Technical Issues in Wireless Networking - Mobility Support -

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Technical Issues in Wireless Networking - Mobility Support -

Kyunghan Lee

Networked Computing Lab (NXC Lab)

Department of Electrical and Computer Engineering Seoul National University

https://nxc.snu.ac.kr [email protected]

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WIRELESS NETWORKING, 430.752B, 2020 SPRING SEOUL NATIONAL UNIVERSITY

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How to Support Mobility

□ Mobility Protocols

§ Designed to ensure session continuity

§ Session continuity requires source/destination IP continuity

□ Session continuity vs. IP philosophy

§ IP addresses are designed to follow the hierarchy represented by prefix (i.e., subnet)

§ IP address hierarchy is essential to keep the cost and complexity of routers low

§ IP address hierarchy enforces a node to have a geographically distinguished subnet that will change as a node moves

• Physical proximity enforced by the concept of a link

• Consider the typical radius of a wireless link

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A B C

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DHCP(Dynamic Host

Configuration Protocol)

Dynamic IP

(Public or Private)

141.76.40.190 or

192.168.0.2 142.35.22.5 or

192.168.1.11

Uplink seems ok.

What about Downlink?

Mobility Support (Uplink/Downlink)

e.g., www.dropbox.com

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Streaming from Youtube

142.35.22.5 141.76.40.190

How to notify the new IP to the server?

Who is responsible for this notification?

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Sending a Message to the Server

How to find the IP of a node whenever it is required?

Is it possible to

immediately identify the IP?

Sending a Message to a Client

Mobility Support (Discontinuous Case)

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Challenges in Mobility Support

□ Link Layer

§ Handoff decision (When to switch cell-tower (wireless AP))

□ Network Layer

§ IP assignment to a mobile node

§ Routing to a mobile node

□ Transport Layer

§ Optimizations for wireless communication

Most importantly, “mobile IP" makes a fundamental conflict with the IP assignment philosophy of Internet (IP: Aggregatable and Localizable)

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Dynamic IP

□ DHCP (Dynamic Host Configuration Protocol)

§ Supports automatic assignment of IP addresses

§ Automatic configuration of network (router, subnet mask, DNS) + optional settings (web server, mail server)

§

DHCP works based on “Subnet”

§

Subnet means “Location”

§

IP = Unique ID (at the moment) + Location Pointer

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Dynamic IP

□ IP Address is Limited

Resource

□ Assignment of IP

∶= Lease of IP for a duration T (Lease Time)

□ Lease Time is related to speed of mobility

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Mobile IP

□ Goal

§ Permanent IP for a mobile node

□ Why is it important?

§ Network controls (flow control, congestion control) are carried out for a session

§ A session is built on a socket

§ A socket is bound to IP addresses (source/destination)

§ For continuous mobility support (e.g., voice), Mobile IP for a

mobile device, which does not change while moving is essential.

□ Ok. Then how?

Split IP into Two Addresses

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Mobile IP

□ Two addresses for a mobile node (i.e., mobile host)

§ Home Address (HA): Permanent IP

§ Care of Address (CoA): Temporary IP for each subnet

□ Agents

§ Home Agents (where mobile host registers and gets HA)

§ Foreign Agents (FA, where mobile host gets CoA)

□ Agent discovery

§ Agent advertisement (Passive)

§ Agent solicitation (Active)

□ Routing

§ Routing messages to HA goes to Home Agents

§ Home Agents forward the messages to CoA

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Mobile IP: Registration

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Mobile IP: CoA Forwarding (with FA)

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Mobile IP: CoA Forwarding (without FA)

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Mobile IP: Problems

□ Tunneling Performance

§ More critical when encryption is needed

□ Triangle Routing (Routing Optimization)

§ Messages always go to Home Agent first and are forwarded

§ If CoA is far from Home Agent, the performance degrades

§ Mobile IPv6 solves this problem (Direct tunneling)

□ Micro Mobility

§ If mobile node frequently changes its CoA, Home Agent becomes too busy for updating the forwarding table

§ Cellular IP has hierarchical management (1 CoA for an Area)

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□ Problems:

§ Requires low-end mobile devices to perform all kinds of mobility signaling to maintain connectivity

§ New CoA after each handoff, so the cache entry needs to be changed

§ Wireless bandwidth wastage due to mobility signaling

§ High handover latency

□ Solution: Network-based Mobility Management

§ Network takes care of all the mobility signaling

§ Network entities are responsible to track the mobile device

§ Network entities send required signaling messages on behalf the mobile devices

Mobile IP: Other Problems

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Proxy Mobile IP (PMIP)

□ Network-assisted Mobile IP (by IETF)

§ LMA (Local Mobility Anchor) and MAG (Mobile Access Gateway) handle bi-directional tunneling (No change on Mobile Node)

§ Mobile Node (MN) needs no change for mobility support (no CoA)

§ No CoA registration initiated from Mobile Node Packet forwarding (CN to MN)

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PMIP Signaling

AAA: Authentication, Authorization and Accounting

BCE: Binding Cache Entry PBU: Proxy Binding Update PBA: Proxy Binding Ack

MN MAG1 MAG2 LMA

MN registrationMN detach eventMN attaches to MAG2

MN enters LMA domain

MN gets IP address

MN moves away from MAG1

MN enters MAG2 region

MN keeps the same IP address

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Network-based Mobility Support

□ Benefits

§ Battery power saving

§ No modification in end devices

§ Unique IP address in the whole LMA-domain

§ Movement detection by the network

§ Reduced signaling in the wireless access network

§ Low handover latency

§ Efficient tunneling

§ Less signaling in each handoff

• No Duplicate Address Detection (DAD) in each handoff

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Network Mobility (NEMO)

□ A collection of nodes moving as a unit

§ e.g., airplane, train, bus, subway, ship

□ Mobility can be managed in an aggregated way in NEMO

□ Mobile Router (MR) acts as default gateway and manages mobility on behalf of mobile network nodes

HA

InternetInternet

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NEMO Architecture

Data path Internet

NEMO MR

LMN

LFN VMN

AR

□ MR is supported by MIP

□ Inside NEMO

§ MR: Mobile Router

§ AR: Access Router

§ LFN: Local Fixed Node

§ LMN: Local Mobile node

§ VMN: Visiting Mobile Node

□ Problems:

§ Routing through HA

§ Heavy load on HA

§ Drop in throughput during handover

HA CN

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Hierarchical MIP (HMIP)

□ For high mobility of nodes, frequent

location updates are given to HA

§ Bandwidth wastage

§ Overhead for HA

□ Hierarchical Mobile IP attempts to

reduce signaling by introducing a new mobility agent:

MAP (Mobile Anchor Point)

Local HA

Local HA

Internet HA CN

MAP

AR₁ AR₂ AR₃

MH

MH movement

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Cellular IP – Similar idea with HMIP

□ Hierarchical IP management

§ To reduce handoff latency (critical)

§ To minimize location management overhead

§ To mitigate HA overload

§ To minimize complexity of mobile node design

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Cellular IP

□ Micro mobility management

§ Base-stations map ports to mobile nodes (like NAT)

§ Base-stations periodically monitor the location of a mobile node

§ Paging cache is used for inactive nodes

• Packets are forwarded later when the node is waked up by a paging packet