Blog from Cisco's Mobility Community, https://www.myciscocommunity.com/community/sp/mobility

1. Service Provider Mobility: Migrating to Packet
Backhaul may not be a technology decision
Posted by Kevin Shatzkamer Jan 20, 2010
Over the course of the last several years, I have spent much time with operators discussing
the evolution to packetized backhaul, and I find that a rather interesting trend. I will try to
explain through a timeline-based approach:
2000-2004:
Focus was less around how to migrate off of TDM infrastructure, but instead extend the life
of TDM/ATM infrastructure as long as possible. Techniques like A-Bis/IuB optimization,
silence suppression, etc were all the rage, given the pending explosion of 3G (EVDO Rev0/
A and UMTS at the time) data usage and the relatively limited reach of Ethernet/packet
networks to towers. Given that voice was fairly predictable in nature - fixed and deterministic
bandwidth, the influx of data was such a serious concern that operators deployed voice and
data over separate leased lines to protect their voice quality.
2004-2008:
The focus shifted towards developing strategies and scenarios for evolving backhaul
networks off of legacy, circuit-switched (or cell-switched, I supposed) transport mechanisms
to more robust, scaleable, and cheaper alternatives - namely, packet transport. There
was no question that the operational simplicity, ubiquitous access to vendor products, and
monthly transport costs of the packet infrastructure were cheaper than that of the circuit
infrastructure, but there was still much debate around the technologies that would be used to
deliver the "Service".
Across numerous standards organizations, many protocols and technologies emerged:
Pseudowire technologies - Pseudowire Edge to Edge (PWE3), Circuit Emulation over
Packet Switched Network (CESoPSN), Structure-Aware Transport over Packet (SAToP)
Timing technologies - differential vs adaptive, Network Time Protocol (NTP), Synchronous
Ethernet (SyncE), Precision Time Protocol (PTP), Timing over IP Connection and Transfer
of Clouc (TICTOC)
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2. Service Provider Mobility: Migrating to Packet Backhaul may not be a technology decision
OA&M - IETF (802.3ag), MEF (E-LMI) and ITU (Y.1731) all played a role here in building
different standards for implementing OA&M
Ethernet - Connection-oriented vs Connectionless debate. With Provider Backbone Bridging
(PBB - 802.1ah), PBB - Traffic Engineering (802.1Qay), Transport MPLS (T-MPLS), etc - the
options were astounding.
So, this period marked the great technology confusion and debate - which technologies
would win, and many service providers spent their days writing RFIs/RFPs to understand
where the industry was moving.
2008-2010:
The technology debate is over - there are clear winners and losers. PBB-TE has mostly
gone by the wayside (With Ciena acquiring both Worldwide Packet and Nortel's MEN
business, there are not many vendors investing in PBB-TE), T-MPLS has disappeared, and
MPLS/MPLS-TP have emerged as the most promising path for building robust, manageable
backhaul transport networks. Of course, support for pseudowires will be especially relevant
through the transition to All IP architectures like LTE or WiMAX, but this is to be expected
during any technology migration.
However, re-emerging in the debate over packet backhaul are the economics. With T1
pricing reaching sub $300 per T1, and 3G networks continuing to rely on oversubscription
models on the backhaul network, it might just be that T1s are sufficient for meeting service
requirements until 4G networks and devices are widely available. Sure, packet backhaul is
getting deployed, slowly, in many areas of the world, but take note that the majority of these
deployments fit into one of two categories:
1) Those service providers who are preparing for an imminent launch of a higher-speed
technology than HSPA or EVDO. This may be HSPA+, or LTE, or WiMAX - the packet
backhaul network is agnostic to the RAN technology.
2) Those service providers who can provide the entire service in-house. So, a mobile SP
who relies on their parent company to provide the transport of their backhaul network.
So, why does the transition for the rest of the mobile SPs continue to be slow? A number of
factors can be seen:
1) Still some longterm leases out there. While most mobile SP are not signing longterm
leases, there are still many that are carrying leases signed nearly a decade ago
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3. Service Provider Mobility: Migrating to Packet Backhaul may not be a technology decision
2) Technology aversion. There have been prior posts around the impact of LTE on
organizational structure. The same holds true for any technology shift - organizations
continue to justify a period of time (an "Aversion window", I call it), during which the impact
of adopting a technology outweighs the impact of not adopting the technology.
3) Ubiquitous service offering. With mobility, consideration of how the user moves, and
ensuring the same level of experience across multiple cell sites is very relevant. For this
reason, it is important that every cell tower within a geographic region has a strikingly similar
performance level (jitter, latency, delay, packet loss, etc). Given the history of packet
(metro/carrier Ethernet) networks to be built for shared access and best effort services,
finding a provider who can offer the SLAs required for mobile voice traffic, at a compelling
price, is not always as straightforward as it might seem.
This begs the question - is the transition to packet backhaul no longer a technology decision,
but instead a business decision? My opinion - yes, but I believe the business decision
determines "when", not "if" ("IF" is a foregone conclusion - packet backhaul will dominate in
the future).
And the business decision is based on a number of factors:
1) Is the OPEX of the packet network outweighed by the CAPEX cost of ripping/replacing
circuit infrastructure with packet infrastructure.
2) Customer experience. As the network becomes dominated by video, oversubscription
models may no longer hold in the backhaul network. Customer experience will suffer
without a more scaleable transport mechanism.
3) Compettive pressures. With competitors moving to packet backhaul, the longterm OPEX
structure they will have enables more aggressive pricing models.
As always, I rely on much of my firsthand experience, augmented with industry research.
Given that I do not have full firsthand visibility into every geography or operator, I look
to Cisco's SP Mobility Community to provide your thoughts on how the packet backhaul
transition will shake out, and what other factors are key.
245 Views
Feb 8, 2010 3:56 PM Mark Grayson
Hi Kevin
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4. Service Provider Mobility: Migrating to Packet Backhaul may not be a technology decision
So I think a key issue that all operators will face is moving from an SDH/PDH mindset,
where capacity was provisioned against base station capacity, towards an IP/E mindset,
where aggregation networks are frequently oversubscribed, access links may fail and
microwave Ethernet vendors include Adaptive Modulation and Coding to improve their
throughput in good conditions.
As RF bandwidths continue to evolve towards the promised 1 Gbps marketing rates
associated with 4G, the bottleneck will frequently not be the radio interface, but could
instead be the transmission network. Today, the cellular architectures defines IP/E interfaces
but still has an SDH mindset, assuming any packet will not suffer congestion in the transport
network.
How does the flattening of the cellular architectures impact the standardization bodies which
produce them? Do we need to look at a close coupling between All-IP Cellular Systems and
All-IP RAN solutions?
- Mark
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