+Intro
+Prephase
+TimePlan
+Outline
+Research Phase
+- > 28 Feb.-
+-5 Mar.-
+-12 Mar.-
+-Odysee
+-19 Mar.-
+-26 Mar.-
+-2 Apr.-
+Develope Tests Spec.
+- 9 Apr.-
+Test Phase
+- 16 Apr.-
+- 23 Apr.-
+- 30 Apr.-
+Review Results
+- 7 May.-
+Prep. Report
+- 14 May.-
+- 21 May.-
+After Project
Wll (wireless local loop)
Term famous since opening of the telephone market and necessarity to over go the last mile. Mainly new, small companies try to provide Internet access points using the VHFs (very high frequency) and ISM band (integrated service and monitor).The first networks, which can be seen as wireless local loop were the telephone networks, which had a own protocol. Each conversation has its own channel. The fact, that a conversation is 90% one way (not both speaking the same time) was mostly neglected. With the GSM (g s m) a digital network had been implemented and data could be send, but in a limited way. Communication with the Internet was restricted to text messages.
Today many approaches has been done combining the data communication, like known from the Internet with the voice communication. One idea was based on detaching the data streams, like in GSM. This would have advantages in handling each communication more accurately, but the big disadvantage would be a Internet user would need to use a special gateway (or proxy) to communicate with the mobile user the same time with audio and video.
Approaches for a wireless data network protocol
The same time the mobile phone network grew, the same time the desire for a mobile Internet was born. Advantages are seen in being reachable with voice, image and all the sensors a computer can have all the time. Having access to the information resources all the time. Or simply keeping distributed databases uptodate, while the data is collected in different places. Companies on exhibition using modern presentation equipment wanted to have a fast and easy way to connect their computers to network without having this ugly wires all over the place. Also companies just formed ad hoc out of small firms for working together for the duration of one project didn t want to invest in expensive cabling of their short term offices.Two different data network requirements
- Bandwidth and reliability is main importance
- Mobility is main importance
Known to me are:
- DECT
- Radio Lan
- UMTS
- Hiperlan (new version of radio lan)
- IEEE 802.11
I only like to make remarks to the Hiperlan, which is an standard from the
ETSI (European Telecomunication Standard
Institute). It implements a whole network stack and requires,
therefor drivers on all OSI levels. This for example would increase the
the complexity if a new product needs to become wireless lan enabled. Today
for 802 Ethernet many standard ICs exist and hups, router and firewalls are
advanced in technology. This is the same time the advantage of the IEEE 802.11 approach. Basically IEEE (Institute of Electrical and Electronic Engineers) tried to extend its layer 2 802 protocol to an wireless layer. In the standard also IR and radio communication are implemented. The big advantage can be seen at the fast success of the Israelic company Lannair (today Breezecom), it s equipment is plugged into the Ethernet and therefor needs no new drivers in the software. A wireless lan bridge can be used most easily to connect two separated lans e.g. in different buildings. However the features introduced into the layer 802.11 are more than the OSI layer model thinks of for layer 2 communication
Different needs for realtime multimedia data
A short intersection for needs of realtime data. Thinking of the situation a person speaks continously the generated bitstream will need a certain amount of bandwidth. This was also shown in the lecture, while giving the coding and bandwidth requirements. The nature of a data network (or better Ethernet IP network) is that sometimes the bandwidth is low (more exact the same bandwidth with more errors). The TCP protocol (OSI layer 3) converts the errors or lower bandwidth into data bursts, retransmitting data if needed.Voice over IP / H323 of ITU (International Telecomunication Union)
Aim of this protocol suite was it to overcome the bursty transmission of the TCP/IP network for adapting to the need of realtime data. In another feature H323 provides different media streams for different capacity networks (e.g. high quality/capacity network segment and low).Key trick for achieving quality transmission at low bit rate is to transmit each piece of data only once and in case of errors live with them and not retransmit the data. Achieved is this by utilizing UDP with an additional RTP header.
Caveat at inter working of H323 and IEEE 802.11
As said before IEEE 802.11 is a physical layer protocol, which means the it has to sense if the channel is free, send the data and forget about it. All error checking, timeouts and retransmission will be done by higher layers. Naturally the radio channel has much less quality than a wire or optic channel. Seen from the point of view of wireless communication this would mean an unusual increase in management overhead from the upper layers. As each timer and header data needs to be resend and it is more likely that a maximum resend timer generates a network unavailable. Therefor the 802.11 implements retransmission in the physical layer. This therefor causes extra delay, which was tried to avoid in the H323. How many problems this glitch causes is not known in the moment. Here I would suggest our project could start.Task for a project
I see three phases or parts, which could be done partly simultaneous.- Researching about the needs of voice data in terms of bandwidth, transmission quality (errors) and burstyness (to be defined somehow).
- The same time trying to learn about the wireless network behavior especially the Breezecom IEEE 802.11 implementation. Important hereby are also ways to influence the behavior.
- Lastly putting the results together into a output, which allows and includes conclusion for further Voice in Wireless Networks.