1 CMPE 257 - Wireless and Mobile Networking CMPE 257 Spring 2006 Wireless Internetworking Wireless and Mobile Networks
Dec 20, 2015
1CMPE 257 - Wireless and Mobile Networking
CMPE 257
Spring 2006Wireless Internetworking
Wireless and Mobile Networks
2CMPE 257 - Wireless and Mobile Networking
Wireless Internet
• Extension of Internet services to wireless/mobile users.
• Issues:– Wireless medium unreliability.
– Node mobility.
3CMPE 257 - Wireless and Mobile Networking
Challenges
• Network-, • Transport-, and • Application layer.
4CMPE 257 - Wireless and Mobile Networking
Address Mobility
• IP assumes fixed nodes.– Hierarchical addresses.
– IP address = network number+host number.
– IP address uniquely identifies host’s PoA.
– Host must attach to network specified by its IP address to send/receive datagrams.
• But what if nodes move?– Change address?
– How about packets destined to them?
5CMPE 257 - Wireless and Mobile Networking
Solution
• Mobile IP.– Manages mobility at the IP layer.
– Hides mobility from upper layers.
6CMPE 257 - Wireless and Mobile Networking
Mobile IP
• Maintains IP addressing scheme with additional support for mobility.– Address redirection.
7CMPE 257 - Wireless and Mobile Networking
Mobile IP: Goals
• Nodes can receive datagrams no matter where they attach to the Internet.
• IMHP (Internet Mobile Host Protocol) as Mobile IP precursor.
8CMPE 257 - Wireless and Mobile Networking
“Last-hop” Mobility
• Mobile IP is the Internet standard for “last-hop” mobility support in IP networks (RFC 2290).
• How do we deliver IP packets when the endpoints move?– Mobile host must be able to communicate after
changing its link-layer point-of-attachment.
– Mobile host must be able to communicate using its permanent (home) IP address.
9CMPE 257 - Wireless and Mobile Networking
Mobile IP: Design Issues
• Issues:– Impact on IP addressing.– Impact on routing.– Impact on higher layers.
• Key design considerations:– Scale.– Compatibility.– Transparency.
10CMPE 257 - Wireless and Mobile Networking
Terminology
Home Agent (HA)
Mobile Host (MH)
Foreign Agent (FA)
HN
FN
CH
11CMPE 257 - Wireless and Mobile Networking
Terminology (Cont’d)
• Similar to cellular.• Mobile Node (MN or MH): node changing its
PoA.• Correspondent Host (CH).• Home Network (HN) and Foreign Network
(FN).
12CMPE 257 - Wireless and Mobile Networking
Terminology (Cont’d)
• Mobility Agents:– Home Agent (HA): router on MN’s HN that tunnels
datagrams to MH when away and keeps MH’s current location info.
– Foreign Agent (FA): router on foreign network; delivers datagrmas to MH while on FN.
• Home Address (HoA) and Care-of Address (CoA):– HoA: MH’s permanent address on HN.– CoA: MH’s temporary address on FN.
13CMPE 257 - Wireless and Mobile Networking
Care of Address
• FA-based.– MN’s address is its current FA’s address.
• FN-based.– Locally-assigned address in FN.
– E.g., DHCP address.
• What’s the difference?
14CMPE 257 - Wireless and Mobile Networking
Mobile-IP: Basic Operation
• MH normally uses its home address HoA.• When MH visits a foreign network,
– Registration with FA.• Discover FA and CoA.
– Registration with HA.• Binding update (HoA -> CoA).
• Communicating with MN: use HoA.• HA forwards packet from HoA to CoA.
15CMPE 257 - Wireless and Mobile Networking
Discovering Agents
Agents periodically beaconadvertisements
16CMPE 257 - Wireless and Mobile Networking
Agent Discovery
• Agent advertisement (beaconing):– Mobile agent broadcast agent advertisement
at regular intervals (“I am here”).
• Agent solicitation:– MH can poll (“anyone here?”).
– Mobile agent responds to poll.
18CMPE 257 - Wireless and Mobile Networking
Agent Advertisement
• Follows ICMP router advertisement message.• List one or more available care-of addresses.• Inform the MN about special features
provided by FA.– Example: Alternate encapsulation techniques,
header compression.
20CMPE 257 - Wireless and Mobile Networking
Registering
• When away, MH registers its CoA with HA (binding update).
• Binding: (HoA->CoA)– Binding has a lifetime.
21CMPE 257 - Wireless and Mobile Networking
Registration Process
• MH sends a registration request with CoA.• HA authenticates request.• HA approves or disapproves the request.• HA adds necessary information to its routing
table.• HA sends registration reply back to MH.
22CMPE 257 - Wireless and Mobile Networking
Registration Process (cont’d…)
• In the case of FA-based CoA:– FA is involved in registration.
– FA is also involved in packet forwarding.
– Encapsulation.
– Tunneling.
23CMPE 257 - Wireless and Mobile Networking
Tunneling
• HA tunnels datagrams destined to MN when MN is away.– Datagrams sent to MH directly.
– Or sent to FA which forwards to MN’s CoA.
• Tunnel terminates at MH’s CoA (either the MH or the FA).
24CMPE 257 - Wireless and Mobile Networking
Tunneling
Tunneled Data Packet
HA keeps bindingbetween MH and CoA
SRC
25CMPE 257 - Wireless and Mobile Networking
Encapsulation
• Tunneling requires encapsulation.– Sending the original packet (CH->MH) in
another packet (HA->CoA).
• Default encapsulation mechanism:– IP-within-IP (tunnel).
– Tunnel header: new IP header inserted by the tunnel source (home agent).
– Destination IP: CoA
27CMPE 257 - Wireless and Mobile Networking
The Triangle Routing Problem
• Aka, “dogleg” routing.• MH->CH: direct.• CH->MH: CH->HA->MH– Inefficient
• Solution: route optimization.– Deliver binding updates directly to CH.
28CMPE 257 - Wireless and Mobile Networking
Route Optimization
• Binding caches:– Nodes can keep caches with CoA for MHs.
– If node has entry for MH, sends data directly.
– Otherwise, “triangulates” with HA.
– Binding cache entries have TTL.
– HA, FA, or MH can send binding cache updates to CH.
29CMPE 257 - Wireless and Mobile Networking
Simultaneous Bindings
• MN can register multiple CoA’swith HA.– Why?
• De-registration.– Explicit.
– Implicit.
30CMPE 257 - Wireless and Mobile Networking
Handoffs
• MH moving among FN.• New CoA registered with HA.• Previous FA not necessarily notified.
– Old registration will expire.• New data delivered to new CoA.• In-flight data?
– Dropped and retransmitted by upper layers, or– FA notified of new CoA; FA forwards data to new CoA.
31CMPE 257 - Wireless and Mobile Networking
Types of Handoffs
• MN-initiated:– Handoff managed by MN.
– MN measures signal strength to AP.
– Decides target AP and switchs over.
• Network-initiated:– APs decide when to hand over and to whom.
32CMPE 257 - Wireless and Mobile Networking
Hard versus Soft Handoff
• Hard handoff: only a single active connection between MN and AP.
• Soft handoff: two active connections during handoff.
33CMPE 257 - Wireless and Mobile Networking
Handoff Signaling
• Forward handoff:– Target AP contacts current AP to initiate
handoff.
• Backward handoff: – Current AP contacts the target one.
34CMPE 257 - Wireless and Mobile Networking
Handoff Delay
• 3 components: – Detect need of handoff.
– Link establishment between MN and new AP.
– Registration with HA.
• Pre- and post-registration handoffs:– Pre-registration registers MN with HA before handoff.
– Post-registration: HA registration happens after handoff.
35CMPE 257 - Wireless and Mobile Networking
Authentication
• Malicious nodes can infiltrate FNs.• Mobile IP registration includes authentication
info exchange.– MH-HA.– MH-FA.– HA-FA.
• Protection against replay attacks.– Timestamp and nonces.
36CMPE 257 - Wireless and Mobile Networking
Mobility Support in IPv6
• Route optimization is default.• Fields for specifying both CoA and permanent
IP address.– No need for encapsulation.
37CMPE 257 - Wireless and Mobile Networking
TCP Performance in Mobile-IP (Choong)
• Source of overhead: triangle routing.– Additional processing at HA and FA.
– Additional delay due to “triangulation”.
– Additional delay due to fragmentation (extra IP header).
– Handoffs.
38CMPE 257 - Wireless and Mobile Networking
Goal
• Determine the impact on TCP performance of– Combined overhead sources.
– Individual overhead sources.
39CMPE 257 - Wireless and Mobile Networking
Methodology
• Several scenarios that compound or isolate overhead sources.
• Compare performance of between scenario pairs.
• FTP transfer btween MH and CH.• Metric: TCP throughput.
40CMPE 257 - Wireless and Mobile Networking
Summary of Results
• Dogleg routing as main cause of TCP throughput degradation.– Solution: route optimization.
• Handoff is second.– Mobile-IP’s inherent delay in re-establish
connectivity with new FA.– Solutions:• Increase frequency of router advertisements.• Use link-layer information to trigger handoff.