FUNCTIONAL ARCHITECTURE 35

Nb. Interface Explanation

1 MMC - MMC

Mobility management messages between terminal and MR. Mo-bility management messaging is used as a new terminal registers in the network and in the case of handovers.

2 WFMP - WFMP Flow management control signaling messages. This is used for establishing and releasing flows.

3 MCP - MCP

Mobile Control Protocol (MCP) provides a reliable peer-to-peer protocol for transmitting WFMP and MMC messages between the MT and the MR. MCP is used for all wireless specific signal-ing.

4 Radio control messages

Radio control messages are used for transmitting radio link con-trol messages. For instance terminal association and radio flow control signaling is carried here.

5 APCP interface

Access Point Control Protocol (APCP) is used for sending radio link control and radio resource management messages between the APs and the mobile router

6 WGMP - WGMP Group management control signaling messages. This protocol is used to trace group members in the access network.

Table 2.1: External control interfaces of the system [SALM⁺98]

on the basis of the differentiated services or on TCP/UDP port information. When the WFMP entity of the mobile router detects a flow, it informs the QoS entity about its evaluation of the flow’s packet throughput. This information can be employed to allo-cate radio link QoS. The QoS manager transmits the alloallo-cated radio link QoS values to the WFMP entity which in turn establishes radio flows with the selected QoS.

Mobility Management Controller (MMC): The MMC entity is responsible for termi-nal mobility management. The MMC entity of the mobile router has a database that contains information about the registered terminals and their current location. During terminal registration, MMC can be used to authenticate the users. The MMC entity of the mobile terminal initializes the handover by sending a handover request message to the mobile router. The MMC entity of the mobile router in turn checks the radio resources in the new AP and requests WFMP to establish new radio flows in the new AP and to release the old radio flows.

Wireless Flow Management Protocol (WFMP): WFMP entity manages the radio flows.

It detects IP traffic and classifies IP flows. Whenever WFMP detects a new flow, it passes the flow information to the QoS manager which assigns the correct radio link priority for the flow. Next, WFMP establishes the radio flow with the allocated priority. WFMP also allocates IP level flow identifiers. The MR includes a master WFMP which classifies the flows and maintains the data base of all the existing flows while the MT includes only a simple WFMP entity that multiplexes the IP level flow identifiers into the correct radio flows.

Mobile Control Protocol (MCP): MCP protocol transmits WFMP and MMC messages

36 CHAPTER 2. WAND WIRELESS IP ARCHITECTURE

Nb. Interface Explanation

7 QoS - WFMP

This is an internal interface which is used for transmitting flow es-tablishment requests and QoS information between the QoS man-ager and the WFMP. As the WFMP entity of the mobile router de-tects a new flow, it sends a query to the QoS manager to find the radio QoS parameters. In a real implementation QoS and WFMP entities can be integrated into a single entity which removes this interface.

8 QoS - RSVP

Wireless specific QoS controller interacts with RSVP module for obtaining resource reservations and converting them into radio resource reservations and radio QoS. The RSVP module requests resources from the QoS manager via this interface.

9 QoS - MMC

This interface is used in the case of handovers. The MMC module informs the QoS entity about the handover and requests the re-establishment of the wireless flows. This re-establishment request is then forwarded to the WFMP entity.

10 WGMP - MMC This interface is used to inform WGMP of the membership changes due to handover.

Table 2.2: Internal control interfaces of the system [SALM⁺98]

between the MTs and the MR. MCP provides a reliable mechanism for transmitting control information. MCP implements a simple retransmission protocol. A separate low layer protocol was added to guarantee reliable transmission of control messages instead of using TCP/IP. This is because TCP/IP does not allow the separation of con-trol messages from other TCP traffic. Therefore, in case of handover the concon-trol mes-sages would be mixed with the user data traffic, which causes a significant delay for the handover procedure and re-establishment of connections. The use of MCP allows control traffic to be prioritized over the user data packets.

Flow Compression (FC) block: The MR and MTs include FC entities which are in charge of header compression. Header compression relies on the fact that many header fields remain the same over the life-time of an IP flow. Fields that do not change between different packets of a flow do not need to be transmitted. Flow compression is used only for the classified IP flows. The other IP traffic is sent without compression.

Radio Resource Manager (RRM): Each AP has an RRM entity that manages its radio resources. In the system, WFMP must send a resource query to RRM each time a new flow is established. The query includes the requested radio flow priority allocated by QoS entity and the flow rate estimated by WFMP. Based on this information, RRM decides whether the connection is accepted.

Access Point Control Protocol (APCP): APCP protocol provides a mechanism for trans-mitting control messages between the APs and the MR. APCP can be located above the TCP/IP stack which guarantees the reliable transmission of control messages. WFMP deploys APCP for RRM queries and for sending flow control information to the radio

2.8. CONCLUSION 37 sub-system.

Wireless Group Management Protocol (WGMP): This entity is responsible to trace group members in the access network. In order to save bandwidth, we only forward traffic destined to a group to the APs with active members of the group. Therefore we need to trace the location of group members in the network.

2.8 Conclusion

In this chapter, we presented the WAND environment and its main objectives. The main achievement of the WAND project was a demonstration system which served as a proof of concept for the developed technology. The user trials were successfully conducted in office and hospital environments. The project was also quite active in the standardization process of ETSI BRAN group. In fact, ETSI HIPERLAN II standard has inherited most of the WAND system design. Although WAND final demonstrator is based on ATM, it does not mean that it is reserved for ATM. As we saw in this chapter, there is no technical problem to use IP protocol directly on the WAND radio sub-system.

We presented a general overview of an IP based access system as well as its functionality.

The main open issues are IP QoS support, IP mobility support, as well as multicast commu-nication support at the access system. These issues are further investigated in the following chapters. Finally, our main contributions were the participation to the overall architecture design of the system, the WGMP entity as well as the description of its interfaces with other blocks [ALSNS98] [SALM⁺98].

38 CHAPTER 2. WAND WIRELESS IP ARCHITECTURE

Chapter 3