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CDMA Network Evolution – Goals, Guidelines & Comments

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This document has been prepared by Starent Networks to assist the development of specifications by 3GPP2. It is proposed to the Committee as a basis for discussion and is not to be construed as a binding proposal on The 3GPP2 Secretariat. Starent Networks specifically reserves the right to amend or modify the material contained herein and to any intellectual property of Starent Networks other than provided in the copyright statement above.

TSG-X

Source: Kuntal Chowdhury: kchowdhury@starentnetworks.comMatt Harper: mharper@starentnetworks.com

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Network Evolution - Goals • Starent suggests that before any cdma2000

network re-architecture task is undertaken by 3GPP2, a set of clear problem statements with the following criteria must be defined:– Illustrate the problem(s) clearly, preferably with real

life data from the field– Provide explanation of why the problem(s) cannot be

solved within the current network architecture– Demonstrate clear benefits of the proposed new

components or proposed changes in the current architecture

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Guidelines • If a new architecture is absolutely

necessary, the following guidelines must be followed:– The new architecture MUST not keep interfaces

(e.g. BS to AGW/CAP interface) closed to stifle competition among vendors

– Avoid introduction of additional network elements to serve the same functionality as in the current architecture

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Comments on the Current Proposals

• At this time there are two contributions that propose architectural changes in the cdma2000 network.

• The subsequent slides include comments on these proposals

• Starent’s Comments are marked in Blue

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X31-20050926-035R1: Cisco• Problem Statement:

– Network complexity due to different levels of mobility

• Is the intent here to say: complexity due to multiple layers of mobility? In today’s architecture, mobility in the RAN does not necessarily involve L3 mobility. The PDSN insulates the core IP network from inter-RAN mobility. Depending on PDSN’s footprint, L3 mobility events may not even occur

– Scalability issue due to tight coupling between bearer data and radio link handoff

• We don’t understand this problem statement. Please clarify

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X31-20050926-035R1: Cisco• Components of the proposal :

– PPP-free operation…IP to the edge (RNC/BS): • Why a new architecture is required to achieve this?• Optimized session setup and transport is feasible with

PPP based signaling as demonstrated in AltPPP scheme– Localized mobility and fast handoff solutions:

• The current architecture is based on localized mobility management by the PDSN and the PCF (A11/A10)

• Fast handoff is also standardized as part of current architecture

• Optimizations can be made to fast handoff procedures w/o any major change to the CDMA architecture

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X31-20050926-035R1: Cisco• Components of the proposal :

– End-2-end QoS (of course using RSVP): • Why a new architecture is required to achieve this?• Moreover, a work item already exists on e2e QoS

– Open RAN architecture: de-couple BS and RRM: • Current Abis interface spec can be revised for HRPD• This is a generic and a very necessary requirement

regardless of the new architecture considerations– Allow native IP host stacks as in wired networks*:

• Please clarify the context: IPv6?

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X31-20050926-035R1: Cisco• Components of the proposal:

– RLP termination at the AGW: i.e. AGW directly connecting to the BS:

• RLP termination at the AGW is a major step• Please explain the rationale

– New element: LMA for micro mobility: • The function of this entity is similar to the PDSN in

current architecture• PDSN insulates the core IP network (HA) from RAN

handoffs…something that LMA seems to achieve

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X31-20050926-029 R2: Qualcomm

• Problem Statement:– Network complexity due to too many interfaces, nodes etc.

• In the current architecture there are 7 nodes (AT, BS, RNC, PCF, PDSN, HA, AAA) and 7 interfaces (Abis, A8/A9, A10/A11, Pi, A12, A13, P-P)

• In Qualcomm’s proposed architecture there are 7 nodes (AT, BS, CAP, LMHA, HA, AAA, DHCP server) and the interfaces are not numbered, but likely add up to something similar as in the current architecture (depending on the handoff and authentication schemes)

• Qualcomm’s proposal introduces a new node: LMHA• A simpler way to reduce number of nodes will be to collapse PCF

with PDSN

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X31-20050926-029 R2: Qualcomm• Problem Statement:

– Latency (signaling and bearer)• We definitely request Qualcomm to substantiate this problem with

the current architecture. A real life data/call log with signaling latency for each of the segments: radio connection, PPP connection, MIP connection (may be TCP connection) will be helpful in understanding this problem

– Inefficiency due to unnecessary bw utilization for HDLC-like framing

• HDLC and PPP header less operation is possible with current network architecture

• This type of operation is already being standardized with current architecture

• No drastic change in the current architecture is required; this can be supported in the current architecture with some changes

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X31-20050926-029 R2: Qualcomm

• Problem Statement:– Excess RAN to PDSN coupling

• Qualcomm needs to clarify this point. What does _Excess_ mean vis-à-vis what is defined in HRPD/1x IOS today?

– Only a single channel for ROHC due to PPP• This is addressed with SO67• Hence, why a new architecture is required to solve this

issue?

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X31-20050926-029 R2: Qualcomm• Components of the proposal :

– Collapse AGW, PCF, RRM into a new entity called CAP• The CAP - BTS interface MUST be standardized• This type of collapsing reduces network deployment flexibility:

operators need to deploy new aggregation points in the network e.g. LMHA

• If AGW and RNC are collapsed into a single node, a standard way to manage the combined node will become necessary

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Issues w/ a Distributed Architecture• In theory, distributed processing is better, but

in practice it is not• A distributed architecture is difficult to

manage and monitor• Reliability of low-cost distributed nodes

cannot be matched with super-hardened high-density nodes

• Network visibility is difficult or not possible in the distributed model

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Issues w/ a Distributed Architecture• Resource utilization is better/simpler in a

high-density node:– Address pool management– Better statistical gain -> less hardware

• Locating/debugging a subscriber’s session becomes extremely difficult

• Network upgrade e.g. s/w upgrade to all the distributed nodes is an operational nightmare

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Issues w/ a Distributed Architecture• Lack of standard management interface to the

distributed nodes– No standard way to manage BSCs/RNCs, where as

AGW/PDSNs support standardized management interfaces• Data/Log collection processing: Management

systems have to collect, collate and synchronize info from large number of distributed nodes

• Handoff management is not as efficient in distributed nodes – Sessions will incur more L3 handoffs therefore, more

nodes required to fix the L3 handoff latency which is introduced by the distributed architecture

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Closing Remarks• The current proposals for re-architecting the

cdma2000 network seem premature and lacking clear problem descriptions

• Most of the CDMA operators migrated their IP networks from distributed model to regionally aggregated model….

• The current network model is stable and it works