复旦大学：《计算机网络 Computer Networking》课程电子教案（PPT课件讲稿）23 mobile_Wireless Networking

15-441: Computer Networking Lecture 21: Wireless Networking

15-441: Computer Networking Lecture 21: Wireless Networking

Wireless Challenges Force us to rethink many assumptions Need to share airwaves rather than wire Don't know what hosts are involved Host may not be using same link technology Mobility Other characteristics of wireless Noisy→ lots of losses Interaction of multiple transmitters at receiver Collisions, capture, interference Multipath interference 1-08-07 ecture 21: Wireless Networking 2

11-08-07 Lecture 21: Wireless Networking 2 Wireless Challenges • Force us to rethink many assumptions • Need to share airwaves rather than wire • Don’t know what hosts are involved • Host may not be using same link technology • Mobility • Other characteristics of wireless • Noisy → lots of losses • Slow • Interaction of multiple transmitters at receiver • Collisions, capture, interference • Multipath interference

Overview Internet mobility TCP over noisy links Link layer challenges 1-08-07 ecture 21: Wireless Networking 3

11-08-07 Lecture 21: Wireless Networking 3 Overview • Internet mobility • TCP over noisy links • Link layer challenges

Routing to Mobile Nodes Obvious solution have mobile nodes advertise route to mobile address /32 Should work ! Why is this bad? Consider forwarding tables on backbone routers Would have an entry for each mobile host ° Not very scalable What are some possible solutions? 1-08-07 ecture 21: Wireless Networking

11-08-07 Lecture 21: Wireless Networking 4 Routing to Mobile Nodes • Obvious solution: have mobile nodes advertise route to mobile address/32 • Should work!!! • Why is this bad? • Consider forwarding tables on backbone routers • Would have an entry for each mobile host • Not very scalable • What are some possible solutions?

How to handle mobile nodes? (Addressing) Dynamic Host Configuration (DHCP) Host gets new IP address in new locations Problems Host does not have constant name/address how do others contact host What happens to active transport connections? 1-08-07 ecture 21: Wireless Networking

11-08-07 Lecture 21: Wireless Networking 5 How to Handle Mobile Nodes? (Addressing) • Dynamic Host Configuration (DHCP) • Host gets new IP address in new locations • Problems • Host does not have constant name/address → how do others contact host • What happens to active transport connections?

How to handle mobile nodes? (Naming) Naming Use dHCP and update name-address mapping whenever host changes address FiXes contact problem but not broken transport connections 1-08-07 ecture 21: Wireless Networking 6

11-08-07 Lecture 21: Wireless Networking 6 How to Handle Mobile Nodes? (Naming) • Naming • Use DHCP and update name-address mapping whenever host changes address • Fixes contact problem but not broken transport connections

How to handle mobile nodes? (Transport) TCP currently uses 4 tuple to describe connection Modify tcp to allow peers address to be changed during connection Security issues Can someone easily hijack connection? Difficult deployment >both ends must support mobility 1-08-07 ecture 21: Wireless Networking 7

11-08-07 Lecture 21: Wireless Networking 7 How to Handle Mobile Nodes? (Transport) • TCP currently uses 4 tuple to describe connection • • Modify TCP to allow peer’s address to be changed during connection • Security issues • Can someone easily hijack connection? • Difficult deployment → both ends must support mobility

How to handle mobile nodes? (Link Layer) Link layer mobility Learning bridges can handle mobility this is how it is handled at Cmu Encapsulated PPP(PptP), Have mobile host act like he is connected to original lan Works for IP ANd other network protocols 1-08-07 ecture 21: Wireless Networking 8

11-08-07 Lecture 21: Wireless Networking 8 How to Handle Mobile Nodes? (Link Layer) • Link layer mobility • Learning bridges can handle mobility → this is how it is handled at CMU • Encapsulated PPP (PPTP) → Have mobile host act like he is connected to original LAN • Works for IP AND other network protocols

How to handle mobile nodes? (Routing) Allow mobile node to keep same address and name How do we deliver iP packets when the endpoint moves? Cant just have nodes advertise route to their address What about packets from the mobile host? Routing not a problem What source address on packet?> this can cause problems Key design considerations Scale Incremental deployment 1-08-07 ecture 21: Wireless Networking 9

11-08-07 Lecture 21: Wireless Networking 9 How to Handle Mobile Nodes? (Routing) • Allow mobile node to keep same address and name • How do we deliver IP packets when the endpoint moves? • Can’t just have nodes advertise route to their address • What about packets from the mobile host? • Routing not a problem • What source address on packet? → this can cause problems • Key design considerations • Scale • Incremental deployment

Basic Solution to Mobile routing Same as other problems in computer scIence Add a level of indirection Keep some part of the network informed about current location Need technique to route packets through this location(interception Need to forward packets from this location to mobile host(delivery) 1-08-07 ecture 21: Wireless Networking 10

11-08-07 Lecture 21: Wireless Networking 10 Basic Solution to Mobile Routing • Same as other problems in computer science • Add a level of indirection • Keep some part of the network informed about current location • Need technique to route packets through this location (interception) • Need to forward packets from this location to mobile host (delivery)