CellularIP Proxy

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Cellular IP: Proxy Service

Reference:Incorporating proxy services into wide area cellular IPnetworks; Zhimei Jiang; L i Fung Chang; Kim, B.J.J.;

Leung, K.K.; Proc. IEEE Wireless Communications and

Networking Conference (WCNC), 2000. pp. 246252(CellularIPImprv-1.pdf)


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Introduction Why Performance enhancing proxies?

Most of existing protocols and AP. aredesigned for wired networks

Many of them do not work properly orefficiently on wireless networks

How does a proxy work?

Mobile users communicate with the proxieswhich in turn exchange information with the

destination servers on behalf of the mobileusers

At the proxy, information from the originalserver is converted to make it suitable for thewireless environment


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CIP Network with Proxies


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Proxies outside CIP Networks

The performance is often compromised by

the long latencybetween mobile users,

proxy server, and original data server

Proxies have only limited accessto

information about the networks and the

users due to security concern and non-

existence of convenient interfaces to

wireless networks


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Proxy Functions


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Proxy Functions (cont)

Application proxy

Caching, prefetching

Two basic mechanisms for reducing access delay

Content transformationConvert data to a format that is more suitable to the

mobile user, based on information such as device

characteristics, link conditions, and QoS requirements

Application protocol translationAllows devices and servers that do not support a

common protocol to exchange information through a

proxy server


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Existing Proxy Services


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Design Considerations for Placing

Proxies into CIP Networks

Two different aspects

Physical locationin terms of the distance from

the proxy to other key components of the net.

1. Close to a gateway router: high concentration oftraffic

2. Close to an access router: aggregated traffic from

a number of base stations

3. Close to a base station: handle traffic for a single

cell

Location of the proxy on the routing path

betweena base station and a gateway router


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Proxies on the Routing Path


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Design Consideration (cont) Information required to support proxy functions

What commitments that the mobile network has made in

terms of service quality

E.g. users QoS profile

What network performancecan currently be supported

by the network E.g. current channel conditions

What usersactually need for their current AP

E.g. AP requirements and user preference

What environment they are in

E.g. location information

What functions the devicescan support?

E.g. device capabilities

Other information: billing method


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Design Consideration (cont)

Network and server requirements

Network capacity

As far as channel information is concerned, the base

station is the best location to obtain such information,while placing proxies close to gateway routers

introduces the largest amount of traffic across the

network

Proxy servercapacity and scalability


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Impact of user mobility


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A proxy may not need to be informed of

the cell change only if all of the following 3

conditions hold:

1. The care-of-address of the mobile station is

the access router

2. The proxy is accessed between the access

router and the gateway router 3. The cell change is within the coverage area

of the same access router


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Location of the proxy functions If a proxy is placed close to the gateway router

It has to be powerful enough to handle the high

concentration of traffic

If a proxy is placed close the access router It has relatively easier access to the device and

channel information

Proxies close to base stations

Enjoy most convenient access to the channelinformation

Other issues

Service discovery, security, reliability, cost, etc.


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Incorporating Proxies into GPRS


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GPRS Overview

General Packet Radio Service Introduced in the GSMphase 2 standard

Two important network entities

Serving GPRS Support Node (SGSN)

Corresponds to the Access Routerin CIP networks

Gateway GPRS Support Node (GGSN)

Corresponds to Gateway Routerin CIP networks

Is connected with SGSNs via an IP-based GPRSbackbone network

Contains the routing information to SGSN for thecurrent GPRS users, which means in mobilitymanagement, the CoA of an MS is the address of itsSGSN


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GPRS Overview (cont)

Interface between SGSN and MSC/VLR

Mobile Service Center/Visitor Location Register

Enable MSC/VLR to send voice paging message

to SGSN, and to have SGSN page the users ifusers subscribe to both GPRS and GSM

services

Interface between GGSN to HLR

Home Location Register

For the GGSN to request subscribers location

information from the HLR if needed


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GPRS Overview (cont)

PDP context

Packet Data Protocol

Contain routing informationfor forwardingpackets between GGSN and MS, and betweenSGSN and public data network respectively

PDP context activation can be initiated by MSor by the network

When an MS wants to activate access to thepublic data network, it needs to inform thenetwork to activate a PDP context


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PDP context Activation


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Inter-SGSN Routing Area Update


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Inter-SGSN Routing Area Update (cont)

1. When an MS detects a new routing area

Sends a Route Area Update Requestto the

new SGSN (step 1)

2. The new SGSN

Requests for the MS state information and data

packets from the old SGSN (step 2-5), so that it

may continue forwarding packets to the MS

3. In addition, location information is

updated (step 6-10)


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Adding Proxies to GPRS

Very difficult to place proxy functions atbase stationsor between base station and

SGSNwithout any major modifications to

the GPRS architecture

Thus, focus on how to support proxy

functions between SGSN and GGSNwith

minor modifications to the GPRS

architecture Routing controlled by PDP context

Mobility management


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Adding Proxies to GPRS (cont)

PDP context and routing

A PDP context is created so that the

corresponding SGSN and GGSN will send

packets to the proxy server instead of to eachother directly

The proxy server also creates a copy of the

PDP context during the PDP context activation

procedure, which contains the addresses of

the SGSN and GGSN that are serving the

mobile station


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Adding Proxies to GPRS (cont) Mobility update

1. Intra-SGSN, hence intra-proxyMS stays within the service area of an SGSN after a

cell change. The proxy does not need to be informed

unless the proxy function requires information that is

specific to the base station

2. Inter-SGSN, but intra-proxy

MS has just moved into the service area of another

SGSN but is still covered by the same proxy server

The proxy server should be informed about the change

The mobility update procedure is very similar to thatshown in Figure 5 (slide 21) except for step 6

Step 6 should update the proxy context at the proxy

server

3. Inter-SGSN and inter-proxy(next slide)


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Summary

Incorporates proxies into cellular networks

Balancing trade-offs between:

What information the proxy requires

The latency requirement for obtaining required

information

The amount of extra traffic it generates

Mobility management

E.g. adding proxy support to GPRS

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