5. mobile networking challenges 5.1 mobile ip

Mobile Networking Challenges 1

5. Mobile Networking Challenges

5.1 Mobile IP Mobile IP 는 IP 주소를 가진 단말이 이동 시에도 그 연결을 항상

보장하는데 필요한 기술이다 . 현재의 인터넷 프로토콜은 인터넷에 접속하는 단말기의 위치가 고정되어 있고 특정 네트워크 상의 고정된 IP 를 사용한다는 가정 하에 서비스가 이루어 지고 있어 다른 네트워크로 이동할 경우 접속할 수 없는 결과를 초래한다 . 하지만 Mobile IP 에서는 이원화된 주소체계를 통하여 이동성을 지원하고 있다 . Mobile IP 는 홈 주소 (Home Address) 와 COA(Care of address) 라는 두 가지 주소체계를 가진다 .

홈 주소는 최초 부여 받은 주소로 통신을 수행할 때 사용되어 변하지 않는 주소이고 , COA 는 단말이 이동했을 때 이동한 지역까지 라우팅하여 가기 위한 주소이다 . 따라서 , COA 는 단말이 이동해서 라우팅 지역이 변하는 것에 따라서 계속 변하게 되어 지속적인 인터넷 서비스를 가능하게 하는 것이다 .


Mobile IP

When the mobile device moves to another area, it receives a care-of address (CoA) from foreign agent (FA).

The foreign agent and home agent will coordinate to provide a connection as through the mobile device can still be reached via its home address.

The home agent maintains a mapping between the mobile device’s home address and foreign address.

Any packet sent to the home address will put into an IP-in-IP tunnel by the HA, and forwarded to the foreign address. At the end of this tunnel is the FA, whose job is to decapsulate the packet and forward the orginal data to the mobile device.

Mobile IP essentially offers a way to identify a mobile device using the same address when it moves to another location and cannot be serviced by its original home agent.


Mobile IP


Mobile IPv6 Mobile Pv6 노드가 홈 링크를 벗어나 다른 링크에 접속되면 해당

노드는 Mobile IPv4 에서와 마찬가지로 방문한 링크에서 사용할 임시주소인 CoA 를 얻게 되며 , 이 주소를 자신의 홈 링크상에 위치한 홈 에이전트에게 등록한다 .

CoA 를 홈 에이전트에 등록한후에 이동노드의 홈 주소를 목적지로 가지는 패킷이 전달되면 홈 에이전트가 이동노드를 대신하여 패킷을 수신한다 . 홈 에이전트는 수신한 패킷을 CoA 를 목적지로 터널링하여 이동노드가 위치한 링크로 전달하며 , 이동노드는 터널링 헤더를 제거하고 원래 패킷을 얻어낸다 . 반대로 이동노드가 상대노드로 패킷을 전송할 경우에 최초의 패킷전송은 홈 에이전트로의 역터널링을 거쳐서 상대노드로 전달된다 . 이때 상대노드는 RR(Return Routability) 라는 방식을 통해 MN 의 CoA 를 등록하며 , 상대노드에 CoA 가 등록된 이후에는 두 노드가 홈 에이전트를 거치지 않고 직접 통신을 수행할 수 있다 . 다음 그림은 MobileIPv6 의 동작을 개략적으로 보여준다 .


5.2 Wireless TCP

TCP provides connection-oriented service over packet switching networks. Acknowledgment schemes are used to ensure TCP connection reliability. Round-trip time (RTT) estimates allow dynamic adjustment of the sliding window in order to achieve maximum throughput.

The flow control and congestion control mechanisms of TCP help the transport adapt to network conditions and endpoint characteristics.

TCP assumes all packets losses are caused by congestion at links where buffers overrun and packets are dropped. Congestion control using slow-start, congestion avoidance, fast re-transmission, and fast recover are commonplace among many TCP implementations.


5.2.1 Wireless TCP Challenges

Wireless communications have imposed a number of challenges on TCP, including:

High packet drop rate

Unreliable wireless link

Mobility

Resource-limited mobile device

Wireless link bandwidth vs. wired link bandwidth

5.2.2 Wireless TCP protocol

Wireless TCP can be enhanced in several ways, including TCP-split, link-layer-assisted TCP, and regular TCP modifications.


Category Examples

TCP-split

Link-layer-assisted TCP

TCP modification

I-TCPM-TCPSnoop/delay duplicated acknowledgementAIRMAILRLPEifelTCP SACKFast start

Wireless TCP Protocols

5.3 Convergence of Heterogeneous Wireless Networks Convergence

Integration of cellular networks and wireless LAN hotspots Integration of wireless LAN and Bluetooth Integration of wireless LAN and cellular for enterprises Integration of wireless LAN and corporate IP private branch exchange (PBX)


5.3.2 Internetworking System Architecture

Tightly coupled internetworking

A wireless LAN gateway is necessary to act as an agent for a group of access points.

Loosely coupled internetworking

Wireless LANs directly connect to the Internet and do not have any links to cellular core elements.

Fig. 5.1 참조


5.5 Wireless LAN and Bluetooth Coexistence

Wireless LAN and Bluetooth boorativeth operate at 2.4-GHz unlicensed frequency band.

The basic approaches can be divided into two categories: collaborative and noncollaborative.

The collaborative approach aims to coordinate frequency use between two types of radios, thus requiring interprotocol communication that must be implemented on the same devices.

The noncollaborative approach looks at only one side; that is, it tries to mitigate interference by reducing the chances of frequency overlapping, but it requires the acting device to detect interference or conduct interference estimation.


5.5 Mobile Next-Generation Networks5.5.1 Mobile IP for Macromobility

The triangular routing path problem can be solved by allowing the home agent to notify the correspondent station the CoA of the mobile station in question using a “binding update” message.

The corresponding station maintains what is called a “binding cache” for the latest known CoA of mobile station.

Direct communication between the two parties can be performed within the home agent’s relay.


Mobile IP enhancements.


5.5.2 Mobile IP for Micromobility GFA is responsible for forwarding those packets to the foreign agent at that poin

t of time, which further relays traffic to the mobile station.

A domain root router for each domain is designated to handle intradomain and interdomain mobility.

When the mobile station moves within the home domain, it performs a path update operation so as to build an updated path to the domain root router.

When it moves to another domain, the domain root router of the new domain will act as the foreign agent to the mobile station, allowing intramobility within the foreign domain.


Mobile IP regional registration and HAWAII.


5.3.3 Link Layer Mobility Management The UMTS standard defines an optional network entity called gateway location r

egister (GLR) for intersystem roaming. In UMTS, the service area is partitioned into gateway location areas (G-LAs), which are further divided into location areas (LAs), which are comprised of a number of cell sites.

G-LA – An HLR location update is performed when a mobile station crosses the boundary of a G-LA.

LA – A GLR location update is performed when a mobile station crosses the boundary of an LA.

Cell – A VLR location update is performed when a mobile station completes d movements between cells, where d is the movement threshold.


Gateway location register (GLR) in UMTS.

5. mobile networking challenges 5.1 mobile ip

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