Design and Implementation of WiFiRE MAC Layer Protocol

1
Design and Implementation of WiFiRE MAC Layer
Protocol

• By
• Sameer Kurkure
• Under guidance of
• Prof. Anirudha Sahoo Prof. Sridhar Iyer

2
Architecture

• Fixed Base Station and Subscriber Terminal
• Multiple BS connected with System

System Architecture 2
3
WiFiRE Test Bed
4

1. Construct MAC PDU
2. Send in proper sequence in FIFO order at every
   clock tick

To TCP/IP Layer
1
WiFiRE MAC1

1. Lookup BSID for corresponding CID of the packet
2. Send packet to appropriate PHY

1. Communicate with peer Ethernet MAC2
2. Send/Receive packet from NIC

2
Ethernet MAC1
NIC
A1
WiFiRE PHY1
System S
A2
WiFiRE PHY2
3
Ethernet Cable
5
WiFiRE MAC2
WiFiRE MAC3

• Steps
• Packet arrives from TCP/IP layer
• Constructs MPDU passed as payload to Ethernet MAC
• Packet is transmitted through NIC using Ethernet
  cable
• Intermediate processing (if required)
• Passes to WiFiRE MAC sublayer
• Transmit packet to appropriate antenna interface

WiFiRE PHY3
A3
6
4
Ethernet MAC2
NIC
WiFiRE PHY4
A4
Layer 2 device
WiFiRE PHY5
A5
WiFiRE PHY6
A6

• Responsibilities
• WiFiRE MAC1 IITB
• Ethernet MAC1 IITB
• Ethernet MAC2 IITM
• WiFiRE MAC2 IITB (if needed)
• WiFiRE MAC3 - IITM

WiFiRE Team IIT Bombay
5
Startup Scenario
6
Base Station
BS_TABLE
Mapping Table
Scheduler
CID Generator
Packet Classifier
DCID
Packet Controller
Timing Mechanism
Set timers

1. Processes Beacon from Scheduler
2. Feed it to Timing Mechanism
3. Forwards to In Thread for broadcast

Timer Clock
Raise SIGALRM
Out Thread
In Thread

1. Operates on clock ticks generated from Timer
   Clock
2. Broadcast Beacon from the interface in first slot
   of frame

eth0
eth1
From ST
To ST
To Server
From Server
7
Subscriber Terminal
ST_TABLE
Set timers

1. Processes Beacon packet
2. Finds slots which are designated to the ST
3. Set Clock timers accordingly

Timer Clock
Timing Mechanism
Set timers
Connection Classifier
Raise SIGALRM
DCID/Connection type

1. Forwards to Timing Mechanism

Packet Controller
In Thread
Out Thread

1. Beacon packet captured at STs interface

eth0
eth1
To Client
From Client
To BS
From BS
8
Connection Management
9
Subscriber Terminal

1. Classifies the incoming packet according to well
   known PORT.
2. Does table lookup, a miss causes a new entry in
   table and requests for DSA creation to Packet
   controller otherwise return a Data CID

ST_TABLE
Set timers
Timer Clock
Timing Mechanism
Connection Classifier
Raise SIGALRM

1. Fetches the packet from buffer and gains packet
   info from Connection Classifier
2. Make decisions for generating various request
   MPDUs
3. Forwards packet for existing connection.
4. Give inputs to timing mechanism

DCID/Connection type
Packet Controller
Out Thread
In Thread

1. Packet arrives at the interface
2. Captured by In Thread

1. Activates at every clock tick
2. Pick up packet from corresponding queue and
   transmits

eth0
eth1
To Client
From Client
To BS
From BS
10
Base Station
BS_TABLE
Mapping Table

1. Classifies the incoming packet according to
   ltIP,PORTgt pair
2. Fetches corresponding Data CID
3. Finds ST/Interface on which packet to be
   transmitted
4. Passes the information to Packet Controller

Scheduler
CID Generator
Packet Classifier
DCID
Packet Controller
Timing Mechanism
Set timers

1. Receives Data CID or Packet type for new
   connections from packet classifier
2. Make decisions for generating MPDUs
3. Give inputs to timing mechanism

Timer Clock
Raise SIGALRM
Out Thread
In Thread

1. Send/Receive packets to/from server according to
   pre-defined clock signals

eth0
eth1
From ST
To ST
To Server
From Server
11
Implementation Issues
12
Why Sockets?

• PF_PACKET family RAW socket
• Packets are directly sent to the application's
  socket without being processed by the network
  stack
• Bypasses the kernel traps and memory copies
• Easy to make desirable changes in the volatile
  design of protocol
• Packet capturing library only intercepts packet
  flow (ex. libpcap)

13
Time Synchronization

• Reception of Beacon message synchronizes BS and
  ST
• Slot Synchronization
• Read the DL and UL MAPs
• Extract associated slots numbers generate
  sync-sequence
• Signals are raised according to the sync-sequence
• Ex. D1 and D3 are the data connections served by
  same ST

Downlink
Uplink
D1
D2
D1
D3
D3
D1
D2
D2
D1
D2
D3
D1
BCN
Frame
1
2
1
1
1
3
2
1
1
Timing displacements
-1
-1
-1
-1
-1
1
1
1
0
Mode
Sync-Sequence
14
Connection Classification

• Connection are classified by well known ports
• Ex Best Effort on port 80(HTTP), nrtPS on
  22(FTP)
• Also can be classified by 802.1Q VLAN header
• Lookup tables are maintained at BS and ST

15-13 bits
12 bit
0-11 bits
User Priority
CFI
VID
15
Additions and Modification in WiFiRE
Specifications

• Add designated CIDs to carry non classified
  necessary packets
• Increased length field from existing 7 to 15 bits
• Update STID from 4 to 6 bytes
• Use ltData CID, Slot gt pair in scheduling
• Include Flow diagrams involving registration and
  ranging at BS and ST

16
Future Work

• Emulate for multiple sector by using multiple
  NICs
• Separate and embed the actual functionality of
  Layer 2 device on hardware chip
• Use hardware clock for more precision
• Complete Ranging over wireless link
• Implement DSC mechanism on scheduler
• Connection classification using 802.1Q VLAN
  extended Ethernet header.

17
Thank you
18
References

• WiFiRe Medium Access Layer (MAC) and Physical
  Layer (PHY) Specifcation Center of Excellence for
  Wireless Technology (CEWiT) June 2006.
• IEEE 802.16. IEEE Standard for Local and
  Metropolitan Area Networks - Part 16 Air
  Interface for Fixed Broadband Wireless Access
  Systems 2002.
• Design and Evaluation of a new MAC Protocol for
  Long-Distance 802.11 Mesh Networks, Bhaskaran
  Raman and Kameswari Chebrolu, 11th Annual
  International Conference on Mobile Computing and
  Networking paper (MOBICOM), Aug/Sep 2005,Cologne,
  Germany
• GuoSong Chu Deng Wang Shunliang Mei A QoS
  architecture for the MAC protocol of IEEE 802.16
  BWA system, IEEE 2002 International Conference on
  Communications, Circuits and Systems and West
  Sino Expositions, pages 435- 439 vol.1, 29 June-1
  July 2002.
• Broadband Wireless Internet Forum, Media Access
  Protocols DOCSIS, Document Number WP-2 TG-1
  Version 1.1, December 5, 2000.
• Wang, H. Li, W. Agrawal, D.P. Dynamic admission
  control and QoS for 802.16 wireless MAN. Wireless
  Telecommunications Symposium, 2005 pages 60- 66,
  April 2005.

19
References (continued)

• Hawa, M. Petr, D.W. Quality of service
  scheduling in cable and broadband wireless access
  systems, Tenth IEEE International Workshop on
  Quality of Service. Pages 247- 255, 2002.
• LAN/MAN standards Committee, Part 11 Wireless
  LAN Medium Access Control (MAC) and Physical
  Layer (PHY) Specications, IEEESA Standards
  Board, June 2003.
• W Richard Stevens UNIX Network Programming,
  Volume 1, Second Edition, Prentice Hall, 1998
• Inside the Linux Packet Filter The packet's
  journey through the kernel, http//delivery.acm.or
  g/10.1145/520000/513092/5617s1.html
• The Linux Socket Filter Sning Bytes over the
  Network, in Linux Journal By Gianluca Insolvibile
  http//www.linuxjournal.com June 2001
• GNU C Library Signal Handling,
  http//www.cs.utah.edu/dept/old/texinfo/glibc-manu
  al-0.02/library 21.html
• Introduction To Unix Signals Programming,
  http//users.actcom.co.il/choo/lupg/tutorials