator, it is a static routing (suitable for small networks)
• If the router builds its own routing tables using information that it receives (via the routing protocols), it is a dynamic routing

The routing table

The routing table is a table of connections between the target machine address and the node according to which the router must deliver the message. In reality it is enough that the message is delivered to the network that contains the machine, it is therefore not necessary to store the complete IP address of the machine: only the network identifier of the IP address (i.e. the network ID) needs to be stored.

The routing table is therefore a table which contains address pairs:

Using this table, the router knowing the address of the recipient encapsulated in the message, will be able to find out what interface to send the message on (this comes back to knowing which network interface card to use), and to which router, directly accessible on the network to which this card is connected, to send the datagram.
This mechanism consisting of only knowing the address of the next link leading to the destination is called next-hop routing.

However, it may be that the recipient belongs to a non referenced network in the routing table. In this case, the router uses a default router (also called the default gateway).

Here, in a simplified way is what a routing table could look like:

The message is therefore sent from router to router by successive hops, until the recipient belongs to a network directly connected to a router. This then sends the message directly to the target machine...

In the case of static routing, it is the administrator who updates the routing table.
In the case of dynamic routing a protocol called a routing protocol enables the automatic updating of the table so that it contains the optimal route at any time.

Routing protocols

The internet is a collection of connected networks. As a result, all routers do not work in the same way, this depends on the type of network upon which they are found.

In fact, there are different levels of routers which operate with different protocols:

• Node routers are the main routers because they link the different networks
• External routers allow a connection to autonomous networks between them. They work with a protocol called EGP (Exterior Gateway Protocol) which develops gradually by keeping the same name
• Internal routers allow routing of information inside an autonomous network. They exchange information using protocols called IGP (Interior Gateway Protocol), such as RIP and OSPF

The RIP protocol

RIP means Routing Information Protocol. It is a Vector Distance type protocol, i.e. each router communicates to the other routers the distance which separates them (the number of hops which separates them). So, when a router receives one of these messages it increments this distance by 1 and sends the message to directly accessible routers. In this way, the routers can then keep the optimal route of a message by storing the next router address in the routing table in such a way that the number of hops to reach a network is kept to a minimum. However this protocol only takes into account the distance between two machines in terms of hops and does not consider the state of the connection so as to select the best possible bandwidth.

The OSPF protocol

OSPF (Open Shortest Path First) is more effective than RIP and is therefore beginning to gradually replace it. It is a protocol route-link type protocol; this means that contrary to RIP, this protocol does not send the number of hops which separates them to the adjacent routers, but the state of the connection which separates them. In this way, each router is capable of sending a card of the state of the network and can as a result choose the most appropriate route for a given message at any time.

In addition, this protocol avoids intermediary routers having to increment the number of hops, which results in much less extensive information making it possible to have more useful bandwidth than with RIP.

WirelessMAN Web Links

IEEE 802.16 maintains a number of web pages and services using the WirelessMAN domain. In some cases, the WirelessMAN URLs are blocked in China. This table lists equivalent alternative URLs that should work there.
Note: The URLs are not case-sensitive. The capitalization of "WirelessMAN" is purely for visual affect.

Topic	Primary URL	Alternate URL
Working Group	http://WirelessMAN.org	http://ieee802.org/16
Upload (details below) [Note: Use WG Member Password, or contact WG Chair for access]	http://upload.WirelessMAN.org	http://dot16.org/upload
FTP Access to Uploaded Files (password blank)	ftp://ftp@dot16.org@ftp.dot16.org/upload
Upload Archive	http://archive.WirelessMAN.org	http://dot16.org/ul_archive
Member Upload for Internal Task Group Activities	http://memberupload.WirelessMAN.org	http://dot16.org/memberupload
Calendar	http://calendar.WirelessMAN.org	http://dot16.org/cal
Calendar - subscribe, iCal format	http://ics.WirelessMAN.org
Calendar - subscribe, RSS feed	http://rss.WirelessMAN.org	See this link for topic-based RSS feeds
Photo	http://photo.WirelessMAN.org	http://www.flickr.com/groups/WirelessMAN
On-Site Server	http://lan.WirelessMAN.org

A number of direct links are provided to areas on the upload server:

Upload Area	Primary URL	Alternate URL
Working Group	http://wg.WirelessMAN.org	http://dot16.org/UL_WG
Task Group m	http://tgm.WirelessMAN.org	http://dot16.org/UL_TGm
Relay Task Group	http://relay.WirelessMAN.org	http://dot16.org/UL_Relay
License-Exempt Task Group	http://le.WirelessMAN.org	http://dot16.org/UL_LE
Maintenance Task Group	http://maint.WirelessMAN.org	http://dot16.org/UL_Maint
WG Letter Ballot #26 (etc.)	http://lb26.WirelessMAN.org	http://dot16.org/UL_lb26
Liaison	http://liaison.WirelessMAN.org	http://dot16.org/UL_Liaison
Temporary Files	http://temp.WirelessMAN.org	http://dot16.org/UL_temp