Services
7750 SR OS Services Guide Page 85
Interface Encapsulation
PFC and ACFC header compression to minimize the required backhaul bandwidth for DS-1 and
E-1 channel groups is supported. PPP channel configuration options support Protocol Field
Compression (PFC) per RFC 1661, The Point-to-Point Protocol (PPP), Section 6.5 and Address
and Control Field Compression (ACFC) as per Section 6.6. This functionality is supported on all
ASAP MDA variants and as well as CMA variants supporting DS-1/E-1 PPP. The configuration
can be changed while a member is active in the bundle. When disabled, PPP will reject a request
from the peer for PFC or ACFC to match earlier implementations.
The DS-1 channels on the channelized interfaces are deployed using ML-PPP encapsulations
supporting 1 to 8 DS-1 channels in the group. As a single MSC can support many BTS sites and
each BTS site has one or more ML-PPP Groups (MLG) supported at the site, a very large ML-PPP
group density is required. Current deployments support up to 256 MLGs per ChOC-12.
Physical Interfaces
In a pure Ethernet network from BTS to MSC/MTSO, service routers have a wide portfolio of
Ethernet physical interface options from 10 Mbps to 10 Gbps supported in the SR OS.
However, in 2G BTS sites, the BTS typically connects to the network over physical DS-1/E-1
TDM links, not Ethernet. The most transparent method to converge DS-1 or E-1 TDM traffic
across an Ethernet network is to use circuit emulation (CE). For example, a CE inter-working
function (IWF) is performed at the BTS or hub site to convert the digital traffic into packet traffic
by literally stuffing the bits into a packet payload and appending headers to identify the
destination. However, mobile service provider networks are typically a large star network from the
BTS to the MSC/MTSO. Therefore, even if each BTS only has 1-2 E-1s requiring CE IWF, the
hundreds of BTS sites homing into a single MSC/MTSO site require a larger capacity CES IWF
function at MSC/MTSO to enable a channelized TDM connection to the BSC.
Service Support
The SR OS supports a wide variety of services including IES, IP-VPNs, VPLS and Ethernet,
ATM, Frame Relay, IP, and TDM pseudowires.
In Alcatel-Lucent Ethernet backhaul networks, there are three primary BTS site CE IWF devices.
Currently, the 7250 SAS can be used for CES over Ethernet or MPLS. In CDMA solution R30, CE
IWF on DMXplore (MATS or EIU) can be used. In many GSM/UMTS networks, the 7705 SAR
can be used for CE IWF.
When the 7705 SAR is used at the BTS site, there typically can be 500-600 cell sites homing into
a single 7750-SR router pair at the MSC. Many of the 7705s can be provisioned with static
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